Sensitivity to Temperature Variation in Beef Cattle: Opportunities and Challenges for Selection

Individual animal variation and the existence of large breed differences as evidenced by regional adaptation suggest underlying genetic control of sensitivity to temperature related stress. Unfortunately this phenotype is not well characterized, at least in part due to the expenses of measuring it and uncertainty over the correct trait definition. Although there exist several tools to collect individual body temperature from different locations (e.g. tympanic, vaginal, rumen, etc.), the relationship between different measurements is still largely unknown. Consequently, studies investigating the underlying genetic control of these traits are sparse in the literature. Initial results from the University of Nebraska used a small sample of crossbred animals (n=239) to explore the sources of genetic variation underlying body temperature regulation. Data were analyzed as either area under the curve (AUC) or by using components from a Fourier series. Results suggested that body temperature regulation was at least moderately heritable, based on a genome-wide association study, and that variants such as Myostatin may play a role in environmental fitness. A tremendous opportunity exists to further knowledge of the genetic control of temperature related fitness traits and to merge this with a growing amount of data being generated from a management perspective. An example would be quantifying the relationship between heat stress and feeding of beta agonists.  In this example, genomic predictors for management could be beneficial. Large-scale studies involving expensive phenotypes represents a clear need for collaboration, as the cost of the phenotypes could potentially exceed that of genotyping.