Effect of duration of early-age thermal conditioning of broiler chickens on production and heat tolerance

Abstract

The main objective of the study was to investigate the appropriate duration of early age thermal conditioning that would improve heat tolerance in broiler chickens with a minimum reduction in production performance. 200 commercial Hubbard broiler chicks were randomly allocated to five treatments. Each of the five treatments was replicated four times, with 10 chicks per replicate in a completely randomized design (CRD). The treatments consisted of birds exposed to air temperature of 37 ± 1 oC for 3, 6, 12 and 24 hrs at 4 days of age against the control that was raised under standard conditions (35 oC in week 1, and reduced by 3 oC every week until room temperature. Temperatures were reduced by raising the positions of infrared lamps until the desired air temperatures were reached.

Early age thermal conditioning significantly (P < 0.05) increased body weight gain, feed intake and water consumption of broilers while there was no significant difference (P > 0.05) in feed conversion ratio (FCR) between thermal conditioned birds and the control. Birds exposed to 12 and 24 hours of thermal conditioning had a significantly higher (P < 0.05) feed intake than the control and other treatments while birds exposed to 12 hours achieved the highest average numerical final weight (1.93 kg) compared to 1.89 kg (24 hours), 1.86 kg (6 hours) and 1.84 g (3 hours), 1.80 kg (control). Birds in the control group had a significantly higher (P < 0.01) cloacal temperature than the mean of the birds in treatment 1 to treatment 4.The birds in the control group also had a higher mortality rate (15%) than the rest of the treatments. The appropriate duration of thermal conditioning that improves production performance is 12 hours.

Sensible heat loss contributes significantly to the overall heat budget of broiler chickens; in this study it was responsible for dissipating up to 30% per degree of temperature difference of the overall excess heat that needs to be dissipated by heat stressed broilers. Birds exposed to early age thermal conditioning significantly (P < 0.01) lost more heat through convection and radiation than their non-conditioned counterparts, thereby achieving better tolerance to heat.