Effects of dietary nutrient density on broiler performance at low and moderate environmental temperatures

Three broiler finishing rations with calculated metabolizable energy values (ME) of 3175, 3250, and 3325 kcal/kg and constant lysine and sulfur-bearing amino acid: energy ratios were evaluated at two environmental temperatures. Broiler chickens were reared from 3 to 7 weeks in either an 18.3 or 26.7 C temperature. At the 18.3 C temperature, 7-week body weights increased linearly 3.1% as energy level increased from lowest to highest level. Feed:gain ratio decreased linearly 5.0% as energy level increased from lowest to highest. At the 26.7 C temperature, no significant differences were found in 7-week body weights due to energy level of the diet. Feed:gain ratio decreased 3.2% as energy level increased from lowest to highest, but the response was not linear. Energy intake increased as dietary energy was increased in the cool temperature; energy intake was less in the warm temperature and did not change appreciably as dietary energy changed. Because lysine and methionine plus cystine were tied to dietary energy by a fixed ratio, the pattern for intake of these amino acids was the same as for energy. It appears that the procedures used to formulate the diets do not give uniform results for the range of environmental temperatures and energy levels tested.