Heat stress and diet utilization in male turkeys : the role of dietary energy and amino acids

Keywords: turkeys, heat stress, energy, amino acids.The commercial turkey industry has changed during the last two or three decades from one that marketed predominantly fresh whole dressed turkeys to one that now markets a large variety of mostly further processed products. Turkey breast meat is the most economically important part that is further processed. The turkey industry improved breast meat yield considerably by selective breeding, and advancements in management and feeding programs. Because breast meat yield is highly correlated with body weight, fast growing strains have been developed, but these strains are more sensitive to high ambient temperatures than earlier strains. This dissertation presents information on how male turkeys deal with chronic heat stress and how dietary amino acid and energy levels may alleviate the adverse effects of heat stress. Turkeys subjected to high ambient temperature will reduce their feed and associated nutrient intake because they need less energy for maintaining body temperature. A beneficial effect of including 10% extra dietary lysine, methionine, and threonine to diets that contained already high amino acid contents relative to NRC (1994), was not observed. Higher arginine to lysine ratios (1.25 vs. 1.00) only improved performance of turkeys when dietary lysine contents were marginal. Different electrolyte balances (164 to 254 meq/kg) did not modulate the effect of dietary arginine to lysine ratios. In an experiment with iso-caloric diets and different levels of dietary lysine (75, 90, 105, and 120% of NRC (1994) recommendations), the lysine requirement for optimum performance was determined to be the same for turkeys raised in either high or low ambient temperature when dietary energy contents met the requirement. In the last experiment, an evaluation was made of the response of male turkeys that were fed different dietary energy contents (NRC (1994) recommendations and ± 10%) and relatively high dietary lysine concentrations (105 and 120% of NRC (1994) recommendations) at high and low ambient temperature. The effect of extra dietary energy in the form of soybean oil had a more pronounced effect on performance at low than at high ambient temperature. High-energy diets resulted in lower breast meat yields