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Estimates of Heritabilities and Correlations of Traits Associated with Pelvic Area in Beef Cattle^1,2,

Louisiana State University Agricultural Center, Baton Rouge 70803

Abstract

Pelvic measurements, cow weights and cow ages were obtained on 703 Angus- and Hereford-sired cows from five Louisiana Agricultural Experiment Station herds. Cows were either purebred or crossbred, ranging in age from 1 to 14 yr, and sired by 52 Angus and 63 Hereford bulls. All pelvic measurements were obtained via the rectum by the same technician. Paternal half-sib heritability estimates and genetic (r_G) and phenotypic (r_P) correlations were computed for pelvic height (PH), pelvic width (PW), pelvic area (PA-I; the product of PH x PW), the ratio of PH to PW and cow weight (CW). Pelvic area was also calculated as an ellipse using the formula PA-II = (PH/2)(PW/2). Mean PA-I was 298.5 cm² while PA-II averaged 234.4 cm². The pooled heritability estimate for PA-I was .68 ± .34, indicating that pelvic area is a highly heritable trait and should respond to selection. The estimate for PA-II was similar (.66 ± .34). The heritability of PW was higher than for PH or PA-I. The heritability of CW was .57 ± .34 and CW was positively correlated (r_G = .47 and r_P = .40) with PA-I. Direct selection for PA-I was estimated to yield a response of 12.2 cm² in one generation with a correlated response for CW of 12.5 kg. If change in CW was held at zero using a restricted selection index, about 90% as much increase in PA-I was estimated compared with ignoring CW in the index. Therefore, selection for increased pelvic area can be accomplished without causing large increases in cow size. This should aid in reducing calving difficulty.

¹ Published with the approval of the Director of the Louisiana Agr. Exp. Sta.

² Appreciation is expressed to Dr. C. P. Bagley, Rosepine Res. Sta., Dr. D. E. Franke, Dept. of Anim. Sci.; Dr. G. M. Hill, formeriy at Iberia Res. Sta., Jeanerette; Mr. A. E Loyacano, Dean Lee Res. Sta., Alexandria; and Dr. L. I. Smart, Dept. of Anim. Sci. for making cattle available for data collection. The authors give special thanks to Dr. W. R. Harvey for his valuable assistance and suggestions in analyzing the data.

³ Rosepine Res. Sta., Rosepine, LA 70659.

⁴ Dept. of Exp. Statist.

⁵ Dept. of Anim. Sci.