PROTEIN-UTILIZATION DURING ENERGY UNDERNUTRITION IN SHEEP SUSTAINED BY INTRAGASTRIC INFUSION - EFFECT OF BODY FATNESS ON THE PROTEIN-METABOLISM OF ENERGY-RESTRICTED SHEEP

The effect of body fat content on the protein metabolism of energy-res tricted sheep has been studied in two experiments, In the first experi ment, six Suffolk-cross wether sheep, three weighing about 39 kg and t hree of about 61 kg, were given, progressively increasing amounts of c asein-N from 0 to 3000 mg N/kg metabolic body weight (W-0.75) daily wi th constant energy, 91 kJ/kg W-0.75 daily, from a high-propionic acid mixture of volatile fatty acids (VFA). In the second experiment, two l ean and two fat sheep of similar body weights were given progressively increasing amounts of casein with the same VFA mixture. All the anima ls attained a positive N balance when they were in negative energy bal ance, N balance was not affected by body fatness of the magnitude stud ied, although lean animals utilized increasing levels of standard VFA (acetate-propionate-butyrate 65:25:10, molar proportions) infusion for N accretion more efficiently than fat animals, Endogenous energy was utilized for protein accretion with an efficiency of 0.56, Supply of g lucogenic VPA equivalent to 28 mmol glucose/kg W-0.75 reduced fasting N excretion by 39 %, Easting heat production decreased from 335 to 300 kJ/kg W-0.75 with the infusion of casein and glucogenic VFA. It is ar gued that fasting induces additional heat losses due to raised protein metabolism and is unsuited as a baseline for dietary assessment.