Performance Evaluation of Two Slow-Medium Growing Chicken Strains Maintained under Organic Production System during Different Seasons

SIMPLE SUMMARY: Expected thermal variations as a consequence of climate change represent a challenge for alternative poultry production because animals graze abroad for long periods of time, where slight variations in ambient temperature may cause negative effects on their productive development. Changes in temperature have been described as factors capable of influencing the development of animals. The objective of this study was to evaluate weather conditions and strain affect the development of slow-medium growing chickens raised in an organic system. No differences were shown between both strains studied; this indicates the high similarity between the strains used. This fact would allow the farmer to include one strain or another in his farm indifferently. Better development was observed in chickens that had been raised under cooler conditions (S1) in organic systems. This fact could be justified by the greater difficulty that chickens find to dissipate heat in warmer environments, which impairs their productive development. In this way, whenever possible, it would be recommended to raise the largest number of chickens during the coldest season. ABSTRACT: A total of 160 1-day-old medium-growing male chicks (Gallus gallus domesticus) were raised for 120 days in a certified organic farming system. A total of two strains were studied (Coloryield, CY; RedBro, RB). Overall, two weather periods were considered based on the outdoor temperature, being S1 colder than S2. In total, 40 chicks per strain were assigned to each period (n = 80). Chickens were fed ad libitum with the same organic feeds. In the first month, chickens were kept indoors and, from day 30, they had access to the pasture. Slaughter live weight (LW), average daily gains, (ADG), the feed conversion ratio (FCR), and mortality rates did not differ between the two strains. LW was (p < 0.05) higher in the S1 and a trend (p = 0.084) was observed for ADG, which was higher in S1. No differences were found for feed intake, FCR, and mortality rates between weather periods. There were no differences for coefficient of variation (CV) between the strains studied, nevertheless, CV for LW in S2 was increased. Differences in the productive performance between these strains raised in organic production systems were slight. However, chickens raised in S1 had a better performance. It would be preferable to raise chickens in these weather conditions whenever possible.