Angus (A) and Hereford (H) cows at one location and A cows at a second location were used to generate purebred controls and six first-cross (F1) types of calf. Foundation sires were A, H, Friesian (F), Jersey (J), and South Devon (Sd) at Location 1, generating FH, FA, JA, SdA, and HA (plus AH) Fl calves, and at Location 2 sires were A and Blonde d'Aquitaine (Ba), generating BaA F1s. Sire breeds were selected as potentially contributing to productive crossbred cows, based on previous F1 cow comparisons. In subsequent years F2, F3, and F4 calves were produced from each of the two-breed crosses, with overlapping generations and contemporary controls providing balanced comparisons of breed types and generations. The experiment consisted of 395 unique sires and 5243 calves born in 1973#x2013;88 at Location 1 and 105 different sires and 2404 calves born in 1976#x2013;86 at Location 2. Growth, reproduction, maternal, and carcass traits were studied. Heterosis was estimated from HA (plus AH) and purebred A and H animals, but only breed #xD7; generation effects were estimated from the other two-breed crosses because of the absence of reciprocal Fl matings. Heterosis from HA crosses was 3.5 and 6.3 for direct effects on weaning and yearling weights respectively, and 9.0 for the maternal (i.e. F1 cow) effect on weaning weight. For reproduction of Fl HA cows, heterosis was 15.2 for calf crop weaned per cow joined, 25.4 for productivity (calf weaning weight per cow joined), and 18.1 for an efficiency ratio (i.e. productivity/ average cow weight). Over all six two-breed crosses, relative to purebred controls, advantages of F1s averaged 4.4 and 8.1 for direct effects on weaning and yearling weights respectively, and 13.3 for the maternal (Fl cow) effect on weaning weight. For reproduction, the F1 cow advantage over controls averaged 9.7 for calf crop weaned per cow joined (range -7.3 to +15.2), 24.7 for productivity (range -8.9 to 47.3), and 16.8 for the efficiency ratio (range -15.7 to +36.3). For the efficiency ratio, breed types were ranked FH (greatest), JA, FA, HA, SdA, A, H, and BaA. On average, the F3 and F4 calves out-performed the F1s by 6.3 in weaning weight but were similar to F1s in yearling weight, whereas for maternal weaning weight the means for F3 cows' calves were 3.4 below those for Fl cows. For reproduction, averages of F3s were below those of F1s but superior to the purebreds by 7.2, 17.7, and 16.3 for calves weaned per cow joined, productivity, and the efficiency ratio respectively. There were also significant breed-group differences in carcass composition.
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