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1.
On 81 farms blood samples were taken from adult dairy cattle, on pasture in October 1986 and after stabling in December 1986, to measure antibody titres against the nematodes Dictyocaulus viviparus, Cooperia spp. and Ostertagia spp., and the trematode Fasciola hepatica, and serum pepsinogen values. Faecal samples, collected in October, were examined to confirm the presence of parasites by means of egg counts and larval identifications. From December until the end of the stabling period, dry cows were either treated with albendazole or left untreated in alternate sequence of calving date. Treated cows produced 132.9 kg milk per cow per lactation more than untreated cows (P less than 0.01). Fat and protein percentage were not significantly influenced by anthelmintic treatment. The mean herd milk yield response to treatment varied from -889 to +1231 kg milk per cow per lactation. There was a significant between-herd variation in antibody titres against nematodes and in pepsinogen values. However no significant correlations between these parameters and the mean herd milk yield response to treatment were found.  相似文献   

2.
Cows and heifers from 22 herds were used in a trial to determine the effect on milk yield of anthelmintic treatment given at calving. Alternate animals were treated with either fenbendazole suspension or a placebo. Cows given fenbendazole showed a mean reduction in milk yield of 221 kg in the subsequent lactation compared with the placebo-treated cows, a difference which was statistically significant. In heifers no significant effect of the treatment was found on milk yield. When looking at the pooled data from both cows and heifers, the reduction in milk yield of the fenbendazole-treated animals was 151 kg, which also was statistically significant. The results indicate that anthelmintic treatment of dairy cows cannot be generally recommended in Norway.  相似文献   

3.
OBJECTIVE: To determine the effect of induction of parturition on health, milk production and reproductive performance of dairy cows. DESIGN: A prospective cohort study in 62 dairy herds. PROCEDURE: Health, milk production and fertility indices were documented for 1449 dairy cows treated with dexamethasone trimethylacetate, with or without prostaglandin to induce calving. Equivalent data was collected for 603 untreated herd mates that calved at approximately the same time. RESULTS: The median interval from initial treatment to calving was 11 days. Induction was associated with a substantially lower calf survival and commercial value of surviving calves. Calf viability and value was lower when induced cows were at an earlier stage of pregnancy. Retained foetal membranes, photosensitisation and other problems were significantly more frequent in the induced group compared to the untreated group. Milk production of induced cows was approximately 4% lower than untreated ones, but the majority of reproductive indices were not significantly different between the two groups. CONCLUSIONS: The practice of induction of parturition in seasonal calving dairy herds is a reliable way of shortening the gestation period of cows. Costs associated with morbidity and mortality of induced cows and losses in lactation and calf production are offset by benefits of improved reproductive performance and more efficient management of the herd. The welfare aspects of induction on calf survival must be considered.  相似文献   

4.
SUMMARY A total of 1061 lactating dairy cows in six different herds were randomly allocated to treatment and control groups. One herd was lot-fed on total mixed rations; three herds were fed on pasture with significant amounts of supplementary concentrates, and two herds were primarily pasture fed. Treated cows received a slow-release, intraruminal capsule containing 32 g sodium monensin within 7 days of calving. Conception rates at first service, days to first oestrus and calving-to-conception interval did not differ significantly between untreated and monensin-treated cows in the 5 herds, 3 herds and 4 herds, respectively, in which these outcomes were examined. Treatment of lactating cows immediately after calving may not be the optimal method to achieve fertility responses with capsules containing sodium monensin. Monensin treatment significantly increased milk yield in one of the six herds. Milk fat or milk protein production was not significantly affected by treatment.  相似文献   

