J. Vet. Med. B 38, 513-522 (1991) 0 1991 Paul Parey Scientific Publishers, Berlin and Hamburg ISSN 0931 - 1793
National Veterinary Institute, P.O. Box 8156, Dep. N-0033 Oslo 1
Assessment of Strategy in Selective Dry Cow Therapy for Mastitis Control 0.@STERAS’, L. SANDVIK~, J. AURSJ0’, G. G. G J U Land ~ A.J0RSTAD5
’
Address of authors: The Norwegian Dairies Association, P.O. Box 58, N-1430 As, Norway *Medstat, P.O. Box 37, N-2011 Stremmen, Norway ’The Regional Veterinary Laboratory in Bergen, P.O. Box 40, N-5032 Minde, Norway ‘The Regional Mastitis Laboratory in Molde, P.O. Box 2038, N-6400 Molde, Norway N-2660 Dombbs, Norway
With 6 tables (Received for publication February 19, 1991)
Summary Seven hundred and three cows were treated at drying off, using three main types of therapy: control, long-acting intramammaria and short-acting intramammaria. Selective dry cow therapy in infected quarters was used. Of the cows with one or two infected quarters one to six weeks before drying off, 57.7 per cent had one or more new infected quarters at drying off. Thus selective dry cow therapy on quarter basis determined from the results of samples taken one to six weeks before drying off would give “inadequate” therapy (i. e. new infection in non-treated quarters at drying off) for more than 50 per cent of the cows. For those cows given “adequate” therapy (no new infection at drying off) long-acting therapy, short-acting and control yielded 53.6 %, 49.3 % and 30.7 % healthy cows respectively two to five weeks postpartum. In cows with “inadequate” therapy the treatment groups yielded 42.9 Yo, 52.9 Yo and 29.7 % healthy cows respectively. O u r conclusion is that if long-acting intramammaria are to be used, all the quarters of infected cows should be treated, whereas if shortacting preparations are to be used, treatment can be restricted to infected quarters only.
Introduction The strategy of dry cow therapy has been discussed throughout the last 20 years. DODDand GRIFFIN(1975) and WILSON(1973) found that all quarters of all cows should be treated at drying off, while SERIEYS and ROGUINSKY (1975) held that selective dry cow therapy is preferable. BRATLIE(1973) concluded that only infected quarters should be treated. Selective dry cow therapy of infected quarters is practised in mastitis control in Norway. Short acting formulas are commonly used as opposed to long acting preparations, which are more often used in overseas countries. Most veterinarians practice selective dry cow therapy on quarter base in order to minimise the use of antibiotics. It is commonly believed that in order to establish a rational selective dry cow therapy it is essential to know what cow and quarters to treat. This is usually achieved by taking milk samples from cows suspected of having mastitis at drying off. These samples are taken one to six weeks before drying off, because transportation of samples to laboratory, laboratory examination and notification by post are time-consuming. U.S.Copyright Clearance Center Code Statement:
0931 - 1793/91/3807-0513$02.50/0
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In Norway individual cow milk cell counts are examined every second month. These counts are often used t o select cows at risk for subclinical mastitis. However, an English study (KINGWILL et al., 1983) has shown that the risk of a new infection is very high at the time of drying off. This sample procedure raises two vital questions: to what extent will a sample taken one to six weeks before drying off give correct information about the situation at drying off, and how will “incorrect information” influence the therapeutic efficacy? T h e object of the present paper is t o address these two questions.
Material and Methods Seven hundred and three cows from 291 Norwegian dairy herds were included in a dry cow therapy trial. Veterinarians from ten different veterinary districts were involved in the treatment and three different regional mastitis laboratories analysed the milk samples. The inclusion criterion were: 1) The farmer was willing to let hidher dairy cows participate in a therapy trial with control groups. 2) The cow had shown > 100,000 somatic cow cells per ml milk in the two last cell counts. 3) An infectious mastitis or bacteriological finding of major pathogens was found in one or more quarters at the first screening test. Major pathogens in this trial were defined as Staphylococcus aureus (S.aureus), Streptococcus (Str.) dyrgalactiae, Str. agalactiae or Actinomyces pyogenes. Cows were excluded from the trial if: 1) The cow had been treated for mastitis 3 or more times during the last lactation period. 2) The cow had been treated for mastitis within the last three weeks before the first sampling. 3) The cow had been treated for mastitis between the first sampling and drying off. 4) The cow had a significant teat lesion in the area of the teat opening. 5) The cow’s milk had been tested for antibiotics and found positive at first or second sampling. The laboratory diagnoses were based on the Nordic recommendation for mastitis diagnosis (KLASTRUPand MADSEN,1974), which prescribes quarter examination by means of the Californian Mastitis Test (CMT) (SCHALMet al., 1971) and bacteriological examination. The results of the examinations were classified and coded as follows (quarter diagnosis): 0 = no finding of major pathogens nor positive CMT. 1 = N o finding of pathogens but positive CMT. 2 = Finding of minor pathogens and positive CMT. 3 = Finding of major pathogens, but negative CMT. 4 = Finding of major pathogens and positive CMT. The cow diagnosis was defined as the highest diagnostic score of any quarter. According to inclusion criterion 3 only cows with cow diagnosis higher than 1 were included. Cows included in the trial were arranged into 4 groups according to a randomisation list: Group A = Control cows; sampling only. Group B = Control/“placebo” cows; given base ointment of “Benestermycin Vet Leo” without antibiotics; one intramammary in each infected quarter. Group C = Benestermycine vet “Leo”; one intramammary in each infected quarter. Group D = Leocillin@with Dihydrostreptomycin vet “Leo”; one intramammary every second day for 6 days in each infected quarter. In groups B and C the treatments were given “double-blind”, i. e. neither the practitioner nor the laboratory personnel knew which of the two treatments was given. The treatment in group C (Benestermycine vet “Leo”) consisted of: Leocillin corresponding to 100,000 IE benzylpenicillin, benethaminpenicillin corresponding to 300,000 IE benzylpenicillin and Framycetin (as sulfat) corresponding to lOOmg neomycin B. The treatment in group D (Leocillin@with Dihydrostreptomycin vet “Leo”) consisted of: Penethamate hydriodide BAN 300 mg (corresponding to 300,000 IE benzylpenicillin), and DHS (as sulfat), 300 mg in sterile vegetable oil suspension. Quarter milk samples were taken 4 times from each cow: 1st sample: Between one and six weeks before drying off. 2nd sample: At drying off (treatment started), 3rd sample: At calving (before first milking) and 4th sample: Between two and five weeks after calving. Selective quarter treatment was administered according to the following scheme: if one quarter was diagnosed infected at first sampling, only this quarter was treated at drying off. If two quarters were infected at first sampling, only these two quarters were treated at drying off. If three or four
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quarters were infected at first sampling, all four quarters were treated at drying off. If the practitioner found a new quarter clinically infected at drying off, this quarter was also treated even if it was defined as healthy at 1st sampling. Among the cows treated in one or two quarters only, three possibilities existed: 1. The therapy was “unnecessary”; i.e. none of the quarters was diagnosed as infected at second sampling. 2. The therapy was “inadequate”; i. e. at least one quarter diagnosed as infected at second sampling was not treated according to the selective treatment regimen. 3. The therapy was “adequate”, i. e. all quarters diagnosed as infected quarters at second sampling were treated. Statistics When comparing frequencies in two groups of cows, a two-sided Fisher-Irwin test was used, with a 5 ‘Yo significance level. Statistical analysis was carried out using the SAS software package.
