Misztal Ignacy, Brito Luiz F, Lourenco Daniela
Animal and Dairy Science, University of Georgia, Athens, GA 30602.
Department of Animal Sciences, Purdue University, West Lafayette, IN 47907.
JDS Commun. 2024 Dec 16;6(3):464-468. doi: 10.3168/jdsc.2024-0651. eCollection 2025 May.
Heat tolerance in dairy cattle has likely deteriorated over time due to unfavorable genetic correlations between milk production level and heat tolerance, with stronger deterioration in later parities. The dairy cattle industry has responded to the challenge of heat stress by implementing management modifications. Methodology exists to calculate genetic prediction of breeding values for high production under heat stress conditions, with high reliabilities of breeding values obtained when incorporating genomic information. However, cows that maintain production during the heat stress peak have an increased likelihood of death. One remedy would be selection for better fertility and survival under heat stress, but with a low volume of data and low heritabilities, corresponding reliabilities may be too low for an efficient selection. In environments where intensive management is too expensive, an ideal cow would maintain production in a favorable climate, would briefly reduce production during heat stress, and would restore production after the heat stress conditions are over. As there are many biological mechanisms involved in heat stress response, in addition to deriving heat tolerance indicators based on variability in performance traits under heat stress conditions, novel traits that capture physiological, behavioral, and anatomical traits related to heat stress response, less dependent on production level, could also contribute to breeding for improved heat tolerance.
随着时间的推移，奶牛的耐热性可能已经下降，这是由于产奶水平与耐热性之间存在不利的遗传相关性，且在后期胎次中下降更为明显。奶牛养殖业通过实施管理调整来应对热应激的挑战。存在一些方法可以计算热应激条件下高产育种值的遗传预测，在纳入基因组信息时可获得可靠性较高的育种值。然而，在热应激高峰期维持产奶的奶牛死亡可能性增加。一种补救办法是选择在热应激下具有更好繁殖力和生存能力的奶牛，但由于数据量少且遗传力低，相应的可靠性可能过低，无法进行有效的选择。在集约化管理成本过高的环境中，理想的奶牛应在适宜气候下维持产奶，在热应激期间短暂降低产奶量，并在热应激条件结束后恢复产奶。由于热应激反应涉及许多生物学机制，除了基于热应激条件下生产性状的变异性得出耐热性指标外，能够反映与热应激反应相关的生理、行为和解剖学性状且较少依赖产奶水平的新性状，也有助于培育耐热性更强的奶牛。
