GLUCOSE METABOLISM IN FAT AND THIN ADULT SHEEP

Abstract

The effect of body fatness on glucose metabolism was studied in six adult crossbred wethers divided into two groups weighing 90 kg (fat) or 55 kg (thin). Glucose turnover measurements were made using 6-3H-glucose by single injection at four levels of metabolizable energy intake: high, 17 MJ/day; intermediate, 10 MJ/day; low, 6 MJ/day; and fasting for both thin and fat groups. The greatest group differences occurred at the high feeding level. Body pool size and glucose space were significantly lower (P < 0.001) for the fat sheep and were reduced at fasting for both fatness levels. The mean irreversible loss rate was not affected by body fatness but was significantly affected (P < 0.001) by feeding level. Glucose recycled as a proportion of total entry rate was significantly affected by body fatness and was dependent on a positive or negative energy balance. When in negative energy balance the sheep maintained blood glucose within the normal range by recycling up to four times more glucose than was utilized. It appears that rate of glucose synthesis is related to energy balance and metabolizable energy intake. A tendency toward insulin insensitivity in the fat sheep could be related to high levels of recycling, and a greater glucose drain or prolonged fast could be more serious with the decreased glucose pool size and space. Key words: Glucose metabolism, ruminant, obese, energy balance