Abstract
1. This study was conducted to assess the impact of genotype and outdoor access (and gender when appropriate) on growth rate and carcass yield. 2. One slow-growing genotype (Bronze; B, n = 129), a commercial fast-growing genotype (Hybrid; H, n = 186) and a medium-growing genotype (crosses; H × B, n = 78) were housed (straight-run) for 21 weeks of age. Each genotype was assigned to 3 pens of 20–23 birds each and raised in indoor floor pens in a curtain-sided house with ventilation fans; the B, H and H × B genotypes were also assigned to 3, 4 and 2 floor pens (2 m2 approximately) with outdoor access (during daylight hours), respectively. All animals were fed ad libitum a commercial diet and birds were commercially processed. After reaching the commercial live weight at 17 and 21 weeks of age, 4 birds (two females and two males) per replicate were slaughtered to determine the yields of carcass, breast, and thigh, abdominal fat and edible inner organs. Gastrointestinal tract characteristics such as length and weight of whole gut were analysed. 3. No significant interaction between genotype and housing systems was observed. Significant differences were found for all traits among genotypes. The live weight was higher in H and H × B genotypes from 7 to 15 weeks and from 7 to 21 weeks of age compared to B genotype, respectively. The live weight of H genotype was higher than that of H × B genotype from 15 to 21 weeks of age. The carcass weight and yield, and the relative weights of the edible inner organs and whole gut, and the relative length of whole gut were significantly affected by genotype and sex of birds. Differences in growth performance, relative weight of breast meat, wings or thighs between birds raised on barn or free-range were negligible. In conclusion, while the development in growth performances was related to strain, the traits at slaughter were related to both strain and sex, and were unaffected by housing system.
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