Results The result of the bacteriological examinations of the two first samples is shown in Table 1. No statistically significant differences in bacteriological findings were found between the therapy groups A, B, C or D in the first and second milk sample. Table 1 demonstrates considerable changes in bacteriological status from the first to the second sample. Only 63 % of quarters with 5.auveus at the first sampling had 5.aureus at the second sampling as well. Only 56 % of quarters having 5.aureus at second sampling had 5.aureus at first sampling. Almost all the “other major pathogens” in Table 1 were Sty. dysgalactiae; only one quarter of these had Sty. agalactiae at first sampling and two quarters at second sampling. Of the quarters infected with “other Streptococcus spp.” in Table 1 five quarters were infected with Sty. ubevis at first sampling and 16 at second sampling. Only one quarter had Sty. ubevis at both first and second sampling. In Table 2 the cows are presented according to number of infected quarters at first and second sampling. Among the cows having one infected quarter at first sampling (n = 352) - 11.9 o /‘ had no infected quarters at second sampling; - 25.6 % had two infected quarters at second sampling; - 16.2 OO/ had three infected quarters at second sampling; - 9.9 % had four infected quarters at second sampling.
Table 1 . Number of quarters by bacteriological/inflammatory status at 1st sample (one to six weeks before drying off) and at 2nd sample (drying off) Status 1st sample
Healthy
Nonspec. m.
S.aureus
Healthy 1,014 Non-spec. m. 88 S.aureus 141 0.major pat. 30 Cns 72 0.strept. 20
192 70 36 10 29 8
215 28 389 16 39
Total
345
1,365
Status 2nd sample 0.major Cns pat.
0.strept.
Total
7
31 6 18 66 4 5
49 10 22 3 82 5
25 5 9 3 5 8
1,526 207 615 128 23 1 53
694
130
171
55
2,760
Healthy = No bacteriological diagnosis nor positive CMT, Non-spec. m. = Nonspecific mastitis (no bacteriological finding, but positive CMT), S.aureus = Staphylococcus aureus, 0. major pat. = Other major pathogens, 0. strept. = Other Streptococcus spp., Cns = Coagulase negative staphylococci.
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Table 2. Number of cows with 0, 1, 2, 3, and 4 infected quarters (quarter diagnosis > 0) at first and second sampling Number of quarters infected at 1st sample
Number of quarters infected at second sample 2 3 4
Total
0
1
1 2 3 4
42 16 6 5
128 51 16 5
90 65 19 10
57 50 17 6
35 29 30 26
352 211 88 52
Total
69
200
184
130
120
703
~~
- 128 cows (36.4 Yo) had one infected quarter also at second sampling, but for 27 (21.1 %) of these cows this infected quarter was not the same as the original one.
Among the 352 cows having one infected quarter at 1st sampling, 209 cows (59.4 YO) were given “inadequate” therapy according to the results of the second sampling, and 42 (11.9 70) of the cows were given “unnecessary” therapy according to the second sampling results. Two hundred and eleven cows had two infected quarters at first sampling; of these - 7.6 % had no infected quarters at second sampling; - 23.7 Yo had three infected quarters at second sampling; - 13.7 % had four infected quarters at second sampling. Of the 65 cows having two infected quarters also at second sampling, 29 cows had infection in different quarters on the two occasions. Of the 51 cows having only one infected quarter at second sampling, 8 cows had this infection in a different quarter than the two quarters infected at first sampling. Of 211 cows having two infected quarters at first sampling, 116 cows (55.0%) were given “inadequate” therapy according to the result of the second sampling at drying off. 16 cows (7.6%) were given “unnecessary” therapy according to the result of the second sampling. A total number of 563 cows (80.1 %) were given selective dry cow therapy in infected quarters, based on mastitis positive diagnoses in only one or two quarters at first sampling. Of these cows 325 cows (57.7 Yo) were given “inadequate” therapy according to the results of the second sampling. 58 cows (10.3 Yo) were given “unnecessary” dry cow therapy according to the results of the second sampling. Thus only 180 (32.0%) of the cows receiving selective therapy were given “adequate” therapy according to the result of the second sampling. In the total material of 703 cows, 325 cows were given “inadequate” therapy in infected quarters and 378 cows were given “adequate” or “unnecessary” therapy. Table 3. Number of cows with 0, 1, 2, 3 , and 4 infected quarters (quarter diagnosis > 0) at second sampling. Cows with only one quarter infected at 1st sampling Bacteriological diagnoses at first sample
Number of quarters infected at second sampling 2 3 4
0
1
Total
Staphylococcus aureus Other major pathogens Minor pathogens
22 5 13
73 18 33
48 13 19
28 10 13
16 4 10
187 50 88
Total
40
124
80
51
30
325
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Assessment of Strategy in Selective Dry Cow Therapy
Table 4. Number of cows with 0, 1, 2, 3, and 4 infected quarters (quarter diagnosis > 0) at second sampling, in relation to quarter diagnosis at first sampling. Only cows with “major pathogens” infection in one quarter at 1st sampling Diagnosis of the one infected quarter at first sampling
0
1
Number of quarters infected at second sampling 2 3 4
Total
3 (major without elevated cell count) 4 (major with elevated cell count)
14
42
31
16
8
111
13
49
30
22
12
126
Total
27
91
61
38
20
237
In Table 3 the cows infected in one quarter at first sampling are presented according to number of infected quarters at second sampling, as well as bacteriological findings at first sampling. 49 % of the cows infected with S. aweus at first sampling had more than one quarter infected at second sampling. Correspondingly 54 % of the cows with other major pathogens and 48 % of the cows with minor pathogens in the infected quarter had more than one infected quarter at drying off. In Table 4 the cows infected in one quarter with major pathogens at first sampling are presented according to number of infected quarters at second sampling, as well as the diagnostic findings at first sampling. The cows are grouped according to CMT reaction at first sampling. 50 70 of the cows without positive CMT had more than one quarter infected at drying off, compared to 51 % of the cows with elevated cell count at first sampling. Table 5 presents the percentage of healthy cows in the therapy groups at third and fourth sampling. A healthy cow was defined as having cow diagnose < 1 (no quarter with positive CMT nor major pathogens). Group A and B were combined because there was no difference in the therapeutic results between these two groups (@STERAS, 1990). Table 6 is similar to Table 5, but with less restrictive criterion for healthy; i. e., no finding of major pathogens in any of the quarters at sampling.
