To apportion the intake of metabolisable energy (MEI) used for synthesis of lean and fat tissue, current knowledge of substrate oxidation and substrate utilisation for biosynthetic reactions has been combined with estimates of fat and protein turnover to develop models of energy metabolism and nutrient fluxes in a lean 20 kg male and a fat 40 kg female sheep, each gaining 200 g/d. When the most efficient pathways and lowest turnover rates are employed the biosynthetic reactions account for 38 and 34% of MEI in the lean and fat animals. These values rise to 45 and 43% of MEI respectively when higher estimates of turnover and less efficient pathways are used in the calculations. Hormonal regulations of metabolite utilisation is believed responsible for such differences but hitherto, only glucose-insulin system has been quantitated. Two techniques used for its quantitation are described to provide examples of the methods needed to elucidate the control of nutrient utilisation and ultimately body composition in ruminants.

DR, Musgrave, and LR Fletcher

Proceedings of the New Zealand Society of Animal Production, Volume 44, , 185-188, 1984
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