THE INCIDENCE OF DYSTOCIA IN FINE-WOOL MERINO EWES J. M. GEORGE, B.Sc.Agr., M.Rur.Sci. CSIRO Division of Animal Physiology, Pastoral Research Laboratory, Armidale, New south Wales, 2350 Introduction
Information on the incidence of difficult birth (dystocia) in ewes has been recorded by Wallace (1949) and Hughes et al (1964). Among the factors which have been inmplicated are oversize lambs due to nutritional management (Dun and Wall 1962), skin fold development (Dun 1964; Dun and Hamilton 1965), overfat ewes (Jeffries and Fearn 1957), clover oestrogens (Bennetts et a1 1946; Maxwell 1970), and malpresentations (Wallace 1949). This paper reports the incidence and some of the factors associated with dystocia in a finewool Merino flock which lambed in winter, spring or summer in 10 successive years. Materials and Methods Aniinols and Pustures Flocks of fine-wool Merino ewes, joined to lamb annually in winter (June/July), spring (September/ October) or summer (December) were maintained over a 10-year period from 1964 to 1973. Thus, there were 30 lambing periods over 10 years. Flocks comprised 90 ewes each for the first 4 years and 45 each, subsequently. In each flock, 5 age groups (1.5 to 5.5 years at joining) were equally represented, the oldest ewes being replaced annually by 1.5 year-old ewes. Rams were replaced every 2 years. The ewes grazed either Phataris tuherosa-white clover (Trijoliunt repens) (1964-1973) or fescue (Festuca arundinacea)-white clover (1964-1967) pastures at 3 stocking rates (8, 12 or 16 ewes/ha) throughout the year.
Definitions The occurrence of dystocia (difficult birth or labour) was assessed by direct observation at parturition (0800 to 1800 hours) or from post-mortem examination of dead lambs. All assisted births were considered as difficult, assistance being given if malpresentation was evident or when a normally presented lamb had not been born within an hour of the rupture of the foetal membranes. The type of presentation of lambs in assisted births was recorded. In addition, sex, birth weight and whether single or twin were recorded for all lambs. Lambs born during the day were weighed soon after birth, and those born between 1800 and 0800 hours were weighed within 15 hours of birth. Ewes were weighed 2 to 3 weeks before lambing commenced. At autopsy, lambs were classed as dystocic when they showed evidence of death during or within a few hours of parturition (McFarlane 1965). The lamb may or may not have breathed and showed no or little evidence of walking as judged by wear of foot membranes. Body fat depots were cream white in
262
appearance, In addition there was localised subcutaneous oedema of the head and neck, sometimes accompanied by liver rupture. There were no significant gross abnormalities indicating predation (McFarlane 19641, starvation, or infection.
Results
Over the 10-year period records were obtained on 1510 parturitions; of these 63 ewes (65 lambs) had a difficult birth (4.2%). Significantly more ewes experienced dystocia during spring than in winter lambings (XZ1= 6.14, P < 0.05) or summer lambings (X21 = 7.38, P < 0.01) (Table 1). Differences in the proportions of dystocia between winter and summer lambings were not significant. Sixty-five per cent (41/63) of the difficult births were assisted and 67% occurred in the 4 years 1966-1969. Four ewes were assisted in 2 consecutive years and 1 ewe in 4 consecutive years. Ten percent of all lamb deaths (47/456) in the 10-year period were attributed to dystocia. The mean birth weights of dystocic single and twin born lambs were 4.19 kg (59 lambs) and 3.38 kg (6 lambs) respectively. The corresponding birth weights of lambs that did not experience dystocia were 3.69 kg (1327 lambs) and 3.00 kg (240 lambs). Of those lambs experiencing a difficult birth 77 % had a normal (anterior) presentation, that is, with head and both forelegs together, 14% had 1 or both forelegs retained and 9% were recorded as posterior (including 1 breech) and other malpresentations (Table 