Genetic parameter estimates and expected progeny differences for mature size in Angus cattle.

Mature size records collected on Angus cows of 5 to 12 yr of age were used to estimate heritabilities, genetic correlations, and EPD for mature weight and mature height. A total of 256 sires were evaluated using mature size data collected on 2,732 daughters. Data were analyzed using REML procedures with a two-trait sire model to estimate sire and error variances for mature weight and height. Models with and without adjustment of weight for body condition score were investigated. The linear model for weight and height included fixed herd-year-month the records were taken, sire genetic group, random sire, and residual error. Using unadjusted mature weights, heritabilities were .48 +/- .10 for weight and .83 +/- .11 for height. When condition score adjustments were made, heritability estimates were .45 +/- .10 for weight and .83 +/- .11 for height. Genetic (phenotypic) correlations between weight and height were .78(.58) for adjusted data and .66(.54) with no adjustment. Spearman rank correlations between sire EPD for adjusted and unadjusted data were .94 for weight and .99 for height. Two-trait models of mature cow weight with immature weights (birth weight, 205-d weight, 365-d weight) were used to assess genetic relations among mature and immature cow weights. Genetic correlations between mature weight and immature weights were .57 with birth weight, .62 with 205-d weight, and .45 with 365-d weight.