5.
OBJECTIVE: To determine the effect of a controlled-release monensin capsule administered at cessation of lactation on incidence of calving-related disorders, fertility, and milk yield in dairy cows. ANIMALS: 290 dairy cows treated with monensin and 290 untreated control cows. PROCEDURE: Treated cows received a capsule that released monensin at 335 mg/d for 95 days. Incidence of calving-related disorders; daily milk yield up to 20 days postpartum; test-day milk yield, fat, protein, and mature-equivalent 305-day milk production; and body condition score at calving were determined. Reproductive variables were conception rate at first service, pregnancy rate, and calving-to-conception interval. RESULTS: Cows treated with monensin were 2.1 times as likely to develop dystocia and 0.8 times as likely to develop metritis as control cows. For milk yield, there was an interaction of treatment X time X parity. In multiparous cows, monensin significantly improved milk yield at test days 4 and 7. In addition, monensin increased body condition score at calving. CONCLUSIONS AND CLINICAL RELEVANCE: Despite increasing the likelihood of developing dystocia and metritis, administration of monensin improved the lactational performance of multiparous cows and may be a promising additive for use at the time of cessation of lactation.  相似文献   

6.
SUMMARY The milk production of cows after induced parturition was compared with that of non-induced cows with similar calving dates, in 37 winter-calving, pasture-fed, commercial dairy herds in south-western Victoria. Parturition was induced when most cows were between 27 and 35 weeks of pregnancy. Milk production was compared for the lactation that commenced immediately after induction. The percentage of cows whose lactations were terminated less than 120 days after calving was increased by induction. Mean percentages for untreated and induced groups were 3.0% and 5.4%, respectively . For cows with lactations of at least 120 days duration, lactation length was not affected by the prior induction of parturition. However, milk production during the subsequent lactation was 9.0% less in induced groups. Fat and protein concentrations were not substantially affected. The reduction in milk production was not affected by stage of pregnancy when cows were induced, but tended to be greater in herds that delayed milking of induced cows .  相似文献   

7.
SUMMARY The effects of anthelmintic treatment on the milk production of cows subjected to contrasting nutritional conditions before and after calving were determined. Half of the cows in each of 2 management treatments were treated with 3.75 grams of fenbendazole on the second day after calving and twice more at weekly intervals. Treated and control cows were grazed together for the entire lactation. Treated cows produced 8% more (P<0.05) milk over the 20 weeks lactation than the untreated cows. One third of the total lactation response to anthelmintic treatment occurred during weeks 5 to 10 of lactation. The observed responses occurred despite equal larval challenge to treated and control cows and therefore the responses obtained are discussed in the context of a reduction in the worm burden.  相似文献   

8.
Milk yield and milk acetoacetate (M-acac) were measured weekly for the first 6 weeks of lactation in 5 herds with a ketosis problem. Ketosis treatments and the corresponding ketotest score, were also recorded. The treatment rate was highest 7-16 days after calving. Most of these early cases were associated with low ketone levels in milk, whereas the treatment rate for cows with high ketone levels was highest 17-31 days after calving. Nearly half of the treated cows were low-ketone animals. They were classified as ketosis cases in the cow health card records, although probably suffering from other post partum disturbances in many instances. About 40% of the cows with high ketone levels recovered spontaneously. Reduction in milk yield associated with peak M-acac levels was transient and moderate. It was concluded that health card statistics overestimates the severity of the ketosis problem in Norway.  相似文献   

9.
The effect of nematode infections on growth performance during winter housing and on first lactation yield was investigated in heifers on 69 farms. Half of each herd was treated with albendazole after housing, which resulted in significantly reduced egg output, antibody titres against Ostertagia and Cooperia, and pepsinogen values compared with the untreated control groups. Albendazole-treated groups gained on average 0.007 cm day-1 heart girth (i.e. 0.05 kg day-1) more than control groups during the housing period (P less than or equal to 0.10), varying from -0.060 to +0.137 cm day-1 among herds. Albendazole-treated heifers produced 195.4 kg milk per 305-day lactation more than untreated heifers (P less than 0.01). Per herd, the mean milk yield response to treatment was +313.8 kg milk (P less than 0.01), varying from -876 to +1950 kg. Milk production of untreated heifers increased by 10.5 kg milk kg-1 extra body weight, adjusted for age, measured after the second grazing season (P less than 0.05). This suggests that nematode infections occurring in the first 2 years of life negatively influence milk production by reducing weight gains and hence body weight at calving.  相似文献   

