Effects of sex and genotype on performance and yield characteristics of free range broiler chickens

The purpose of this work was to evaluate the effect of genotype and sex on the performance characteristics (weight gain, feed conversion and livability) and yields (carcass, breast and legs) of six free-range genotypes: Pesadão Vermelho (GEN1), Carijó (GEN2), Pescoço Pelado 1 (GEN3), Pescoço Pelado 2 (GEN4), Pescoço Pelado 3 (GEN5) and Pescoço Pelado 4 (GEN6). A total of 1584 sexed one day old chicks (792 males and 792 females) were housed in 48 pens, 33 birds per pen. The experimental design was a completely randomized factorial 2 x 6 (six genotypes and two sexes) design, with four replicates each. Diets were based on corn and soybean meal (no animal protein) provided in a feeding program in four phases: pre-starter (1 to 21 days), starter (22 to 42 days), growth (43 to 77 days) and finisher (78 to 91 days). Feed intake, feed conversion and livability were measured at 21, 42, 77 and 91 days of age. There was no genotype x sex interaction. The effect of sex was observed in all ages regarding weight gain, feed conversion (except at 21 days) and yields. For all these characteristics, males performed better than females, except in breast yield, which was higher in females. For the livability and feed conversion at 21 days no effect of sex was found. The effect of genotype was observed only in carcass and breast yields. The fast (GEN1) and intermediate (GEN2, GEN5 and GEN6) growing genotypes showed higher weight gain than the slow growing genotypes (GEN4 and GEN3). Carcass and breast yields of naked neck genotypes (GEN3, GEN4, GEN5 and GEN6) did not differ among themselves, and were higher than the Carijó genotype (GEN2) and are therefore recommended for production systems that sell industrialized birds.