Abstract 238

O'Kelly,JC

CSIRO, Division of Tropical Animal Science, Tropical Cattle Research Centre, Box 5545, Rockhampton Mail Centre, Qld. 4702, Australia.

Comparative-Biochemistry-and-Physiology,-A-Comparative-Physi logy. 1987, 87: 3, 677-682; 23 ref.

Crossbred British and Brahman X British 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 isoenergetic were used. The PCLC, the net esterification of cholesterol by the lecithin:cholesterol acyltransferase system and faecal fat excretion were increased by the HF diet which reduced urinary nitrogen loss. Hyperthermia disturbed lipid metabolism in all cattle and reductions in the concentrations of plasma cholesterol and phospholipid paralleled the increases in the quantities of fat excreted in the faeces. Within groups the cattle on the HF diet maintained a higher PCLC, lower body temperature and conserved more body N during hyperthermia than did cattle on the LF diet.