Genetic Associations of Early Growth and Ultrasound Scanned Traits in Several Beef Breeds

Genetic association of early growth traits with ultrasound scanned traits in heifers and bulls of Angus, Charolais, Hereford, Simmental and Santa Gertrudis were examined. Early growth traits such as birth weight (BW), 200 day weight (200D) and 400 day weight (400D) along with ultrasound scanned rump (P8), intramuscular fat (IMF) and eye muscle area (EMA) in heifers and bulls, were considered in this analysis. Estimated genetic correlations between BW and scanned fat traits were negative and ranged from -0.48 to -0.04. The 200D and 400D had positive genetic correlations with the scanned fat of heifers of all breeds, and also for the scanned fat of Angus and Herefords bulls. Breed influence on the genetic correlation of early growth traits with scanned traits was evident for all traits. The magnitude of the estimated genetic correlations of early growth traits with scanned fat traits may not be adequate to cause significant correlated changes in these traits. Therefore, selection objectives, combining early growth and ultrasound scanned traits, is required if it is necessary to change these traits in the five breeds studied.