10.
Breeding and production data were collected from 20 town-supply dairy herds in the Manawatu/Horowhenua region. Calving interval, calving to first service interval, first service to conception interval, inter-service interval, calving rate to first service and services per cow calving were 384, 85, 11, 43 days, 51% and 1.7, respectively, for the pooled population of 12, 056 calvings. The mean milk yield was 3730 litres per cow and the mean lactation length 291 days. Age, herd, season within year, and year, had statistically significant effects on reproductive performance, although the amount of variation due to these variables was small. The younger cows (2-year-olds) were relatively poor performers. Reproductive performance was best during the spring. Days from calving to first service, and from first service to conception, were of similar importance in determining differences in calving interval. A high incidence (25%)of return intervals of more than 49 days was found between first and second service. It was concluded from the data that a programme for breeding each cow as she comes into oestrus 46–66 days post-partum is a simple and appropriate procedure for achieving a 365-day calving interval. Such a programme is more likely to be successful if continued attention is paid to both heat-detection procedures and the nutritional requirements of animals during rearing, late pregnancy and early lactation, and if routine pregnancy testing 6 to 8 weeks after service is used to recognise the problems of post-service anoestrus.  相似文献   

11.
Four autumn-calving dairy herds were selected to investigate the effect of an injection of prostaglandin in the period 14 to 28 days (mean 22 days) after calving on subsequent fertility. The cows were selected on the basis of having a condition likely to affect their fertility, including assisted calving, endometritis, retained fetal membranes, milk fever, cows with five or more lactations, cows having twins, or a combination of any of these conditions. They were assigned to treatment or control groups and paired as closely as possible on the basis of their condition and date of calving. Milk progesterone concentrations were measured on the day of treatment and then three and 10 days later. The trial ran for four months and involved 90 treated and 90 control cows. The combined data from all the animals in the trial failed to show any difference between the calving to conception interval, the first service conception rate or the numbers of services per conception of the treated and control groups. A Student's paired t test for groups of cows with a particular condition, both within individual herds and in all the herds, failed to show any significant effect of treatment (P greater than 0.05). Milk progesterone data showed that the presence of a corpus luteum did not influence the outcome of prostaglandin treatment. There was no evidence for excessive failure of luteolysis. It was concluded that there was no benefit in a routine injection of prostaglandin to dairy cows in the period 14 to 28 days after calving when re-breeding commenced more than 70 days after calving.  相似文献   

