Jones Arthur L, Berghaus Roy D, Studstill Matthew W, Segers Jacob S, Duggin Jason D, Cannon Patsie T, Stewart R Lawton
Department of Population Health, The University of Georgia, Tifton, GA.
Department of Population Health, The University of Georgia, Athens, GA.
Transl Anim Sci. 2018 Apr 10;2(1):74-80. doi: 10.1093/tas/txy002. eCollection 2018 Feb.
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 () 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 (), weight 70 d prior to breeding as a percentage of target weight, hip height () 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 ( = 0.001), and by 20% for every 30-d increase in heifer age at the start of the breeding period ( = 0.019). Although RTS was associated ( = 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 ( > 0.05). RTS and heifer age were not associated ( > 0.05) with time to conception in the multivariable analysis and were not included in the final model. However, HH was significantly ( 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); 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.
本研究调查了繁殖季节前30 - 70天测量的生殖道评估和生长特征对1）妊娠结果和2）后备肉用小母牛受孕时间的预测价值。2006年至2011年期间，共有1992头小母牛（体重329±42千克；年龄347±27天）被送到两个地点参加佐治亚小母牛评估与生殖发育（）项目。除了传统上在该项目中测量的发育性状外，还选择了身体性状来评估小母牛进入该项目之前的管理情况，包括：生殖道成熟度评分（）、配种前70天的体重占目标体重的百分比、配种前40 - 50天的髋高（）以及配种前40 - 50天的平均日增重。进入该项目的牛年龄相近，且接受类似的营养和管理方案。使用卡方同质性检验（妊娠状态）和Kaplan - Meier乘积限法（从初次配种到受孕的天数）来分析与预测变量的单变量关联。分别使用逻辑回归和Cox回归对妊娠状态和受孕时间进行多变量分析。髋高每增加2.5厘米，妊娠几率增加15%（P = 0.001），配种期开始时小母牛年龄每增加30天，妊娠几率增加20%（P = 0.019）。虽然在单变量分析中生殖道评分（RTS）与妊娠状态相关（P = 0.015），但在对最终多变量模型中包含的其他变量进行调整后，没有显著关联（P>0.05）。在多变量分析中，RTS和小母牛年龄与受孕时间无关（P>0.05），未包含在最终模型中。然而，在对入组地点和年份进行调整后，髋高与受孕时间显著相关（P = 0.005）。35天后，髋高每增加2.5厘米，受孕风险率增加15%[风险比（95%置信区间）= 1.15（1.04, 1.26）；P = 0.005]。旨在表明先前管理情况的变量（平均日增重和配种前70天的体重占目标体重的百分比）与妊娠或受孕时间无关。结果表明，与成熟度相关的因素可用于选择更有可能受孕且受孕时间缩短的小母牛。