2). Oedema of the head and/or neck was recorded for 31 of those lambs that died at or soon after a difficult birth and 6/65 had a ruptured liver. The proportion of lambs that survived assisted delivery was 13/41. There were no significant differences in the number of lambs surviving a difficult birth at a winter (4/17) than at a spring (9/37) or summer (3/11) lambing. The mean birth weights of lambs that survived were 0.4 kg greater than those that did not survive. There were 42/65 lambs that had a difficult birth with birth weights greater than 4.0 kg. The proportion of all lambs with birth weights greater than 4.0 kg was significantly greater (P < 0.001) Australian Veterinary Journal, Vol. 51, May, 1975
TABLE 1 The Incidence o f Dystocia in Ewes in Relation to Season of Lambing and Pre-Lambing Bodyweights Winter
Spring
No. of Ewes Dystocia Lambing
1
1964 1965 1966 1967 1968 1969 1970 197 1 1972 1973
0 4 4 4 1
1 1 0 1
Total
17 3.1
%
Wt. kg
No. of Ewes Dystocia Lambing
53 4s 41 50 44 44 47
81 "77 76 81 40 41 40 *36 *35 "39
50
53 49
546
83 69 77 82 32 *42 44 43 43 "43
3 3
4 5 2 8 3 2 2 3 35 6.3
Summer No. of Ewes Dystocia Lambing
Wt. kg 56 40 39 47 46 48 49 47 51 52
0
52
0
*32 *48 51 78 36 *33 *38 *34 *37
41 42 50 46 43 43 50 44
1
*39
44
11 2.6
426
a
3 5 1 1 0
1,
558
Wt. kg
* No ewes were assisted at these lambinss.
at spring lambing (232/616) than at winter (156/571) and greater at summer (155/444) than at winter lambings (P < 0.01). The proportion of all single born lambs that died from all causes with birth weights greater than 4.0 kg was significantly greater in spring (41/128, P < 0.05) and summer (26/66, P < 0.01) than during winter (27/145) lambings. There was no significant difference between spring and summer lambings in the proportion of lambs born with birth weights greater than 4.0 kg. Similarly, there was no significant difference between spring and summer lambings in the proportion of singleborn lambs that died with birth weights greater than 4.0 kg. There were only 3/118 twin born lambs with birth weights greater than 4.0 kg. The proportions of lambs born with birth weights greater than 4.0 kg for each stocking rate and lambing season are shown in Table 3. Significantly more ewes experienced dystocia when stocked at both 12 and 16 per ha than at 8 per ha (P < 0.05); differences between 12 and 16 per ha were not significant (Table 4). Fifty per cent of recorded dystocias occurred in ewes stocked at 16 per ha, 40% at 12 per ha and
10% at 8 per ha. The mean pre-lambing body weights for ewes stocked at 8, 12 and 16 per ha were 50, 48, and 44 kg respectively. The incidence of dystocia for 2, 3, 4, 5 and 6 year-old ewes was 19, 21, 14, 24 and 22 per cent respectively and did not differ significantly between age groups. Only 2 ewe deaths occurred at parturition during this study. Discussion
The incidence of dystocia (4.1 %) in these finewool Merino ewes was low in comparison to some other breeds. For example, in studies in New Zealand, as many as 70% of pedigree Southdown ewes received assistance (Laing, 1949) and 28% for Romney Marsh ewes (Quinlivan et a2 1966). In New South Wales Hughes et a1 (1964) recorded a lower incidence of prolonged births, in Merinos (range 7-12% of dead lambs) compared to crossbreds (range 10-34% of dead lambs). Dun and Hamilton (1965) attributed 17% of the difference in net reproductive rate between Folds Plus and Folds Minus Merino ewes to higher neonatal death rate in the Folds Plus flocks due to dystocia. On the other hand, Merino ewes
TABLE 2 Type o f Presentation of Lambs Experiencing Dystocia i n Relation to Birth Weight
Classification
-
Anterior normal (a) 1 foreleg retained (b) 2 forelegs retained Posterior (including breech) Other malpresentations"
No.
%
No. Survived
Mean Birth Weight (kg)
50 2
76.9 10.8 3.1
13 1 1
4.10 4.43 4.00
3 3
4.6 4.6
1 0
3.73 4.03
7
One case each of: .lateral deviation of head and neck; lateral deviation of head and neck with retention of 1 foreleg; dorsotransverse presentation.
