This article was downloaded by: [University of Bristol] On: 25 January 2015, At: 21:12 Publisher: Taylor & Francis Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK

New Zealand Veterinary Journal Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/tnzv20

Factors influencing the reproductive capacity of a dairy herd a

A. de Kruif & A. Brand

a

a

Clinic for Veterinary Obstetrics, A. I. and Reproduction , State University Utrecht , Yalelaan 7, de Uithof, Utrecht, The Netherlands Published online: 23 Feb 2011.

To cite this article: A. de Kruif & A. Brand (1978) Factors influencing the reproductive capacity of a dairy herd, New Zealand Veterinary Journal, 26:7, 178-189, DOI: 10.1080/00480169.1978.34535 To link to this article: http://dx.doi.org/10.1080/00480169.1978.34535

PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content. This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http:// www.tandfonline.com/page/terms-and-conditions

NEW ZEALAND VETERINARY JOURNAL

178

VOL. 26

REVIEW ARTICLE Factors influencing the reproductive capacity of a dairy herd + A. de Kruif* and A. Brand*

Downloaded by [University of Bristol] at 21:12 25 January 2015

N.Z.vel.J.26: 178 and 183-9

ABSTRACT

ENVIRONMENT AND MANAGEMENT CONDITIONS

An attempt has been made to categorize the various factors that may influence the fertility of a dairy herd. This broad categorization comprises environmental and managerial conditions, managerial factors as such and genetic conditions. A closer examination of these factors reveals that they seldom exert their influence individually but, rather, in an interacting fashion, making it difficult to identify a single factor for fertility failure. It is mentioned that, under certain environment and management conditions, management usually falls short. It is advocated therefore, that these failures should be prevented by advising the dairyman, during regular visits (Herd Fertility Programme), so that he will focus his attention on his management practices.

Climate Climate directly affects the reproductive capacity of the cow, and indirectly affects it through the quality and quantity of its food(2l3). However, it is difficult to separate both effects on reproduction. There is convincing evidence from the literature to indicate that high humidity, and/or high average ambient temperatures, depress fertility mainly by increasing the numbers of services per conception and prolonging the calving to conception interval. Other effects are: . • delayed onset of puberty. • reduced intensity of oestrus. • reduced oestrus length. • silent oestrus or anoestrus. • prolonged cycle length caused by an increased embryonic death rate. • depression of spermatogenesis and sperm quality in bullsl2 \) (17) (82) (83) (86) (87) (102) (lSI) (116) (201) (204) (211) (213) (214) (216) (228) (229) Both the calving-to-conception interval and the number of services per conception are significantly higher in cows exposed to heat stress than in cows bred during cool weather (151). The shortened length and weak manifestation of oestrus requires careful and frequent oestrus observation before declaring cows to be in heat-stress anoestrusl118) (228).

INTRODUCTION

The profits of a dairy farm are largely determined by milk production and the number of calves born. Many reports have been published from a number of countries throughout the world indicating that a calving interval of approximately 12 months is optimal to maximize milk and calf production during the productive life of a COW(29) (3\) (66) (111) (112) (111) (l9S)(2241. Once a cow has calved, only 85 days (365-280) are available to get her in-calf again, if a calving interval of I year is to be maintained. Under present management systems a rest period of at least 40 days is needed, leaving only 45 days for successful re-mating. Ifsuch a fertility level could be obtained in a herd of dairy cattle, it would mean that the profits would be optimal. A measurement of the level of fertility of a dairy herd can be determined by combining three fertility parameters into a fertility status formula ISS ). The fertility parameters are: - pregnancy rate after first insemination. - number of inseminations per conception. - average interval between parturition and conception. The fertility status formula combine these criteria in order to interpret those parameters of reproduction relative to each other and to express the level of fertility numerically. The fertility level of a dairy herd is determined by an interplay of management aspects applied by the farmer and factors intrinsic to the cow in any given environment. Many factors can influence this interplay and these can broadly be grouped under: environment and management conditions, management itself and genetic conditions. This paper attempts to discuss broad fields that may influence the fertility of a dairy herd. Attention will be focussed particularly on the relationship between these factors and the three parameters of fertility.

* Clinic for Veterinary Obstetrics, A. I. and Reproduction, State University Utrecht, Yalelaan 7, de Uithof, Utrecht, The Netherlands.

+ Presented to the NZVA Conference 1978.

Season With regard to season we have to differentiate between effects of tropical and temperate areas. In temperate regions, fertility is higher in spring breeding(2) (54) (147) than autumn and winter breeding. The general explanation given for lowered fertility in autumn and winter is that there are more difficulties in detecting oestrus, as cows are confined and oestrus signs are less obvious. It is further supposed that the short day length may contribute to this lowered fertilit y l2l( 40 )(SI)(S4)(I22)1182). The lowered fertility results in a lowered conception rate after first insemination, more repeat breeders and a longer interval between calving and conception (2) (23)(24)(25) (54)19S) In the tropics, relatively poor reproductive performances have been observed in cows bred during the dry season. The main failures manifested were those of increased number of inseminations per conception, and anoestrus. The finding may be explained by heat stress and the reduction offodder. A seasonal pattern of high fertility has been associated with rainy months II os II 173) •

Housing System The pasture can be regarded as the natural environment for cows. In many countries, cows stay in the fields throughout the year. If cows have to be housed during the winter, the conception rate after first insemination may be affected negatively depending on the housing system. Housing may also be associated with a lengthened interval from calving to first oestrus Continued on page 183

Continued from page 178

because the oestrus detection rate in winter time is also lowered. These factors together result in a lengthened interval from calving to first insemination and conception. Reproductive disorders caused by infections are also noticed more frequently in cows living in confinement (2 )(54)(65)(114)(221)(224)(225). In addition to the housing system. other factors such as nutrition, season, and hygiene may also affect the ultimate reproductive capacity of a herd under these circumstances. Oestrus detection is much more difficult in tie-stalls than in loose housing systems where freedom of movement exists and where behavioural signs of oestrus such as grouping, mounting and riding, and the standing reflex are easy to observe. Expression of oestrus may also be affected by the light intensity in the stall. especially in tie-stalls. Dim light makes it difficult to see physical signs of oestrus while, at the same time, the endocrinological stimulus to show overt oestrus may be depressed. Oestrus may also be absent in winter time due to less active ovaries in heifers, primiparous and to a lesser extent, in secondiparous cows with a high milk yield. This is especially true in cows in tie-stalls during winter(57) (123) but also in the countries in which the cows are not housed (139).

Downloaded by [University of Bristol] at 21:12 25 January 2015

183

NEW ZEALAND VETERINARY JOURNAL

1978

Size of the herd The effect of herd size on reproductive capacity is fully dependent on the efficiency of the existing management system. An increase in size of a dairy herd is often accompanied by a lowered conception rate at first service (2) (9) (32) (55) (60) (92) (138) (140) (162) (163)(194) In contrast to small herds, the interval from calving to conception is generally shorter in large-sized herds(55)(194). This is mainly due to starting breeding sooner after calving which also results in lower conception rate at first insemination. In spite of the fact that more inseminations per conception are needed, the average interval to conception is still shortened in large herds. In large herds, cows not conceiving after two or three inseminations are culled earlier. In turn this may affect the average number of inseminations per conception and the interval from parturition to conception positively. In many large-sized herds, milk production is high, indicating that general management is above average. If, however, the number of cows per herdsman increases above a critical point, there is less time to watch cows for oestrus and for recording. This may result in several effects, such as longer intervals from calving to first insemination and to conception, insemination of cows not in oestrus or too soon after calving, irregular oestrus and service intervals and ultimately to involuntary culling(32) (95) (132). Thus, mass handling beyond this point appears to be less conducive to efficient reproduction. Regular reproduction requires individual attention to each cow from calving to conception (29). Therefore, institution of a herd fertility programme may be very helpful in large herds. A sudden increase in herd size by purchase of cows, together with alteration of the housing system from a tie to a loose (cubicle) stall, is often accompanied by low conception rates. Improvement will only occur when dairy men and cows have adjusted themselves to the new environment and management system (54) (55)(223).