12.
A newly developed milk dot blot test was used to detect anti-bovine leukaemia virus (BLV) antibody in milk samples from 2079 lactating adult cows from among 61 herds. The milk dot blot test was highly repeatable; the concordance rate, compared with the agar gel immunodiffusion test performed on serum, was 83.5%. All herds contained BLV-positive cows; the prevalence rate was 36%. BLV-positive cows tended to come from larger herds and were older and more often later in lactation. Fourteen production and related variables (herd size, age, days open, days in milk, milk somatic cell count, milk, fat, and protein produced in the current lactation, projected production of milk, fat, and protein, and breed class average deviations for milk, fat, and protein) were compared between BLV-positive and BLV-negative cows. Although somatic cell count, milk produced, and projected production of milk and protein were related significantly to BLV status using simple tests of association, once the variables herd size, age and days in milk were controlled, these differences were removed. Further analyses using logistic (outcome: individual cow BLV status) and least-squares regression (outcome:herd proportion of BLV-positive cows) failed to show an association between any of the measured production or related variables and BLV-positivity. We concluded that the effect of BLV on production and related variables in dairy cows was below the sensitivity of our analytical techniques or was non-existent.Abbreviations ABCA herd average breed class average for milk, fat, and protein production - AVGAGE average age of the herd - ADIM herd average for days in milk - AGID agar gel immunodiffusion - AVGSCC herd average milk somatic cell count - BCA breed class average, a milk, fat and protein production index calculated by comparing a cow's actual 305-day lactation production to the corresponding BCA standard for the same breed, age, and month of calving - BLV bovine leukaemia virus - CALVINT calving interval - COWAGE cow age - DBCA breed class average deviation for milk, fat, and protein production, the difference between an individual cow's BCA and the herd average - DIM days in milk - HS herd size corresponding to the number of lactating cows in a herd - LACT actual amount of milk, fat, and protein produced in a cow's lactation - ODHIC Ontario Dairy Herd Improvement Corporation - PCTPOS percentage of herd that is BLV-positive - PROJ projected 305-day production for milk, fat, and protein by fitting to a standard lactation curve adjusted for days in milk and age at calving - RHBCA rolling herd average for breed class average for milk, fat, and protein production, the average for all cows that completed a lactation (cows must have completed a 305-day lactation) during the previous 12 months - SCC milk somatic cell count  相似文献   

13.
An indirect Ostertagia ostertagi ELISA was used in late lactation milk samples from cows in confined and semi-confined dairy herds to determine if it could predict milk production response after endectocide treatment at calving. Holstein cows from 9 dairy farms from Prince Edward Island (PEI), 5 from central Nova Scotia and 16 from southern Ontario that were participating in a clinical trial of endectocide treatment around calving were used in this study. The cows were randomly treated with either eprinomectin pour-on endectocide or a placebo solution. Milk samples were obtained from cows late in the lactation before treatment was applied. These samples were tested for antibodies to gastrointestinal nematodes (GIN) using the indirect ELISA with the results expressed as optical density ratios (ODR). Production records were obtained from a computerized database of dairy herd improvement data. Pre-calving ODR showed a seasonal pattern. They were higher in the summer and fall and lower during the winter months. Older animals had higher pre-calving ODR values compared with younger cows. Similarly, cows from semi-confined herds had higher parasite antibody levels compared with cows from confined herds. The endectocide treatment did not affect the milk production response in the overall study population. However, the interaction effect between treatment and pre-calving ODR on milk production response after endectocide treatment was significant (P = 0.02), with some evidence of positive treatment response in cows with an ODR > 0.4. The relationship between pre-calving ODR and production response appeared to be quadratic rather than linear.  相似文献   

14.
AIMS: To determine the impact of treatment with internal teat sealant (ITS) compared to no treatment at drying-off on the incidence of clinical mastitis (CM) during the dry period and 84 days after calving, and the prevalence of cows with somatic cell counts (SCC) ≥200,000?cells/mL at the first lactation herd test, for cows wintered on forage crops.

METHODS: In four dairy herds in the South Island of New Zealand, cows with no history of CM or individual SCC >100,000?cells/mL during the 2015–16 season were randomly assigned to treatment with ITS in each quarter (ITS group) at drying-off or no treatment (Control group). Cows were otherwise treated similarly, wintered on forage crops and transferred to pasture for calving and lactation. Cows were monitored over the dry period and for 84 days after calving, and any case of CM recorded. Individual SCC were recorded at the first herd test after calving.

