Feed form and nutritional level for rearing growing broilers in thermoneutral or heat stress environments

The present study aimed to investigate the effects of different physical forms of feed and feeding programs on nutrient digestibility and performance of grower-finisher broilers under thermoneutrality or thermal stress. Three experiments were conducted using male broiler chickens (n = 720) aged 19-42 d. The design of two of the experiments was fully randomized in a 2 x 2 factorial arrangement with two forms of feed (mash and pellet) and two nutritional levels (13.19 MJ/kg and 194.8 g/kg CP - normal level and 13.61 MJ/kg and 210.3 g/kg CP - high level). The experiments took place in a climate-controlled room: Experiment 1 at thermoneutrality (21-23 degrees C and 58-60% relative humidity) for 24 h/day; Experiment 2 under thermal stress cycle (31-32 degrees C and 63-65% relative humidity), for 6h/day and thermoneutrality (21-23 degrees C, 58-60% relative humidity) for 18h/day. The nutrient digestibility and performance was analyzed. The design of the third experiment was fully randomized with two ambient condition treatments (thermoneutral and thermal stress) on heat production, caloric increment and net energy. Pellet feed obtained higher digestibility of dry matter, digestibility of crude protein, AME and AMEn (P < 0.05) than mash feed for broilers reared in the thermoneutral environment. At the high nutritional level there was no effect of treatments on the coefficient of dry matter and crude protein (DCCP) (P > 0.05), while the highest digestibility of AME and AMEn were obtained by the high nutritional level diet (P < 0.05). Pellet feed had higher DCCP (P < 0.05) than mash feed for broilers reared under cyclic heat stress. Broiler chickens under cyclic stress experienced increased caloric increment, rectal temperature and respiratory rate. The appropriate strategy to minimize these effects in both ambient conditions is to pellet feed.