Table 5. Percent healthy cows after dry cow therapy classified according to “adequate”, “inadequate” and “unnecessary” therapy. Healthy cows are defined as having normal CMT and no finding of minor pathogens nor major pathogens in any quarter (cow diagnosis < 1). 3rd sample taken at time of calving, 4th sample taken two to five weeks post partum Result 3rd sample Healthy
Result 4th sample Healthy
Yo
YO
Therapy group n = number of cows
Therapy class
A + B (n = 68) C (n = 52) D (n = 71)
“adequate” “adequate” “adequate”
33.8 67.3 56.3
23.5 53.9 43.7
A + B (n = 99) C (n = 109) D (n = 103)
“inadequate” “inadequate” “inadequate”
26.3 38.5 55.3
26.3 37.6 48.5
A + B (n = 17) C (n = 21) D (n = 23)
“unnecessary” “unnecessary” “unnecessary”
58.8 100.0 100.0
52.9 71.4 65.2
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Table 6. Percent healthy cows after therapy classified according to “adequate”, “inadequate” and “unnecessary” therapy. Healthy cows are defined as no finding of major pathogens in any quarter (cow diagnosis < 3). 3rd sample taken at parturition, 4th sample two to five weeks post partum
Yo
Result 4th sample Healthy Yo
“adequate” “adequate” “adequate”
37.1 67.9 59.2
30.7 53.6 49.3
A + B (n = 74) C (n = 84) D (n = 70)
“inadequate” “inadequate” “inadequate”
27.0 39.3 55.7
29.7 42.9 52.9
A + B (n = 2 6 ) C (n = 21) D (n = 23)
“unnecessary” “unnecessary” “unnecessary”
53.9 81.0 82.6
57.7 81.0 73.9
Therapy group n = number of cows
Therapy class
A + B (n = 62) C (n = 56) D (n = 71)
Result 3rd sample Healthy
Among cows receiving “adequate” therapy, the percentage of healthy cows at 3rd and 4th sampling was significantly higher in group C and D than in group A + B (Tables 5 and 6). Similar results were found among cows given “unnecessary” therapy. For cows given “inadequate” therapy, the percentage of healthy cows was significantly higher in group D than in group A + B. In group C the percentage was higher than in group A + B, but lower than in group D (Tables 5 and 6). The percentage of healthy cows in group D was similar for those given “adequate” and “inadequate” therapy. Discussion In Norway, the bacteriological diagnoses in chronic subclinical mastitis are dominated by S. aureus, coagulase negative Staphylococci, and Str. dysgahctiae. S t y . agalactiae has been very infrequent in mastitis screening samples during the past ten to twenty years. Str. ubevis bacteria has also been recorded at very low frequencies (Central Bureau of Statistics of Norway 1990). The findings in this study correspond well with the general findings in mastitis diagnostic work in Norway. No significant differences between therapy groups were found in our study before therapy in regard to bacteriological findings, lactation age, number of quarters infected and quarter diagnosis (@STERAS et al., in preparation). Furthermore there were n o significant differences between the two control groups A and B in terms of the frequency of healthy cows 2 to 5 weeks post partum P STE ERAS, 1990). We therefore chose to combine the control groups A and B when we compared them with the treatment groups C and D. Table 1 illustrates the great discrepancy in bacteriological findings between the first et al. (1983) and second sampling. This is in good agreement with the findings of KINGWILL and may show a high new infection rate during the last weeks before drying off o r diagnostic inaccuracy. Accordingly, it is difficult to predict infected quarters at drying off on the basis of sampling a few weeks earlier. Thus, it is difficult to know which quarters to treat at drying off when using a regimen of selective quarter therapy. The bacteriological findings at drying off suggest that all quarters should be treated if a cow had been found to be infected in at least one quarter a few weeks earlier. This is also in agreement with earlier findings of D O D D and GRIFFIN (1975). The results in our study indicate that in selective dry cow therapy, more than 50 % of the cows received “inadequate” therapy, i. e. they had been given no therapy in at least one infected quarter according to the results of the 2nd sampling.
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Mastitis diagnosis is very complicated. The cell counts varies from day to day and at et al., 1985). Since the major least S. aureus intermittently occurs in milk samples (MATTILA source of infection for S. aureus, Str. dysgalactiae and other major pathogens is considered to be the infected udder or teat lesions (BRAMLEY, 1981), the cows with only one infected quarter at first sampling were classified according to infection type (Table 3). Our results demonstrate that there was no significant difference in number of infected quarters at 2nd sampling between a primary finding of S. aureus, other major pathogens nor minor pathogens (Table 3). This result illustrates that the new infection rate at drying off in cows already infected in one quarter in late lactation is similar for different species of udder pathogens diagnosed at 1st sample. The new infection rate was similar for major pathogens and for environmental infection at this stage of lactation. Table 4 was compiled to evaluate whether the inflammatory reaction at first sampling could predict the new infection rate at drying off. The number of quarters infected at drying off was independent of whether the cow had an inflammatory reaction in the one quarter infected about six weeks earlier. The cell count or the inflammatory reaction a few weeks before drying off could not predict the new infection rate at drying off. This finding indicates that bacteriological findings (quarter diagnose = 3) and mastitis with major pathogens (quarter diagnose = 4) should be regarded in the same manner regarding the risk of new infection in quarters at drying off. The diagnostic problems are even greater at drying off because the normal involution process taking place in the udder at this stage is very alike the inflammatory process during mastitis (DODDand GRIFFIN,1975). This could bring into question the value of diagnosis at drying off as used in this trial. The CMT reaction is an essential part of the diagnostic routine, especially in mastitis with minor pathogens. At drying off we must compare the CMT-reaction in the four quarters (KLASTRUP and MADSEN,1974), and if we have a physiologically skewed distribution of the CMT reaction between the quarters, there is a high possibility of false positive mastitis diagnosis. Despite our efforts to obtain aseptic sampling, there were considerable problems with false positive bacteriological findings of environmental bacteria such as coagulase negative Stupbylococcus spp. and “other” Streptococcus spp. The diagnosis of major pathogens should not pose that great a problem. Major pathogens as defined in this study are not commonly found as contaminants in mastitis diagnosis (BARNES-PALLESEN et al., 1987). The visualisation of S. aureus in plate culture is quite characteristic, indicating that the diagnosis of major pathogens is relatively reliable. ERSKINE and EBERHART (1988) found far more agreement in duplicate samples in quarters infected with Str. ugalactiue and S. aureus than for other Streptococcus spp. and coliform SPP. In 50 per cent of the cows, there was at least one infected quarter at drying off that was not treated in the treatment groups. What are the therapeutic consequences of this “inadequate” therapy? To try to answer this question, the cows infected in one or two quarters at first sample were arranged into three groups: “adequate”, “inadequate” and “unnecessary” therapy (see definition under Material and Methods). Table 5 illustrates the result when cows with all types of infection, also minor pathogens, are defined as “not healthy”. These results should be interpreted with care because of the diagnostic problems in the second sample due to inclusion of minor pathogens. The results presented in Table 6 are more reliable because of minor diagnostic problems, as only major pathogens were defined as positive findings. In this way the problems of evaluating the cell count in the involution period and the evaluation of contaminants of minor pathogens are excluded as far as possible. The results presented in Tables 5 and 6 are quite similar, indicating that the diagnostic criteria in this study have little influence of the overall results. The results presented in Tables 5 and 6 demonstrate that therapy C (Benestermy&@ vet “Leo”) is slightly more efficient than D (Leocillinm with Dihydrostreptomycin vet ”Leo”) in cows receiving “adequate” therapy. This corresponds with the results of JENSEN et al. (1977). However, group D showed a slightly better result than group C for the cows