Australian Veterinary Journal, VoI. 51, May, 1975
263
TABLE 3
TABLE 4
Mean Birth Weight of Lambs (k,) and the Proportion of Lambs exceeding 4.0 kg in Relation to Stocking Rate and Season of Lambing
Ewes per Hectare
n Mean lamb birth weight 3.60 Proportion ( % ) of Lambs exceeding 4.0 kg Winter 38.8 Spring 32.4 Summer 3C.1
Incidence of Dystocia in Relation to Season of Lambing and Stocking Rate
12 3.59 22.0
41.0 34.4
3.58
26.3 40.9
Ewes per Hectare
Lambing Season Spring Summer
8
Incidence % Incidence % Incidence %
O/llS 0.0 3/ 122 2.5 2/98 2.0
12
16
8/182 4.4 I4/187
91249 3.6 18/249
7.5
7.2
3/145
6/IH3 3.3
2.1
39.1
~~
grazing pastures of oestrogenic subterranean clover have been reported to have an incidence of dystocia that varied from 12 to 30% (Maxwell 1970). In Of the 30 lambing periods no dystocia was observed and in 13 it was not necessary to assist any During the years 19"1969 there was an increase in the proportion of ewes that experienced dystocia but this increase did not appear to be to the Pre-lambing bodyweights. The high incidence of dystocia in spring lambings could possibly be explained by the fact that the ewes were weaker, having been pregnant in the harsh winter months, while the winter and summer lambing groups were in stronger condition at lambing, having been pregnant during the autumn and spring respectively, when in general, there was adequate pasture. No explanation can be offered for the high incidence of dystocia in spring 1969 when the mean prelambing bodyweights were neither high nor low. The proportion of normal (anterior) presentations (77%) with head and both forelegs presented together was slightly higher than that re(1949) for Romney Marsh ported by sheep (69%). The present results are in general agreement with those of Kennedy and Bettenay (1950) who noted that the most common malpresentation encountered in Merinos was anterior presentation with retcntion of one or both forelegs. The lower incidence of dystocia at 8 ewes per ha compared to 12 or 16 ewes per ha, which appears to be a paradox, was possibly due to the ewes at the lowest stocking rate being stronger than the ewes at the higher stocking rates. The mean bodyweight of ewes stocked at 8 per ha was slightly greater than those at 12 and 16 yet the mean birth weights of all lambs were almost identical. This could indicate that a stronger ewe could give birth more easily than a lighter or weaker ewe. 264
Approximately 28% of all single born dead lambs and 65% of lambs that had a difficult birth had birth weights greater than 4.0 kg, which is consistent with the hypothesis that foeto-pelvic disproportion was a major cause of dystocia. The high proportion of lambs born and of single dead lambs with birth weights greater than 4.0 kg was possibly due to nutritional factors. In most years actively growing spring pastures were available during the last month of gestation, whereas at winter lambing, pasture growth was minimal or semi-dormant and at summer it was fibrous and maturing* The aSSOCiatiOn between dystocia in Merinos and oversized lambs has been reported earlier (Dun and Wall 1962; Dun and Hamilton 1965). In the present study, the criteria for establishing a relationshb between lamb deaths and dystocia, in unassisted cases, were relatively crude. If the technique of Hauehey (19731, which involves the detection of meningeal haemorrhages, had been available, the recorded incidence of dystocia may have been higher. Acknowledgments
The field assistance given by Mr. J. T. Elliott throughout the course of these observations is gratefully acknowledged. Summary
The mean incidence of dystocia in 1,510 finewool Merino Over a ten-year period was 4.1% of ewes lambing. In the 10 year period, 10% of all neonatal mortality was attributed to dystocia and in only 23% of dystocias was lamb presentation abnormal. The incidence of dystocia was not related to age of ewe. Significantly more ewes experienced dystocia at spring than winter (P < 0.05) or summer (P < 0.01) lambings. The mean birth weights of dystocic single and twin barn Iambs were 4.19 and 3.38 kg respectively. The corresponding birth weights of lambs that did not experience dystocia were 3.69 and 3.00 kg. Australian Veterinary Journal, Vol. 51, May, 197.5
More ewes experienced dystocia when stocked at 12 or 16 per ha than at 8 per ha (P < 0.05). Fifty per cent of recorded dystocias occurred in ewes stocked at 16 per ha, 40 per cent at 12 per ha and 10 per cent at 8 per ha. Ewe body weight pre-lambing was not related to the incidence of dystocia but it would appear that weaker ewes are more likely to have a difficult birth than ewes that are stronger and in better condition. References Bennetts, H. W., Underwood, E. J. and Shier, F. L. ( 1 9 4 6 ) - - A ~ s t . vet. J . 22: 2. Dun, R. B. (1964)--Aust. J . exp. Agric. Anim. Husb. 4: 376. Dun, R. B. and Hamilton, B. A. (1965)-Aust. J. exp. Agric. Anim. Husb. 5: 236.
