Identification of Escherichia coli and Salmonella enterica organisms with reduced susceptibility to ceftriaxone from fecal samples of cows in dairy herds.

OBJECTIVE: To estimate the relationship between therapeutic use of ceftiofur and recovery of Escherichia coli and Salmonella spp with reduced susceptibility to ceftriaxone from feces of dairy cattle. ANIMALS: 3,840 mature dairy cows on 50 dairy herds in Ohio. Procedures-Fecal samples were obtained from up to 100 mature dairy cows on each farm. Samples were screened for E coli and Salmonella spp with reduced susceptibility to ceftriaxone by use of selective media. RESULTS: E coli with reduced susceptibility to ceftriaxone was recovered from 92% (46/50) of the herds and 60.9% (2,338/3,840) of cows. Salmonella spp were recovered from 44% (22/50) of the herds and 9.9% (382/3,840) of cows. No association was found between ceftiofur use and recovery of E coli with reduced susceptibility to ceftriaxone at the herd level. However, recovery of E coli with reduced susceptibility to ceftriaxone was more likely from cows in herds in which Salmonella spp were also recovered on the day of collection (odds ratio, 24.96; 95% confidence interval, 3.17 to 196.68) than from herds in which Salmonella spp were not recovered. Odds of recovery of E coli with reduced susceptibility to ceftriaxone from an individual cow increased 62% (odds ratio, 1.62; 95% confidence interval, 1.16 to 2.25) for every 454-kg increase in herd milk production. CONCLUSIONS AND CLINICAL RELEVANCE: No evidence was found that the use of ceftiofur on dairy farms increases the prevalence or dissemination of Salmonella spp or E coli with reduced susceptibility to ceftriaxone.

Evaluation of a contract breeding management program in Ohio dairy herds: test day summary and economic measures.

A field study was conducted to assess the impact of a contract breeding program that was offered by a breeding co-operative and featured tail chalking and daily evaluation of cows for insemination by co-operative technicians; dairy employees no longer handled estrous detection and insemination activities. From early 2002 until mid-2004, herd-level test day summary records related to production and reproduction were obtained for 32 herds identified as well-managed client herds of the breeding co-operative. Using analyses that controlled for other predictors and random herd-level effects, average days to first service were less by 13 days (P=0.0037) and estrous detection rate was greater by 12% (P=0.0011) for program than for non-program herds. Although first service conception rate was slightly less and the program herds used 0.34 more services per conception (P=0.1488) than non-program herds, the program herds averaged 16 fewer days before pregnancy (P=0.028). Test day summary information and representative estimates of feed, milk, and semen prices were used in a spreadsheet-based model to estimate a partial budget annuity value for an average cow in each herd on each test day. Value of an average cow from a contract herd did not significantly differ from a non-contract herd, even though the analyses suggested an economic benefit for the program herds; the modeling did not, however, account for costs of the program implementation. Additional analyses did not find any significant associations between technician and on days to first service, first service conception rate, estrous detection rate, services per conception, or days open.

Evaluation of vaccination with a commercial subunit vaccine on shedding of Salmonella enterica in subclinically infected dairy cows.

OBJECTIVE: To estimate the efficacy of a commercially available Salmonella enterica subunit vaccine on the subclinical shedding of S enterica in dairy cattle. DESIGN: Randomized, controlled trial. ANIMALS: 175 mature cows on 2 dairy farms with a history of S enterica infection. PROCEDURES: 25% of the mature cows from each herd were systematically randomized to receive an S enterica subunit vaccine following label guidelines. The remaining 75% of cows in each herd served as nonvaccinated controls. Fecal samples were collected from all cows at the time of initial vaccination (day 0), booster vaccination (day 14), 2 weeks following the booster vaccination (day 28), and 10 weeks following the start of the trial (day 70). All samples were processed on the day of collection and cultured for S enterica. RESULTS: 651 fecal samples were obtained over the entire study period. Salmonella enterica was recovered from 46 (7.1%) of the samples. Shedding of S enterica was similar for vaccinated and nonvaccinated control cows on each of the collection dates. CONCLUSIONS AND CLINICAL RELEVANCE: The study revealed no evidence that extralabel vaccination with a commercial subunit S enterica vaccine reduced shedding of S enterica in subclinically infected dairy cows in these herds.

Evaluation of a contract breeding management program in selected Ohio dairy herds with event-time analysis II. Parametric frailty models.

