Effect of sub-clinical parasitism on the absorption of nutrients from the gastro-intestinal tract of sheep with special reference to calcium and phosphorus
Wilson, Wilma Duncan
Recent studies have established that abomasal and intestinal parasitic infections can reduce the growth and mineralisation of the skeleton of growing lambs. One possible cause for the skeletal effect is that the parasites induce a mineral deficiency by reducing the absorption of dietary Ca and P and/or increasing the endogenous loss of these two elements.The importance of these factors was investigated in this study,This was achieved by using growing lambs fitted with cannulae in the rumen, abomasum and ileum and infected daily with Trichostrongylus colubriformis larvae,Ostertagia circumcincta larvae or no larvae. The lambs were fed the complete diet Ruminant A and the flow rates were measured by reference to soluble and particulate radioactive markers. The endogenous fraction of Ca and P in faeces and digesta was measured by the method of isotope dilution involving a single intravenous dose of 32P and 45Ca.A preliminary investigation showed that the best method for calculating the fraction of Ca and p which is of endogenous origin was the area method using a two day delay and that the SR in plasma was more reliable than the SR in urine,0. circumcincta infection was without effect on the absorption and secretion of Ca and p in the digestive tract, other than producing a small but significant increase in the endogenous faecal Ca excretion. There was, however, a striking increase in the flow of digesta at the abomasum,the DM and Ka content of which was consistent with an increased secretion from the mucus - type cells in the abomasal mucosa. The extra digesta was absorbed in the small intestine,T, colubriformis infections reduced the absorption of exogenous p by about 30% and increased losses of endogenous P due to the action of worms on the mucosa of the small intestine. The net effect of this v;as to induce a P deficiency in TC lambs leading to a reduced flow of salivary P and a reduction in the plasma concentrations of p. The effect of T, colubriformis on Ca metabolism was limited to an increase in endogenous faecal excretion.