Addit Ive and Heterosis Effects on Preweaning Traits, Maternal Abil Ity and Reproduction from Crossing of the Angus and Brown Swiss Breeds in Florida 1

Angus (A), Brown Swiss (S) and A X S reciprocal F t (AS) dams were mated to A, S and AS (also reciprocal F 1 ) sires resulting in nine breed groups of progeny with varying proportions of Angus and Brown Swiss breeding. Breed group of dam and of sire significantly influenced birth weight, preweaning daily gain, weaning weight, 205-d weight, condition score and frame size. The means for birth weight and weaning weight were 33 and 213 kg, respectively. Brown Swiss bulls sired calves with the heaviest birth and weaning weights. Calves produced by S dams likewise were heavier at birth and weaning. Pregnancy rates were influenced significantly by year, age and breed of dam and averaged 79, 95 and 92% for S, AS and A cows, respectively. Survival rate averaged 97% and was not influenced significantly by any of the effects examined. Because survival rates were similar for all breed groups, the results for weaning rate paralleled those for pregnancy rate. Genetic influences on preweaning growth traits and survival rate were partitioned into additive breed differences (B) and heterosis (H) effects for direct (d) and maternal (m) components. Pregnancy and weaning rates were examined using similar analyses except that genotype of service sire of dam replaced that of the offspring for the direct additive breed and direct heterosis components. The B d values indicated that the Angus breed was inferior (P<.01) to the Brown Swiss breed for all preweaning growth traits except for condition score, in which the Angus breed surpassed (P<.O1) the Brown Swiss. The B m values also showed an advantage for the Brown Swiss breed for all preweaning growth traits. The additive maternal effect (the genotype of the females exposed), Bin, was important for pregnancy rate and weaning rate (P<.001 and P<.05) but not for survival rate (P>.10). The direct additive breed effect was not important for any reproductive trait. Direct heterosis did not affect any of the preweaning or reproduction traits; however, maternal heterosis (H m) significantly affected all traits except birth weight, frame score and survival rate. The H m estimates were 12.0 and 8.4 kg for weaning weight and 205-d weight, respectively. The H m estimates for pregnancy rate, survival rate and weaning rate were 10, 2 and 13%, respectively. (