Abstract
IMPROVEMENT of economically important traits in commercial herds of livestock depends to a considerable extent on the genetic merit of sires which are supplied by the purebred industry. However, in many instances there is a wide disparity in the nutritional conditions under which purebred and commercial herds are maintained. If different sets of genes are required for superior performance in different environments (Falconer and Latyszewski, 1952), it may be necessary to develop seed stocks specifically for particular kinds of feeding conditions. Theoretical considerations underlying the concept of genotype×environment interaction have been reviewed by McBride (1958). The results presented in this paper are from a pilot study which was conducted to evaluate the effects of sire line×nutritional regimen interaction on postweaning growth rate, feed intake, efficiency and body composition of the rat. Materials and Methods A foundation population was established by crossing four, unrelated lines of rats. One line was derived from Fischer 344 stocks which were obtained from the Cancer Research Laboratory, University of Miami. Two lines, one hooded, the other albino, were used in previous experiments at the University of Nevada and had been propagated as closed populations for a number of years. Another strain, designated LEW, was obtained from a commercial source.4 The Fischer 344 and LEW rats were highly inbred; inbreeding levels of the other two lines could not be determined exactly, but undoubtedly were lower. Reciprocal crosses were made between Fischer 344 and LEW, and between the albino and hooded lines. The F1's were combined reciprocally to form a four-way cross. Copyright © 1970. American Society of Animal Science . Copyright 1970 by American Society of Animal Science