Dun, R. B. and Wall, T. A. (1962)-Proc. Aust. Soc. Anim. Prod. 4: 187. Haughey, K. G . (1973)-Aust. vet. J . 49: 1. Hughes, K. L., Hartley, W. J.. Haughey, K. G. and McFarlane, D. (1964)-Proc. Aust. SOC. h i m . Prod. 5: 92. Jefferies, B. C. and Fearn, J. T. (1957)-J. Aust. Znst. agric. Sci. 23: 149. Kennedy, J. F. and Bettenay, 1. .. R. A. (1950)-Aust. agric. Res. 1: 7 6 . Laing, A. D. M. G . (1949)--N.Z. J1 Agric. 79: 11. McFarlane, D. (1964)--Wool Technul. Sheep Breed. 11: 1 1 . McFarlane, D. (1965)--N.Z. vet. J . 13: 116. Maxwell, J. A. L. (1970)-Aust. vet. J . 46: 533. Quinlivan, T. D., Martin, C. A., Taylor, W. B. and Cairney, I. M. (1966)-J. Reprod. Fert. 11: 379. Wallace, L. R. (1949)-Proc. N . Z . Soc. Anim. Prod. 9: 8 5 . (Received for publication 2 August 1974)
BOOK REVIEWS PRODUCTION FROM LARGE HERBIVORES This book* is a collection of 37 separate contributions arranged into 15 parts in the following 4 sections: 1 introduction; 2 energy flow and secondary productivity; 3 components of energy flow, for example animal numbers and densities, categories and age determination, measuring quantity and quality of diet, metabolism, post-natal growth; and 4 management for secondary production including husbandry of wild animals, handling wild herbivores, environmental physiology, reproduction, nutrition, habitat manipulation, epizooti* c & a c t i c a l guide to the study of the productivity of large herbivores. Ed. Frank B. Golley and Helmut K. Buechner. International Biological Programme. Blackwells, Oxford, 1968. Pp 308. (1BP Handbook No. 7) S2.00 stg.
ology and conversion factors for productivity measurements. The book will be of interest to veterinarians engaged in production research particularly in extensive grazing systems and if engaged in investigations on undomesticated livestock. It is of note that estimates on energy conversion by steers showed that they produce 12 times as much growth as elephants and 5 times as much as deer, which is a plausible reason for questioning the use of native animals under intensive conditions. The book is intended to be a useful starting point, rather than a compendium of detailed information. A. N. Sinclair
BEHAVIOUR OF FARM ANJ!MALS This introduction* to Farm Animal Behaviour (Ethology) is in 4 parts: firstly principles of ethology, theoretical ethology and physiological ethology: secondly. behaviour patterns of horses, .cattle, sheep and pigs, environmental influences on behaviour and managemental ethology; thirdly reproduction, for example sexual behaviour, fetal behaviour, parturition and neonatal behaviour and fourthly abnormal behaviour, that is behaviour and clinical disorders and anomalous behaviour. There is a glossary of terms. This is an introductory book so it may be of use to veterinary students, particularly those who have need to supplement their rural experience. There is a useful list of further reading at the end of each chapter which may be of value to the student or research worker who wishes to go further into the subject. Practising veterin*Farm Animal Behaviour. Andrew London. 1974. Pp 196. f 2 . 2 0 stg.
F.
Fraser.
Bailliere.
