Ultrasound adjustment factors for purebred yearling Limousin bulls and heifers
For this study, 1,267 yearling Limousin heifers and 2,745 yearling Limousin bulls were analyzed using PROC MEANS, GLM, and STEPWISE procedures of SAS to compute age-constant adjustment factor equations. In early analysis, embryo transfer calves exhibited a significant difference in weaning weight and scan weight and were therefore removed from this analysis. Bulls were adjusted to a 365-day endpoint, whereas heifers were adjusted to 380 days as well as to a bull equivalent. Significant covariates for rump fat, 12th-13th rib fat thickness, and ribeye area were actual percent Limousin blood and scan weight. R2 values for bulls and heifers on rump fat were .44 and .51, .52 and.55 for rib fat, and .57 and .58 for ribeye area. Percent intramuscular fat R2 values were .42 for both bulls and heifers. Actual percent Limousin blood and scan age were the covariates used for percent intramuscular fat. Although age of dam at scanning was significant (p-value < .10), no distinct trends were found and the R2 value was not improved enough to include age of dam in the model at this time. Yearling Limousin heifers seem to show more fat variation and more percent intramuscular fat variation. Additionally, the change in percent Limousin blood also has more impact on ultrasound traits of heifers than bulls. These results indicate breeders should be encouraged to scan their replacement females as well as their yearling bulls.