Dias Nicholas W, Timlin Claire L, Santilli Felipe V, Harvey Kelsey M, Cooke Reinaldo F, Clark Sherrie, Currin John F, Mercadante Vitor R G
School of Animal Sciences, Virginia Polytechnic Institute and State University, Blacksburg, VA, 24061, USA.
Prairie Research Unit, Mississippi State University, Prairie, MS, 39756, USA.
Transl Anim Sci. 2022 Dec 6;6(4):txac156. doi: 10.1093/tas/txac156. eCollection 2022 Oct.
Cattle temperament significantly impacts production traits such as reproduction. The objective of this study was to assess the effects of temperament on pregnancy rates to fixed-timed artificial insemination (TAI) in beef heifers. A total of 297 Angus influenced heifers from 3 different locations were evaluated for temperament based on chute score and exit velocity on the first day of the estrus synchronization protocol (d-9) and classified by temperament type based on temperament score (calm ≤ 3 < excitable). Pregnancy status was determined by transrectal ultrasonography approximately 40 d after TAI. Hair from the tail switch was collected at d-9 and at d0 (TAI) for cumulative cortisol evaluation. A subset of 43 heifers from location 3 had blood samples collected at all handling events and evaluated for cortisol concentrations. Overall, 71% of heifers were classified as calm whereas 29% as excitable. Pregnancy rates to TAI were reduced ( = 0.042) in excitable heifers compared to calm heifers (36% vs. 55%, respectively). Mean concentration of cortisol in the hair was reduced over time ( < 0.001) from d-9 (3.5 ± 0.3 pg/mg) to d0 (1.74 ± 0.3 pg/mg) in all heifers, regardless of temperament. In addition, excitable heifers had increased circulating concentrations of cortisol when compared to calm heifers in all handling events ( = 0.015). More interestingly, despite of temperament, concentrations of circulating cortisol were reduced as the protocol events progressed, with greater cortisol concentrations on d-9, intermediate on d-3, and lesser on d0 ( = 0.031). Therefore, the present study demonstrates that heifer temperament has negative effects in pregnancy rates to TAI programs. However, according to blood cortisol concentrations, no chronic stress response was detected due to cattle handling for the TAI protocol. In fact, blood cortisol concentration was reduced between the initiation and completion of the protocol, indicating that heifers were acclimated to handing. These results support the adoption of acclimation protocols and proper cattle handling as a strategy to increase fertility of heifers that are exposed to TAI.
牛的性情对繁殖等生产性状有显著影响。本研究的目的是评估性情对肉牛小母牛定时人工授精（TAI）妊娠率的影响。在发情同步方案的第一天（第9天），根据通道评分和出栏速度对来自3个不同地点的总共297头受安格斯影响的小母牛的性情进行评估，并根据性情评分（平静≤3＜易激动）将其分为不同的性情类型。在TAI后约40天通过经直肠超声检查确定妊娠状态。在第9天和第0天（TAI）采集尾梢毛发用于累积皮质醇评估。来自地点3的43头小母牛的一个子集在所有处理环节采集血样并评估皮质醇浓度。总体而言，71%的小母牛被归类为平静型，而29%为易激动型。与平静型小母牛相比，易激动型小母牛的TAI妊娠率降低（P = 0.042）（分别为36%和55%）。在所有小母牛中，无论性情如何，毛发中皮质醇的平均浓度随时间从第9天（3.5±0.3 pg/mg）降至第0天（1.74±0.3 pg/mg）（P＜0.001）。此外，在所有处理环节中，与平静型小母牛相比，易激动型小母牛的循环皮质醇浓度升高（P = 0.015）。更有趣的是，无论性情如何，随着方案环节的推进，循环皮质醇浓度降低，第9天皮质醇浓度更高，第3天居中，第0天更低（P = 0.031）。因此，本研究表明小母牛的性情对TAI方案的妊娠率有负面影响。然而，根据血皮质醇浓度，未检测到由于TAI方案的牛处理而产生的慢性应激反应。事实上，在方案开始和结束之间血皮质醇浓度降低，表明小母牛已适应处理。这些结果支持采用适应方案和适当的牛处理作为提高接受TAI的小母牛繁殖力的策略。