Age composition of the herd The conception rate after first insemination and the interval from calving to conception is influenced by the age of the cow. Low conception rates have been reported in primiparous cows and in cows over seven years (2) (23) (24) (25) (55) (59) (60) (l7l). Most authors report that primiparous cows have a longer interval from calving to conception. The lengthening of the interval, and the lowered conception rate, is attributed to more problems in these cows

around the time of parturition and early post-partum period. This was shown by de Kruif(55) who found no differences in conception rate when primiparous cows, which had calved normally and in which the placenta had not been retained, were compared with a similar group of secundiparous, triparous and quadriparous cows. The lengthened interval from calving to conception in primiparous cows may be due partially to a longer interval to the first oestrus. This is usually the consequence of ovarian inactivity, rather than a weak expression of oestrus. The higher incidence of anoestrus in primiparous cows, due to inactive ovaries, is attributed either to a competition for food by the smaller, younger cows in large herds (139)(150) or to confinement and high milk production during winter time (26)(54). Another age-related fertility problem is the occurrence of cystic ovarian disease which is most common in 4 to 6-year-old COWS(l6O). It can be concluded that, when examining the fertility status of a herd. the age-composition has always to be included. Chance The overall conception rate in a population of cattle is dependent on several factors, such as conception rate after first and subsequent services which, in turn, is dependent on semen quality, correct oestrus detection and insemination and, above all. embryonic and foetal death rate (48) (64). Other factors, such as season, age, herd size, breed, infectious and/or accidental diseases, and calving-to-first-service interval may also affect conception rate (2)(54) (164). Overall conception rates may vary considerably within herds from time to time. If an equal number of cows fail to conceive in two herds of different sizes the effect on herd fertility is much more pronounced in the smaller herd. The infertility problem is, in most cases, a temporary streak of bad luck"·'1 referable to a few individual cows, or to a special bull. Other cases emerge, as standing seasonal effects, or problems of disease, or management, which affect the herd as a whole(48). Thus. chance, based on accidental conditions, has a greater influence on conception rate and fertility in small herds, e.g. up to 30 cows, than in larger herds. In small herds, therefore, conception rates may vary markedly from year to year (20) (162) (164) 11981. Correct interpretation of data o'n reproduction must not be based on a single criterion in one period of time but on a combination of criteria used together over a number of years.

MANAGERIAL FACTORS

Breeding policy The average conception rate of a dairy herd at first insemination can be markedly influenced by the way breeding is performed. Many factors are involved such as semen quality, natural or artificial insemination, time of insemination, the skill of the inseminator and choice of the bull.

Choice of the bull There are various ways in which a bull can influence fertility. For example conception rates may be low ifsemen is inferior in quality, or a bull may be fertile but may sire mostly heavy calves which are associated with increasing calving difficulties. Dystocia. measured by stillbirth rates and calving difficulty, usually results in lower subsequent conception rates due to gross changes in the genital tract. Thus, increased calf-size can be an indirect influence of the sire on the level offertility(II) (16) (17) (55) (58) 159J(76J( 119J( 131)( 159)( 174)( 179)( 180). Dystocia rates should be published for each bull so that farmers can choose bulls associated with smooth deliveries.

NEW ZEALAND VETERINARY JOURNAL

184

Freezing of semen has enabled some excellent bulls to dominate breeding for generations. This may have produced inbreeding, with its associated depression of fertility, and increased perinatal death rates l42 ) (141) 1)1) (23». These workers advocated the remedy of outbreeding to introduce hybrid vigour which should result in higher than normal pregnancy rates.

Downloaded by [University of Bristol] at 21:12 25 January 2015

Natural service and artificial insemination

When natural service is used, fertility problems may be related to the wide variation in bull fertility. Bulls may be used for long periods before their infertility is detected. Natural service is also connected with the spread of venereal diseases(8)(84)(92)(112)(181). When AI is used, the semen quality is under daily control and bulls with inferior semen are usually not used. There is, however, a variation in fertility rate in AI of up to 15% between bulls. This occurs because bulls with poor fertility, but with outstanding breeding value, are sometimes not discarded. Another reason may be lowered survival rate of semen of some bulls after deepfreezing(24)(142). Knowledge ofthe fertility level of bulls used in a herd is a prerequisite, when investigating a fertility problem. Natural service provides a significant advantage in both first service conception rates and services per conception (62) (72) (1l8) (158) (161) (112). This is thought to be mainly due to accurate heat detection when natural service is used, although semen processing and artificial insemination procedures may also be involved.

Skill of the inseminator

In AI operations, semen is deposited into the cranial part of the cervix, or body of the uterus, by rectocervical manipulations. A variation in conception rates for various technicians between, and within, AI organizations has been confirmed by computerized results of 60 to 90 day, non-return rates(84). The variation often ranges from 5- 10%. This is usually traceable to poor training of the technicians or to loss of concentration on his work, due to personal problems or poor AI management(l69).

Time of insemination

The best conception rates are obtained when cows are inseminated from the middle.to the end of oestrus and reasonably good results are obtained up to 6 hours after the end of oestrus (I) (13) 128) (50) (87) (164) (181) 1208 ). Optimum time for insemination must be based on the time when heat begins. However, most studies under practical conditions indicate that dairy men seldom know when heat actually begins and therefore have little basis for knowing when service should be given(l64). Conception rates with AI have tended to be low because too many cows are bred that are not truly in oestrus or are at stages of oestrus incompatible with good fertility. This is mainly due to inadequate oestrus detection. There are errors in diagnosis and communication, mistaken identity, and less-than-optimum timing of insemination relative to first signs of oestrus 16)(112). Thus, prompt and accurate detection of standing oestrus is very important to obtain the highest possible conception rate. As suggested by Trimberger(21l9), cows observed in oestrus in the morning should be inseminated the same day, preferably in late afternoon, and cows noticed in the afternoon and evening should be inseminated the following morning.

VOL. 26

Oestrus detection and record keeping The farmer is the most important element of the factors involved in oestrus detection (farmer, cow and environment). Failure to detect cows in oestrus in the pre-service, service and post-service period results in: • a delayed interval from calving to first service. • a false classificaton of oestrus that results in a low conception rate and irregular cyclicity. • a delayed interval from first service to conception. • a delayed interval from calving to conception. • an absence of pre-service oestrus dates to guide future oestrus anticipations and early recognition of irregularly cycling cows due to ovarian dysfunction. • a low submission rate in herds with a restricted breeding period. • an erroneous assumption of anoestrus as a herd problem. • a high percentage of empty, bred COWS(6) (14) 118)129) 161)167)(68)(91) I100) 1117)1)51)1171)1172)1224)1225) mOl (233)

Most authors stress that inadequate oestrus detection results a loss of gross income caused by: lowered annual milk production. decreased annual calf production. higher costs for veterinary services and AI due to "created" problem-breeders. • reduced culling potential of low producers. The "created" problem-breeders result in culling of more valuable cows at prices which are too low compared to expensive replacement cows or heifers. Adequate oestrus detection is based upon good identification, recording of all oestrus dates, and three-times-daily observation: early in the morning, around noon and late in the evening for at least 20 minutes each time(6) 1)4) 128)(29)(6))(67)168) 191)(100) (117)(151)(158) 1J71) 1172) 1225) 1230) 1l3J). Poor identification of cows and a poor record keeping system lead to lack of knowledge of the last date of calving, insemination of cows too soon or too late after calving, and no records of previous services. These herds are continuously managed from a deficient base of information. Even well-managed dairies, with skilled herdsman and adequate identification and record keeping systems, are presented many times with problems such as: • variability of behavioural oestrus intensity associated with different housing systems and environment. • oestrus periods of short length. • a diurnal oestrus expression pattern. • less marked signs of oestrus, or silent heats early postpartum 16 (68) 1100) 1104) (10611117) (126) 1151) (152) 11551 (1771 (185) 1228) (229) 1234). in • • •

From time to time, veterinarians are presented with anoestrus as a difficult problem. Anoestrus in cows which have calved more than 60 days is reported to vary from II to 34%(26)(57)(86)(101)1 150). These figures may reflect poor observation, because most, apparent. anoestrus herd-problems can be tracked back 90%, or more, to the failure to observe oestrus or to deficiencies in the management system rather than to problems with the cows 129) 187) (117)1 224 )1233). In poorly managed herds, a herd fertility programme, which includes an adequate record keeping system, a regular pregnancy diagnosis, and a preventive medicine and education scheme, will help to eliminate the mismanagement. Oestrus detection can be improved by teaser bulls or by heat detection devices I63 )(161)(193)(225). However, regardless of the aid used for oestrus detection, careful observation by herdsmen still appears to be the most accurate method of oestrus detection (31). Infectious diseases and hygiene Infectious diseases such as Trichomoniasis, Vibriosis, Brucellosis, Infectious Bovine Rhinotracheitis (lBR), Lepto-

1978

NEW ZEALAND VETERINARY JOURNAL

Downloaded by [University of Bristol] at 21:12 25 January 2015

spirosis and Bovine Viral Diarrhoea (BVD) affect the reproductive system of the cow. Infertility caused by these agents may be manifested by either repeat breeding or increased number of services per conception or prolonged cycle lengths due to (early) embryonic death, metritis, mummification, abortions, stillbirth or weak newborn calves (15) (22) (39) (89) (107) (113) (118) 1168) 1186) 1199) 1205) 1218) 1227) Trichomoniasis and vibriosis are typical venereal diseases, spread through natural service. However, most protozoa, bacteria and viruses are as capable of surviving the freezing process as spermatozoa. This means that spread of these opportunistic organisms may also occur following AI of contaminated and/or improperly processed semen from infected bulls. In countries in which dairy husbandry is less developed, the infectious diseases are still common and cause great economic losses each year. In countries free from trichomoniasis, vibriosis and brucellosis, IBR may still be a problem, especially at AI stations that have infected bulls. If semen contaminated with IBR virus is introduced into the uterus at the time of artificial insemination, endometritis may occur resulting in prolonged calving intervals. AI Stations should be under regular veterinary control to prevent spread of IBR and other infectious diseases through artificial insemination I22 )(1I3). Other less known infectious diseases are mycoplasmosis and chlamydiasis(2°O). Lack of adequate laboratory facilities leads to inadequate understanding of the occurrence and spread ofthese diseases, resulting in contradictory descriptions as causes for infertility (7) (98) (130) ()87) (222).

