Abstract
Genetic selection for lower fatness is commonly practiced in sheep breeding programs to improve consumer appeal for sheep meal products. This selection strategy may result in changes to glucose production. In particular liver glucose output, which is of particular importance for breeding Merino ewes since then ability to build energy stores in nutritionally marginal environments is paramount for reproductive success. Hepatic glucose output can be measured by administering controlled doses of adrenaline which is a strongly catabolic hormone that among other things stimulates the liver to rapidly increase the output at glucose. This release of glucose is the net result of adrenaline-stimulated mobilisation of stored glycogen combined with glucose synthesis from gluconeogenic precursors. The rate of gluconeogenesis in response to adrenaline may he higher in genetically fat sheep as both the basal and adrenaline-stimulated rates of glucose synthesis are higher in genetically fat rats (Rohner—Jeanrenaud et al., 1986. Sanchez-Gutierrez et al., 2000) Furthermore, obese humans have higher rates of gluconeogenesis and higher concentrations of hepatic glycogen than their lean counterparts, both of which would favour greater glucose release in response to adrenaline (Muller et al., 1997). Thus we hypothesise that glucose output following an adrenaline challenge will be lower in ewes that are genetically leaner.