Cloacal temperature responses of broiler chickens administered with betaine and ascorbic acid during the hot-dry season Ifeanyichukwu Chukwuemeka Egbuniwe a *, Joseph Olusegun Ayo a , Mohammed Umar Kawu a and Aliyu Mohammed b a Faculty of Veterinary Medicine, Department of Veterinary Physiology, Ahmadu Bello University, Zaria, Nigeria; b Faculty of Human Medicine, Department of Human Physiology, Ahmadu Bello University, Zaria, Nigeria (Received 3 August 2014; accepted 7 October 2014) The experiment was performed to evaluate cloacal temperature (CT) responses in broiler chickens, administered with betaine and ascorbic acid (AA) during the hot– dry season. Broilers were divided into four groups: Group I (control) was given sterile water; Group II, betaine at 250 mg/kg; Group III, AA at 50 mg/kg and Group IV, betaine (250 mg/kg) + AA (50 mg/kg). The different solutions were given orally for 42 days. Dry-bulb temperature (DBT), relative humidity (RH) and temperature- humidity index (THI) in the pen, and CT of each broiler chicken were measured bihourly (06:00–18:00 h) on days 28, 35 and 42. DBT, RH and THI values were outside the thermo-neutral zone for broiler chickens. Results showed that AA lowered ( p < 0.001) CT, while betaine + AA increased ( p < 0.001) CT, compared with controls. In conclusion, betaine + AA or AA alone modulated CT responses of broiler chickens subjected to the thermal stress in the hot–dry season. Keywords: heat stress; body temperature 1. Introduction There has been substantial improvement in genetic selection for fast-growing broiler chickens due to the demand for heavier broilers. However, the ability of the birds to cope with high ambient temperature (AT) diminishes as they increase in age (Piestun et al. 2013). Continuous exposure to high AT, especially in combination with high rela- tive humidity (RH), overwhelms the ability of poultry to maintain thermal homeostasis. This may compromise the health and productivity of birds because these extremes con- siderably decrease poultry production due to reduced food intake and nutrient utilisation (Rhoads et al. 2013). Also, brain-gut neuropeptides which regulate food intake are altered by heat stress, leading to decreased feed consumption (Lei et al. 2013). Heat stress diminishes broiler performance and breast yield (Oliveira et al. 2013); it also exerts adverse effects on the immune system, activating the central nervous system and increasing corticosterone levels, which decreases the body immune system and, increases susceptibility to Salmonella spp. (Palermo-Netoa et al. 2013). Heat stress also induces oxidative stress, resulting in the generation of excessive reactive oxygen species (ROS) (Lin et al. 2006). *Corresponding author. Email: ifeanyiegbuniwe@gmail.com © 2014 Taylor & Francis Biological Rhythm Research, 2015 Vol. 46, No. 2, 207–219, http://dx.doi.org/10.1080/09291016.2014.974931