185

must be bred early post-partum in order to get them in-calf by approximately 85 days after their previous calving date (29) (66) (132) (136) (171) (172) (190) (195) (207) (212). However, in cows with a good lactation persistency, a prolonged c.l. is economically acceptable (92). Many factors may influence the calving-to-conception interval. In all breeds, the interval from calving to first service primarily and substantially affects the average calving-to-conception interval even though more inseminations per conception are required for cows bred during the first 2 months post-partum (31)(32) (55) (90) (J08) (140) (16)11)65) (188) '(190) (194) (2)9). Assessment offertility, therefore, should not be based on a single criterion such as the pregnancy rate, but on all criteria in relationship to each other. Low pregnancy rates are not invariably evidence of poor fertility(57). The interval from calving to first service is influenced by: (I). A.I. and farm policy; for example: better conception rates, and so fewer repeat services, are obtained when breeding is started late post-partum, when calving does not occur during cold weather or during crop harvest, or when milk prices are low. (2). Oestrus detection rate; the greatest variation in calving to first oestrus and to first service has been attributed to the differences in method of detection of oestrus (29) (68) (72) (87) (117) (143) (172) (190) (194)(224) Inadequate oestrus detection is also often the cause of increased intervals between infertile services in empty, bred cows 129)168) 1140)1)71) (190).

Besides specific disease entities, non-specific genital infections are usually present in one or more cows in nearly every herd, especially in the early post-partum period. Inadequate hygiene at the time of calving, all types of calving difficulties, and abnormalities in the early post-partum period, such as retained' placenta, may result in purulent infections of the uterus. These conditions result in a 5-20% decrease in conception rate at first insemination, a lengthened calving-to-conception interval, and a higher percentage of cows culled for reproductive failures (10) (30)

Other factors influencing the calving to conception interval are: conception rate(l43)(l94); parity (2) (24) 155) (136) (140) ()43) ()55) ()94); season 121 155) 183) (84); herd size 1140) I)94); reproductive disorders (17211203); restricted breeding season (140)(154); and milk production(95)('56)()94). The most important prerequisite for successful early breeding is evaluation of the individual cow. She should have a normal calving and puerperial history, good body condition, and a normal reproductive tract. She should have had at least one oestrus prior to breeding and her past record of conception should be good (91155)(10811137). Early breeding appears not to have a negative affect on reproductive performance at later stages of reproductive life(l65)

(52) (54) (154) (172) (181) (203) •

4219}

The lowered conception rate and extended calving interval could be improved by decreasing the frequency of difficult birth and by improving sanitation when handling obstetrical cases. Post-parturient, uterine infection may also be seen frequently in loosely housed cattle in winter or summer. Confinement encourages close contact between cows discharging virulent micro-organisms and healthy animals may also become infected. It is essential to observe strict hygienic measures during calving and separate parturient cows into clean maternity facilities to maintain sanitary conditions(55) (234). Special attention has to be paid to corynebacteria pyogenes infections in primiparous cows. Due to an inadequate immune response. these cows are more likely to become infected and their fertility is decreased.

In conclusion, long calving intervals are mainly due to delayed first service, missed oestruses and/or low conception rate. The interval in many herds can be reduced by breeding normal cows on the first heat beyond 45 days post-partum.

Interval calving to breeding The effect of calving-to-first-service interval, and other factors, on the calving-to-conception interval have been studied many times because of their economic importance. Many workers have shown that a long (> 90 days) calving-to-service interval results in higher conception rates after first insemination, decreased inseminations per conception, and a shortened interval from first service to conception, and also in a prolonged interval from calving to conception (23) (3) (48) (63) (75)()64)()88)(207) (2JO) (1Il) (219) . From an economic point of view a l2-month-calving interval (C.I.) is desirable because the dairyman obtains a greater return over feed costs than with longer intervals. This means that cows

Nutrition and milk yield Most reports on the relationship between nutrition and fertility suggest a positive relationship when liveweight changes are used as an index. They give experimental evidence that low planes of nutrition lead mainly to anoestruS, and to a lesser extent, to reduced conception rates (33) (34)(35)(43)(74)(94)(97) (109){IIO) (115) (lib) (128) (134) (135) (144) (183) (206) (226)

In contrast, Munro (157) could find no conclusive evidence for a relationship between fertility and live weight. Boyd (2S) reported an improvement in conception when cows were gaining weight but his data were not statistically significant. Moreover, he observed that weight-loss was not detrimental to fertility. It has also been observed that, under field conditions, it is difficult to find a single nutrient deficiency(5) (156) I)67). It is difficult to pinpoint for certain a single nutrient deficiency or excess as the basis of a fertility problem. There is, therefore, no nutrient antidote for infertility - a misconception that has long been created in the minds of dairymen by the marketers of feed additives supposed to aid fertilit y I3)(4). In general, it can be stated that, if the nutritive requirements for production (milk yield, gestation and general body health) are met, the animal's nutritive requirements for reproduction should be adequate. However, it is often discovered that, in cases

186

NEW ZEALAND VETERINARY JOURNAL

where nutrition is incriminated as a likely cause of infertility, other managerial factors are also inferior, so the infertility is created by the unskilled dairyman. Milk production is closely related to nutrition. The affect of stress on milk yield has long been a controversial subject. Some authors claim it depresses fertility (45) (46) (49) (73) (95) (96) (99) (129) (153) (154) (156) (194) (217). Others claim that there is no evidence for the negative relationship between production levels of milk and the parameters of fertility (9) (25) (27)(44) (120)(121) (148)(157) (191)(207); to resolve this

Downloaded by [University of Bristol] at 21:12 25 January 2015

question, more critical experimental work should be devised to include all the evidence in a convincing mathematical model. Culling rate To correctly interpret the reproductive information from a herd, it is essential to know the total number of cows culled and the number of inseminations in each non-pregnant cow culled. In certain breeding and pedigree herds, insemination of particularly valuable cows is occasionally continued over prolonged periods (55) (60). This may lead to a long average interval between parturition and conception and more services per conception. Cows which do not become pregnant immediately in some other herds are culled rapidly; this naturally decreases the interval between parturition and conception and the average number of inseminations per conception (60). Culling rates are highest in heifers and old cows(21). GENETIC CONDITIONS

Hereditary factors The incidence of hereditary disorders that can influence the reproductive efficiency of a cattle population presents an iceberg-like phenomenon. Anomalies, which are rooted in the base population from years ago, continue to exert deleterious effects upon reproductive performance from time to time. The origin of the responsible gene can usually be traced back to the introduction of valuable breeding bulls or stud cows. The clas~ical examples of these afflictions are: • • • •

•

Hypoplasia of the gonads in the Swedish Mountain Breeds of dairy cattle which occuruni- or bilaterally in both sexes(64)(127). Aplasia or hypoplasia of the genital ducts or White Heifer Disease(19)(70)( 173) (197). Double cervix (18) (I 11)(133) (189)(196). Lethals caused by genes which affect the viability of the foetus prior to, or after, birth and which are important in overall reproductive efficiency. Examples are the "bull-dog" calf, hydrocephalus and muscle contractures (79). Lethal genes may cause increased stillbirth and calving difficulties which, in turn, may give rise to infertility. Cystic ovaries. This is usually found in association with families that have high milk production (38) (78) (80)(93) (146) (181) (192)