Australian Veterinary Journal, Vol. 5 1 , May, 1975
arians may feel that much of the book is devoted to stating the obvious which they probably consider is already known, but more careful reading indicates that most observers could be aided by attempts to make observations more systematically and, if possible, in objective terms. Unfortunately, the writer occasionally lapses into generalisations which are not substantiated by the evidence presented in the text. This leads to the feeling that these may have originated from material in the references. It is disappointing to find that the author has overlooked publications of Australian research on ram behaviour and its effects on oestrus in ewes, and on oestrus of cattle, as well as recent work on parturition behaviour of cattle. These deficiencies detract from the application of this particular book in practice here in Australia. A. N. Sinclair 265
Information on the incidence of difficult birth (dystocia) in ewes has been recorded by Wallace (1949) and Hughes et al (1964). Among the factors which have been inmplicated are oversize lambs due to nutritional management (Dun and Wall 1962), skin fold development (Dun 1964; Dun and Hamilton 1965), overfat ewes (Jeffries and Fearn 1957), clover oestrogens (Bennetts et a1 1946; Maxwell 1970), and malpresentations (Wallace 1949). This paper reports the incidence and some of the factors associated with dystocia in a finewool Merino flock which lambed in winter, spring or summer in 10 successive years. Materials and Methods Aniinols and Pustures Flocks of fine-wool Merino ewes, joined to lamb annually in winter (June/July), spring (September/ October) or summer (December) were maintained over a 10-year period from 1964 to 1973. Thus, there were 30 lambing periods over 10 years. Flocks comprised 90 ewes each for the first 4 years and 45 each, subsequently. In each flock, 5 age groups (1.5 to 5.5 years at joining) were equally represented, the oldest ewes being replaced annually by 1.5 year-old ewes. Rams were replaced every 2 years. The ewes grazed either Phataris tuherosa-white clover (Trijoliunt repens) (1964-1973) or fescue (Festuca arundinacea)-white clover (1964-1967) pastures at 3 stocking rates (8, 12 or 16 ewes/ha) throughout the year.
Definitions The occurrence of dystocia (difficult birth or labour) was assessed by direct observation at parturition (0800 to 1800 hours) or from post-mortem examination of dead lambs. All assisted births were considered as difficult, assistance being given if malpresentation was evident or when a normally presented lamb had not been born within an hour of the rupture of the foetal membranes. The type of presentation of lambs in assisted births was recorded. In addition, sex, birth weight and whether single or twin were recorded for all lambs. Lambs born during the day were weighed soon after birth, and those born between 1800 and 0800 hours were weighed within 15 hours of birth. Ewes were weighed 2 to 3 weeks before lambing commenced. At autopsy, lambs were classed as dystocic when they showed evidence of death during or within a few hours of parturition (McFarlane 1965). The lamb may or may not have breathed and showed no or little evidence of walking as judged by wear of foot membranes. Body fat depots were cream white in
262
appearance, In addition there was localised subcutaneous oedema of the head and neck, sometimes accompanied by liver rupture. There were no significant gross abnormalities indicating predation (McFarlane 19641, starvation, or infection.
Results
Over the 10-year period records were obtained on 1510 parturitions; of these 63 ewes (65 lambs) had a difficult birth (4.2%). Significantly more ewes experienced dystocia during spring than in winter lambings (XZ1= 6.14, P < 0.05) or summer lambings (X21 = 7.38, P < 0.01) (Table 1). Differences in the proportions of dystocia between winter and summer lambings were not significant. Sixty-five per cent (41/63) of the difficult births were assisted and 67% occurred in the 4 years 1966-1969. Four ewes were assisted in 2 consecutive years and 1 ewe in 4 consecutive years. Ten percent of all lamb deaths (47/456) in the 10-year period were attributed to dystocia. The mean birth weights of dystocic single and twin born lambs were 4.19 kg (59 lambs) and 3.38 kg (6 lambs) respectively. The corresponding birth weights of lambs that did not experience dystocia were 3.69 kg (1327 lambs) and 3.00 kg (240 lambs). Of those lambs experiencing a difficult birth 77 % had a normal (anterior) presentation, that is, with head and both forelegs together, 14% had 1 or both forelegs retained and 9% were recorded as posterior (including 1 breech) and other malpresentations (Table 2). Oedema of the head and/or neck was recorded for 31 of those lambs that died at or soon after a difficult birth and 6/65 had a ruptured liver. The proportion of lambs that survived assisted delivery was 13/41. There were no significant differences in the number of lambs surviving a difficult birth at a winter (4/17) than at a spring (9/37) or summer (3/11) lambing. The mean birth weights of lambs that survived were 0.4 kg greater than those that did not survive. There were 42/65 lambs that had a difficult birth with birth weights greater than 4.0 kg. The proportion of all lambs with birth weights greater than 4.0 kg was significantly greater (P < 0.001) Australian Veterinary Journal, Vol. 51, May, 1975
TABLE 1 The Incidence o f Dystocia in Ewes in Relation to Season of Lambing and Pre-Lambing Bodyweights Winter
Spring
No. of Ewes Dystocia Lambing
1
1964 1965 1966 1967 1968 1969 1970 197 1 1972 1973
0 4 4 4 1
1 1 0 1
Total
17 3.1
%
Wt. kg
No. of Ewes Dystocia Lambing
53 4s 41 50 44 44 47
81 "77 76 81 40 41 40 *36 *35 "39
50
53 49
546
83 69 77 82 32 *42 44 43 43 "43
3 3
4 5 2 8 3 2 2 3 35 6.3
Summer No. of Ewes Dystocia Lambing
Wt. kg 56 40 39 47 46 48 49 47 51 52
0
52
0
*32 *48 51 78 36 *33 *38 *34 *37
41 42 50 46 43 43 50 44
1
*39
44
11 2.6
426
a
3 5 1 1 0
1,
558
Wt. kg
* No ewes were assisted at these lambinss.
