Selection for high eight-week body weight in normal and dwarf chickens under high-protein and high-energy diets

A study was conducted to examine genetic parameters associated with selection for high 8-wk BW in normal and dwarf Athens Canadian randombreds under two nutritional environments (high protein and high energy) and to determine the influence of the selection diet on subsequent water to feed ratios and abdominal fat levels. High-protein lines (HP) received a diet containing 25% CP and 3,100 kcal ME/kg, whereas high-energy lines (HE) received a 22% CP diet containing 3,200 kcal ME/kg. Body weights, selection gains, selection differentials, and heritabilities were similar for normal HP and HE lines. There was evidence, however, that the realized heritability was greater in the HE than the HP dwarf line. Similar selection differentials indicate that this difference was apparently due to the expression of greater genetic variation in the HE dwarf line. Water intake, feed intake, water to feed ratio, and abdominal fat data for the four lines under "selection" and "reciprocal" environments differed between experiments. In Experiment 1, when fed the HE diet, normal birds selected under the HP environment had higher (P < .05) water to feed ratios and lower abdominal fat levels than contemporaries selected under the HE diet. However, these differences were not significant in Experiment 2.