Exploratory Analysis of Genetic Variants Underlying Body Temperature in Beef Cattle

Individual animal variation in body temperature (BT) and response to climatic stress suggests underlying genetic control. We used crossbred steers and heifers of unknown pedigree and varying percentages of Angus, Simmental, and Piedmontese (n=239) that were segregating Myostatin (C313Y) to explore the sources of genetic variation underlying this trait and to determine if re-ranking of genotypes occurred across seasons. Hourly BT measurements were collected for 5 d during heat and cold stress events. Data were analyzed using a model that included Myostatin genotype (MG), season, management group, trigonometric function (sine + cosine) periodicities of 12 and 24 h and a residual with an autoregressive covariance structure. A three-way interaction of MG, season, and trigonometric function periodicities of 24 hr (P < 0.001) and 12 hr (P < 0.02) indicate that a genotype-by-environment interaction exists. For MG during summer stress events the additive estimate was 0.10 °C (P < 0.01) and dominance estimate was -0.12 °C (P < 0.001). During winter stress events the additive estimate was 0.10 °C (P < 0.001) and dominance estimate was 0.05 °C (P > 0.05).  We also conducted a genome-wide association study for area under the curve (AUC) of 5-day hourly BT during summer (AUCS5D) and winter (AUCW5D). Posterior heritability estimates were 0.68 and 0.21 for AUCS5D and AUCW5D, respectively.  Results suggest that body temperature regulation is at least moderately heritable, and variants such as Myostatin may play a role in environmental fitness.