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that were given “inadequate” therapy. O u r results indicate that the efficacy of regimen D is largely independent of whether all quarters infected at drying off are treated (Tables 5 and 6). However, this was not true for regimen C, which was less efficient when the treatment was “inadequate”. From a statistical point of view, the groups presented in Tables 5 and 6 are rather small, i.e. the differences between the groups must be rather large to be statistically significant. Thus a difference between two groups may be important even though the observed difference is not statistically significant. The present material is small and significant differences are found only between each of the two therapy groups compared to the control group. Our results indicate that when using long-acting intramammaria such as Benestermycin@vet “Leo”, all the quarters of an infected cow should be treated. The results in group D indicate that when using short-acting intramammaria in dry cow therapy similar results may be obtained by treating only the infected quarters at first sampling. The better result in group D than in group C among “inadequately” treated cows may indicate that the effect of a higher dose of antibiotics when using short-acting formulas, as in group D, will increase the possibility of having a systemic effect on the quarters which are not treated. The results also indicate that such an effect is not found when using long-acting formulas. This is in good agreement with earlier literature on the effect of dry cow therapy using long-acting formulas (DODDand GRIFFIN,1975). However, very few studies have been carried out on the effect of dry cow therapy using short-acting intramammaria. It has been shown that different penicillium preparation are absorbed differently to the udder lymph and blood system (ZIV, 1980; FRANKLIN et al., 1986) and some preparations give significantly higher Penicillium G concentration in untreated quarters after intramammaria treatment (FRANKLIN et al., 1986).JENSEN (1977) found better effect of Benestermycin than Leocillin in dry cow therapy. The relative better effect of Leocillin@with Dihydrostreptomycin vet “Leo” in this study could either he due to the Dihydrostreptomycin component or to the six days therapy in group D in this trial. MEINand BROWNING (1990) found no significant difference in cure rate between cows treated infected quarters only, compared to cows treated all quarters. SCHULTZE (1983) found that therapy failed to control new infections in the late dry and peripartum periods, thus therapy of healthy cows before drying off should be unnecessary. BRATLIE(1973) also concluded that in dry cow therapy only infected quarters should be treated. This study still raises these questions: What would the effect be of supplementation of general intramuscular therapy in group D, and what would the effect be of supplementation of one intramammary in all quarters the last day of treatment in group D ? These questions should be answered in a later dry cow therapy study. In a study of antibiotic therapy on S. aureus infected cows during lactation, OWENS et al. (1988) found 30% healthy cows after intramammary infusion for six milkings with 62.5 mg amoxicillin, compared to 48 O h healthy cows when intramuscular infusion of 9,000,000 U procain penicillin G for 3 days was given in addition. SOBACK et al. (1990) found better effect of systemic dry cow therapy than only local dry cow therapy. The results in Tables 5 and 6 for cows treated “unnecessarily” illustrate that cows which have one or two infected quarters at first sampling and no infected quarters at second sampling have a better prognosis than cows which also have infected quarters at second sampling. This finding is in good accordance with SOL et al. (1990). This result indicates that these cows should be treated with antibiotics at drying off. The result also indicates that long-acting formulas such as Benestermycin@vet “Leo” had a slightly better effect than short-acting formulas such as Leocillin@with Dihydrostreptomycin vet “Leo”.
Conclusion From this study we conclude that the correspondence in bacteriological findings from samples taken about six weeks prior to drying off and from samples taken at drying off is low. The new infection rate of quarters in already infected cows was similar for cows
Assessment of Strategy in Selective Dry Cow Therapy
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infected with minor pathogens and major pathogens. It was also similar for cows which had major pathogens with high cell count (mastitis) and cows which had only bacteriological findings of major pathogens. In all, 57.7% of the cows with one o r two quarters infected at one to six weeks before drying off had a new infected quarter at drying off. The results of this study indicate that all quarters of infected cows should be treated, even when only one infected quarter was found at drying off, if long-acting intramammaria are used. O u r results indicate that only one or two quarters could be treated, provided that only such a number of quarters was found to be infected at one to six weeks before drying off, if short-acting intramammaria are used four times during the course of six days at drying off.
Acknowledgements The authors would like to thank “Lsvens kemiske Fabrik”’s division in Norway, P.O. Box 7186, Homansbyen, 0307 Oslo 3, for free delivery of all the antibiotics and placebos used in this trial, and for their assistance in achieving randomisation of the trial. We would also like to thank the Dairy Association’s extension services in (astlandmeieriet, Vestlandmeieriet, Sunnmsre Meieri and Nordmore og Romsdal Meieri for their helpfulness in motivating the farmers and collecting samples one and four. Last but not least, we would like to thank all the veterinary practitioners who treated the cows and took the samples at drying off.
References BARNES-PALLESEN, F.D., P.BLACKMER, A.BRI?TEN,R.B. BUSHNELL,D.M. VAN DAMME,and F. WELCOME,1987: Laboratory and Field Handbook on Bovine mastitis. National Mastitis Council, Inc., Arlington. VA, 208 pp. A . J., 1981: The role of hygiene in preventing intramammary infection. In: BRAMLEY, A. J., BRAMLEY, F. H. DODD,and T. K. GRIFFIN,Mastitis Control and Herd Management. Technical Bulletin 4, The National Institute for Research in Dairying, Reading, England, 53 -66. BRATLIE,O., 1973: Dry cow therapy. Vet. Rec. 93, 430-431. Central Bureau of Statistics of Norway, 1990: Veterinary Statistics 1988. Oslo-Kongsvinger, 86 pp. 1975: The role of antibiotics treatment at drying off in the control of DODD,F. H., and T. K. GRIFFIN, mastitis. Proc. of Seminar of Mastitis Control. Document 85. International Dairy Federation. Bruxelles, 282-302. ERSKINE, R. J., and R. J. EBERHART, 1988: Comparison of duplicate and single quarter milk samples for the identification of intramammary infections. J. Dairy Sci. 71, 854-856. FRANKLIN, A,, M. HORNAF ~ N Z I E N. N ,OBEL,K. OSTENSSON, and G. A S T R ~ M 1986: , Concentration of penicillin, streptomycin and spiramycin in bovine udder tissue liquids. Am. J. Vet. Res. 47, 804-807.
JENSEN,A. J. H., J. A. MADSEN,and P. S. PEDERSEN, 1977: Goldyverterapi. Dansk Vet. Tidsskr. 60, 754 -764.
