|Van Vleck, Lloyd|
Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/24/2007
Publication Date: 6/1/2007
Citation: Van Vleck, L.D., Cundiff, L.V., Wheeler, T.L., Shackelford, S.D., Koohmaraie, M. 2007. Across-breed adjustment factors for expected progeny differences for carcass traits. Journal of Animal Science. 85:1369-1376.
Interpretive Summary: Notter and Cundiff (1991) developed a method to compare EPD for birth weight (BWT), weaning weight (WWT), and yearling weight (YWT) from different breed associations having different base years for use on cows from different breeds. The common base when used with breed association EPD allows a herd owner to compare bulls of many breeds. The original method (Cundiff, 1993) has undergone relatively minor statistical changes. Barkhouse et al. (1994, 1995, 1998) added random sire and dam effects to obtain more appropriate standard errors for breed of sire solutions. In the 1996 analysis, a mixed model, including dam effects, was used to estimate regression of progeny records at USMARC on breed association EPD (Van Vleck and Cundiff, 1996). Van Vleck and Cundiff (2001) used estimates of heterosis from a Hereford by Angus diallel experiment to adjust all progeny records to the basis of 100% heterozygosity, as the purpose of the evaluation is to compare sires of different breeds to produce crossbred calves. Annual updates of across-breed adjustment factors for BWT, WWT, YWT, and maternal milk have been available since 1993 (Van Vleck and Cundiff, 2005). The purpose of this paper was to develop a similar procedure for adjusting EPD of 11 breed associations to a comparable base for marbling score (MAR), fat thickness (FAT), ribeye area (RIB), and retail product percentage (RPP). Differences exist among breeds of sire for the carcass traits of marbling score, fat thickness, ribeye area, and retail product percentage. These traits also exhibit genetic variation in progeny raised under USMARC.
Technical Abstract: Adjustment factors to allow comparison of EPD from several breed associations for birth, weaning and yearling weights have been available for more than 10 years. This paper describes steps to calculate adjustment factors for EPD for four carcass traits: marbling score (MAR), fat thickness (FAT), ribeye area (RIB), and retail product percentage (RPP). The required information is the same as for the weight traits: 1) breed of sire solutions based on measurements on progeny at the US Meat Animal Research Center (USMARC) which have sires with breed association EPD, 2) weighted mean EPD of sires with progeny at USMARC (USMARC progeny not included in breed association EPD), and 3) mean EPD of non-parents (defined as animals born two years prior to calculation of EPD). Records at USMARC are adjusted to 100% heterozygosity, as the goal is adjustment factors to allow prediction of performance of progeny of sires mated to other breeds of dam. A critical step is to adjust breed of sire solutions, which are based on an earlier sample of sires, to the equivalent of a sample from a more recent non-parent group using the difference between mean EPD for information sources 2) and 3). The difference is multiplied by the coefficient of regression of USMARC progeny on EPD of their sires. With weight traits, these coefficients are not greatly different from unity. With the carcass traits, two sets of coefficients are used depending on whether the EPD are based on traditional or ultrasound measurements. The regression coefficients also reflect differences in conditions for USMARC progeny (all steers) and factors associated with breed association EPD. Only for marbling score were estimates of these coefficients near unity and for ribeye area for ultrasound measures used to calculate EPD (0.88). For other traits and EPD source, the coefficients ranged from 1.65 to 2.82. The solutions for breed of sire, differences in mean EPD, and regression coefficients are then used to calculate adjustment factors for EPD of 11 breeds including the arbitrary base breed, Angus.