Physical traits, performance data, and reproductive tract maturity score can be used to predict fertility and likelihood of early conception in beef replacement heifers consigned to a heifer development program in the southeastern United States.

OBJECTIVE: To identify growth and reproductive measurements that can be used to select heifers with the potential to be more reproductively efficient. SAMPLE: A total of 2,843 heifers consigned to the Georgia Heifer Evaluation and Reproductive Development program between 2012 and 2021 with a mean (min, max) age of heifers at delivery of 347 days (275, 404). PROCEDURES: Reproductive tract maturity score (RTMS), weight at delivery as a percentage of target breeding weight, hip height 3 to 4 weeks after delivery, and average daily gain during the first 3 to 4 weeks after delivery were evaluated as potential predictors of the variables of interest. RESULTS: The model-adjusted odds of pregnancy were 1.40 to 1.67 times higher for heifers with an RTMS of 3, 4, or 5 when compared to heifers with an RTMS of 1 or 2. For every 2.5-cm increase in hip height and every 1-month increase in age at the beginning of the breeding period the model-adjusted odds of pregnancy were 1.10 and 1.16 times higher, respectively. The model-adjusted pregnancy hazard rate for heifers with an RTMS of 3, 4, or 5 was 1.19 to 1.25 times higher than that of heifers with an RTMS of 1 or 2. For every 2.5-cm increase in hip height, the model-adjusted hazard rate for pregnancy was 1.04 times greater. CLINICAL RELEVANCE: Physical traits related to animal maturity and attainment of early puberty can be used to select heifers that are more likely to become pregnant early in their first breeding season.

Using performance data and reproductive measurements to predict fertility in replacement beef heifers.

This study investigated the predictive value of reproductive tract evaluation and growth characteristics measured 30-70 d prior to the breeding season on 1) pregnancy outcome and 2) time to conception in replacement beef heifers. A total of 1,992 heifers (BW 329 ± 42 kg; age 347 ± 27 d) were delivered for enrollment in the Georgia Heifer Evaluation and Reproductive Development (HERD) program between 2006 and 2011 at two locations. Physical traits were selected to assess management of heifers prior to entering the program in addition to developmental traits traditionally measured in the HERD program and included: reproductive tract maturity score (RTS), weight 70 d prior to breeding as a percentage of target weight, hip height (HH) 40-50 d prior to breeding, and average daily gain 40-50 d prior to breeding. Cattle entered in the program were of similar age and subjected to comparable nutritional and management programs. Chi-square test of homogeneity (pregnancy status) and the Kaplan-Meier product limit method (number of days from initial breeding to conception) were used to analyze univariate associations with predictor variables. Multivariate analyses of pregnancy status and time to conception were performed using logistic regression and Cox regression, respectively. The odds of pregnancy increased by 15% for every 2.5 cm increase in HH (P = 0.001), and by 20% for every 30-d increase in heifer age at the start of the breeding period (P = 0.019). Although RTS was associated (P = 0.015) with pregnancy status in the univariate analysis, after adjusting for the other variables included in the final multivariable model there was no significant association (P > 0.05). RTS and heifer age were not associated (P > 0.05) with time to conception in the multivariable analysis and were not included in the final model. However, HH was significantly (P = 0.005) associated with the time to conception after adjusting for location and year of enrollment. After 35 d, the hazard rate for conception increased 15% for every 2.5 cm increase in HH [hazard ratio (95% confidence interval) = 1.15 (1.04, 1.26); P = 0.005]. Variables intended to indicate prior management (average daily gain and weight 70 d prior to breeding as a percentage of target weight) were not found to be associated with pregnancy or time to conception. The results suggest that factors relating to maturity can be used to select heifers that are more likely to achieve pregnancy and have reduced times to conception.

Comparison of 4- versus 5-day Co-Synch + controlled internal drug release (CIDR) + timed artificial insemination protocols in dairy heifers.

The objective of this study was to compare the pregnancy rate after timed artificial insemination (P/TAI) in dairy heifers treated with 4- versus 5-day Co-Synch + controlled internal drug release (CIDR) protocols. A total of 120 Holstein heifers were randomly assigned to one of two groups. The heifers received an intravaginal CIDR insert containing 1.38 g of progesterone for 4 days (Monday-Friday 4-day Co-Synch + CIDR; n = 60) or 5 days (5-day Co-Synch + CIDR; n = 60). At the time of CIDR removal, 25 mg of PGF2α was injected intramuscularly, and 72 hours after CIDR removal, the heifers received 100 µg of GnRH intramuscularly and were artificially inseminated. Artificial insemination was performed by an experienced technician, using commercial frozen-thawed semen from a single sire. Pregnancy diagnosis was performed by ultrasonography per rectum 32 days after TAI. Categorical data were analyzed using proc logistic and the chi-square test, whereas continuous variables were analyzed using the t-test of Statistical Analysis Systems. Heifers in the 4-day Co-Synch + CIDR group had an acceptable P/TAI32 (55.0%, 33 of 60), which was not different (P = 0.35) from that observed in the 5-day Co-Synch + CIDR group (63.3%, 38 of 60). Progesterone concentration at CIDR insertion or estradiol concentration at TAI did not influence the pregnancy outcomes. Interestingly, estradiol concentration at TAI was greater in the 4-day Co-Synch + CIDR group compared to the 5-day Co-Synch + CIDR group (P < 0.01). In conclusion, the Monday to Friday 4-day Co-Synch + CIDR protocol resulted in adequate P/TAI in dairy heifers, which was similar to that of the 5-day Co-Synch + CIDR protocol. This novel protocol might represent a promising hormonal treatment for TAI in dairy heifers, facilitating their reproductive management routine, while maintaining an adequate fertility.

Evaluation of novel oral vaccine candidates and validation of a caprine model of Johne's disease.

Johne's disease (JD) caused by Mycobacterium avium subspecies paratuberculosis (MAP) is a major threat to the dairy industry and possibly some cases of Crohn's disease in humans. A MAP vaccine that reduced of clinical disease and/or reduced fecal shedding would aid in the control of JD. The objectives of this study were (1) to evaluate the efficacy of 5 attenuated strains of MAP as vaccine candidates compared to a commercial control vaccine using the protocol proposed by the Johne's Disease Integrated Program (JDIP) Animal Model Standardization Committee (AMSC), and (2) to validate the AMSC Johne's disease goat challenge model. Eighty goat kids were vaccinated orally twice at 8 and 10 weeks of age with an experimental vaccine or once subcutaneously at 8 weeks with Silirum® (Zoetis), or a sham control oral vaccine at 8 and 10 weeks. Kids were challenged orally with a total of approximately 1.44 × 10(9) CFU divided in two consecutive daily doses using MAP ATCC-700535 (K10-like bovine isolate). All kids were necropsied at 13 months post-challenge. Results indicated that the AMSC goat challenge model is a highly efficient and valid model for JD challenge studies. None of the experimental or control vaccines evaluated prevented MAP infection or eliminated fecal shedding, although the 329 vaccine lowered the incidence of infection, fecal shedding, tissue colonization and reduced lesion scores, but less than the control vaccine. Based on our results the relative performance ranking of the experimental live-attenuated vaccines evaluated, the 329 vaccine was the best performer, followed by the 318 vaccine, then 316 vaccine, 315 vaccine and finally the 319 vaccine was the worst performer. The subcutaneously injected control vaccine outperformed the orally-delivered mutant vaccine candidates. Two vaccines (329 and 318) do reduce presence of JD gross and microscopic lesions, slow progression of disease, and one vaccine (329) reduced fecal shedding and tissue colonization.