Reciprocal crossbreeding of Angus and Hereford cattle 3. Cow weight, reproduction, maternal performance, and lifetime production

Abstract

Abstract Dam breed, sire breed, and heterosis effects on cow weight, reproduction, maternal performance, and lifetime production were estimated from purebred Angus (A × A), purebred Hereford (H × H), and crossbred (H × A and A x H) cows bred at the Waikite Land Development block near Rotorua over a 3-year period (1970 – 72). They were first mated as yearlings and the experiment lasted until the calves born in 1982 were weaned. The 273 cows represented 57 sire groups. The sire breed effect on cow weights was significant; Herefords were 5 – 11 kg (1 – 3%) heavier than Angus. The dam breed effect was in the same direction but not always significant. Heterosis, taken here as the crossbred value divided by the average purebred value, was 5 – 6% for cow weight. Surviving cows remained in the experiment for an average of six joinings, with sire breed and dam breed effects on survival (neither significant) favouring Angus. There was 9.6% heterosis for cow survival, with 29 crossbred cows (20% of those entering the experiment) and 13 (10%) purebreds surviving to calving 1982. Breed differences in pregnancy rate, calf survival, and the overall dam trait, calf weaning rate (per 100 cows to the bull), all favoured Angus over Hereford for both sire and dam breed effects, although only three of the six values were significant. Heterosis estimates for the three traits were 10.2, 2.3, and 15.1% respectively. The Hereford sire breed and dam breed effects on calving date were both positive (i.e., later calves); the crossbred mean calving date was 5.7 days earlier than for the purebreds. Sire breed effects on calf weights (at 2 months and weaning at 5 months) as a dam trait were in favour of the Angus breed, although neither was significant; dam breed effects were inconsistent in sign. Heterosis ranged from 6.9 to 10.6% for calf weights as dam traits. For the ratio of calf weight (2 months or 5 months) to dam weight, there were significant sire breed effects favouring Angus, no significant dam breed effects, and heterosis ranged from 2.0 to 6.0%. Combining lifetime cow survival, annual reproduction rates, calf weight production (not adjusted for calving date), and allowing for cow food intake effects assumed proportional to weight differences, heterosis for lifetime cow-calf productive efficiency was estimated at 30.7%. The pregnancy rate (over all including yearling matings) was high, averaging 0.86. The H × A crossbred cows were heavier than A × H but produced lighter calves. Repeatability and heritability estimates were obtained for all annual reproduction traits, cow weights, and calf weight traits (as traits of the dam) using restricted maximum likelihood techniques. Estimates for both parameters were high (0.49–0.63) for cow weights, 0.05 and 0.19 respectively for calving date, low (0.01 – 0.07) for cow reproduction, and intermediate (0.12 – 0.35) for calf weights (except birth weight heritability, 0.08). The weight of 2-month-old calves (adjusted for calving date) and weight at weaning were similar as criteria for assessing differences in cow maternal performance; the standard deviations were 10.2 and 19.0 kg respectively, but coefficients of variation were both 12%. The use of yearling heifer weight as a culling criterion was estimated to give small increases in lifetime reproduction and calf weights.