SELECTION FOR HIGH 8-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 se lection for high 8-wk BW in normal and dwarf Athens Canadian randombre ds under two nutritional environments (high protein and high energy) a nd to determine the influence of the selection diet on subsequent wate r to feed ratios and abdominal fat levels. High-protein lines (HP) rec eived a diet containing 25% CP and 3,100 kcal ME/kg, whereas high-ener gy 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 dwar f line. Similar selection differentials indicate that this difference was apparently due to the expression of greater genetic variation in t he HE dwarf line. Water intake, feed intake, water to feed ratio, and abdominal fat data for the four lines under ''selection'' and ''recipr ocal'' environments differed between experiments. In Experiment 1, whe n fed the HE diet, normal birds selected under the HP environment had higher (P < .05) water to feed ratios and lower abdominal fat levels t han contemporaries selected under the HE diet. However, these differen ces were not significant in Experiment 2.