GENETIC AND PHENOTYPIC STUDY OF PRE- AND POST-WEANING WEIGHTS AND GAINS IN SWINE

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Abstract
Data on body weights at five ages (birth, 21, 42, 56 and 140 days) and pre- and post-weaning average daily gains of 6846 pigs from 780 dams and 161 sires in three lines were analyzed to determine the effects of some environmental factors, to estimate heritabilities, to calculate genetic and phenotypic correlations and to ascertain the associations between these traits and some economically important characters in swine. Significant year effects occurred in all traits other than birth and 21-day weights; line effects were highly significant for birth and 21-day weights but were not significant at subsequent stages. Sex effect was pronounced only at older ages. Males were consistently heavier than females up to weaning age. Unweighted averages of estimates of heritability derived by two methods were 0.17, 0.09, 0.11, 0.13, 0.10, 0.12, and 0.07 for weights at birth, 21, 42, 56, and 140 days, and pre- and post-weaning average daily gains, respectively. The genetic and phenotypic correlations between the seven characters were positive and generally high. Favorable genetic and phenotypic associations were found between birth, weaning and 140-day weights and feed utilization, age at finish, carcass length and average backfat thickness. Weights at weaning and 140 days of age were negatively correlated with carcass score and loin eye area.