Preweaning growth traits for Senepol, Hereford, and reciprocal crossbred calves and feedlot performance and carcass characteristics of steers

We conducted a multiyear study in two phases to determine preweaning perfor mance traits of Senepol (S x S), Hereford (H x H), and reciprocal (S x H an d H x S) F-1 crossbred calves and feedlot performance and carcass character istics of steers. In Phase I, from 1985 to 1989, data from S x S (n = 194), H x H (n = 383), and S x H (n = 120) calves were used. Numbers of S x S co ws were increased during Phase I so that data from H x S (n = 74) calves co uld be included in Phase II (1990 to 1992) in addition to S x S (n = 118), H x H (n = 130), and S x H (n = 56) calves. Also during Phase II, feedlot p erformance and carcass characteristics were determined for S x S (n = 30), H x H (n = 26), H x S (n = 36), and S x H (n = 26) steers. In Phase I, S x S calves had heavier (P < .01) birth weights and heavier (P < .01) 205-d ad justed weaning weights than H x H calves. Birth weights of S x H calves wer e heavier (P < .01) than the mean of the purebred calves, but 205-d adjuste d weaning weights did not differ(P > .10). In phase II, direct heterosis wa s 3.5% for birth weight (P < .05) and 5.1% for 205-d adjusted weaning weigh t (P < .01). Senepol 205-d adjusted weaning weight (P < .01). Senepol mater nal breed effects were 1.9 kg for birth weight (P < .10) and 37.9 kg for 20 5-d adjusted weaning weight (P < .01). Levels of direct heterosis, Senepol maternal breed effects, and Hereford direct breed effects were significant for most feedlot performance traits of steer calves that were fed to a comm on end point. Breeds did not differ (P > .10) for USDA yield and quality gr ades, and direct heterosis was not significant for Warner-Bratzler shear fo rce. These results demonstrate significant levels of heterosis in preweanin g performance between S x S and H x H calves and in feedlot performance of steers. Levels of heterosis were smaller and nonsignificant for-most carcas s traits including meat tenderness, which did not differ between S x S and H x H steers in this study.