It is doubtful, however, whether there is genetic correlation between the milk yield and cystic ovarian disease. • Lack of libido - impotentia coeundi in bulls(12)(S3). Gross hereditary malformation is not important in the fertility 'issue; for example, the bilaterial-gonad-hypoplasia condition gives rise to complete aspermia in bulls and anoestrus in heifers; these cause natural selection for fertility. More important situations, however, are those of partial malformation which permit the carrier to perpetuate the hidden anomaly at a reduced level of fertility. Thus, the more reason for careful sire selection, especially of AI bulls. For example, studies conducted by Gustafsson(81) on chromosomes from the blood lymphocytes demonstrated the occurrence of a centric fusion in the Swedish red and white breeds of cattle which appeared to be related to lowered conception rates (47) (69) (36) and Halnan (88) have since

VOL. 26

demonstrated similar results with other breeds of bulls in Europe. Reproductive traits Reasonably accurate methods for determining the heritability and repeatability values for the specific parameters of fertility, such as intensity of oestrus, calving-to-conception interval and non-return rates have been devised (184) (103) (85) (71)(215)(124)(125). Unhappily, all these workers determined that these reproductive traits show values of repeatability and heritability that are too low to be of any use for the improvement 'of conception. However, since large variations exist both between, and within, breeds and since a high reproductive rate has fundamental importance for breeding stock, the values of these traits should always be given, when available, for bulls in breeding centres(76). In discussing the complex problem of fertility, it is relevant to note that the animal is under the dictates of both its environment and its genotype. It is always difficult to separate genetic influences on general fertility, especially since heritabilities are so low. It is clear that heat detection is one of the environmental and managerial factors which still remains the most important influence, rather than hope, to breed for fertility. DISCUSSION

Realizing the complex nature of fertility, it is not surprising to find that it has long been difficult to develop internationally acceptable standards. However, some workers have already designed quite acceptable criteria (55)(153)(181). Ideal criteria are: • a pregnancy rate of 80% at first insemination. • an average of 1.3 inseminations per conception. • an average of 85 days between parturition and conception. These ideal values are not easily attainable in practice because of the influence of the factors discussed above. When infection is involved as a factor in infertility, it can be due to either specific (brucellosis, trichomoniasis, IBR, etc.), or to non-specific, genital infections. The former often strike a whole herd, causing a storm of abortions and repeat-breeding. The latter are opportunists of unsanitary conditions during calving, dystocia and abnormal puerperium. They often take an insiduous course. However, specific infections have been eradicated, or at least controlled, in many countries, but they are still enzootic in a big part of the globe. The advice usually rendered to the latter countries is to follow the example of the countries which have succeeded in eradicating these specific maladies. Then, they can dream of uplifting the standards of their livestock industries by other means. It is generally agreed that the main, negative influence on fertility of a dairy herd stems, not as much from specific or non-specific infections, as from the effects of a host of other factors. These factors seldom exert their effects individually but interact together, making it difficult to analyse infertility in a given herd. For example, the advancement of animal husbandry practices has increased both herd size and production, but man hours per cow have dwindled. The direct result of this decrease is less time for detecting heat and instituting hygienic measures. The inadequacy of heat detection with its disastrous end-results are well known (32)(68) (132) (224). This is a simplification of the whole issue because it is never as direct as that. Modern farming in large herds is generally coupled with lower conception rates at first service. This is partly because of a tendency to start breeding early in these larger herds, compared to small herds which usually attain low management standards. Early breeding results in more services per conception but also in a shorter calving interval. The increase in the number of

NEW ZEALAND VETERINARY JOURNAL

Downloaded by [University of Bristol] at 21:12 25 January 2015

1978

services per conception tends to increase the culling rates in these advanced large herds which paradoxically may lower the number of inseminations per conception. Other factors may interfere as well. Thus the final fertility status ofsuch a herd is the result of interactions of a whole range of factors from environmental conditions such as season, herd size, age composition, to pure managerial factors like breeding policy, oestrus detection, etc. Breeding efficiency depends almost totally on whether or not the skill of the farmer can cope with these factors in his herd. Much of the genetic cause of infertility can be reduced by early diagnosis and culling, combined with selection at AI stations. This has been shown by the workers in Sweden. The incidence of cystic ovarian follicles in cattle was reduced from 10.8% in 1954 to 5.1 % in 1961 by eliminating all those bulls with susceptible daughters. This is an example of a sacrifice of milk, as the cystic disease is known to be associated with high milk-yields(220). Fertility of a dairy herd is thus a relative phenomenon, expressing what the cows have been able to achieve in the face of a host of interacting factors. It should explain why a Friesian cow in the tropical regions may produce a calf per two years instead of annually as the interaction of climate and nutrition will form the limiting situation. To avoid a deterioration of fertility below the accepted standards, the advice given to the farmer hinges on how he can best manage his herd under given environmental and management conditions. Many workers have advocated that such advice can best be given by paying regular visits to the farmer (Herd Fertility Control Programme) so as to impress upon him the relevant factors of management (56) (1 12) (166) (2321

REFERENCES (I) Almquist. F. O. (1973): Arlificial insemination in farm animals - Dairy Cattle. 94-141. Edited by Enos J. Perry 41h Ed. (2) Andersen, H. (1966): The effect of season of the year, age of the cow and size of the herd on fertility in cows. Arsbereln. Insl. f Sierililelsforskn: 227-47 (3) Anon. (1957): A.I. Digesl. 5: 17. (4) Anon. (1957): A.I. Digesl. 5: 21. (5) Anon. (1968): Prenatal and postnatal mortality in cattle. N.A.S. Publicalion 1685. • Washington, D.C. (6) Appleyard, W. T. & C. Cook. B. (1976): The detection ofoestms in dairy cattle. Vel. Rec. 99: 253-6. (7) Archibald, L. F., Gibson, C. D., Schulz, R. H., Fahning. M. L. & Zemjanis, R.. (1973): Effects of intrauterine inoculation of bovine viral-diarrhea-mucosal-disease virus on uterine tubes and uterus of non-pregnant cows. Am. J. vel. Res. 34: 1133-7. (8) Ayalon, N. (1964): Sterilitassine materia. Proc. 51h Int. Congr. Anim. Reprod. &A.I.• Trento, v. 47-80. (9) Ayalon, N. Harrari. H. H., Lewis, I., Posener, L. A. & Cohen, Y. (1971): Relation of the calving -to service interval to fertility in dairy cows with different reproductive histories. production levels and management practices. Refuah Vel. 28: 155-65. (10) Bach. S. & Priebus. G. (1972): Untersuchungen zum Puerperaiverlauf in Rinderherden. Mh. Vel. Med. 27: 499-502. (II) Baier, W., BOSledt, H. & Schmidt. G. (1973): Uber die Fruchtbarkeitslage nach Schwergeburten beim Rind. Berl. Munch. Tierarzll. Wschr. 86: 3-7. (12) Bane. A (1954): Sexual functions of bulls in relation to heredity. rearing intensity and somatic conditions. A cia. Agric. Scand. 4: 95-103. (13) Bane, A, (1964): Fertility and reproductive disorders in Swedish cattle. Br. vel. J. 120: 431-41. (14) Barr. H. L. (1975): Influence of estrus detection on days open in dairy herds.l. Dairy Sci. 58: 246-7. (15) Bartlett, D. E. (1968): Bovine venereal trichomoniasis and bovine abonion. In: Abortion, Disease of LiveSlock. L.. C. Faulkner (ed.). Charles C. Thomas, Springfield. lIIinois. (16) Bellows. R.A.Short, R. E., Anderson, D. c., Knapp. B. W.andPahnish,O. F.(1971): Cause and effect of relationship associated with calving difficulty and calf birth weight.J. Anim. Sci. 33: 407-15. (17) Bellows. R. A. (1971): Calf losses in beef callie. Mimeo. U.S. Range Livetock Exp. Sla .. Miles City. Montana. ( 18) Benesch. F. (1944): Erkrankungen der cervix als Sterilitatsursache beim. Rind. Ber/. Munch. Tierurzi/. Wschr.• 314 (Vel. Bull., Wyebridge, 17.477, no. 2014, (1947». (19) Bennett. R. C. Olds, D., Deaton, O. W. & Thrift, F. A. (1973): Nature of white heifer disease (Partial genital aplasia) and its mode of inheritance. Am. J. Vel. Res. 34: 13-19. (20) Bishop, M. W. H. (1964): Paternal contribution to embryonic death.J. Reprod. Ferl. 7: 383-96. (2 I) Bond. 1. and MacDowell, R. E. (1972): Reproductive performance and physiological responses of beef females as affected by a prolonged high environmental temperature. J. Anim. Sci.: 820-7. (22) Bouters. R .. Vandelplassche. M., F1orent, A., & Leunen,J. (1964): Vimsinfectie en steriliteit bij runderen. Vlaams Diergeneesk. Tijdschr. 33: 405-21. (23) Boyd. H. & Reed, H. C. B. (196Ia): Investigation into the incidence and causes of infertility in dairy caule. - Fertility variations. Hr. Vel. J. 117: 18-31. (24) Boyd. H. & Reed, H. C. B. (196Ib): Investigation into the incidence and causes of infertility in dairy cattle: - Influence of some management factors, factors affecting the semen and inseminalion conditions. Hr. vel. J. / J 7: 74-86.