at spring lambing (232/616) than at winter (156/571) and greater at summer (155/444) than at winter lambings (P < 0.01). The proportion of all single born lambs that died from all causes with birth weights greater than 4.0 kg was significantly greater in spring (41/128, P < 0.05) and summer (26/66, P < 0.01) than during winter (27/145) lambings. There was no significant difference between spring and summer lambings in the proportion of lambs born with birth weights greater than 4.0 kg. Similarly, there was no significant difference between spring and summer lambings in the proportion of singleborn lambs that died with birth weights greater than 4.0 kg. There were only 3/118 twin born lambs with birth weights greater than 4.0 kg. The proportions of lambs born with birth weights greater than 4.0 kg for each stocking rate and lambing season are shown in Table 3. Significantly more ewes experienced dystocia when stocked at both 12 and 16 per ha than at 8 per ha (P < 0.05); differences between 12 and 16 per ha were not significant (Table 4). Fifty per cent of recorded dystocias occurred in ewes stocked at 16 per ha, 40% at 12 per ha and
10% at 8 per ha. The mean pre-lambing body weights for ewes stocked at 8, 12 and 16 per ha were 50, 48, and 44 kg respectively. The incidence of dystocia for 2, 3, 4, 5 and 6 year-old ewes was 19, 21, 14, 24 and 22 per cent respectively and did not differ significantly between age groups. Only 2 ewe deaths occurred at parturition during this study. Discussion
The incidence of dystocia (4.1 %) in these finewool Merino ewes was low in comparison to some other breeds. For example, in studies in New Zealand, as many as 70% of pedigree Southdown ewes received assistance (Laing, 1949) and 28% for Romney Marsh ewes (Quinlivan et a2 1966). In New South Wales Hughes et a1 (1964) recorded a lower incidence of prolonged births, in Merinos (range 7-12% of dead lambs) compared to crossbreds (range 10-34% of dead lambs). Dun and Hamilton (1965) attributed 17% of the difference in net reproductive rate between Folds Plus and Folds Minus Merino ewes to higher neonatal death rate in the Folds Plus flocks due to dystocia. On the other hand, Merino ewes
TABLE 2 Type o f Presentation of Lambs Experiencing Dystocia i n Relation to Birth Weight
Classification
-
Anterior normal (a) 1 foreleg retained (b) 2 forelegs retained Posterior (including breech) Other malpresentations"
No.
%
No. Survived
Mean Birth Weight (kg)
50 2
76.9 10.8 3.1
13 1 1
4.10 4.43 4.00
3 3
4.6 4.6
1 0
3.73 4.03
7
One case each of: .lateral deviation of head and neck; lateral deviation of head and neck with retention of 1 foreleg; dorsotransverse presentation.
