| dc.description.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. | en |
