Genetic evaluation of beef carcass data using different end point adjustments

¹ Department of Animal and Range Sciences, Montana State University, Bozeman 59717
² American Simmental Association, Bozeman, MT 59715
³ Agriculture and Agri-Food Canada Research Centre, Lethbridge, Alberta T1J 4B1, Canada
⁴ Department of Animal Sciences, Colorado State University, Fort Collins 80523
⁵ Department of Animal Sciences, Cornell University, Ithaca, NY 14853

^* To whom correspondence should be addressed. E-mail: janice{at}montana.edu.

	Abstract

Carcass data from 6,795 Simmental sired animals born from 1992 to 2001 were used to determine whether adjustment to a constant age, backfat, hot carcass weight, or marbling score would result in differences in heritability of the carcass traits and correspondingly, if EPD calculated using those variance components and adjustments would result in sire reranking. End points were age (EPA), backfat (EPF), hot carcass weight (EPC), or marbling (EPM). Traits analyzed were 12^th rib backfat (FAT), hot carcass weight (HCW), marbling (MRB), longissimus muscle area (LMA), and percent retail cuts (PRC). Data were analyzed using an animal model where contemporary group was included as a fixed effect and was comprised of slaughter date, sex, and herd. Random effects included in the model were direct genetic and residual. Estimates of heritability ranged from 0.12 to 0.14, 0.32 to 0.34, and 0.26 to 0.27 for FAT, HCW, and LMA, respectively for the corresponding end points. Heritability for MRB was estimated to be 0.27 at all end points. For PRC, estimates of heritability were more variable with estimates of 0.23 ± 0.05, 0.32 ± 0.05, 0.21± 0.05, and 0.20 ± 0.04 for EPA, EPF, EPC, and EPM, respectively. However, because the EPF and EPC adjustments adjust for a component trait of PRC (FAT and HCW, respectively), the adjustments may be altering the trait to one different from PRC. Spearman rank correlations between EPD within a trait using EPA compared to the other end points were > 0.90 (P < 0.01) for FAT, HCW, MRB, and LMA. For PRC, Spearman rank correlations with EPA EPD were 0.73 (P < 0.01), 0.93 (P < 0.01), and 0.95 (P < 0.01) for EPF, EPC, and EPM, respectively. For most traits and end points, there was little reranking among sires when alternative end points were used. However, adjusting PRC to EPF appears to result in a greater heritability and substantial reranking of sires, potentially due to the adjustment changing the trait to one other than PRC.

Key Words: beef cattle, carcass, end point, genetic evaluation, heritability, variance components