|Van Vleck, Lloyd|
Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/3/2003
Publication Date: 2/2/2004
Citation: NEPHAWE, K.A., CUNDIFF, L.V., DIKEMAN, M.E., CROUSE, J.D., VAN VLECK, L.D. GENETIC RELATIONSHIPS BETWEEN SEX-SPECIFIC TRAITS IN BEEF CATTLE: MATURE WEIGHT, WEIGHT ADJUSTED FOR BODY CONDITION SCORE, HEIGHT AND BODY CONDITION SCORE, HEIGHT AND BODY CONDITION SCORE MEASUREMENT OF COWS AND CARCASS TRAITS OF THEIR STEER RELATIVES. JOURNAL OF ANIMAL SCIENCE. 2004. 82:647-653. Interpretive Summary: Breeding objectives for beef cattle have evolved to meet production standards, resources, consumer demands, and marketing practices. The current trend in the beef industry is to focus not only on growth and maternal traits, but also on carcass and meat composition. Reliable estimates of genetic correlations are needed to determine whether improvement in one or more traits would compromise improvement in others and also to design economic indexes to maximize economic gain. As an example, as producers have tried to improve such traits as overall growth (e.g., weaning weight and slaughter weight), an important question is whether mature cow size is being increased beyond levels required for optimum economic returns because of high maintenance costs associated with large mature cows. If breeders were to select to optimize mature cow size, knowledge of the genetic relationships between mature size and other economically important traits, most importantly carcass traits, would be needed to improve more efficiently both female productivity and carcass composition. Information on how mature size of cows is related to carcass traits is scarce. Using data from USMARC information on carcass traits of steers and mature size of their paternal half-sib sisters were analyzed simultaneously to examine consequences of selection strategies to improve carcass merit and(or) reduce mature cow size. The conclusions were that selection for mature cow weight and/or height could be effective for changing size but would not be expected to result in much change in carcass and meat traits such as percentage retail product, marbling and tenderness. However, genetic correlations of hot carcass weight with mature cow traits may be too large to ignore given current pricing systems for carcass beef.
Technical Abstract: Data from the first four cycles of the Germplasm Evaluation Program at the U.S. Meat Animal Research Center (USMARC) were used to investigate the genetic relationships between mature weight (MW, n = 37710), mature weight adjusted for body condition score (AMW, n = 37676), mature height (HT, n = 37123) and body condition score (CS, n = 37676) from 4 to 8-yr old cows (n = 1800) and carcass traits measured on their crossbred paternal half-sib steers (n = 4027). Co-variance components among traits were estimated using REML. Estimates of heritability for hot carcass weight (HCWT), retail product percentage, fat percent, bone percent, rib eye area, adjusted fat thickness, estimated kidney, pelvic and heart fat percentage, marbling score, Warner-Bratzler shear force, and taste panel tenderness measured on steers were moderate to high (0.26 to 0.65), suggesting that selection for carcass and meat traits could be effective. Estimates of heritability for taste panel flavor and taste panel juiciness were low and negligible (0.05 and 0.01, respectively). Estimates of heritability from overall cow data were high for MW, AMW and HT (0.52, 0.57, 0.71; respectively) and relatively low for CS (0.16). Pair-wise analyses for each female mature trait with each carcass trait were with bivariate animal models. Estimates of genetic correlations between cow mature size and carcass composition or meat quality traits (with the exception of HCWT) were relatively low. Selection for cow mature size (weight and/or height) could be effective for changing size and would not be expected to result in much, if any, correlated changes in carcass and meat composition traits. However, genetic correlations of cow traits (with the possible exception of CS) with HCWT may be too large to ignore. Selection for steers with greater HCWT would lead to larger cows. Selection for smaller cows would lead to steers with smaller HCWT.