Changes in lipid metabolism in genetically different types of calves during chronic hyperthermia.

I . The effects of chronically raised body temperature on lipid metabolism wcrc studied in groups of 3-month-old British (Shorthorn x Hereford) and Zebu (Africander x British) bull calves. Calves in control groups at ambient temperature were pair-fed to calvcs housed in a climate room. 2. In control groups, concentrations of plasma cholesterol and phospholipid were significantly higher and the excretion of fatty acids 14:o, 16:oand 18:o waslower in the Zebu than in the British calves. 3. In the climate room the constant daily environmental temperature required to maintain anincrease in rectal temperature of 1.3' was 33O for British and 38" for Zebu calvcs. Changes in respiration rate, water metabolism and nitrogen metabolism associated with hyperthermia were similar in both breeds. 4. Hypcrthcrmia in all animals was associated with lowered plasma concentrations of cholesterol and phospholipid and increases in the ratio of free to total cholesterol. It was without effect on the circulating concentrations of non-esterified fatty acids and about twice the amount of fat was excreted without change in its fatty acid composition. 5 . The results showed that, when control of normal body temperature was lost, increased rectal temperature led to similar metabolic changes in animals of both breeds.