THE EFFECT OF PHYSICAL CHARACTERISTICS OF HAY DIETS ON PHOSPHORUS METABOLISM IN SHEEP

The experiments were carried out to study the effect of physical forms of hay diet on phosphorus metabolism by offering sheep roughage diets containing a low phosphorus content. The sheep were fed coarse hay, short hay or finely ground pelleted hay. The physical forms of hat diet had little effect on the pathway of phosphorus excretion. In all groups, the most of phosphorus was excreted in feces and urinary phosphorus excretion was negligible. Duodenal fluid flow, rumen fluid outflow and estimated salivary flow appeared to be relatively high in sheep fed the coarse hay diet as compared to those in sheep fed the finely ground diet. The amount of phosphorus flow to the duodenum tended to be high in the coarse diet group as compared to those in other two groups. On the other hand, phosphorus concentrations in the duodenal fluid and the rumen fluid were lower in sheep fed the coarse hay diet than those in sheep fed the ground hay. Net intestinal phosphorus absorption tended to be higher in sheep fed the coarse hay than that in sheep fed the ground hay or pelleted hay. However, a negative phosphorus balance was observed in the coarse hay diet group although a positive phosphorus balance was found in other two groups. It was considered that salivary phosphorus secretion was greater than the amount of salivary phosphorus reabsorbed from the intestine, resulting in the negative of phosphorus balance in sheep fed the coarse hay.