Impact of cold stress on birth and weaning weight in a composite beef cattle breed

Beef cattle are often exposed to extreme environmental conditions with varying temperatures, humidity, wind speed, and solar radiation. The objective of this study was to investigate the impact of cold stress on growth-related traits and to assess its variation between sire families in a composite beef cattle breed in eastern Montana. Weather data were collected from an airport close to the research station. Comprehensive climate index (CCI), a measure of cold load, was used to classify cold stress into mild (CCI < -5), moderate (CCI < -15), and severe (CCI < -25). The phenotypic data consisted of 4,221 and 4,217 records for birth weight (BWT) and weaning weight (WWT), respectively. For both traits, the statistical model included an overall mean, contemporary groups, and a regression on cold stress load. For WWT, the model included additional regressions on birth weight and age at weaning. The results showed that mild and moderate cold stress increased BWT by 5.88 and 0.71 kg, respectively. However, severe cold stress slightly decreased BWT (-0.010 kg). Cold stress resulted in a significant decrease in WWT for mild (27.90 kg) and moderate (17.42 kg) cold stress, while the decrease in WWT for severe (2.07 kg) cold stress was insignificant. Using only data from three different sire families with the largest paternal half-sib families, estimates of within family regression coefficients on cold stress were statistically different (based on Welch's t-test) for BWT and WWT. These results seem to indicate that cold stress has a limited negative (often positive) effect on BWT which could be due to some nutritional prioritization of nutritional resources toward the fetus. Furthermore, comparing cold stress effects across different sire families indicated the existence of potential genetic variation in cold stress response.