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 is more than or equal to 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. Long-term gains for carcass merit from marker-assisted selection will be primarily for difficult-to-measure traits (e.g., tenderness).
Implications
The scientific literature indicates that the use of within-breed selection in combination with crossbreeding will provide the greatest profit opportunities across the widest range of formula pricing systems. Several studies have reported moderate to high genetic relationships between carcass measures collected on young seedstock via ultrasound and carcass measures collected on slaughter cattle. Therefore, consideration should be given to the use of ultrasound measures to supplement or replace traditional slaughter carcass measures in genetic programs. For traits that are currently widely evaluated in national cattle evaluation programs (e.g., growth rate), marker-assisted selection will not help a great deal. The usefulness of DNA-based selection tools for carcass trait selection will ultimately depend on the marker characteristics of the loci used and the ability to collect large amounts of carcass data either directly on slaughter cattle, with ultrasound, or both.
Key Words: Beef, Carcass Quality, Genetic Markers, Quantitative Trait Loci, Ultrasound
© 2001, by the American Society of Animal Science. All rights reserved.
J. Anim. Sci. 2001. 79:E190-E200
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