EFFECT OF DECREASING THE LEVEL OF CRUDE PROTEIN IN NAKED NECK BROILERS .2. CARCASS INDEXES

Eighty heavy chickens (40 males and 40 females) of 49 days of age; 40 heterocygote naked neck (Nana+) and 40 normal sibs (na+ na+) were sele cted from an experiment where they consumed a control diet and another ration low in CP from 1 to 49 days of age to study their effects on t he carcass indicators in a factorial arrangement 2 x 2 x 2 for the sou rces of variation, genotype, diet and sex. The genotype affected the w eight of the hot carcass (1050 and 1010 g/bird) of the cold carcass (1 030 and 995 g/bird) thighs + breasts (582 and 560 g/bird) and thighs breast as percentage of the liveweight (37.0 and 36.2%) and were high er (P < 0.05) in heterozygotic naked neck chickens. A genotype x diet interaction was found for the weight of the thigh muscle favourable to the Nana+ chickens with the low CP diet. Results show that the indica tor thighs + breast is higher in Nana+ chickens than in the na+na+, as absolute and relative value to the liveweight, regardless the CP leve l. In the case of the thigh muscle it was evident that part of the pro tein ingested by the naked neck birds and not used in feather formatio n could be deviated to the muscles,which indicates the existence of lo wer protein requirements for these birds.