Abstract:
Heat stress is a cause of great economic loss in poultry production throughout the world. Many methods have been researched to find a solution to alleviate the negative effects of heat stress. Methods include but are not limited to: adequate ventilation and facility orientation, the acclimation of birds to elevated temperatures, electrolyte and acid-base balance to maintain body fluid homeostasis, water management to aid in evaporative cooling, feed management by means of fasting and nutrition to ensure a balance diet during reduced intake and non-nutritive feed additives to improve performance. Previous research has shown that the inclusion of virginiamycin (VM) in poultry diets during periods of heat stress may improve growth rate, feed intake, feed conversion ratio, survivability and carcass weight. This was tested by conducting an experiment on 1408 male broilers. A randomised block design was used with 32 pens in each side of the house. Chicks were randomly assigned to four treatments with 16 replications, each containing 22 broilers. Data was statistically analysed as a randomised block design with the GLM model and mortality data by Chi-square. The broilers were subjected to a temperature profile which simulated a cyclic heat wave with high temperatures during the day and lower temperatures at night. From day 16 to 32, house temperature was gradually increased from 8:00-11:00 until the set maximum temperature of the profile was achieved and decreased at 18:00 to 24 °C. The control group received a diet without antibiotic growth promoters. The second group which was a positive control group received a diet with zinc bacitracin 15% (334 g/ton). The third group received a diet with VM (20 g/ton) in all feeding phases whilst the fourth group received VM (20 g/ton) in all feeding phases with exception of the post-finisher phase. Broiler performance, intestinal morphology and carcass and blood composition of birds were measured. The addition of VM to the feed of broilers subjected to heat stress had no significant (P<0.05) effect on body weight or carcass and blood composition. Mortality within the third and fourth group was significantly lower, both before and after the onset of high cyclic temperatures. Supplementation of VM could be beneficial to lower the mortality rate of birds subjected to heat stress.