RESULTS: Between drying-off and 84 days after calving 36/470 (7.7%) cows in the ITS groups and 73/442 (16.5%) cows in the Control group were diagnosed with CM (RR=0.46; 95% CI=0.26–0.73). The final multivariable logistic regression model included an interaction between treatment group and length of dry period. For a Friesian/Jersey cow, aged 4–8 years, with a dry period of 30–80 days, dried off without ITS, the probability of CM in the study period was 0.12 (95% CI=0.09–0.16), and for such a cow treated with ITS the probability was 0.07 (95% CI=0.05–0.10). For an equivalent cow, with a dry period of 81–140 days, which was untreated, the probability was 0.21 (95% CI=0.14–0.29), and for such a cow treated with ITS it was 0.05 (95% CI=0.02–0.11). At the first herd test after calving 77/383 (20.1%) cows in the Control group and 57/425 (13.4%) cows in the ITS group had SCC ≥200,000?cells/mL (RR=1.51; 95% CI=1.10–2.06).

CONCLUSIONS AND CLINICAL RELEVANCE: For these farms, treatment of cows with no history of elevated SCC or CM with ITS at drying-off halved the incidence of CM between drying-off and 84 days after calving, and reduced by 33% the proportion of cows with SCC≥200,000 at the first herd test after calving, compared with untreated cows. Treatment with ITS reduced the risk of CM proportionally more for cows with a dry period of 81–140 days than for cows with a shorter dry period.  相似文献   

15.
This study aimed at investigating associations between management routines including feeding, housing, and milking around calving, and udder health of first-parity cows in early lactation in Swedish large, high producing, low bulk-milk somatic cell count (SCC) dairy herds housed in free stalls. Seventy-two dairy herds participated and data concerning 1189 first-parity cows calving during the study period (October 2005-January 2006) was collected. Multivariable regression analysis were performed with three different outcomes; within-herd number of first-parity cows veterinary treated for clinical mastitis at days -10 to 60 after calving, within-herd number of first-parity cows with a SCC> or =200,000cells/mL at first test-day, and SCC of first-parity cows at first test-day. Cow factors significantly associated with good udder health of first-parity cows (few cases of clinical mastitis and or low SCC) were being of the Swedish Red breed, having a high milk yield at first test-day, and a milk-urea > or =5mmol/L at first test-day. Herd factors significantly associated with good udder health were having mattresses as flooring in the cubicles in the lactating cow housing, and to house the first-parity cows in tie stalls 1 month before calving. Cow factors significantly associated with poor udder health of first-parity cows were having a milk-urea <4mmol/L at first test-day. Herd factors significantly associated with poor udder health of first-parity cows were feeding first-parity cows sugar-beet pulp or corn silage, and to give silage from a different batch to pregnant heifers than to lactating cows. Moreover, to have sawdust or shavings in the calving pen, to be moved from the calving pen > or =2 days after calving, to milk first-parity cows at the calving site instead of in the parlor, and to rinse, clean or disinfect milking units before a first-parity cow was milked were also significantly associated with poor udder health of first-parity cows. The results indicate that different control measures must be taken depending on the nature of the udder health problem.  相似文献   

16.
Three hundred and thirty-one dairy cows in six herds were used to study the effect of a single injection of 25 mg dinoprost, a prostaglandin F2 alpha derivative, administered eight days after calving on several indices of fertility. A detailed comparison was made between 113 treated cows and 113 control cows of the same parity, which had calved within seven days of each other on the same farm and had experienced the same degree of dystocia. In cows which had calved without assistance, the treatment reduced the mean interval between calving and first heat from 40 days to 37 days but increased the mean interval between calving and conception from 83 days to 85 days. In cows which had required assistance at calving, the treatment reduced the mean interval between calving and first heat from 44 days to 34 days and reduced the mean calving to conception interval from 86 days to 68 days. The cows which benefited most were those which had required assistance during their second, third or fourth calvings; their calving to conception intervals were shortened by 22.5 days. An average of 1.39 services was required to establish conception in the treated cows which calved unaided, with 70 per cent conceiving to the first service, compared with an average of 1.34 services per conception and a 72 per cent conception rate to first service for their untreated herdmates.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   