187

(25) Boyd. H. & Reed, H. C. B. (196Ic). Investigation into the incidence and causes of infertility in dairy caUle: - Influence of kale feeding, milk production and management. Br. vel. J. 117: 192-200. (26) Boyd. H. (1977): Anoestrus in caule. Vel. Rec. 100: 150-53. (27) Boyd. L. J., Sheath. D. M. & Olds, D. (1954): Relation between the level of milk production and breeding efficiency in dairy cattIe.J. Anim. Sci. /3: 89-93. (28) Boyd, L. J. (1970): Managing dairy cattle for fertility. J. Dairy Sci. 53; 969-72. (29) Bozworth, R. W., Ward. G .. Call, E. P. & Bonewitz, E. R. (1972): Analysis of factors affecting calving intervals of dairy cows. J. Dairy Sci. 55: 334-38. (30) Brands, A. F. A. (1966): Enige :wotechnische aspecten van retentio secundinarium bij runderen. Thesis. Utrecht. (3 I) Brill, J. H. (1975): Early post partum breeding in dairy cows. A review.J. Dairy Sci. 58: 266-71. (32) Brill, J. H. (1977): Strategies for managing reproduction and controlling health problems in groups of cows. J. Dairy Sci. 60: 1345-53 (33) Broster, W. H.(1971): The effect on milkyieldofthecowoftheleveloffeedingbefore calving. Dairy Sci. A bSlr. 33: 253-70 (34) Broster. W. H. (1972): Effect on milkyield of the cow of the level of feeding during lactation. Dairv Sci. A bSlr. 34: 265-88. . (35) Broster. W. H. (1973): Liveweight change and fertility in lactating dairy cows: A review. Vel. Rec. 93: 417-20. (36) Bruere. A. N. & Chapman. H. M. (1973): Autosomal translocation in two exotic breeds of callie in New Zealand. Vel. Ree. 92: 615. (37) Carroll, E. 1. & Hoerlein. A. B. (1972): Diagnosis and control of bovine genital vibriosis. J.A. V.M.A. 161: 1359-64. (38) Casida. L. E. & Chapman, A B. (1951): Factors affecting the incidence of cystic ovaries in a herd of Holstein cows. J. Dairy Sci. 34: 1200-5. (39) Clark, B. L. (1971): Review of bovine vibriosis. Ausi. Vel. J. 47: 103. (40) Cohen, Ph. (1956): Een statistisch ondenoek omtrent retentio secundinarum en enige andere, met de voortplantingsamenhangende processen bij hetmnd. Thesis, Utrecht. (41) Conlin. B. J. (1974): Use of records in managing for good lactational and reproductive performance. J. Dairy Sci. 57:: 377-85. (42) Conneally, P. M., Stone, W. H., Tyler, R., Casida, L. E. & Morton. N. E. (1963): Genetic load expressed as fetal death in cattle. J. Dairy Sci. 46: 232-6. (43) Crowley. 1. P. (1968): Anfora< lalunlais Agricultural Institute Dunsinea. Research report. (44) Currie, E. J. (1956): The influence of milk yield on fertility in dairy caule. J. Dairy Res.• 32: 301-4. (45) Damm. H. 1. (1965): Beziehungen zwischen Milchleistung and Fruchtbarkeit beim Rind (Untersuchungen in GrUnland betrieben) Thesis. Hannover. (46) Dannenberg. K. (1967): 1st die Konzeptionsbereitschaft beim Rind leistungsabhiingig? Thesis, GOllingen. (47) Darre, R., Queinnec, G. & Berland, H. M. (1972): La translocation 1-29 des bovins. Etude generale et imponance du pheno-mene dans Ie sud-ouest. Revue M.d. Vel. 123: 477-94. (48) David: -J. S. E., Bishop, M. W. H. & Cembrowicz, H. J. (1971): Reproductive expectancy and infertility in caule. Vel. Rec. 89: 181-5. (49) Dawson. F. L. M. (1963): The effect on fenility of high milk production in cattle. Refuah Vel. 20: 237-42. (50) Deas, D. W. (1970): The timing of insemination. Vel. Rec. 88: 450-1. (51) Deas. D. W. (1971): The effect of supplementary light on winter infertility in callie. Vel. Rec. 89: 242. (52) De Bois, C. H. W. (1961): Endometritis en vruchtbaarheid bij het rund. Thesis, Utrecht. (53) De Groot, T. & Numans, S. R. (1946): OverdeerfeIijkheid der impotentiacoeundii bij stieren. Tijdsch. Diergeneesk. 71: 372-9. (54) De Kruif, A. (1975a): Fertiliteit en subfertiliteit bij het vrouwelijk rund. Thesis, Utrecht. (55) De Kruif, A. (l975b): An investigation of the parameters which determine the fertility of a cattle population and of some factors which influence these parameters. Tijdschr. Diergeneesk. 100: 1089-98. (56) De Kruif, A. (1976): A fertility control programme in The Netherlands. Tijdschr. Diergeneesk. 101: 428-30. (57) De Kruif, A. (1977): Een onderzoek van runderen in anoestrus. Tijdschr. Diergeneesk. 102,247-253. (58) Dieten, S. W. 1. van (1963): Monaliteit van kalveren bij de partus a terme van M.R.Y.-runderen. Thesis. Utrecht. (59) Dieten, S. W. J. van (1964): Fenility after stillbirth in callie. ProI-Christensen, L., Lederer, J., McClintock, A. E., Mocquot, J. C. and Philipsson, J. (1977): Livesl. Prod. Sci., 4: 115-28. (77) Gangwar, P. c., Branton, C. and Evans, D. L. (1965): Reproductive and physiological responses of Holstein heifers to controlled and natural climatic conditions. J. Dairy Sci., 48: 222-7. (78) Garm, 0., (1949): A study on bovine nymfomania. A cIa endoer.: Vol. 2 Suppl. 3. (79) Gilmore, L. O. (1949): The inheritance of functional causes of reproductive efficiency: A review. J. Dairy Sci. 32: 71-91. (80) Goossens, J. H. H.; (1971): Psychogene milieuinvloeden als oonaak van bedrijfssteriliteit. Tijdschr. Diergeneesk. 96: 603-22. (81) Gustafsson, I. (1969): Cytogenetics, distribution and phaenotypic effects of a translocation in Swedish cattle. Heredilas 63: 68. (82) Gwazdauskas, F. C., Thatcher, W. W. & Wilcox, C. J. (1973): Physiological, environmental and hormonal factors at insemination which may affect conception.J. Dairy Sci. 56: 873-7. (83) Gwazdauskas, F. c., Wilcox, C. J. & Thatcher. W. W. (1975): Environmental and managemental factors affecting conception rate in a subtropical climate. J. Dairy Sci. 58: 88-92. (84) Hafez, E. S. E. (1974): Reproductive failure in males and artificial insemination in: Reproduclion infarm animals. Third edition 1974, pp. 373-83 and 409-31. (85) Hahn,J. (1969): Inheritance of fertility in cattle inseminated artifically. J. Dairy Sci. 52: 240-4. (86) Hall, 1. G., Branton, C. and Stone, E. J. (1959): Oestrus, oestrous cycles, ovulation time, time of service and fertility of dairy cattle in Louisiana, J. Dairy Sci. 42: 1086-94. (87) Hall, J. G., Branton, C. and Stone. E. J. ( 1959): Heat detection efficiency in open cows in Louisiana. J. Dairy Sci. 42: 1086-94. (88) Halnan, C. R. E. (1975): Chromosomes of cattle: Present clinical status and promise. Vel. Rec. 96: 148-51. (89) Hanson, L. E. (1960). Bovine leptospirosis: A review. J. Dairy Sci. 43: 453-62. (90) Harrison, D. S., Meadows, G. E., Boyd, L. J., Britt, J. H. (1974): Effect ofintervalto first service on reproduction. lactation and culling in dairy cows. J. Dairy Sci. 57: 628 (abstr.). (91) Hartigan, P. J. (1972): The veterinarian and fertility in the dairy herd. Irish. vel. J. 26: 153-9. (92) Heimann, M. M. (1977): Ergebnisse und Erkenntnisse aus der Besamungszucht in Israel. DIsch. Tieriirzll. Wschr. 84: 205-9. (93) Henricson, B. (1956): Genital and statistical investigations into the cystic ovaries in cattle. Proc. 3rd into Congr. Anim. Reprod. & A.I" Cambridge, Vol. II, 49-51. (94) Hentegs, J. F. (1967): Level offeeding and bull performance. In: FaClors affecling calfcrop. Edited by Cunha, Warnick & Koger, Gainesville, University of Florida Press. (95) Hewett, C. D. (1968): A survey of the incidence of the repeat breeder cow in Sweden with reference to herd size, season, age and milkyield. Br. vel. J. 124: 342-52. (96) Hewett, C. D. (1971): A study of the possible effects of certain environmental factors on fertility and milk production of dairy cows in Sweden. Nord. Vel. Med 23: 65-85. (97) HiIl,J, R., Lamond, R., Henricks, D. M., Dickey,J. F. and Niswender, G. D. (1970): Effects of undernutrition on ovarian function and fertility in beef heifers. Bioi. Reprod 2: 78-84. (98) Hirth, R. F., Plastridge, W. N., Toutellotte, M. E. & Nielson, S. W. (1966): Genital mycoplasmosis in cattle and man. J. Am. vel. med Ass. 148: 277. (99) Horvath, M. (1967): Reproduction in high producing cows. Animal breeding abo slracts 35: 241 (Abstract no. 1330). (100) Hurnik, J. F., King, G. J., Robertson H. A. (1975): Oestrous and related behaviour in post partum Holstein cows. Appl. Anim. Ethol. 2: 55-65. (101) Hurst, V. (1959): Studies on anoestrum in dairy cows. J. Am. vel. med. Ass. 135: 471-5. (102) Ingraham, R. H. (1973): Estimation of conception rate depression of Holstein cows by adverse temperature and humidity in tropical and subtropical climates. 1nler. J. Biomeleor. 17: 131-4. (103) Inskeep, E. K., Tyler, W. J. & Casida, L. E. (1961): Hereditary variation in

