F1 Cross between Mildly Inbred Hereford Selection Lines of Common Genetic Origin

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Abstract
F1 heterosis and combining ability effects in diallel cross matings (N = 419) between two mildly inbred Hereford selection lines that were formed from a common base population were evaluated. Inbreeding of sires, dams and line-bred calves averaged 11%, 8% and 13%, respectively. Characters studied were calving ratio at birth (fraction of females exposed for breeding that produced a full term calf), fraction of calves born alive (fraction of full term calves that were normal and alive shortly after birth), survival of live calves (number of calves weaned/number of calves that were normal and alive shortly after birth), calving ratio at weaning (number of calves weaned/number of dams exposed for breeding), age of calf at weaning and weaning weight. Sire line, dam line and reciprocal effects were generally unimportant. Heterosis in percent calves weaned, although not statistically significant, was approximately equivalent to estimates of inbreeding loss incurred during the period of line development. Heterotic advantage in calf age at weaning and weaning weight was practically nil. Estimates of linecross superiority expressed as a percent of mid-parent values were as follows: calving ratio at birth, 4.4%; fraction of calves born alive, 1.0%; survival of live calves, .8%; calving ratio at weaning, 6.2%; weaning age of calf, .6%; unadjusted weaning weight, .6%; weaning weight corrected for calf age and dam maintenance weight effects, .3%. Copyright © 1977. American Society of Animal Science . Copyright 1977 by American Society of Animal Science.