Genomic Analysis of the Effects of Inbreeding on Size and Reproductive Traits Across Four Generations of Nellore-Angus Crossbred Cattle
Abstract
The objective of the study was to evaluate genomic based inbreeding within a closed population of Nellore-Angus crossbred cows and the effect it has on growth and reproductive traits. From 2003 to 2018, cows were evaluated for heifer weight (649 heifers averaging 354.11 (SD = 40.366) kg), cow weight (1,460 records averaging 470.09 (SD = 57.527) kg), and weaning rate (1,647 records averaging 0.79 (SD = 0.407)). Inbreeding coefficients (F) were derived from the genomic relationship matrix (GRM) and runs of homozygosity (ROH). Average FROH and FGRM across all cows was 0.064 and 0.046 respectfully. There was a moderate correlation between FROH and FGRM (r = 0.416) with a 95% confidence interval of (0.347, 0.481). When heifer weight was regressed on FGRM, estimates of regression coefficients indicated inbreeding depression (0.727 ± 0.3491 kg and 1.020 ± 0.3210 kg with every 1% increase in inbreeding from models that included pedigree matrix or the GRM, respectively). When regressed on FROH, a 1% increase in inbreeding showed a depression of 0.316 ± 0.0073 kg without inclusion of additive genetic effects. There was no significant inbreeding depression indicated by regression of cow weight on either form of inbreeding coefficient. Most importantly, there was a 0.05 ± 0.01 decrease in cow weaning rate through 5 years of age corresponding to a 1% increase in FROH. When regressed on FGRM, there was no depression in weaning rate due to inbreeding. The inclusion of inbreeding within a herd can increase uniformity but could be at the cost of herd performance which was significantly impacted by weaning rate.
Citation
Wilson, Kyle Everett (2021). Genomic Analysis of the Effects of Inbreeding on Size and Reproductive Traits Across Four Generations of Nellore-Angus Crossbred Cattle. Master's thesis, Texas A&M University. Available electronically from https : / /hdl .handle .net /1969 .1 /195687.