(123) Kordts, E. & Gravert, K. O. (1972): Einfluss vonkiinsllichem Licht und Bewegung auf die Fruchtbarkeit der KUhe. Proc. 71h Int. Congr. Anim. Reprod. & A.I., MUnchen, III, 2016. (124) Krausslich, H. (1974): Der Einfluss der Rastzeit aufverschiedene Fruchtbarkeitsparameters. Berl. Munch. Tieriirzll. Wschr. 87: 276-8. (125) Krausslich, H., Osterkorn, K. & Richter, H. (1977): Die zUchterische Auswertung von Non-Return-Werten in Besamungspopulationen. Ziichlungskunde 49: 92-8. (126) Labhsetwar, A. P. (1963): Genetic and environmental factors affecting quiet ovulations in Holstein callie. J. Dairy Sci., 46: 843-7. (127) Lagerlof, N. & Boyd, H. (1953): Ovarian hypoplasia and other abnormal conditions in the sexual organs of cattle of the Swedish Highland Breed: results of post mortem examination of over 6000 cows. Cornell Vel, 43: 64-79. (128) Lamond, D. R. (1970): The influence of undernutrition on reproduction in the cow. Anim. Breed. Abslr. 38: 359-71. (129) Lampo, P.. Vanschoubroek. F. & WilIcm, A. (1963): De invloed van de kalvingsmaand. de melkproductie, het vet-, eiwit- en het laktosegehalte op de duur van de tussendracht-periode bij Oost-Vlaamse Stamboekvaarzen. Vlaams Diergeneesk. Tijdschr: 32: 217-34. (130) Langford. E. V. (1975): Mycoplasma species recovered from the reproductive tracts of Western Canadian Cows. Can. J. Compo Med. 39: 133-8. (131) Laster. D. B.• Glimp. H. A., Curdiff, LL. V. & Gregory, K. E. (1973): Factors affecting dystocia and the effects of dystocia on subsequent reproduction in beef call1e.J. Anim. Sci: 36: 695-705. (132) Lauderdale. J. W. (1974): Oestrus detection and synchronization of dairy cattle in large herds. J. Dairy Sci. Vol. 57: 348-54. ( 133) Locn. A. van ( 1961): A contribution to the knowledge of the double cervix condition in bovine callie. Thesis. University of Utrecht. (134) LOllhammer, K. H. (1974): Haufige FUtterungsfehler als Ursache der Herdensterilitlil. Prakl. Tierarzl. 55: 38-53. (135) Lotthammer, K. H. & Ahlswede, L. (1973): Beziehungen zwischen FUtterung und Fruchtbarkeit beim weiblichen Rind I + II. Ubersichlen zur Tiererniihrung. 1: 147-61: 325-53. ( 136) Louca. A. & Legates J. E. (1968): Production losses in dairy caule due to days open. J. Dairv Sci. 51: 573-85. (137) Machnai, B. & Kali. J. (1971): Early insemination after parturition in three dairy herds. Refuah Vel. 28: 112-5. (138) Macmillan. K. L.& Watson.J. D. (1971): Short estrous cycles in New Zealand dairy callie. J. Dairy Sci. 54: 1526-9. (139) Macmillan. K. L, Fielden, E. D., Watson, J. D. (1975): The anoestrus syndrome in New Zealand dairy cattle. N.Z. vel. J. 23: 4-8. (140) Macmillan. K. L. & Moller. K. (1977): Aspects of reproduction in New Zealand dairy herds II. Calving interval, breeding and non-pregnancy rates. N.Z. vel. J. 25: 220-4. (141) Mares. S. E. Menge. A. c., Tyler, W. J. & Casida, L. E. (1961): Genetic factors affecting conception rate and early pregnancy loss in Holstein cattle.J. Dairy Sci. 44: 96-103. (142) Mann, T. (1976): Relevance of physiological and biochemical research to problems in animal fertility. Prot. R. Soc. Lond. B 193: 1-15. (143) Marion. G. B.. Norwood, J. S. & Gier. H. T. (1968): Uterus of the cow after parturition: Factors affecting regression. Am. J. Vet. Res. 29: 71-5. (144) McClure. T. J. (1965): Experimental evidence for the occurrence of nutritional infertility in otherwise clinically healthy pasture-fed lactating dairy cows. Res. Vel. Sci. 6: 202. (145) McKercher, D. G. (1969): Cause and prevention of epizootic bovine abortion. J. Am. vel. med. Ass. 154: 1192-6. (146) Menge. A. C.. Mares. S. E.. Tyler, W. J.. & Casida, L. E. (1962): Variation and association among post partum reproduction and production characteristics in Holstein-Friesian callie. J. Dairy Sci. 45: 233-44. (147) Mercier. E.& Salisbury.G. W.( 1947): Fertilitylevel in artificial breeding associated with season. hours of daylight and the age of callie. J. Dairy Sci. 30: 817-26. (148) Metz. J. H. M. & Politiek, R. D. (1970): Fertility and milk production in Dutch' Friesian callie. Nelh. J. Agric. Sci. 18: 72-7. (149) Miller, R. B. (1977): A summary of some of the pathogenic mechanisms involved

(104) Ithamar, U. and Schindler, H. (1976):: Length of oestrus and mounting activity of post partum dairy cows. VIJJlh Inler. Congr. Anim. Reprod. & A. 1" Krakow. Vol. V.1192-3. (105)Jainudeen, M. R. 1976): Effects of climate on reproduction among female animals in the tropics. VI/llh Int. Cong. Anim. Reprod. & A.I. Krakow, Vol. II, 29-38. (106) Johnson, K. R. (1966): Oestrus intensity in dairy cattle. J. Dairy Sci. 49: 731-2. (107) Kahrs, R. F (1973): Effects of bovine viral diarrhoea on the developing foetus. J. Am. vel. med Ass. 163: 877-8. (108) Kalay, D. (1972): Early insemination after parturition. Congr. Proc. Vll Inlern. Congr. Anim. Reprod & A.I., MUnchen. 1408-14. (109) KaIi, J. & Amir, S. (1970): Commission on animal management and health. Proc. Eur. Ass. Anim. Prod, GOdOllo, Hungary. (110) Kali, J. and Amir, S. (1968): Liberal feeding of concentrates as a means of higher production. Part IV: Fertility in dairy cows in relation to plane of nutrition. 2nd Ann. Reporl of Res. USDA. p.34. (III) Keller, K. (1920): Demonstration einer Fleischspange vordem Muttermunde einer Kuh. Wien. TieriirZII. Mschr. 7: 69. (112) Kelly, 1. W. (1974): A modified herd reproductive status (HRS) programme for south Carolina dairy herds. Symposium paper 69th Ann. Dairy Sci. Assn. Annual Meeling, June 23-26. (113) Kendrick, W. J. & McEntee, K. (1967): The effect of artificial insemination with semen contaminated with IBR-IPV virus, Cornell Vet. 57: 3-11. (114) Kiddy, C. A. (1977): Variation in physical activity as an indication of estrus in dairy cows. J. Dairy Sci. 60: 235-43. (115)King,G.J. (1967): Changes in body weight and milk composition in cows. Vel. Ret.

