The utilisation of a supplementary energy supply and its effects on urea metabolism and rumen function were examined in sheep fed indoors on fresh lucerne (Medicago sativa cv. Rere) (N content, 34 g/kg DM). Sheep were fed hourly and infused intraruminally with either water (1200 ml/d; n=5; N intake, 33.0 g/d) or similar volume containing sucrose (160 g/d; n=4; N intake, 32.1 g/d). The additional energy resulted in a lower rumen fluid ammonia concentration (264 v 142 mg N/l). In a comparable experiment with sheep fed chopped lucerne hay, continuous infusion of sucrose also resulted in increased propionic acid levels in the rumen which was reflected in an increase in plasma glucose production (113 v 188 g/d) in the infused group. The results suggest that supplementary fermentable carbohydrate is effective in improving the efficiency of utilisation of pasture protein. The effect appears to be 2-fold: excess ammonia-N i9s captured as microbial protein which is then available for enzymic digestion in the lower gut; the additional fermentative activity increases propionate production which in turn is available for glucose production, thus sparing amino acids for tissue protein utilisation.
Proceedings of the New Zealand Society of Animal Production, Volume 48, , 225-230, 1988
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