SULFATE SUPPLEMENTATION OF ANGORA-GOATS - SULFUR METABOLISM AND INTERACTIONS WITH ZINC, COPPER AND MOLYBDENUM

Effects of S intake on Zn, Cu, and Mo metabolism in Angora goats were studied. Animals were fed isocaloric and isonitrogenous diets containing 0.16%, 0.23%, 0.29% or 0.34% S of DM. Dietary Zn, Cu and Mo were constant at 29.2, 8.8 and 1.0 ppm, respectively. Supplementation of dietary S level did not affect (P>0.20) feed intake, fecal DM output, urinary volume, and fecal S output; but increased urinary S output (linear, P<0.0001), sulfate concentration in feces (linear, P< 0.0001; quadratic, P<0.05), and apparent absorption and net retention of S (linear, P<0.001). Metabolic fecal S, endogenous urinary S, and biological values of supplemented S were 0.55 g/d (32.2 mg/BW(kg)0.75), 0.48 g/d (27.8 mg/BW(kg)0.75) and 62.7%, respectively. Serum Cu and Zn concentrations were not affected by added S, although concentrations were lower (P<0.05) at 2 and 4 h than at 0 and 6 h postprandial. Concentration of protein S in the rumen, apparent absorption of Zn (quadratic, P<0.05), and Zn retention (quadratic, P<0.05) increased with S intake. Urinary Zn excretion increased (P<0.05) when diets containing higher amounts of S were fed. Presumably, this was due to enhanced absorption of Zn by S amino acids at lower S intake, but ZnS precipitation was greater at higher S intake. Urinary Cu output decreased (quadratic, P<0.01), and metabolism of Mo was not altered (P> 0.10) by S supplementation. The models for S-Cu, S-Mo and S-Mo-Cu interactions proposed by Huisingh et al. (1973) were updated in view of these findings.