KINGWILL, R. G., F. H. DODD,and F. K. NEAVE,1983: Machine milking and mastitis. In: THIEL, C. C., and F. H . DODD,Machine Milking, Technical Bulletin 1, The National Institute for Research in Dairying, Reading, England, 231 -285. KLASTRUP, O., and P. S. MADSEN,1974: Nordic recommendations in mastitis investigations of quarter samples. Nord. Vet.-Med. 26, 197-204. MATTILA,T., S. PyijRii~A,and M. SANDHOLM, 1985: Comparison of milk antitrypsin, albumin, Nacetyl-b-D-glucosaminidase, somatic cells and bacteriological analysis as indicators of bovine subclinical mastitis. Vet. Res. Commun. 10, 113- 124. MEIN,G. A., and J. W. BROWNING, 1990: Dry cow therapy for mastitis control. In: Proceedings of the International Symposium on Bovine Mastitis, Indianapolis, Indiana, U.S.A. Sept. 13- 16, National Mastitis Council, 124- 128. OWENS, W. E., J. L. WATTS,R. L. BODDIE,and S. C. NICKERSON, 1988: Antibiotic treatment of mastitis; Comparison of intramammary and intramammary plus intramuscular therapies. J. Dairy Sci. 71, 3143-3147. STE ERAS, O., 1990: The effect of dry cow therapy. An evaluation of long-acting and short-acting intramammaria. In: Proceedings of the International Symposium on Bovine Mastitis, Indianapolis, Indiana, U.S.A. Sept. 13-16, National Mastitis Council, 129-133.
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SCHALM,0.W., E. J. CAROLL,and N. C. JAIN, 1971: Bovine Mastitis. Lea & Febiger, Philadelphia. 360pp. SCHULTZE, W. D., 1983: Effects of selective regimen of dry cow therapy on intramammary infection and on antibiotic sensitivity of surviving pathogens. J. Dairy Sci. 66, 892-903. SERIEYS, F., and M. ROGUINSKY, 1975: Comparative tests with dry cow therapy for some or all cows in a herd. Proc. of Seminar of Mastitis Control. Document 85. International Dairy Federation. Bruxelles, 349-351. SOBACK, S., G. ZIV, M. WINKLER, and A. SARAN,1990: Systemic dry cow therapy - A preliminary report. J. Dairy Sci. 73, 661 -666. SOL,J., J.HARINK,and A. VAN UUM,1990: Factors affecting the result of dry cow treatment. In: Proceedings of International Symposium on Bovine Mastitis, Indianapolis, Indiana, U.S.A. Sept. 13-16, National Mastitis Council, 118-123. WILSON,C. D., 1973: BRATLIE, 0.:Dry cow therapy. Letter. Vet. Rec. 93, 616. ZIV,G., 1980: Drug selection and use in mastitis: Systemic vs local therapy. J. Am. Vet. Med. Assoc. 176, 1109-1115.
National Veterinary Institute, P.O. Box 8156, Dep. N-0033 Oslo 1
Assessment of Strategy in Selective Dry Cow Therapy for Mastitis Control 0.@STERAS’, L. SANDVIK~, J. AURSJ0’, G. G. G J U Land ~ A.J0RSTAD5
’
Address of authors: The Norwegian Dairies Association, P.O. Box 58, N-1430 As, Norway *Medstat, P.O. Box 37, N-2011 Stremmen, Norway ’The Regional Veterinary Laboratory in Bergen, P.O. Box 40, N-5032 Minde, Norway ‘The Regional Mastitis Laboratory in Molde, P.O. Box 2038, N-6400 Molde, Norway N-2660 Dombbs, Norway
With 6 tables (Received for publication February 19, 1991)
Summary Seven hundred and three cows were treated at drying off, using three main types of therapy: control, long-acting intramammaria and short-acting intramammaria. Selective dry cow therapy in infected quarters was used. Of the cows with one or two infected quarters one to six weeks before drying off, 57.7 per cent had one or more new infected quarters at drying off. Thus selective dry cow therapy on quarter basis determined from the results of samples taken one to six weeks before drying off would give “inadequate” therapy (i. e. new infection in non-treated quarters at drying off) for more than 50 per cent of the cows. For those cows given “adequate” therapy (no new infection at drying off) long-acting therapy, short-acting and control yielded 53.6 %, 49.3 % and 30.7 % healthy cows respectively two to five weeks postpartum. In cows with “inadequate” therapy the treatment groups yielded 42.9 Yo, 52.9 Yo and 29.7 % healthy cows respectively. O u r conclusion is that if long-acting intramammaria are to be used, all the quarters of infected cows should be treated, whereas if shortacting preparations are to be used, treatment can be restricted to infected quarters only.
Introduction The strategy of dry cow therapy has been discussed throughout the last 20 years. DODDand GRIFFIN(1975) and WILSON(1973) found that all quarters of all cows should be treated at drying off, while SERIEYS and ROGUINSKY (1975) held that selective dry cow therapy is preferable. BRATLIE(1973) concluded that only infected quarters should be treated. Selective dry cow therapy of infected quarters is practised in mastitis control in Norway. Short acting formulas are commonly used as opposed to long acting preparations, which are more often used in overseas countries. Most veterinarians practice selective dry cow therapy on quarter base in order to minimise the use of antibiotics. It is commonly believed that in order to establish a rational selective dry cow therapy it is essential to know what cow and quarters to treat. This is usually achieved by taking milk samples from cows suspected of having mastitis at drying off. These samples are taken one to six weeks before drying off, because transportation of samples to laboratory, laboratory examination and notification by post are time-consuming. U.S.Copyright Clearance Center Code Statement:
0931 - 1793/91/3807-0513$02.50/0
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In Norway individual cow milk cell counts are examined every second month. These counts are often used t o select cows at risk for subclinical mastitis. However, an English study (KINGWILL et al., 1983) has shown that the risk of a new infection is very high at the time of drying off. This sample procedure raises two vital questions: to what extent will a sample taken one to six weeks before drying off give correct information about the situation at drying off, and how will “incorrect information” influence the therapeutic efficacy? T h e object of the present paper is t o address these two questions.
