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Maternal productivity of straightbred, F₁and F₂ cows of a five-breed diallel
Measures of fertility, calf survival and calf size and growth were analyzed to characterize five breeds and to estimate some of the genetic effects of crossing these breeds. The five breeds were Angus (An), Brahman (Br), Hereford (He), Holstein (Ho) and Jersey (Je). Straightbred (SB) and F2 calves were produced in the first generation during the years 1975 to 1979, while SB and F3 calves were produced in the second generation during the years 1977 to 1983. Longer postpartum and calving intervals (CI) and lower first service conception rates (FSCR) were observed in Br. Estimates of average individual heterosis (h^I) were negative for the reproductive characters. Brahman CB were the major contributors to negative h^I estimates for postpartum interval to first service and FSCR. Importance of epistatic effects (gg^I) on reproductive characters was estimated as the deviation of F2 heterosis from the expectation of 1/2 F1 heterosis. These estimates suggest that gg^I are important in Br crosses for PPIC and Cl. Holstein exhibited the highest levels of dystocia, while Je, Br and their CB had the lowest levels. Angus and He CB groups had the highest rates of dystocia among the CB. Jersey tended to have lower survival rates. The effect of h^I appeared to be more important than maternal heterosis (h^M) for survival to 24 h, but the relative importance of the heterotic effects was reversed for survival to weaning. Estimates of average heterosis retained (h^R) in the F3 CB for calving difficulty and survival to 24 h and to weaning were -1.5, 4.3 and 3.3%, respectively. Longer gestations were observed in Br and Br CB, while Je and Je CB exhibited the shortest. Holstein and Ho CB tended to be more similar to An than to He. Average estimates of h^I, h^M and h^R were small for this character. Holstein and Ho CB tended to be the largest for all measures of calf size analyzed at birth and weaning. Jersey and Je CB were the smallest calves at birth and at weaning. Differences in size among An, Br and He were small at birth, but Br were larger at weaning. Estimates of h^R for birth and weaning weight were 2.7 and 4.6%, respectively. Estimates of h^R, excluding Je and Je CB, were 5.0 and 6.7% for birth weight and weaning weight, respectively. These results suggest that a substantial amount of heterosis will be retained for characters related to preweaning growth and size in advanced generations of crossbreeding.
Includes bibliographical references (leaves 109-120).