Heart rate as an indicator of heat stress in broilers.

Experiments were conducted in a semi-controlled environmental condition, to assess heart rate (HR) as an indicator of heat stress (HS) in broilers. Thirty two broilers (Hubbard) were used. Chickens were identified by sex and were allocated to two treatments: treatment 1 (T1); “hot room” and treatment 2 (T2); “fresh room”. Each group was constituted by 16 broilers (eight males and eight females). Chickens from each treatment were placed in four fences (repetitions) per treatment of four broilers per repetition. The “fresh room” was characterized by a maximum environmental temperature (ET) of 30°C during the experimental phase, while the maximum ET of the “hot room” was 32°C. Both, body temperature (BT) and ET were measured (four times a day) for seven days between 28 and 35 days old. The body weight (BW) and HR (beats/min) was measured on days 28 and 35. The BT was similar (P >0,05) between treatments (T1: 41,43±0,05°C vs T2: 44,50±0,05°C). The HR of broilers from T1 was significantly (P <0,05) lower than T2 (T1: 345,8±2,9 lat/min vs T2: 353,9±2,5 lat/min). No significant differences were observed in HR between sexes, although males tended to have a lower HR. It is concluded that HR could be a sensible variable to determine the moderate HS level in broilers under an average ET between 30 and 32°C. It is recommended to include the HR to study variations in the level of heat stress in broilers.