Material and Methods Seven hundred and three cows from 291 Norwegian dairy herds were included in a dry cow therapy trial. Veterinarians from ten different veterinary districts were involved in the treatment and three different regional mastitis laboratories analysed the milk samples. The inclusion criterion were: 1) The farmer was willing to let hidher dairy cows participate in a therapy trial with control groups. 2) The cow had shown > 100,000 somatic cow cells per ml milk in the two last cell counts. 3) An infectious mastitis or bacteriological finding of major pathogens was found in one or more quarters at the first screening test. Major pathogens in this trial were defined as Staphylococcus aureus (S.aureus), Streptococcus (Str.) dyrgalactiae, Str. agalactiae or Actinomyces pyogenes. Cows were excluded from the trial if: 1) The cow had been treated for mastitis 3 or more times during the last lactation period. 2) The cow had been treated for mastitis within the last three weeks before the first sampling. 3) The cow had been treated for mastitis between the first sampling and drying off. 4) The cow had a significant teat lesion in the area of the teat opening. 5) The cow’s milk had been tested for antibiotics and found positive at first or second sampling. The laboratory diagnoses were based on the Nordic recommendation for mastitis diagnosis (KLASTRUPand MADSEN,1974), which prescribes quarter examination by means of the Californian Mastitis Test (CMT) (SCHALMet al., 1971) and bacteriological examination. The results of the examinations were classified and coded as follows (quarter diagnosis): 0 = no finding of major pathogens nor positive CMT. 1 = N o finding of pathogens but positive CMT. 2 = Finding of minor pathogens and positive CMT. 3 = Finding of major pathogens, but negative CMT. 4 = Finding of major pathogens and positive CMT. The cow diagnosis was defined as the highest diagnostic score of any quarter. According to inclusion criterion 3 only cows with cow diagnosis higher than 1 were included. Cows included in the trial were arranged into 4 groups according to a randomisation list: Group A = Control cows; sampling only. Group B = Control/“placebo” cows; given base ointment of “Benestermycin Vet Leo” without antibiotics; one intramammary in each infected quarter. Group C = Benestermycine vet “Leo”; one intramammary in each infected quarter. Group D = Leocillin@with Dihydrostreptomycin vet “Leo”; one intramammary every second day for 6 days in each infected quarter. In groups B and C the treatments were given “double-blind”, i. e. neither the practitioner nor the laboratory personnel knew which of the two treatments was given. The treatment in group C (Benestermycine vet “Leo”) consisted of: Leocillin corresponding to 100,000 IE benzylpenicillin, benethaminpenicillin corresponding to 300,000 IE benzylpenicillin and Framycetin (as sulfat) corresponding to lOOmg neomycin B. The treatment in group D (Leocillin@with Dihydrostreptomycin vet “Leo”) consisted of: Penethamate hydriodide BAN 300 mg (corresponding to 300,000 IE benzylpenicillin), and DHS (as sulfat), 300 mg in sterile vegetable oil suspension. Quarter milk samples were taken 4 times from each cow: 1st sample: Between one and six weeks before drying off. 2nd sample: At drying off (treatment started), 3rd sample: At calving (before first milking) and 4th sample: Between two and five weeks after calving. Selective quarter treatment was administered according to the following scheme: if one quarter was diagnosed infected at first sampling, only this quarter was treated at drying off. If two quarters were infected at first sampling, only these two quarters were treated at drying off. If three or four
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quarters were infected at first sampling, all four quarters were treated at drying off. If the practitioner found a new quarter clinically infected at drying off, this quarter was also treated even if it was defined as healthy at 1st sampling. Among the cows treated in one or two quarters only, three possibilities existed: 1. The therapy was “unnecessary”; i.e. none of the quarters was diagnosed as infected at second sampling. 2. The therapy was “inadequate”; i. e. at least one quarter diagnosed as infected at second sampling was not treated according to the selective treatment regimen. 3. The therapy was “adequate”, i. e. all quarters diagnosed as infected quarters at second sampling were treated. Statistics When comparing frequencies in two groups of cows, a two-sided Fisher-Irwin test was used, with a 5 ‘Yo significance level. Statistical analysis was carried out using the SAS software package.
Results The result of the bacteriological examinations of the two first samples is shown in Table 1. No statistically significant differences in bacteriological findings were found between the therapy groups A, B, C or D in the first and second milk sample. Table 1 demonstrates considerable changes in bacteriological status from the first to the second sample. Only 63 % of quarters with 5.auveus at the first sampling had 5.aureus at the second sampling as well. Only 56 % of quarters having 5.aureus at second sampling had 5.aureus at first sampling. Almost all the “other major pathogens” in Table 1 were Sty. dysgalactiae; only one quarter of these had Sty. agalactiae at first sampling and two quarters at second sampling. Of the quarters infected with “other Streptococcus spp.” in Table 1 five quarters were infected with Sty. ubevis at first sampling and 16 at second sampling. Only one quarter had Sty. ubevis at both first and second sampling. In Table 2 the cows are presented according to number of infected quarters at first and second sampling. Among the cows having one infected quarter at first sampling (n = 352) - 11.9 o /‘ had no infected quarters at second sampling; - 25.6 % had two infected quarters at second sampling; - 16.2 OO/ had three infected quarters at second sampling; - 9.9 % had four infected quarters at second sampling.
Table 1 . Number of quarters by bacteriological/inflammatory status at 1st sample (one to six weeks before drying off) and at 2nd sample (drying off) Status 1st sample
Healthy
Nonspec. m.
S.aureus
Healthy 1,014 Non-spec. m. 88 S.aureus 141 0.major pat. 30 Cns 72 0.strept. 20
192 70 36 10 29 8
215 28 389 16 39
Total
345
1,365
Status 2nd sample 0.major Cns pat.
0.strept.
Total
7
31 6 18 66 4 5
49 10 22 3 82 5
25 5 9 3 5 8
1,526 207 615 128 23 1 53
694
130
171
55
2,760
Healthy = No bacteriological diagnosis nor positive CMT, Non-spec. m. = Nonspecific mastitis (no bacteriological finding, but positive CMT), S.aureus = Staphylococcus aureus, 0. major pat. = Other major pathogens, 0. strept. = Other Streptococcus spp., Cns = Coagulase negative staphylococci.
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Table 2. Number of cows with 0, 1, 2, 3, and 4 infected quarters (quarter diagnosis > 0) at first and second sampling Number of quarters infected at 1st sample
Number of quarters infected at second sample 2 3 4
Total
0
1
1 2 3 4
42 16 6 5
128 51 16 5
90 65 19 10
57 50 17 6
35 29 30 26
352 211 88 52
Total
69
200
184
130
120
703
~~
- 128 cows (36.4 Yo) had one infected quarter also at second sampling, but for 27 (21.1 %) of these cows this infected quarter was not the same as the original one.