Australian Veterinary Journal, VoI. 51, May, 1975
263
TABLE 3
TABLE 4
Mean Birth Weight of Lambs (k,) and the Proportion of Lambs exceeding 4.0 kg in Relation to Stocking Rate and Season of Lambing
Ewes per Hectare
n Mean lamb birth weight 3.60 Proportion ( % ) of Lambs exceeding 4.0 kg Winter 38.8 Spring 32.4 Summer 3C.1
Incidence of Dystocia in Relation to Season of Lambing and Stocking Rate
12 3.59 22.0
41.0 34.4
3.58
26.3 40.9
Ewes per Hectare
Lambing Season Spring Summer
8
Incidence % Incidence % Incidence %
O/llS 0.0 3/ 122 2.5 2/98 2.0
12
16
8/182 4.4 I4/187
91249 3.6 18/249
7.5
7.2
3/145
6/IH3 3.3
2.1
39.1
~~
grazing pastures of oestrogenic subterranean clover have been reported to have an incidence of dystocia that varied from 12 to 30% (Maxwell 1970). In Of the 30 lambing periods no dystocia was observed and in 13 it was not necessary to assist any During the years 19"1969 there was an increase in the proportion of ewes that experienced dystocia but this increase did not appear to be to the Pre-lambing bodyweights. The high incidence of dystocia in spring lambings could possibly be explained by the fact that the ewes were weaker, having been pregnant in the harsh winter months, while the winter and summer lambing groups were in stronger condition at lambing, having been pregnant during the autumn and spring respectively, when in general, there was adequate pasture. No explanation can be offered for the high incidence of dystocia in spring 1969 when the mean prelambing bodyweights were neither high nor low. The proportion of normal (anterior) presentations (77%) with head and both forelegs presented together was slightly higher than that re(1949) for Romney Marsh ported by sheep (69%). The present results are in general agreement with those of Kennedy and Bettenay (1950) who noted that the most common malpresentation encountered in Merinos was anterior presentation with retcntion of one or both forelegs. The lower incidence of dystocia at 8 ewes per ha compared to 12 or 16 ewes per ha, which appears to be a paradox, was possibly due to the ewes at the lowest stocking rate being stronger than the ewes at the higher stocking rates. The mean bodyweight of ewes stocked at 8 per ha was slightly greater than those at 12 and 16 yet the mean birth weights of all lambs were almost identical. This could indicate that a stronger ewe could give birth more easily than a lighter or weaker ewe. 264
Approximately 28% of all single born dead lambs and 65% of lambs that had a difficult birth had birth weights greater than 4.0 kg, which is consistent with the hypothesis that foeto-pelvic disproportion was a major cause of dystocia. The high proportion of lambs born and of single dead lambs with birth weights greater than 4.0 kg was possibly due to nutritional factors. In most years actively growing spring pastures were available during the last month of gestation, whereas at winter lambing, pasture growth was minimal or semi-dormant and at summer it was fibrous and maturing* The aSSOCiatiOn between dystocia in Merinos and oversized lambs has been reported earlier (Dun and Wall 1962; Dun and Hamilton 1965). In the present study, the criteria for establishing a relationshb between lamb deaths and dystocia, in unassisted cases, were relatively crude. If the technique of Hauehey (19731, which involves the detection of meningeal haemorrhages, had been available, the recorded incidence of dystocia may have been higher. Acknowledgments
The field assistance given by Mr. J. T. Elliott throughout the course of these observations is gratefully acknowledged. Summary
The mean incidence of dystocia in 1,510 finewool Merino Over a ten-year period was 4.1% of ewes lambing. In the 10 year period, 10% of all neonatal mortality was attributed to dystocia and in only 23% of dystocias was lamb presentation abnormal. The incidence of dystocia was not related to age of ewe. Significantly more ewes experienced dystocia at spring than winter (P < 0.05) or summer (P < 0.01) lambings. The mean birth weights of dystocic single and twin barn Iambs were 4.19 and 3.38 kg respectively. The corresponding birth weights of lambs that did not experience dystocia were 3.69 and 3.00 kg. Australian Veterinary Journal, Vol. 51, May, 197.5
More ewes experienced dystocia when stocked at 12 or 16 per ha than at 8 per ha (P < 0.05). Fifty per cent of recorded dystocias occurred in ewes stocked at 16 per ha, 40 per cent at 12 per ha and 10 per cent at 8 per ha. Ewe body weight pre-lambing was not related to the incidence of dystocia but it would appear that weaker ewes are more likely to have a difficult birth than ewes that are stronger and in better condition. References Bennetts, H. W., Underwood, E. J. and Shier, F. L. ( 1 9 4 6 ) - - A ~ s t . vet. J . 22: 2. Dun, R. B. (1964)--Aust. J . exp. Agric. Anim. Husb. 4: 376. Dun, R. B. and Hamilton, B. A. (1965)-Aust. J. exp. Agric. Anim. Husb. 5: 236.
