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Genetic Characterization of Pelvic Measures in Beef Cattle: Heritabilities, Genetic Correlations and Breed Differences^1,2,

Colorado State University, Fort Collins 80523

Abstract

Internal pelvic height (H) and width (W) were obtained per rectum on 787 females located in two Colorado State University experimental beef herds. Both yearling heifer and mixed-age (2 to 15 yr) groups, including Angus, Brangus, Hereford, Red Angus and Simmental breeds, were measured. Pelvic area (PA) was determined as the product of H and W. Data were analyzed with least squares procedures using two mixed models. Model 1 included the fixed effects of breed (BD), age of animal in years (AGE) and group (G). Model 1 also included the random effect of sire within breed (S/BD), the regression on age in days (DAY) and subclass regressions of DAY x AGE. Model 2 was the same, except that body weight (WT) was substituted for DAY. Data were analyzed by location in three subsets: mixed-age cows, yearling heifers and a combined cow and heifer group. Breed and age differences were significant, with increases in pelvic size plateauing at 5 yr. Brangus animals had larger H relative to W, whereas the Simmental breed was characterized as relatively equal in H and W. Angus and Brangus animals tended to have the largest overall PA. Estimates of heritability from Model 1 were high (.19 to 1.01), with SE ranging from .16 to .46. Genetic correlation estimates between H and W were low to moderate (.23 to .45). Results indicate that considerable genetic variation exists in pelvic dimensions of beef cattle.

¹ Agric. Exp. Sta., res. pub. project no. 28.

² Appreciation is expressed to G. V. Richardson, USDA-ARS, Fort Collins and R. M. Bourdon for statistical assistance.

³ Current address: Dept. of Anim. Sci., A218L Anim. Sci. Complex, Univ. of Nebraska, Lincoln 68583.

⁴ Dept. of Anim. Sci.