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Effects of Method of Scaling on Heritability Estimates and Sire Evaluations for Frame Size at Weaning in Angus Cattle

University of Illinois¹, Urbana 61801

Abstract

The data in this study included 24, 215 calves weaned between 1967 and 1979, representing 1,699 sires in 824 herd years in the Illinois Beef Performance Testing Program. Four methods were used to scale frame scores: linear scores from 1 to 7 (LS), Snell's scores based on the logistic distribution (SS), within sire group scores (WS) and "canonical" scores (CS). Heritability estimates were obtained by minimum norm quadratic unbiased estimation with zero priors (MINQUE-Ø) and by Hender son's "simple" method (HSM). Best linear unbiased prediction was used to compute sire evaluations for frame score for each of the four scales. The mixed model equations were solved by Gaussian elimination. Within herd year HSM heritability estimates were ²_LS = .201, ²_SS = .212, ²_WS = .586 and ²_CS = .241; MINQUE-Ø estimates were negative. Spearman and Kendall rank correlations among sire evaluations ranged between .9943 and .9998, and .9372 and .9883, respectively. Average absolute changes in rank were: 6.99 (LS vs SS), 9.92 (LS vs CS) and 35.91 (LS vs WS). Maximum changes in rank were: 89 (LS vs SS), 111 (LS vs CS) and 380 (LS vs WS). Method of scaling affected estimates of genetic parameters and sire evaluations for frame score.

¹ Dept. of Anim. Sci.