Growth analysis in two lines of rats and their reciprocal F1 crosses under two nutritional environments. Heterosis for body weight and maturing rate.

The heterotic effects for body weight during the early postweaning period and on the von Bertalanffy growth equation parameters in relation with the growth pattern as a whole were investigated in rats with caloric restriction (20%) and in controls with ad libitum feeding. Body weight at fixed ages, weight-age curves, asymptotic weight, mature size and maturing curves were evaluated in a cross between two highly inbred lines of rats. Growth curve parameters were combined in a single value by the multivariate method of principal components in order to characterize the particular growth pattern of each group. Positive and significant heterotic effects for body weight were observed suggesting the presence of non-additive genetic variation for this trait. Additivity was an important source in asymptotic size. An heterotic response was observed in mature rate showing a dominant deviation towards high values of this character. Caloric restriction diminished body weight, but asymptotic size was not modified. Maturity was affected along the period studied. Hybrids reached an intermediate asymptotic weight in relation to parental lines exhibiting greater maturity in the prepuberal period. It is suggested that in livestock production crossbreeding will be profitable if additivity for asymptotic weight and dominance deviation for maturing rate could be combined in the F1 hybrid. Maternal breed should be lighter and mature more rapidly than the paternal one if maintenance costs of the breeding stock and growing potentiality of the crossbred progeny are considered.