Genotype by environment interactions (GxE) affect a range of production traits in beef cattle. Quantifying the effect of GxE in commercial and multi-breed herds is challenging due to unknown genetic linkage between animals across environment levels. The primary aim of this study was to use multi-trait models to investigate GxE for three heifer fertility traits, corpus luteum (CL) presence, first pregnancy and second pregnancy, in a large tropical beef multibreed dataset (n = 21,037). Environmental levels were defined by two different descriptors, burden of heat load (temperature humidity index, THI) and nutritional availability (based on mean average daily gain for the herd, ADWG). To separate the effects of genetic linkage and real GxE across the environments, 1000 replicates of a simulated phenotype were generated by simulating QTL effects with no GxE onto real marker genotypes from the population, to determine the genetic correlations that could be expected across environments due to the existing genetic linkage only. Correlations from the real phenotypes were then compared to the empirical distribution under the null hypothesis from the simulated data. By adopting this approach, this study attempted to establish if low genetic correlations between environmental levels were due to GxE or insufficient genetic linkage between animals in each environmental level. The correlations (being less than <0.8) for the real phenotypes were indicative of GxE for CL presence between ADWG environmental levels and in pregnancy traits. However, none of the correlations for CL presence or first pregnancy between ADWG levels were below the 5th percentile value for the empirical distribution under the null hypothesis from the simulated data. Only one statistically significant (P < 0.05) indication of GxE for first pregnancy was found between THI environmental levels, where rg = 0.28 and 5th percentile value = 0.29, and this result was marginal. Only one case of statistically significant GxE for fertility traits was detected for first pregnancy between THI environmental levels 2 and 3. Other initial indications of GxE that were observed from the real phenotypes did not prove significant when compared to an empirical null distribution from simulated phenotypes. The lack of compelling evidence of GxE indicates that direct selection for fertility traits can be made accurately, using a single evaluation, regardless of environment.

中文翻译：

---

通过环境相互作用研究澳大利亚北部商业畜群肉牛生育力性状的基因型，并进行多性状分析


环境相互作用的基因型 （GxE） 影响肉牛的一系列生产性状。由于不同环境水平的动物之间的遗传联系未知，量化 GxE 在商业和多品种畜群中的影响具有挑战性。本研究的主要目的是使用多性状模型在大型热带牛肉多品种数据集 （n = 21,037） 中研究小母牛生育性状的三个 GxE，黄体 （CL） 的存在，第一次怀孕和第二次怀孕。环境水平由两个不同的描述符定义，即热负荷负担（温度湿度指数，THI）和营养可用性（基于畜群的平均日增重，ADWG）。为了区分遗传连锁和真实 GxE 跨环境的影响，通过模拟没有 GxE 的 QTL 效应对来自群体的真实标记基因型产生 1000 次模拟表型的重复，以确定由于现有遗传连锁而可以预期的跨环境遗传相关性。然后将真实表型的相关性与模拟数据中零假设下的经验分布进行比较。通过采用这种方法，本研究试图确定环境水平之间的低遗传相关性是由于 GxE 还是每个环境水平上动物之间的遗传联系不足。真实表型的相关性 （小于 <0.8） 表明 ADWG 环境水平和妊娠性状之间 CL 存在的 GxE。然而，ADWG 水平之间 CL 存在或首次怀孕的相关性均不低于模拟数据原假设下经验分布的第 5 个百分位值。只有一个具有统计学意义 （P < 0.05） 在 THI 环境水平之间发现第一次怀孕的 GxE 指示，其中 rg = 0.28 和第 5 个百分位值 = 0.29，这个结果是微不足道的。在 THI 环境水平 2 和 3 之间，第一次怀孕仅检测到一例具有统计学意义的生育性状 GxE。与模拟表型的经验零分布相比，从真实表型观察到的其他 GxE 初始迹象并不显著。缺乏令人信服的 GxE 证据表明，无论环境如何，都可以使用单一评估准确地直接选择生育性状。