Ojo Tijesunimi O, Vandenplas Jeremie, Mulder Han A, van Pelt Mathijs L, Calus Mario P L
Animal Breeding and Genomics, Wageningen University and Research, 6700 AH, Wageningen, the Netherlands.
Cooperation CRV, Animal Evaluation Unit, 6800 AL, Arnhem, the Netherlands.
J Dairy Sci. 2025 Feb;108(2):1699-1713. doi: 10.3168/jds.2024-25316. Epub 2024 Dec 16.
This study aimed to use temperature-humidity index (THI) as an indicator for assessing heat stress conditions for fertility traits in the Holstein dairy cattle breed in the Netherlands. Data from AI and calving events of 416,814 first-parity cows from the Netherlands were used, considering different THI definitions based on different numbers of days before and after artificial insemination events. To achieve our aim, we investigated first, at population level, the relationship between different THI definitions and 4 fertility traits: conception rate, interval calving to first insemination, interval first to last insemination, and calving interval. Second, to investigate individual variation in the relationship between THI and fertility, variance components were estimated for each trait using the so-called broken stick model. This model assumes that breeding values are dependent on THI above but not below a THI threshold identified at the population level and explores the presence of genetic variation associated with fertility decline during heat stress. This study revealed considerable changes in fertility traits during periods of heat stress, with a THI threshold of 60 for conception rate and interval first to last insemination and 50 for interval calving to first insemination and calving interval. Interestingly, as THI levels increased, genetic variance and heritability also increased, indicating that at higher THI levels associated with reduced fertility, the genetic variation of fertility traits is greater. Furthermore, significant genotype-by-environment interactions were observed for all 4 fertility traits, suggesting changes in sire rankings between THI levels below and above the threshold. This study provides insights that may help breeding programs and farmers breed animals resilient to heat stress conditions.
本研究旨在使用温湿度指数（THI）作为评估荷兰荷斯坦奶牛繁殖性状热应激状况的指标。研究使用了来自荷兰416,814头初产奶牛的人工授精和产犊事件数据，并根据人工授精事件前后不同天数考虑了不同的THI定义。为实现我们的目标，我们首先在群体水平上研究了不同THI定义与4个繁殖性状之间的关系：受孕率、产犊至首次人工授精间隔、首次至末次人工授精间隔以及产犊间隔。其次，为研究THI与繁殖力关系中的个体差异，使用所谓的折断棍模型估计了每个性状的方差成分。该模型假设育种值取决于群体水平确定的THI阈值以上而非以下的THI，并探索热应激期间与繁殖力下降相关的遗传变异的存在。本研究揭示了热应激期间繁殖性状的显著变化，受孕率和首次至末次人工授精间隔的THI阈值为60，产犊至首次人工授精间隔和产犊间隔的THI阈值为50。有趣的是，随着THI水平升高，遗传方差和遗传力也增加，表明在与繁殖力降低相关的较高THI水平下，繁殖性状的遗传变异更大。此外，在所有4个繁殖性状中均观察到显著的基因型与环境互作，表明阈值上下THI水平之间父系排名发生了变化。本研究提供的见解可能有助于育种计划和养殖者培育对热应激条件具有抗性的动物。