(150) Moller. K. (1970): Uterine involution and ovarian activity after calving. N.Z. vel. J. 18: 140-5. (151) Monty, D. E & Wolff, L. K. (1974): Summer heat stress and reduced fertility in Holstein-Friesian cows in Arizona. Am. J. vel. Res. 35: 1495. (152) Morris. C. A.• Hurnik. J. F., King. G. J., Robertson, H. A. (1976): A cost-benefit analysis for monitoring systems to detect oestrus in cows. Can. J. Anim. Sci. 56: 291-8. (153) Morrow, D. A. (1966): Analysis of herd performance and economic results of preventive dairy herd health programmes. Part I + Part II. Vel. Med. 61: 474 + 577. (154) Morrow. D. A.. Roberts, S. J. & McEntee, K. (1969a): A review ofpost-partum activity and involution of the uterus and cervix in caule. Cornell Vel. 59: 134-54. (155) Morrow, D .. A.. Roberts, S. J. & McEntee, K. (I 969b ): Post-partum ovarian activity and involution of the uterus and cervix in dairy cattle. I. II and Ill. Cornell Vel. 59: 173-89,190-8,199-210. . ( 156) Morrow. D. A. ( 1970): Diagnosis and prevention of infertility in caule.J. Dairy Sci. 53: 961-9. (157) Munro. I. B. (1970): Personal communication. (158) Mylrea, P. J. (1962): Clinical observation on reproduction in dairy cows. Ausi. vel. 1. 38: 253-8. (159) Nelson. L. A. & Huber. D. A. (1971): Factors inftuencingdystocia in hereford dams. J. Anim. Sci. 33: 1137 (abstr.) (160) Nessan.G. K.. King,G.J., McKay,G. W., Thomson,J. D.and Bertrand, W.(1977): Treatment of cystic ovarian degeneration in dairy cows with gonadotrophic releasing hormone or human chorionic gonadotrophic hormone. Can. vel. J. 18: 33-7. (161) O'Farrell. K. J. (1975): The role of management in dairy herd fertility. Irish vel. J. 29: 118-24. (162) Olds. D.. Colvin, L. D.. Cooper, T. & DealOn. O. W. (1966): Sources of variance affecting dairy herd fertility and delayed returns to service.J. Dairy Sci. 49: 1004-5. (163) Olds, D. & Deaton. O. W. (1968): Effect of herd size on fertility and delayed returns. Prog. Rep. Ky Agrie. Exp. Stn No. 32. (164) Olds, D .. (1969): An objective consideration of dairy herd fertility.J. Am. vel. med.

conception rates of Holstein Friesian cattle. 1. Dairy Sci. 44: 1857-62.

«

81: 458-60.

(116) King, G. J. (1971): Nutrition & Fertility in dairy cows. Vel. Rec. 89: 320-4. (117) King, G. J., Hurnik, J. F., Robertson, H. A. (1976): Ovarian function and oestrus in dairy cows during early lactation. J. Anim. Sci. 42: 688-92. (118) Kirkbride, C. A., Bicknell, E. J., Reed, D. E., Robl, M. G., Knudtson, W. U. & Wohlgemuth, K. (1973): A diagnostic survey of bovine abortion and stillbirth in the northern plains states. J. Am. vet. med Ass. 162: 556-60. (119) Konermann, H., Dearr, H. C. & Frerking, H. (1969): Fruchtbarkeit and Milch .. leistung nach Schwergeburten beim Rind. DIsch. TieriirZll. Wschr. 79: 229-34 (120) Koopman, J. J. & Wijbenga, A. (1973): Vruchtbaarheid en melkproductie bij FH koeien in Noord-Holland. Tijdschr. Diergeneesk. 98: 565-76. (121) Koopman, J. J. & Wijbenga, A. (1975): Nader onderzoek naar de invloed van bedrijfsomstandigheden en de melkproductie op de vrucht-baarheid. Tijdschr. Diergeneesk. 100: 875-22. (122) Kordts, E. (1974): MOglichkeiten zur Verbesserung der Fruchtbarkeit weiblicher Rinder. Prakl. Tierarzl. 374-7.

in bovine abortion. Can. vet. J. 18: 87-95.

Ass. 154: 253-8.

(165) Olds. D. & Cooper. T. (1970): Effect of post-partum rest period in dairy cattle on the occurence of breeding abnormalities and on calving intervals. J. Am. vel. med. Ass. 157: 92-7.

(166) Oxender. W. D. (1973): Dairy herd management and veterinary service in MiChigan. Bovine Praclitioner 8: 46-7. (167) Parker, B. N. J. & Blowey, R. W. (1976): Investigations into the relationship of selected blood components to nutrition and fertility of the dairy cow under

Downloaded by [University of Bristol] at 21:12 25 January 2015

1978

NEW ZEALAND VETERINARY JOURNAL

commercial farm conditions. Vel. Rec. 99: 394-404. (168) Parsonson. J. M. & Snowdon. W. A. (1975): The effect of natural and artificial breeding using bulls injected with. or semen contaminated with infectious bovine rhinotracheites virus. Ausl. vel. J. 51: 365-9. (169) Paufler. S. K. (1974): Klmslliche Besamung und Eilransplantalion bei Tier und Mensch. Verlag M. and H. Schaper. Hannover. (170) Pearson de Vaccaro. L. (1973): Some aspects of the performance of the pure bred and cross dairy caule in the tropics. I. reproductive efficiency in females. Animal Breed Abslr. 41: 571-91. (171) Pelissier. C. L. (1972): Herd breeding problems and their consequences. J. Dairy Sci. 55: 385-91. (172) Pelissier. C. L. (1976): Dairy cattle breeding problems and their consequences. Theriogenology 6: 575-83. (173) Perkins. J. R .. Olds. D. & Sheath. D. M. (1954): A study of 1000 bovine genitalia. J. Dairy Sci. 37: 1158-63. ( 174) Philipsson. J. ( 1976) Studies on calving difficulty. stillbirth and associated factors in Swedish caule breeds. A cIa Agric. Scand 26: 211-20. (175) Pirchner. F .. Chakrabarti. S.• Erlacher. J.. Schleger. W. & Rohrbacher. H. (1971): Heterozygotie und Fruchtbarkeit bei Rindem. DISCh. Tieriirztl. Wschr. 78: 111-4. (176) Plasse. D .. Warnick. A. C. & Koger, M. (1970): Reproductive behaviour of bos indicus in subtropical environment. IV. length of oestrous cycle, duration of oestrus. time of ovulation. fertilization and embryo survival in grade brahman heifers. J. A nim. Sci. 30: 63-71. (177) Pope.G. S .. Leaver.J. D .. Majzlik.l.& Ball. P.J. H.(l976):A.R.C. Research Review, vol. 2 number 2 pp. 49-54. ( 178) Poston. H. A .. Ulberg. L. C. & Legates, J. E. (1962): Analysis of seasonal fluctuations of reproductive performance of dairy cows. J. Dairy Sci., 45: 1376-9. ( 179) Rem men. J. W. A. (1976): Een onderzoek naar mogelijkheden om perina tale sterfte bij het rund te beperken. Thesis, Utrecht. (180) Rice. L. E. & Wiltbank.1. N. (1970): Dystocia in beefheifer.;.J. Anim. Sci. 30: 1042 (Abstr.). ( 181) Roberts. S. J. (1971): Veterinary obstetrics and genital diseases. Edwards Brothers, Inc .. Ann Arbor. Michigan. (182) Roine, K. (1973): The most frequent reproductive disorders and their seasonal variation in dairy cows. Nord. vet. Med.15: 242-7. (183) Rook. J. A. F. & Line, C. (1961): Brilish J. NUlrition 15: 109-9. (1S4) Rottensten, K. & Touchberry, R. W. (1957): Observations on the degree of expression of estrus in caule. J. Dairy Sci. 40: 1457-65. (lS5) Sambraus. H. H. (1973): Das Sexualverhalten der domestizierten einheimischen Wiederkauer. J. Compo EthOlogy, Suppl. 12. (186) Sattar, S. A., Bohl, E. H. & Trap, A. L. I. (1961): Abortion in cattle caused by experimental infection with infectious bovine rhinotracheitis virus. Cornell Vet. 48: 438-43. (1S7) Schoop, G., Kruger-Hansen, U. & Wachendorfer, G. (1965): Zur Isolierung von Miyagawanellen aus abortierten Rinderfeten. Zenlhl. Vet. Med. B, 12: 23-30. (lS8) Shannon. F. D .• Salisbury, G. W. & VanDemark, N. L. (1952): The fertility of cows inseminated at various intervals after calving. J. Anim. Sci. I I: 355-60. (189) Sittmann, K., Rollins, W. C. & Kendrick, J. W. (1961): A genetic analysis of the double cervix condition in cattle. J. Hered. 52: 26. (190) Slama. H., Wells. M. E., Adams, C. D., Morrison. R. D. (1976): Factor.; affecting calving interval in dairy herds. J. Dairy Sci. 59: \334-9. (l91)Smith,J. W.& Legates,J. E. (1962): Relation of days open and days dry to lactation . milk and fat yields. J. Dairy Sci. 45: 1192-8. (192) Sonnenbrodt & Ranniger. (1950): Die Nymphomanie in der Rindvlezucht des Wladviertels (Niederdonau) eine Erbkankheit. Z. Tierziicht. Ziicht. Bioi. 58: \08-18. (193) Sorensen, A. M. (1975): Estrous detection in caule. Soulhweslern Vet. 18: 127-43. (194) Spalding. R. W., Everett. R. W. & Foote, R. H. (1975): Fertility in New York artificially inseminated Holstein herds in dairy herd improvement.J. Dairy Sci. 58: 718-23. (195) Speicher, 1. A., Meadows, C. (1967): Milk production and costs associated with length of calving intervals of Holstein cows. J. Dairy Sci. 50: 975 abstr. (196) Spriggs, D. N. (1945): Double external os in caule. Br. Vet. J. 101: \38-43. (197) Spriggs. D. N. (1946): White heifer disease. Vet. Rec. 58: 405-19. (198) Stiimpfli, G. (1973): Erfahrungen eines Tierarztes bei Unter.;uchungen iiber die Hcrdcnstcrilitiit. Schweiz. Landw. M. 51: 465-82. (199) Stoenner. H. G. (1968): Bovine leptospiral abortion. In: Abortion Diseases of Livestock. L. C. Faulkner (ed). Charles C. Thomas, Springfield, Illinois. (200) Storz, J. (1971): Chlamydia and Chlamydia-Induced Diseases, pp. 175-83. C. C. Thomas, Springfield. Illinois. (201)Stolt,G. H.& Williams. R.J.( 1962): Causesoflowbreedingefficiencyindairycattle associated with seasonal high temperatures. J. Dairy Sci. 45: \369-75. (202) Stott, G. H .. Wiersma, F. & Woods, J. M. (1972): Reproductive health programme for cattle subjected to high environmental temperatures. J. A m. vel. med. Ass. 161: 1339-44. (203) Tennant, B. & Peddicord, R. G. (1968): The influence of delayed uterine involution and endometritis on bovine fertility. Cornell. Vet. 58: 185-92. (204) Thatcher, W. W. (1974): Effects of season. climate and temperature on reproduction and lactation. J. Dairy Sci. 57: 360-S. (205) Todd, J. D.. Volnec, F. J. & Paton, I. M. (1971): Intranasal vaccination against