Among the 352 cows having one infected quarter at 1st sampling, 209 cows (59.4 YO) were given “inadequate” therapy according to the results of the second sampling, and 42 (11.9 70) of the cows were given “unnecessary” therapy according to the second sampling results. Two hundred and eleven cows had two infected quarters at first sampling; of these - 7.6 % had no infected quarters at second sampling; - 23.7 Yo had three infected quarters at second sampling; - 13.7 % had four infected quarters at second sampling. Of the 65 cows having two infected quarters also at second sampling, 29 cows had infection in different quarters on the two occasions. Of the 51 cows having only one infected quarter at second sampling, 8 cows had this infection in a different quarter than the two quarters infected at first sampling. Of 211 cows having two infected quarters at first sampling, 116 cows (55.0%) were given “inadequate” therapy according to the result of the second sampling at drying off. 16 cows (7.6%) were given “unnecessary” therapy according to the result of the second sampling. A total number of 563 cows (80.1 %) were given selective dry cow therapy in infected quarters, based on mastitis positive diagnoses in only one or two quarters at first sampling. Of these cows 325 cows (57.7 Yo) were given “inadequate” therapy according to the results of the second sampling. 58 cows (10.3 Yo) were given “unnecessary” dry cow therapy according to the results of the second sampling. Thus only 180 (32.0%) of the cows receiving selective therapy were given “adequate” therapy according to the result of the second sampling. In the total material of 703 cows, 325 cows were given “inadequate” therapy in infected quarters and 378 cows were given “adequate” or “unnecessary” therapy. Table 3. Number of cows with 0, 1, 2, 3 , and 4 infected quarters (quarter diagnosis > 0) at second sampling. Cows with only one quarter infected at 1st sampling Bacteriological diagnoses at first sample
Number of quarters infected at second sampling 2 3 4
0
1
Total
Staphylococcus aureus Other major pathogens Minor pathogens
22 5 13
73 18 33
48 13 19
28 10 13
16 4 10
187 50 88
Total
40
124
80
51
30
325
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Assessment of Strategy in Selective Dry Cow Therapy
Table 4. Number of cows with 0, 1, 2, 3, and 4 infected quarters (quarter diagnosis > 0) at second sampling, in relation to quarter diagnosis at first sampling. Only cows with “major pathogens” infection in one quarter at 1st sampling Diagnosis of the one infected quarter at first sampling
0
1
Number of quarters infected at second sampling 2 3 4
Total
3 (major without elevated cell count) 4 (major with elevated cell count)
14
42
31
16
8
111
13
49
30
22
12
126
Total
27
91
61
38
20
237
In Table 3 the cows infected in one quarter at first sampling are presented according to number of infected quarters at second sampling, as well as bacteriological findings at first sampling. 49 % of the cows infected with S. aweus at first sampling had more than one quarter infected at second sampling. Correspondingly 54 % of the cows with other major pathogens and 48 % of the cows with minor pathogens in the infected quarter had more than one infected quarter at drying off. In Table 4 the cows infected in one quarter with major pathogens at first sampling are presented according to number of infected quarters at second sampling, as well as the diagnostic findings at first sampling. The cows are grouped according to CMT reaction at first sampling. 50 70 of the cows without positive CMT had more than one quarter infected at drying off, compared to 51 % of the cows with elevated cell count at first sampling. Table 5 presents the percentage of healthy cows in the therapy groups at third and fourth sampling. A healthy cow was defined as having cow diagnose < 1 (no quarter with positive CMT nor major pathogens). Group A and B were combined because there was no difference in the therapeutic results between these two groups (@STERAS, 1990). Table 6 is similar to Table 5, but with less restrictive criterion for healthy; i. e., no finding of major pathogens in any of the quarters at sampling.
Table 5. Percent healthy cows after dry cow therapy classified according to “adequate”, “inadequate” and “unnecessary” therapy. Healthy cows are defined as having normal CMT and no finding of minor pathogens nor major pathogens in any quarter (cow diagnosis < 1). 3rd sample taken at time of calving, 4th sample taken two to five weeks post partum Result 3rd sample Healthy
Result 4th sample Healthy
Yo
YO
Therapy group n = number of cows
Therapy class
A + B (n = 68) C (n = 52) D (n = 71)
“adequate” “adequate” “adequate”
33.8 67.3 56.3
23.5 53.9 43.7
A + B (n = 99) C (n = 109) D (n = 103)
“inadequate” “inadequate” “inadequate”
26.3 38.5 55.3
26.3 37.6 48.5
A + B (n = 17) C (n = 21) D (n = 23)
“unnecessary” “unnecessary” “unnecessary”
58.8 100.0 100.0
52.9 71.4 65.2
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Table 6. Percent healthy cows after therapy classified according to “adequate”, “inadequate” and “unnecessary” therapy. Healthy cows are defined as no finding of major pathogens in any quarter (cow diagnosis < 3). 3rd sample taken at parturition, 4th sample two to five weeks post partum
Yo
Result 4th sample Healthy Yo
“adequate” “adequate” “adequate”
37.1 67.9 59.2
30.7 53.6 49.3
A + B (n = 74) C (n = 84) D (n = 70)
“inadequate” “inadequate” “inadequate”
27.0 39.3 55.7
29.7 42.9 52.9
A + B (n = 2 6 ) C (n = 21) D (n = 23)
“unnecessary” “unnecessary” “unnecessary”
53.9 81.0 82.6
57.7 81.0 73.9
Therapy group n = number of cows
Therapy class
A + B (n = 62) C (n = 56) D (n = 71)
Result 3rd sample Healthy
Among cows receiving “adequate” therapy, the percentage of healthy cows at 3rd and 4th sampling was significantly higher in group C and D than in group A + B (Tables 5 and 6). Similar results were found among cows given “unnecessary” therapy. For cows given “inadequate” therapy, the percentage of healthy cows was significantly higher in group D than in group A + B. In group C the percentage was higher than in group A + B, but lower than in group D (Tables 5 and 6). The percentage of healthy cows in group D was similar for those given “adequate” and “inadequate” therapy. Discussion In Norway, the bacteriological diagnoses in chronic subclinical mastitis are dominated by S. aureus, coagulase negative Staphylococci, and Str. dysgahctiae. S t y . agalactiae has been very infrequent in mastitis screening samples during the past ten to twenty years. Str. ubevis bacteria has also been recorded at very low frequencies (Central Bureau of Statistics of Norway 1990). The findings in this study correspond well with the general findings in mastitis diagnostic work in Norway. No significant differences between therapy groups were found in our study before therapy in regard to bacteriological findings, lactation age, number of quarters infected and quarter diagnosis (@STERAS et al., in preparation). Furthermore there were n o significant differences between the two control groups A and B in terms of the frequency of healthy cows 2 to 5 weeks post partum P STE ERAS, 1990). We therefore chose to combine the control groups A and B when we compared them with the treatment groups C and D. Table 1 illustrates the great discrepancy in bacteriological findings between the first et al. (1983) and second sampling. This is in good agreement with the findings of KINGWILL and may show a high new infection rate during the last weeks before drying off o r diagnostic inaccuracy. Accordingly, it is difficult to predict infected quarters at drying off on the basis of sampling a few weeks earlier. Thus, it is difficult to know which quarters to treat at drying off when using a regimen of selective quarter therapy. The bacteriological findings at drying off suggest that all quarters should be treated if a cow had been found to be infected in at least one quarter a few weeks earlier. This is also in agreement with earlier findings of D O D D and GRIFFIN (1975). The results in our study indicate that in selective dry cow therapy, more than 50 % of the cows received “inadequate” therapy, i. e. they had been given no therapy in at least one infected quarter according to the results of the 2nd sampling.
