Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/1/2008
Publication Date: 6/1/2008
Citation: MacNeil, M.D., Northcutt, S.L. 2008. National cattle evaluation system for combined analysis of carcass characteristics and indicator traits recorded using ultrasound in Angus cattle. Journal of Animal Science 86: 2518-2524. Interpretive Summary: Price discrimination based on quality and yield grades provides economic incentive for beef producers to select breeding stock based on carcass merit. Since 1974, American Angus Association has collected data for genetic evaluation of carcass traits. More recently, similar data have been collected from yearling bulls and heifers using ultrasound. Potential exists for inconsistencies between results from separate analyses of these data and confusion on the part of producers using the results. We sought to resolve these issues by developing a system for one joint analysis using both sets of data. The necessary estimates of heritability and genetic correlation were calculated in this research. The American Angus Association will make use of this research to conduct National Cattle Evaluations for marbling score, longissimus muscle area, subcutaneous fat thickness and carcass weight for Angus seedstock breeders and their commercial customers.
Technical Abstract: Objectives of this study were to 1) evaluate genetic relationships of sex-specific indicators of carcass merit obtained using ultrasound with carcass traits of steers, 2) estimate genetic parameters needed to implement combined analyses of carcass and indicator traits to produce unified national cattle evaluations (NCE) for longissimus muscle area (LMA), subcutaneous fat depth (FD), and marbling (MRB) with the ultimate goal of publishing only EPD for the carcass traits; and 3) compare resulting evaluations with previous ones. Four data sets were extracted from the records of the American Angus Association (AAA). Records from 33,857 bulls, 33,737 heifers, and 1,805 steers that had measures of intramuscular fat content (IMF), LMA, and subcutaneous fat depth (SQF) derived from interpretation of ultrasonic imagery, and weight recorded at the time of scanning. Also used were 38,296 records from steers with MRB, FD, carcass weight, and LMA recorded upon harvest. (Co)variance components were estimated with ASREML using the same models as used for NCE by AAA. Heritability estimates for carcass measures were 0.45±0.03, 0.34±0.02, 0.40±0.02, and 0.33±0.02 for MRB, FD, carcass weight, and LMA, respectively. Genetic correlations of carcass measures from steers with ultrasonic measures from bulls and heifers indicated gender specific relationships for IMF (0.66±0.05 vs. 0.52±0.06) and LMA (0.63±0.06 vs. 0.78±0.05), but not for weight at scanning (0.46±0.07 vs. 0.40±0.07) or SQF (0.53±0.06 vs. 0.55±0.06). For each trait, estimates of genetic correlations between bulls and heifers measured using ultrasound were greater than 0.8. Prototype national cattle evaluations were conducted using the estimated genetic parameters with the proposed joint analyses resulting in some re-ranking of sires relative to previous analyses. Rank correlations of high impact sires were 0.91 and 0.84 for the joint analysis of MRB and IMF with previous separate analyses of MRB and IMF, respectively. Corresponding results for FD and SQF were 0.90 and 0.90, and for LMA 0.79 and 0.89. Unified national cattle evaluation for carcass traits using measurements from harvested animals and ultrasonic imagery of seedstock in a combined analysis appropriately weights information from these sources and provides breeders estimates of genetic merit consistent with traits in their breeding objectives upon which to base selection decisions.