infectious bovine rhinotracheitis: Studies on early onset of protection and use of

vaccine in pregnant cows. J. Am. vet. med. Ass. 159: \370-4. (206) Topps,J. H. (1977): The relationship between reproduction and under-nutrition in beef cattle. World Review of Animal Prod. Vol. XIII, no. 2,43-9. (207) Touchberry, R. W .• Rottensten, K. & Andersen, H. (1959): Association between service interval. interval first service to conception and level of butterfat production. J. Dairy Sci. 42: 1157-70. (208) Trimberger, G. W. & Davis. G. K. (1943): The relationship between time of insemination and breeding efficiency in dairy cattle. Res. Bull. Neb. Agric. Exp. SIn., No. 129. (209) Trimberger, G. W. (1948): Breeding efficiency in dairy cattle from A.I. at various intervals, before and after ovulation. Nebraska Univers. Agric. Exp. Station Res. Bul.153. (2\0) Trimberger, G. W. (1954): Conception rates in dairy cattie from services at various intervals after parturition. J. Dairy Sci. 37: 1042-9. (211) Ulberg, L. C. & Burfening, P. J. (1967): Embryo death resulting from adverse environment on spermatozoa or ova. J. Anim. Sci. 26: 571-7. (212) Vandemark, N. L. & Salisbury, G. W. (1950): The relation of the post-partum breeding interval to reproductive efficiency in the dairy cow.J. Dairy Sci. 9: 307-13. (2\3) Venter, H. A. W .• Bonsma,J. c., Skinner,J. D. (1973): The influence of climate on the reproduction ofcaule.lnt. J. Biomeleor. 17:: 147-51. (214) Vincent, C. K. (1972): Effects of season and high environmental temperature on fertility in cattle. A reviewJ. Am. vet. med. Ass. 161: \333-8. (215) Wegner, W. (1973): Genetische Einfliisse auf die Fruchtbarkeit beim Rind. DIsch. Tieriirzll. Wschr. 80: 434-7.

189

(216) Wier.;ma, F. & Stott, G. H. (1969): New concepts in the physiology of heat stress in cattle of interest to engineers. Tr. Anim. Soc. Agric. Engineers /2: 130-32 (217) Weseloh. E. (1968): Zusammenhiinge zwischen Milchleistung; Fruchtbarkeit und Lebensdauer beim Rind, untersucht an Deutschen Schwarzbunten der Herdbuchgesellschaft Osnabrock. Thesis, GOuingen. . .. (218) White. M. B. & Snowdown, W.A. (1973): The breedmgrecordsofcowsmsemmated with a batch of semen contaminated with mfechous bovme rhmotrachelhs VIruS. Ausl. vet. J. 49: 501-600. (219) Whitmore, H. L., Tyler, W. J. & Casida, L. E. (1974a): Effects of early post-partum breeding in dairy cattle. J. Anim. Sci. 38: 339-46.. .. (220) Whitmore, H. L., Tyler, W. J. & Casida, L. E. (l974b): InCIdence OfCYShC ovanes in Holstein-Friesian cows. J. Am. Vet. Med. ass. 165: 693-4. (221) Willems, C. M. T. (1971): Een vergelijking van de bevruchtingsresultaten met K. I. op Iigboxstallen en andere stallen. I en II. Tijdschr. Diergeneesk. 96: 215-8 and 1457-9. (222) Williams, B. M., Shreeve. B. J., Heebert. C. N. & Swize, P. W. (1977): Bovine mycotic abortion: Some epidemiological aspects. Vet. Rec. 100: 382-5. (223) Williams, G. (1960): Observations on the fertility of newly estabhshed herds. Vet. Rec. 72: 197-200. (224) Williamson, N. B., Morris, R. S., Blood, D. C. & Cannon, C. M. (1972): A study of oestrous behaviour and oestrus detection methods in a large commerical dairy herd. I. The relative effieiency of methods of oestrus detection. Vel. Rec.. 91: 50-7. (225) Williamson, N. B., Morris, R. S., Blood, D. c., Cannon, C. M. and Wnght, P. J. (1972): A study of oestrous behaviour and oestrus-detection methods 10 a large commereial dairy herd. II. Oestrus signs and behaviour patterns. Vet. Rec. 91: 58-61. (226) Wiltbank, J. N., Rowden, W. W., Ingalls, J. E. & Zimmerman, D. R. (1964): Influence of post-partum energy level on reproductive performances of hereford cows restricted in energy intake prior to calving. J. A nim. Sci. 23: 1049-53. (227) Winter, A. J. (1973): Vibriosis: toward an under.;tanding of immunity in genital infections. Cornell Vel. 63: 5-16. (228) Wolff, L. K. & Monty, D. E. (1974): Physiologic response to intense summer heat and its effect on the estrous cycle of non-lac tat 109 and lactatmg Holstem-Fretstan cows in Arizona. Am. J. Vel. Res. 35: 187-92. (229) Wolff, L. K., Vaught, L., Monty, D. E., Foot, W. C. (1977): The effectofsummer heat stress on serum luteinizing hormone and progesterone values tn Holstem Friesian cows in Arizona. Am. J. vet. Res. 38: \027-30. (230) Wood, P. D. P. (1976): A note on detection of oestrus in cattle bred by artificial insemination, and the measurement of embryonic mortality. Anim. Prod. 22: 275-8. (231) Woodward & Graves (1946): Results of inbreeding grade Holstein/Friesian cattle. U.S. Dept. of Agric. Tech. Bull. 927. (232) Zemjanis, R. (1974): Vaccination for reproductive efficiency in cattle. J. Am. vel. med Ass. 165: 689-92. (233) Zemjanis, R., Fahning, M. L. & Schulz, R. H. (1969): Anestrus, the practitioners dilemma. Vet. Scope 14: 15-19. (234) Zikken, A. (1978): Enkele aspecten van het puerperium bij het rund. Thesis, Utrecht. (In preparation.)