Comparing different water supplementation in cyclic heat stressed broilers. The effect of selected antioxidant mixtures, betaine, functional amino acids and electrolyzed reduced water

Combating heat stress (HS) has become an emerging topic in temperate regions. Supplementing drinking water additives may alleviate the adverse effects of HS in broilers. The effects of commercially available additives on performance, body temperature, respiration rate, oxidative status and physiology during induced HS were assessed in two separate trials. In each experiment, 756 Ross 308 male broilers were allocated to four treatments (n = 9). Treatments were supplied continuously during the finisher phase until slaughter. In Exp. 1, animals received polyphenols (1 mL/L) with vitamin C (25 %; added at 0.25 mL/L) (PP + VIT C), essential oils (25 %) with vitamin E (1 %; added at 0.1 mL/L) (EO + VIT E), betaine hydrochloride (0.7 g/L) (BET) or unsupplemented water (CON). In Exp. 2, treatments included electrolyzed water at 10 % (ERW10) or 100 % (ERW100), a mixture of crystalline amino acids (AA): l-arginine (4.5 g/L), l-monosodium glutamate (3 g/L) and l-threonine (2.5 g/L), and CON. All pens were subjected to cyclic HS (32 ± 2 °C; 60 %-70 % RH; 09:30-15:30) until slaughter. On average, birds showed a body temperature of 42.6 °C and a breathing frequency of 186 breaths/minute, while reducing feed intake during daytime HS compared to thermoneutral nighttime (circa 24 °C), which was not affected by any treatment. Likewise, performance, meat quality, oxidative metabolism and physiological responses during HS were not significantly affected by the treatments, except for AA, which decreased feed intake by 9.6 %, but improved FCR by 0.10 compared to CON. AA also reduced the water holding capacity of breast muscle and resulted in paler meat colour. Deviations in water quality (e.g. microbiological and organoleptic parameters) suggested that AA may have promoted microbial growth under HS. In conclusion, despite clear HS responses, characterized by high body temperature and breathing frequency, and a significant difference in feed intake following a cyclic pattern as the model, none of the drinking water additives effectively improved performance or key physiological features during cyclic HS in the finisher phase.