Region, season, and altitude as sources of genotype by environment interactions for growth in United States beef cattle
Williams, Jamie Leah
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Identification of environmental factors important in genotype by environment (GxE) interactions will help producers in making the most optimal selection decisions given their management setting. Studies on growth in beef cattle have typically focused on genotype by region or genotype by country interactions. However, season is another environmental variable of interest because it encompasses potential environmental factors affecting growth such as forage quality and availability as well as temperature and humidity. The objective of the first study was to investigate the importance of genotype by region and season interactions for weaning weight in US Angus cattle. Altitude is known to be associated with brisket disease, a noninfectious cardiac pulmonary condition characterized by edema in the brisket and lower body. The objective of the second study was to determine if sires perform consistently across altitude and to quantify the genetic relationship between growth and survival at differing altitudes of Angus cattle born in Colorado. Adjusted weaning weight (WW) records from 85,044 fall born calves in the Southeast, 64,389 winter born calves in the Southeast, 73,172 spring born calves in the Northwest, and 184,919 winter born calves in the Northwest were considered different, but genetically correlated traits in a multivariate analysis in order to investigate the presence of GxE. Genetic correlations ranged from 0.89 to 0.97 among direct effects and from 0.63 to 0.92 among maternal effects. Sires performed consistently across regions and seasons whereas maternal effects were variable across regions and seasons. Growth records including 102,233 adjusted WW and 54,448 adjusted postweaning gain (PWG) were split into three traits, those measured at low, medium, and high altitude. A binary trait, survival (SV), accounted for censored records at yearling for each altitude. Genetic correlations between growth traits measured at different altitude were medium to high in magnitude, 0.47 to 0.83 for WW and 0.43 to 0.79 for PWG and indicate evidence for reranking of sires across altitude. Favorable positive genetic correlations were estimated between SV and PWG within the same altitude, suggesting that calves with genetics for increased growth from weaning to yearling also have increased genetic potential for SV at low, medium, and high altitude.