RESTRICTED MAXIMUM-LIKELIHOOD-ESTIMATES OF GENETIC-PARAMETERS OF ADULT MALE AND FEMALE RHODE-ISLAND RED CHICKENS DIVERGENTLY SELECTED FOR RESIDUAL FEED CONSUMPTION

In adult chickens, feed intake can be predicted by multiple linear reg ression from body weight, change in body weight during the recording p eriod (for males and females), and egg mass (for females). Residual fe ed consumption (RFC) is estimated by the deviation of observed from pr edicted values for feed intake. A divergent selection experiment has b een conducted since 1975 in a Rhode Island Red population. Each sex wa s selected on the basis of its own RFC, Line R+ for high values of RFC and Line R- for low values. In addition to the traits measured to obt ain RFC, egg production traits and body measurements (BM) have been re corded, including wattle length, shank length, and rectal temperature. After pooling data from the two lines and the base population, the da ta set included 1,064 males, each with 7 variables, and 3,780 females, each with 11 variables. Genetic parameters were estimated by a multiv ariate derivative-free-restricted maximum likelihood procedure, which yields estimates free of bias due to selection and inbreeding. The RFC appeared to be moderately heritable in males (h(2) = .33) and in fema les (h(2) = .27) and poorly correlated between sexes, with a genetic c orrelation of .19 between RFC in males (RFCm) and in females (RFCf). T he RFCm and RFCf were weakly correlated with egg production traits. Si gnificant, positive correlations were found between RFCm and the BM tr aits that were related to heat dissipation. Correlations between feed intake, body weight, and FM traits recorded in males or in females wer e always <1, except for shank length. These results suggested that sel ection for RFCf can further improve feed efficiency of layers but that information on male relatives would be of limited interest.