Effects of season, genotype, and rearing system on broiler chickens raised in different semi-intensive systems: performance, mortality, and slaughter results.

This study aimed to determine the effects of chicken genotype (fast-growing and slow-growing), various semi-intensive production systems (extensive indoor, free-range, and traditional free-range), and season (spring and summer) on animal performance, mortality, growth curve, and slaughter results under semi-environmentally controlled conditions in a subtropical region. Production systems were applied in conformity with the EU standards. While the summer experiment improved performance during brooding (1st-28th days), hot conditions led to a decline in performance during the growing period. In addition, negative effects were determined for all parameters of Gompertz growth curve in summer (P < 0.05, for all). In spring, fast-growing showed 36% higher final live weights than slow-growing, and this difference decreased in summer (16% for extensive indoor and 25% for free-range) (P < 0.05, for all). Fast-growing in extensive indoor and free-range displayed similar weight gains in the growing period, whereas grazing ones consumed less feed (P < 0.05) and thus showed better (P < 0.05) feed conversion. The same situation was true for slow-growing in spring. The mortality was approximately 1% in all groups in spring, while it was 17.36 and 18.06% for fast-growing in extensive indoor and free-range and 1.39, 2.78, and 4.29 for slow-growing in extensive indoor, free-range, and traditional free-range in summer. It is advantageous to choose fast-growing if short-term (56 days) fattening especially under optimum conditions is to be preferred. If the growing period coincides with summer, slow-growing should definitely be preferred and the fattening period should be extended to 82 days. Grazing improved feed conversion (P < 0.05) by reducing cereal-based diet consumption in both genotypes but did not affect carcass yield. However, grazing had a positive effect on fleshing.