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Effect of Creep Feeding Bull Calves on Dam Most Probable Producing Ability Values¹

Colorado State University, Fort Collins 80523

Abstract

Weaning weight records collected at the San Juan Basin Research Center, Hersperus, Colorado on 1,540 Hereford and Angus calves were used to: (1) evaluate the effects of creep feeding and sex on weaning weight, (2) estimate repeatabilities of weaning weight by sex and treatment group and (3) determine the effects of creep feeding on dam productivity values. Weaning weights were taken from 1969 to 1973, when creep feeding was not practiced, and from 1974 to 1976, when only bull calves were creep fed. Most Probable Producing Ability (MPPA) values were computed for 889 Hereford and Angus cows divided into three groups: creep-fed bull progeny, noncreep-fed heifer progeny and noncreep-fed bull progeny. The advantage in weaning weight from creep-feeding was 13.6 kilograms. Repeatability estimates of weaning weight for creep-fed bull progeny, noncreep-fed heifer progeny and noncreep-fed bull progeny were .30, .49 and .52, respectively. The analyses of MPPA values for Hereford cows indicated that creep feeding reduced variation associated with MPPA values and resulted in nonsignificant effects for all factors in the model. All factors had significant effects in the analysis of MPPA values computed from data on noncreep-fed bull progeny. Only sire line and dam's sire line had significant effects on MPPA values computed from data on noncreep-fed heifer progeny. The analysis of MPPA values for Angus cows showed irregular results, perhaps because of small numbers. Product-moment correlations between MPPA values for the same cow in different sex-treatment groups indicated that creep feeding deWeaning weight records collected at the San Juan Basin Research Center, Hersperus, Colorado on 1,540 Hereford and Angus calves were used to: (1) evaluate the effects of creep feeding and sex on weaning weight, (2) estimate repeatabilities of weaning weight by sex and treatment group and (3) determine the effects of creep feeding on dam productivity values. Weaning weights were taken from 1969 to 1973, when creep feeding was not practiced, and from 1974 to 1976, when only bull calves were creep fed. Most Probable Producing Ability (MPPA) values were computed for 889 Hereford and Angus cows divided into three groups: creep-fed bull progeny, noncreep-fed heifer progeny and noncreep-fed bull progeny. The advantage in weaning weight from creep-feeding was 13.6 kilograms. Repeatability estimates of weaning weight for creep-fed bull progeny, noncreep-fed heifer progeny and noncreep-fed bull progeny were .30, .49 and .52, respectively. The analyses of MPPA values for Hereford cows indicated that creep feeding reduced variation associated with MPPA values and resulted in nonsignificant effects for all factors in the model. All factors had significant effects in the analysis of MPPA values computed from data on noncreep-fed bull progeny. Only sire line and dam's sire line had significant effects on MPPA values computed from data on noncreep-fed heifer progeny. The analysis of MPPA values for Angus cows showed irregular results, perhaps because of small numbers. Product-moment correlations between MPPA values for the same cow in different sex-treatment groups indicated that creep feeding decreased somewhat the predictive value of MPPA as an indicator of cow productivity.

¹ Supported by the Colorado State Univ. Exp. Sta. and published as Scientific Series Paper No. 2588.

² Present address: Departmento de Genetica y Bioestadistica, Ciudad Universitaria, Mexico 20 D.F.