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Growth Patterns of Angus, Hereford and Shorthorn Cattle. II. Relationship of Growth Patterns of Dams with Progeny Performance¹

University of Tennessee, Knoxville 37901; US Department of Agriculture, Knoxville, TN 37901 Virginia Polytechnic Institute and State University, Blacksburg 24061

Abstract

Relationships between estimated growth curve parameters of dams and performance traits of their progeny were studied in Angus, Hereford and Shorthorn herds, each divided into four inbred and two noninbred lines. Growth curve parameters were calculated from the growth function Y_t = A(1-Be^-Kt), where Y_t was weight at age t, A was estimated mature weight, B was an estimate related to early life weight changes and provided for a Y-intercept term and K was estimated general rate of maturing. Least-squares analyses of progeny variables were calculated separately for each breed and sex. Line differences did not influence any of the progeny variables except weaning type score of Shorthorn males (P<.01). Birth year exerted a curvilinear effect on birth weights of Angus female progeny (P<.01), a linear influence on 205-d weights of Shorthorn male progeny (P<.05) and a curvi-linear effect on weaning type scores of Angus and Shorthorn male progeny (P<.01). Regression coefficients on weaning age indicated that calves born earlier in the calving season had lighter birth weights and that older calves at weaning received higher type scores. Inbreeding of the progeny negatively influenced (P<.05) birth weights of Angus male and Hereford female progeny. Hereford male and Shorthorn female 205-d weights were negatively affected (P<.05) by inbreeding, while weaning type scores of Shorthorn female progeny were negatively influenced (P<.001) by inbreeding. Regression coefficients of all progeny variables on inbreeding in all analyses indicated negative trends. Estimated A values of dams were significantly associated with birth weights of both sexes in all breeds. Regression coefficients indicated a 1 to 2 kg increase in birth weights when A values were 100 kg heavier. Birth weights of Angus and Hereford male progeny and Shorthorn female progeny increased .5 to .8 kg as K values of dams increased by .010. The 205-d weights of Angus and Shorthorn progeny significantly increased by 7 to 12 kg when A values of dams were 100 kg heavier, while an increase of .010 in K values of dams of all three breeds was associated with 2.7- to 5.2-kg increases in 205-d weights of progeny. Growth curve parameters of dams were not associated with weaning type scores of progeny.

¹ Published with the approval of the Dean of the Univ of Tennessee Agr. Exp. Sta.

² ARS, USDA, The Univ. of Tennessee, Knoxville.

³ Dept. of Anim. Sci., Univ. of Tennessee, Knoxville.

⁴ Dept. of Anim. Sci., Virginia Polytechnic Institute and State Univ., Blacksburg.