Influence of dietary fat on some metabolic responses of cattle to hyperthermia induced by heat exposure.

1. Two breeds of cattle which differ in their plasma concentrations of lipid components (PCLC) and ability to tolerate heat were used to study metabolic responses to hyperthermia. Two maintenance diets, LF (2.5% Fat) and HF (9.2% Fat), which were isonitrogenous and isocaloric were used. 2. The PCLC, the net esterification of cholesterol by the lecithin: cholesterol acyl transferase system and faecal fat excretion were increased by the HF diet which reduced urinary N loss. 3. Hyperthermia disturbed lipid metabolism in all animals and reductions in the concentrations of plasma cholesterol and phospholipid paralleled the increases in the quantities of fat excreted in the faeces. 4. Within breeds the animals on the HF diet maintained a higher PCLC, lower body temperature and conserved more body nitrogen during hyperthermia than animals on the LF diet. 5. The results point to a role for dietary lipid in ameliorating the metabolic disturbances in animals during chronic hyperthermia.