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Mastitis diagnosis is very complicated. The cell counts varies from day to day and at et al., 1985). Since the major least S. aureus intermittently occurs in milk samples (MATTILA source of infection for S. aureus, Str. dysgalactiae and other major pathogens is considered to be the infected udder or teat lesions (BRAMLEY, 1981), the cows with only one infected quarter at first sampling were classified according to infection type (Table 3). Our results demonstrate that there was no significant difference in number of infected quarters at 2nd sampling between a primary finding of S. aureus, other major pathogens nor minor pathogens (Table 3). This result illustrates that the new infection rate at drying off in cows already infected in one quarter in late lactation is similar for different species of udder pathogens diagnosed at 1st sample. The new infection rate was similar for major pathogens and for environmental infection at this stage of lactation. Table 4 was compiled to evaluate whether the inflammatory reaction at first sampling could predict the new infection rate at drying off. The number of quarters infected at drying off was independent of whether the cow had an inflammatory reaction in the one quarter infected about six weeks earlier. The cell count or the inflammatory reaction a few weeks before drying off could not predict the new infection rate at drying off. This finding indicates that bacteriological findings (quarter diagnose = 3) and mastitis with major pathogens (quarter diagnose = 4) should be regarded in the same manner regarding the risk of new infection in quarters at drying off. The diagnostic problems are even greater at drying off because the normal involution process taking place in the udder at this stage is very alike the inflammatory process during mastitis (DODDand GRIFFIN,1975). This could bring into question the value of diagnosis at drying off as used in this trial. The CMT reaction is an essential part of the diagnostic routine, especially in mastitis with minor pathogens. At drying off we must compare the CMT-reaction in the four quarters (KLASTRUP and MADSEN,1974), and if we have a physiologically skewed distribution of the CMT reaction between the quarters, there is a high possibility of false positive mastitis diagnosis. Despite our efforts to obtain aseptic sampling, there were considerable problems with false positive bacteriological findings of environmental bacteria such as coagulase negative Stupbylococcus spp. and “other” Streptococcus spp. The diagnosis of major pathogens should not pose that great a problem. Major pathogens as defined in this study are not commonly found as contaminants in mastitis diagnosis (BARNES-PALLESEN et al., 1987). The visualisation of S. aureus in plate culture is quite characteristic, indicating that the diagnosis of major pathogens is relatively reliable. ERSKINE and EBERHART (1988) found far more agreement in duplicate samples in quarters infected with Str. ugalactiue and S. aureus than for other Streptococcus spp. and coliform SPP. In 50 per cent of the cows, there was at least one infected quarter at drying off that was not treated in the treatment groups. What are the therapeutic consequences of this “inadequate” therapy? To try to answer this question, the cows infected in one or two quarters at first sample were arranged into three groups: “adequate”, “inadequate” and “unnecessary” therapy (see definition under Material and Methods). Table 5 illustrates the result when cows with all types of infection, also minor pathogens, are defined as “not healthy”. These results should be interpreted with care because of the diagnostic problems in the second sample due to inclusion of minor pathogens. The results presented in Table 6 are more reliable because of minor diagnostic problems, as only major pathogens were defined as positive findings. In this way the problems of evaluating the cell count in the involution period and the evaluation of contaminants of minor pathogens are excluded as far as possible. The results presented in Tables 5 and 6 are quite similar, indicating that the diagnostic criteria in this study have little influence of the overall results. The results presented in Tables 5 and 6 demonstrate that therapy C (Benestermy&@ vet “Leo”) is slightly more efficient than D (Leocillinm with Dihydrostreptomycin vet ”Leo”) in cows receiving “adequate” therapy. This corresponds with the results of JENSEN et al. (1977). However, group D showed a slightly better result than group C for the cows
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that were given “inadequate” therapy. O u r results indicate that the efficacy of regimen D is largely independent of whether all quarters infected at drying off are treated (Tables 5 and 6). However, this was not true for regimen C, which was less efficient when the treatment was “inadequate”. From a statistical point of view, the groups presented in Tables 5 and 6 are rather small, i.e. the differences between the groups must be rather large to be statistically significant. Thus a difference between two groups may be important even though the observed difference is not statistically significant. The present material is small and significant differences are found only between each of the two therapy groups compared to the control group. Our results indicate that when using long-acting intramammaria such as Benestermycin@vet “Leo”, all the quarters of an infected cow should be treated. The results in group D indicate that when using short-acting intramammaria in dry cow therapy similar results may be obtained by treating only the infected quarters at first sampling. The better result in group D than in group C among “inadequately” treated cows may indicate that the effect of a higher dose of antibiotics when using short-acting formulas, as in group D, will increase the possibility of having a systemic effect on the quarters which are not treated. The results also indicate that such an effect is not found when using long-acting formulas. This is in good agreement with earlier literature on the effect of dry cow therapy using long-acting formulas (DODDand GRIFFIN,1975). However, very few studies have been carried out on the effect of dry cow therapy using short-acting intramammaria. It has been shown that different penicillium preparation are absorbed differently to the udder lymph and blood system (ZIV, 1980; FRANKLIN et al., 1986) and some preparations give significantly higher Penicillium G concentration in untreated quarters after intramammaria treatment (FRANKLIN et al., 1986).JENSEN (1977) found better effect of Benestermycin than Leocillin in dry cow therapy. The relative better effect of Leocillin@with Dihydrostreptomycin vet “Leo” in this study could either he due to the Dihydrostreptomycin component or to the six days therapy in group D in this trial. MEINand BROWNING (1990) found no significant difference in cure rate between cows treated infected quarters only, compared to cows treated all quarters. SCHULTZE (1983) found that therapy failed to control new infections in the late dry and peripartum periods, thus therapy of healthy cows before drying off should be unnecessary. BRATLIE(1973) also concluded that in dry cow therapy only infected quarters should be treated. This study still raises these questions: What would the effect be of supplementation of general intramuscular therapy in group D, and what would the effect be of supplementation of one intramammary in all quarters the last day of treatment in group D ? These questions should be answered in a later dry cow therapy study. In a study of antibiotic therapy on S. aureus infected cows during lactation, OWENS et al. (1988) found 30% healthy cows after intramammary infusion for six milkings with 62.5 mg amoxicillin, compared to 48 O h healthy cows when intramuscular infusion of 9,000,000 U procain penicillin G for 3 days was given in addition. SOBACK et al. (1990) found better effect of systemic dry cow therapy than only local dry cow therapy. The results in Tables 5 and 6 for cows treated “unnecessarily” illustrate that cows which have one or two infected quarters at first sampling and no infected quarters at second sampling have a better prognosis than cows which also have infected quarters at second sampling. This finding is in good accordance with SOL et al. (1990). This result indicates that these cows should be treated with antibiotics at drying off. The result also indicates that long-acting formulas such as Benestermycin@vet “Leo” had a slightly better effect than short-acting formulas such as Leocillin@with Dihydrostreptomycin vet “Leo”.
Conclusion From this study we conclude that the correspondence in bacteriological findings from samples taken about six weeks prior to drying off and from samples taken at drying off is low. The new infection rate of quarters in already infected cows was similar for cows
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infected with minor pathogens and major pathogens. It was also similar for cows which had major pathogens with high cell count (mastitis) and cows which had only bacteriological findings of major pathogens. In all, 57.7% of the cows with one o r two quarters infected at one to six weeks before drying off had a new infected quarter at drying off. The results of this study indicate that all quarters of infected cows should be treated, even when only one infected quarter was found at drying off, if long-acting intramammaria are used. O u r results indicate that only one or two quarters could be treated, provided that only such a number of quarters was found to be infected at one to six weeks before drying off, if short-acting intramammaria are used four times during the course of six days at drying off.
Acknowledgements The authors would like to thank “Lsvens kemiske Fabrik”’s division in Norway, P.O. Box 7186, Homansbyen, 0307 Oslo 3, for free delivery of all the antibiotics and placebos used in this trial, and for their assistance in achieving randomisation of the trial. We would also like to thank the Dairy Association’s extension services in (astlandmeieriet, Vestlandmeieriet, Sunnmsre Meieri and Nordmore og Romsdal Meieri for their helpfulness in motivating the farmers and collecting samples one and four. Last but not least, we would like to thank all the veterinary practitioners who treated the cows and took the samples at drying off.
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