The effect of a contract breeding program offered by a breeding co-operative was assessed using parametric frailty models with event-time analysis technique in a field study of Ohio dairies. The program featured tail chalking and daily evaluation of cows for insemination by co-operative technicians; dairy employees no longer handled estrus detection activities. Test day records were obtained between early 2002 and mid-2004 for 16,453 lactations representing 11,398 cows in 31 herds identified as well-managed client herds by the breeding co-operative. Various parametric distributions for event times available in a commercial software (Stata 9.1, College Station, TX) were tested to assess which distribution fit the calving-to-conception data best. After identifying the distribution with the best fit, a full model with potential confounders and other significant predictors of time to pregnancy was developed and then frailty terms were included in the model. Generalized gamma and log-normal distributions fit the data best, but since gamma distribution does not allow the use of frailty effects, log-normal distribution was used in further modeling. Separate accelerated failure time models with frailty terms to account for latent effects at the herd, cow, or lactation level were developed, testing both gamma and inverse Gaussian frailty distributions. In these models, potential confounders and statistically significant predictors were also controlled for, and the association between the contract breeding program and the mean time to pregnancy was characterized using time ratios. The log-normal model identified that interval to pregnancy was associated with breed, herd size, use of ovulation synchronization protocols, parity, calving season and somatic cell score (above or below 4.5) and maximum milk yield prior to pregnancy or censoring. While controlling for these factors, there was a reduction in average time to pregnancy among cows managed under the contract breeding program. All frailty terms were highly significant, regardless of whether it was an individual frailty at the lactation level or a shared frailty at the cow or herd level, suggesting that there was considerable heterogeneity within these levels. Inclusion of a frailty term at the herd level changed the estimate for the contract breeding program considerably, while a frailty term on other levels did not, indicating that herd characteristics (e.g., overall management) have a substantial impact on reproductive performance and should be accounted for in the analysis. Interpretation using time ratios with or without a shared herd frailty found that the contract breeding program was associated with a reduction of 6.5% and 14.1% in mean time to pregnancy, respectively.

Evaluation of a contract breeding management program in selected Ohio dairy herds with event-time analysis I. Cox proportional hazards models.

An observational study was conducted in order to assess the impact of a contract breeding program on the reproductive performance in a selected group of Ohio dairies using event-time analysis. The contract breeding program was offered by a breeding co-operative and featured tail chalking and daily evaluation of cows for insemination by co-operative technicians. Dairy employees no longer handled estrus detection activities. Between early 2002 and mid-2004, test-day records related to production and reproduction were obtained for 16,453 lactations representing 11,398 cows in a non-random sample of 31 dairies identified as well-managed client herds of the breeding co-operative. Of the 31 herds, 15 were using the contract breeding at the start of the data acquisition period, having started in the previous 2 years. The remaining 16 herds managed their own breeding program and used the co-operative for semen purchase. Cox proportional hazards modeling techniques were used to estimate the association of the contract breeding, as well as the effect of other significant predictors, with the hazard of pregnancy. Two separate Cox models were developed and compared: one that only considered fixed covariates and a second that included both fixed and time-varying covariates. Estimates of effects were expressed as the hazard ratio (HR) for pregnancy. Results of the fixed covariates model indicated that, controlling for breed, herd size, use of ovulation synchronization protocols in the herd, whether somatic cell score exceeded 4.5 prior to pregnancy or censoring, parity, calving season, and maximum test-day milk prior to pregnancy or censoring, the contract breeding program was associated with an increased hazard of pregnancy (HR=1.315; 95% CI 1.261-1.371). The results of the time-varying covariates model, which controlled for breed, herd size, use of ovulation synchronization protocols, somatic cell score above 4.5, parity, calving season, and testing season also found that the program was associated with an increased hazard of pregnancy (HR=1.387; 95% CI 1.327-1.451). The fixed and time-varying covariates models both found similar sets of predictors when analyzing the association of the contract breeding program with hazard of pregnancy. Both models identified a 30% or greater increase in hazard of pregnancy associated with use of the contract breeding program, suggesting that herds subscribing to the program achieved pregnancies in a more timely fashion.

Use of a non-traditional university ambulatory practice to teach large animal medicine.

While many other veterinary schools have moved away from a traditional university-based ambulatory practice, the Ohio State University's Large Animal Practice has continued to provide a cost-effective and valuable method of preparing students for today's careers in veterinary medicine. The practice provides a full array of services to production, equine, and camelid clients, including herd health, individual animal medicine and surgery, and emergency services. Acquiring established practices from alumni has formed the client base. Four full-time veterinarians operate the clinic. While these same clinicians do some classroom teaching, their primary responsibility is devoted to the five to six fourth-year veterinary students who rotate through the clinic every two weeks. Teaching methods and objectives for these students include case discussions, homework, truck quiz books, and practice management issues. Financially, the clinic runs as a private practice, with minimal support from the college (201,000 US dollars per fiscal year) and a gross income of 676,000 US dollars per year. Thus, in a cost-effective manner, this required core ambulatory rotation provides students with a scientific learning experience that exposes them to all aspects of large animal production medicine in a real-world setting.