17.
A comprehensive database was established on the milk production and reproductive performance of dairy cows in 19 selected herds in Northern Ireland, varying in size, management system and genetic merit. Data were obtained for 2471 cows, 1775 of which calved in a second year, and 693 were culled from the herd for specific reasons. The estimated mean rate of heat detection (assessed by the interheat interval during the main breeding season) in all the herds was 71 per cent, with a range from 53 to 92 per cent The average conception rate to first insemination was 37.1 per cent (range 21 to 66 per cent). The average calving interval for the retained cows was 407.2 days (range 359 to 448 days). Twenty-eight per cent of the cows that calved were culled, with infertility being the largest single reason (26.8 per cent of the cows culled). There were major differences in reproductive performance between the herds, but heat detection rate, conception rate and calving interval did not appear to be affeded by a herd's genetic merit. The herds with shorter calving intervals were characterised by better heat detection efficiency (83 v 61 per cent, P<0.01), a shorter interval from calving to first insemination (74 v 97 days; P<0.05), a higher conception rate to first insemination (45 v 34 per cent, P>0.10) and a lower removal rate (23 v 37 per cent, P<0.01). Furthermore, the cows in these herds had lower body condition scores (BCS) in the dry period (3.0 v 3.3; P<0.05) but lost less body condition in early lactation (0.3 v 0.6 BCS units, P<0.05). These results show that dairy herd fertility in Northern Ireland is generally low and similar to that previously reported for England and the USA, but that in some herds changes in herd management practices improved the cows' fertility.  相似文献   

18.
AIM: To describe the effect of treatment of cows not detected in oestrus (NDO) with progesterone (P4) and oestradiol benzoate (ODB) in one lactation, on the reproductive and productive performance in the subsequent lactation. METHODS: Cows (n=770 from nine herds) which were NDO 10 days before the planned start of the seasonal breeding programme (PSM) were blocked by herd, age (2 or >2 years old) and ovarian status (i.e. with or without a palpable corpus luteum; CL), and treated either with an intravaginal progesterone-releasing device and ODB and resynchrony, or were left as untreated controls. In the following lactation, data were collected on the occurrence of endometritis, NDO, breeding dates, pregnancy test results and milk production. The effect of treatment and ovarian status in the previous lactation on the incidence of disease, and the proportions submitted for service, conceived and pregnant in the subsequent lactation were analysed. Calving dates and intervals from start of breeding to first insemination and conception were analysed using Kaplan Meier survival analysis. Additional multivariate analyses were undertaken to include known confounders such as age, breed, herd, calving date and milk production, as well as the cyclic status (i.e. previously cycling, NDO, or "late-calving") in the previous lactation, to examine the potential "carryover" effects of previous status on the reproductive performance in the subsequent lactation. RESULTS: Treatment of NDO cows resulted in an earlier calving date (Julian calving date 214, 95% CI=207-221, vs 224, 95% CI=220-228; p=0.005), more female calves reared (31.4% vs 23.3%; p=0.01), and reduced risk of being NDO (33.9% vs 46.1%; p=0.002) in the subsequent lactation compared with controls. There were no differences in the incidence of peripartum disease, or the proportion of cows submitted, conceived or pregnant between the Treatment and Control groups in the subsequent lactation (p>0.2). Previously CL-positive (+ve) NDO cows were less likely to produce a female calf that was reared (19.0% vs 29.9%; p=0.005), more likely to be treated as NDO (26.4% vs 18.6%; p=0.02), less likely to conceive by the end of the subsequent lactation's breeding programme (82.2% vs 87.8%; p=0.09), and took longer to conceive (41 vs 33 days from the PSM to conception) than cows that were NDO-CL-negative (-ve) in the previous lactation. There was no interaction between ovarian status and treatment for any of the outcome variables (p>0.05). Cows that were NDO or late-calving in the previous lactation were more likely to be NDO (p<0.005), treated as NDO (p<0.005), and have longer PSM to conception intervals (p<0.005) in the subsequent lactation than cycling herdmates, despite inclusion of factors known to confound reproductive performance in analyses. CONCLUSIONS: Treatment of NDO cows resulted in more female calves reared, earlier calving and a reduced risk of being NDO in the subsequent lactation. Status (i.e. NDO-CL+ve or NDO-CL-ve) affected some reproductive measures in the subsequent lactation, and the effect of treatment in the subsequent lactation differed between the two groups for some measures. Reproductive performance in the subsequent lactation was not improved despite the earlier calving date and longer calving to PSM intervals. Additionally, the previous season's status was still important in the subsequent season's reproductive performance, despite adjusting for known confounders of fertility. CLINICAL RELEVANCE: The economic benefits from treatment of NDO cows are likely limited to effects of an earlier calving date and potential for longer lactation and increased milk yield, increased number of calves derived from artificial insemination and from a reduced number of NDO cows in the subsequent lactation. Effects of improved reproductive performance in the subsequent lactation were not demonstrated and hence should not be included in any economic analysis of therapy of NDO cows.  相似文献   

