Sulfur Supplementation of Urea-containing Silages and Concentrates. II. Ration Digestibility, Nitrogen, and Sulfur Balances

Abstract Metabolism trials were conducted on 16 cows at three stages of lactation to evaluate effect of sulfur supplementation on utilization of urea in corn silage and concentrate portions of ration and on digestibility and nitrogen and sulfur balance. Treatments arranged in a 2 × 2 × 2 factorial consisted of: .5% urea-treated or 3.5% soybean meal-treated corn silage; 0 or .8% urea-containing 18% crude protein concentrates; and 0 or .8% concentrate anhydrous sodium sulfate. Treatments did not affect digestibility of ration dry matter, cell walls, acid detergent fiber, or crude protein. Sulfur digestibility was improved by sulfur supplementation. Cows fed urea-treated corn silage had lower nitrogen balances (– 14.0 vs. 4.2 grams per day) than cows fed soy-treated corn silage. Neither concentrate nitrogen source, sulfur supplementation, nor treatment interactions affected nitrogen utilization. Urea was better utilized when included in the concentrate rather than corn silage portion of the ration, and on a low sulfur ration sodium sulfate supplementation did not affect nitrogen utilization. Sulfur balances were not affected by treatments although absorbed sulfur and urinary sulfur were increased by sulfur supplementation.