Genetic evaluation for beef carcass traits

Abstract

Industry movement toward alliances and grid pricing has led to increased interest in EPD for carcass traits. The literature suggests that carcass EPD can be used to select sires within a breed that can increase marbling score or tenderness without adversely affecting percentage retail product relative to the breed mean; however, the literature also suggests that using within breed selection alone to move the mean of a high cutability breed appreciably closer to the mean of a high marbling breed without decreasing cutability will be extremely difficult. Ultrasound has been investigated as a cheaper means of collecting carcass information. The literature indicates that carcass traits measured via ultrasound on yearling seedstock will respond to selection. Although the literature is variable on the subject, there are reported genetic correlation (rg) estimates between live animal ultrasound and actual carcass attributes that are greater than 0.70 for all ultrasonically measured carcass traits. When rg between seedstock ultrasound and slaughter cattle carcass measures are ≥0.70, similar or greater genetic progress in finished cattle carcass merit could be achieved by using ultrasound information entirely compared to using typical carcass progeny information; however, the maximum accuracy of prediction using ultrasound information in lieu of finished cattle carcass information would be rg. Significant advances toward identification of QTL affecting carcass merit have been made in the last decade. The first QTL searches yielded a number of linked microsatellite markers to QTL for both yield and palatability traits, although some studies have reported difficulty in detecting QTL effects under differing environmental endpoints. Projects to validate carcass trait QTL across breeds and families are underway in several countries. Ultimately, positional cloning of actual genes will be necessary to allow development of direct gene testing and full utilization of DNA technology in genetic evaluation. The marginal gains possible from inclusion of QTL data in carcass genetic evaluation will depend on trait heritability, availability of directly measured carcass information, and the informativeness of the QTL genotyped. Longterm gains for carcass merit from marker-assisted selection will be primarily for difficult-to-measure traits (e.g., tenderness).