Rotational Crossbreeding of Beef Cattle: Reproduction by Generation

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Abstract
Records on 3,327 matings, involving Angus (A), Brahman (B), Hereford (H) and all possible two-breed rotational crosses (AB, AH and BH), were analyzed to determine the effects of mating group (M), generation (G), sires within mating group and M × G interaction on pregnancy, survival and weaning rates. Three generations of rotational crosses along with contemporary straightbreds were included. Mating group affected pregnancy rate (P<.05) with group averages varying from 89.9% for the AH rotational crosses to 72.0% for the straightbred Brahmans. Generation was not a significant source of variation and interaction effects for M × G likewise were nonsignificant. Mean hybrid vigor levels for successive generations of crossbred dams were 6.0 (P<.05), 3.7 and 5.9%, respectively, for F1, backcross and 3/8–5/8 dams. Survival rate was affected by generation (P<.01), but effects for mating group and M × G interaction were nonsignificant. Survival rate increased in both straightbred and rotational crossbred groups over generations. This resulted in decreasing heterosis levels for this trait during successive generations, being 7.5 (P<.05), 2.4 and −.5%, respectively, for G1 through G3. Weaning rate for all mating groups showed an increase during each successive generation except for the straightbred Brahmans and Brahman-Hereford crosses which had slightly lower weaning rates in G2 than in G1 and G3. Hybrid vigor for weaning rate averaged 13.6 (P<.01), 3.4 and 7.6% (P1, G2 and G3. The M × G interaction was nonsignificant. This decline, as for survival, was due to straightbreds making more progress over generations than did the crossbreds. Copyright © 1978. American Society of Animal Science . Copyright 1978 by American Society of Animal Science.