Date of this Version
Cattle are reared in environments that differ and vary greatly in climate, thus the ability to regulate body temperature across multiple environments is essential. However, inherent differences between animals do exist and can influence their response to extreme temperatures. The objectives of the current study were to model the impact of myostatin genotype (MG) on body temperature during heat and cold stress and conduct a genome-wide association study (GWAS) to better understand the genetic basis of body temperature regulation during extreme temperatures.
Crossbred steers and heifers (n= 239) with varying degrees of Piedmontese influence were fed in four groups over a two-year period, where groups 1 and 3 consisted of calf-fed steers and groups 2 and 4 consisted of yearling heifers. Prior to arrival, animals were genotyped to determine their MG as either homozygous normal (0-copy), heterozygous (1-copy), or homozygous for inactive myostatin (2-copy). Hourly Tympanic and Vaginal temperature (°C) measurements were collected for steers and heifers, respectively, for 5 days during times of anticipated heat and cold stress. A GWAS was conducted for area under the curve using hourly body temperature observations for five days and during the maximal stress cycle to where body temperature equals zero.
A genotype-by-environment interaction was found between MG and trigonometric functions (sine + cosine), with 0 copy and 2 copy animals deviating the greatest from the average body temperature of 38.6 °C during summer and winter conditions, respectively. Moderately negative Genomic-EBV correlations were found between winter and summer stress events (rGEBV = -0.40 to -0.50), although a small percentage of the top 5% 1 Mb windows were in common between winter and summer stress events.
Knowledge of how a genotype responds to environmental stress can aid in the management of cattle to ensure optimal performance. Genetic antagonisms between heat and cold stress can be circumvented using marker-assisted selection, which allows for improved selection for decreased heat and cold susceptibility.
Advisor: Matthew L. Spangler