Effect of inbreeding on the body weight in Japanese quail (Coturnix c. japonica)

The usefulness of a slow rate of inbreeding achieved by double first cousin mating over a rapid rate achieved by full sib mating for preventing depression of characters on inbreeding is discussed in the present report. Estimations of parental and offspring inbreeding components were made. The experiment was conducted on two closed Japanese qu~il -lines for six generations. The characters studied were body weights measured at day old, 7, 14, and 35 days, and daily gain from 1-14 and 14-35 days. It was observed that the depression of characters was more pronounced at the slow than the rapid rate. The underlying reason was the greater inbreeding of the parents in the slowly inbred lines compared with the rapidly inbred lines up to a given inbreeding coefficient of the progeny. The body weights taken at an earlier age showed greater depression due to parental inbreeding than the body weight taken near sexual maturity. Of the parental components, the maternal inbreeding component was more important than the paternal inbreeding component. The contribution of the maternal inbreeding to the depression of character was more pronounced on day old chicks. As the chicks grew older, the depression due to maternal inbreeding declined. On the 35th day i.e. near sexual maturity, depression in body weight due to maternal inbreeding was low and non-significant. Crossbred progenies obtained from inbred parents showed heterosis over inbreds and controls. Crossbred progenies of two controls did not show heterosis. At a constant inbreeding of the parents, the inbred individuals were significantly lighter than the non-inbreds in most of the cases. Genetic, phenotypic and environmental correlations were higher between successive body weight measurements. The correlations declined as the characters widened in age. Females were significantly heavier and had higher growth rate than males as early as the 14th day~