EFFECTS OF DIET COMPOSITION ON FEED-INTAKE AND GROWTH OF CHICKS UNDER HEAT-STRESS .1. DIETARY-FAT LEVELS

In 5 experiments an attempt was made to reduce the effects of heat stress on broiler chicks by lowering the heat increment of the diet. Percentage of energy derived from fat was increased by replacing corn starch with fat, calorie for calorie, which reduced formula weight and increased diet density. In 1 treatment total protein level was reduced also while maintaining adequate essential amino acid levels. The effect of caloric and nutrient density was separated from that of percentage fat calories by the use of a non-nutrient filler in 1 diet. Experimental rations were fed to male broiler chicks from 4-7 wk of age in hot (31.1 .+-. 2.degree. C) vs. cool (20.0 .+-. 2.degree. C) controlled temperature chambers. In all experiments, metabolizable energy (ME) intake was increased when fat calories replaced carbohydrate (CHO) calories. In the high fat treatments, chicks gained significantly more body weight than did the high CHO control groups. This increase was similar at both temperatures, indicating that the beneficial effect of dietary fat was independent of temperature. A portion of the improvement in ME intake and weight gains resulting from increased ratio of fat to non-fat calories was retained when diet density was equalized. Heat production measured by energy balance studies was numerically lower in chicks fed diets with the high ratio of fat to non-fat calories.