Nutritional status and intake regulation in sheep. I. Effects of duodenally infused single doses of casein, urea, and propionate upon voluntary intake of a low-protein roughage by sheep

Abstract

In each of two experiments, single infusions of casein administered to sheep per duodenum produced substantial and rapid increases in voluntary intake of chaffed oaten hay diets of low nitrogen content (0.62–0.70% nitrogen). The effect commenced within 16 hr of completion of the infusion, and occurred before any observed change in the rate of cellulose digestion in the rumen.

When urea was infused per duodenum at the same level of nitrogen as with the casein, an increase in intake occurred on the day following infusion in one experiment. In a second experiment no such response occurred. Faster rates of cellulose digestion were observed on the day of infusion, apparently due to recycling of nitrogen to the rumen. Of the 10 g of nitrogen infused, 7.4 g of casein nitrogen and 5 g of urea nitrogen were retained.

Propionate, infused in an attempt to reproduce the gluconeogenic properties of casein, did not have any major effect on daily dry matter intake, although it caused a depression in intake during the period of infusion in one experiment.

Results are discussed in relation to the possible mechanism of response to the protein supplement. The possibility is suggested that the protein status of the animal is a component of a chemoregulatory mechanism governing the intake of low nitrogen diets by sheep.