19.

The effects of calving intervals of 12 and 15 months on milk yield and milk composition were studied in 105 Swedish Red and White (SRB) and 46 Swedish Holstein (SLB) cows with 280 initiated lactations and 165 completed lactations (followed by another calving). The cows were divided into two groups, one early inseminated and the other late inseminated. The cows in the early group were inseminated at first oestrus 50 days after calving, aiming at a conventional 12-month calving interval, and the second group 140 days after calving, aiming at an extended calving interval of 15 months. Effects were studied by mixed-model analysis. Compared with the 12-month groups, total milk yield increased by 15-16% in the extended calving interval groups of both breeds, while fat, protein and lactose contents were slightly lower. The duration of lactation was 55-60 days longer in the 15-month than in the 12-month groups of both breeds. Given the possibility of a longer lactation, primiparous cows generally maintained their production longer than multiparous cows. SLB cows, especially those with a high peak yield, maintained their production longer than SRB cows. Average milk production per day within a calving interval tended to be slightly lower (2-5%) in both breeds when the interval was extended, owing to longer periods with low production and longer dry periods.  相似文献   

20.
The objective of this study was to investigate if treatment of cows with eprinomectin around calving had any beneficial effects on the calving to first artificial insemination interval, calving to conception interval, and number of services per conception in totally- and semi-confined dairy herds. In totally-confined herds lactating- and dry-cows were housed throughout the summer and had no access to pasture. In semi-confined herds lactating- and dry-cows had limited outdoor exposure to a small pasture or paddock but were still fed a ration that met all their nutritional requirements. The study was carried out between February 2002 and February 2003 in 35 herds (2381 cows) located in Quebec, Ontario and Minnesota (USA) participating in a larger clinical trial. The herds kept electronic reproduction records. Cows were randomly allocated to receive eprinomectin or a placebo, with treatment being administered on or close to the day of calving. Monthly bulk tank milk samples from each farm were tested with an indirect ELISA using a crude Ostertagia ostertagi antigen and these data were averaged over the study year. The optical density ratio (ODR) values were then dichotomized into high and low using a cut-point of 0.50. Treatment effects were analyzed using Cox proportional hazards survival models with herd frailty effects for calving to conception and calving to first service intervals. Aalen's linear hazards model was used to investigate time-varying effects in the Cox models. A random effects poisson regression model was used to model the number of services per conception. Other predictor variables tested in the models were lactation number, calving season, study site, peak milk production, ODR and the lactating- and dry-cow housing variables. Overall, there was no significant effect of treatment on the three indices of reproductive performance. The effect of season of calving depended on how much time had passed since calving. Presumably this effect reflected a seasonal effect at the time of breeding. Hazard of conception in younger cows was higher than in older cows. Early bred cows tended to have a higher number of inseminations per conception than those bred late. The results of the study suggested that eprinomectin treatment at calving was not beneficial to reproduction.  相似文献   

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