Rotation crosses and inter se matings with Angus and Hereford cattle for five generations

Abstract

A total of 3768 calves and 4950 cow mating-years were involved in a study of heterosis retention. Crosses included first and subsequent inter-crosses between Angus and Hereford breeds as far as the fifth calf generation (F1, F2,…F5), back crosses (B1) using both F1 sires and F1 dams, and rotation crosses as far as the fifth calf generation (R2, R3, R4 and R5). Records collected were calf traits to the yearling stage, cow reproduction and maternal traits, and steer carcass data. Effects were estimated for 27 breed types for calves and 23 for cows. Breed type effects were then replaced by multiple regression coefficients for genetic effects including: an average individual (Angus) breed effect (g I), average maternal (g M) and average grandmaternal (g MG) breed effects, individual (d I), maternal (d M) and paternal (d P) dominance effects, and epistatic effects. From these, individual (h I) and maternal (h M) heterosis and other parameters were derived. For the Angus breed, g I was generally negative and g M positive for direct calf weights and cow weight; g I was positive for calf weaning weight (WW) as a maternal trait. The Angus breed was superior to the Hereford for net reproduction, productivity (weight of calf weaned per cow mated) and an efficiency ratio (productivity/average cow weight). Relative to the average of the purebreds, the superiorities of F1, F3 to F5, and R4 animals were respectively 2.1, 3.2 and 5.0% for birth weight, 6.5, 3.7 and 7.9% for yearling weight, 6.7, −2.2 and 3.4% for cow weight, 10.3, 0.7 and 11.7% for calf WW as a maternal trait, 7.4, −1.3 and 5.7% for number of calves weaned per cow mated, 19.4, 1.0 and 18.4% for productivity, and 11.2, 2.1 and 14.0% for the efficiency ratio. For calf traits and cow weight, d M and h I were generally significant and positive (except negative for calving date), whilst only h I was generally significant for calf weights as maternal traits. For the reproductive traits, the trends were for h I to be positive, but standard errors were large. For carcass traits, the interbreds and rotation crosses were generally like the heavier, fatter (i.e. Hereford) purebred. Overall, for productivity and the efficiency ratio, the rotation crosses (especially R4) were superior to the purebreds but generally not to the Fls, whilst the interbreds were similar to the purebred average.