Dun, R. B. and Wall, T. A. (1962)-Proc. Aust. Soc. Anim. Prod. 4: 187. Haughey, K. G . (1973)-Aust. vet. J . 49: 1. Hughes, K. L., Hartley, W. J.. Haughey, K. G. and McFarlane, D. (1964)-Proc. Aust. SOC. h i m . Prod. 5: 92. Jefferies, B. C. and Fearn, J. T. (1957)-J. Aust. Znst. agric. Sci. 23: 149. Kennedy, J. F. and Bettenay, 1. .. R. A. (1950)-Aust. agric. Res. 1: 7 6 . Laing, A. D. M. G . (1949)--N.Z. J1 Agric. 79: 11. McFarlane, D. (1964)--Wool Technul. Sheep Breed. 11: 1 1 . McFarlane, D. (1965)--N.Z. vet. J . 13: 116. Maxwell, J. A. L. (1970)-Aust. vet. J . 46: 533. Quinlivan, T. D., Martin, C. A., Taylor, W. B. and Cairney, I. M. (1966)-J. Reprod. Fert. 11: 379. Wallace, L. R. (1949)-Proc. N . Z . Soc. Anim. Prod. 9: 8 5 . (Received for publication 2 August 1974)
BOOK REVIEWS PRODUCTION FROM LARGE HERBIVORES This book* is a collection of 37 separate contributions arranged into 15 parts in the following 4 sections: 1 introduction; 2 energy flow and secondary productivity; 3 components of energy flow, for example animal numbers and densities, categories and age determination, measuring quantity and quality of diet, metabolism, post-natal growth; and 4 management for secondary production including husbandry of wild animals, handling wild herbivores, environmental physiology, reproduction, nutrition, habitat manipulation, epizooti* c & a c t i c a l guide to the study of the productivity of large herbivores. Ed. Frank B. Golley and Helmut K. Buechner. International Biological Programme. Blackwells, Oxford, 1968. Pp 308. (1BP Handbook No. 7) S2.00 stg.
ology and conversion factors for productivity measurements. The book will be of interest to veterinarians engaged in production research particularly in extensive grazing systems and if engaged in investigations on undomesticated livestock. It is of note that estimates on energy conversion by steers showed that they produce 12 times as much growth as elephants and 5 times as much as deer, which is a plausible reason for questioning the use of native animals under intensive conditions. The book is intended to be a useful starting point, rather than a compendium of detailed information. A. N. Sinclair
BEHAVIOUR OF FARM ANJ!MALS This introduction* to Farm Animal Behaviour (Ethology) is in 4 parts: firstly principles of ethology, theoretical ethology and physiological ethology: secondly. behaviour patterns of horses, .cattle, sheep and pigs, environmental influences on behaviour and managemental ethology; thirdly reproduction, for example sexual behaviour, fetal behaviour, parturition and neonatal behaviour and fourthly abnormal behaviour, that is behaviour and clinical disorders and anomalous behaviour. There is a glossary of terms. This is an introductory book so it may be of use to veterinary students, particularly those who have need to supplement their rural experience. There is a useful list of further reading at the end of each chapter which may be of value to the student or research worker who wishes to go further into the subject. Practising veterin*Farm Animal Behaviour. Andrew London. 1974. Pp 196. f 2 . 2 0 stg.
F.
Fraser.
Bailliere.
Australian Veterinary Journal, Vol. 5 1 , May, 1975
arians may feel that much of the book is devoted to stating the obvious which they probably consider is already known, but more careful reading indicates that most observers could be aided by attempts to make observations more systematically and, if possible, in objective terms. Unfortunately, the writer occasionally lapses into generalisations which are not substantiated by the evidence presented in the text. This leads to the feeling that these may have originated from material in the references. It is disappointing to find that the author has overlooked publications of Australian research on ram behaviour and its effects on oestrus in ewes, and on oestrus of cattle, as well as recent work on parturition behaviour of cattle. These deficiencies detract from the application of this particular book in practice here in Australia. A. N. Sinclair 265
