Aspects of Glucose Synthesis in Sheep

Abstract

It was established that gluconeogenesis in sheep was affected by the quantity and quality of the diet. With diets of similar digestible energy content but of varying proportions of maize to lucerne, the proportion of plasma glucose arising from propionate produced in the rumen was highest on the diet containing the greatest quantity of lucerne and decreased as the proportion of starch in the diet increased. The low volatile fatty acid concentrations and the reduced conversion of propionate to glucose on the high starch diets, despite similar propionate production rates and irreversible losses of plasma glucose, may have been due to starch escaping fermentation. With different roughage diets, the irreversible loss of glucose increased linearly with the digestible energy and crude protein intake. As the correlation with protein intake was lower than that for energy intake and as the amount of protein which passes to the small intestine is to a large degree independent of the protein intake, it is suggested that protein intake is not causally related to the irreversible loss of plasma glucose. There was no apparent effect of diet on the proportion of plasma glucose derived from propionate or on the proportion of propionate produced in the rumen that was converted into glucose. This indicates for the roughage diets used, that the relative contribution of glucogenic products of ruminal fermentation, particularly propionate and amino acids, to glucose synthesis is similar.