Sulfate supplementation of growing goats: effects on performance, acid-base balance, and nutrient digestibilities.

Castrated male goat kids (20 Alpine, 12 Angora) were individually fed isonitrogenous and isoenergetic diets containing 2.28% N and S (added as CaSO4) at either .11 (basal), .20, .28, or .38% of dietary DM. Sulfate supplementation during the 8-wk growth trial quadratically increased ADG (P < .05) and tended to increase quadratically the DMI (P < .07) of goats, with a peak value for the .20% S diet. Even when analyzed using DMI as a covariate, ADG was quadratically increased (P < .05) by added S. Sulfate supplementation linearly increased (P < .001) S intake, fecal S output, and S retention. Sulfate supplementation tended to increase quadratically (P < .06) the blood plasma concentration of L-lactate. However, sulfate supplementation did not significantly affect (P > .10) plasma sulfate, plasma cystine, ruminal ammonia N concentrations, or purine N content of isolated ruminal bacteria. Sulfate supplementation quadratically increased (P < .05) fractional N retention. Urinary output of uric acid increased quadratically (P < .01) with S supplementation, presumably reflecting ruminal bacterial protein synthesis. Calculated by regression, the optimal dietary S content for maximum ADG was .22% S (N:S = 10.4:1), for maximum DMI it was .24% S (N:S = 9.5: 1), for maximum N retention it was .23% (N:S = 9.9: 1), and for maximum absorbed N retained it was .22% (N:S = 10.4:1). These results support the current estimate of the S requirement of goats for growth (N:S = 10:1).