The effect of dietary sulfur on performance, mineral status, rumen hydrogen sulfide, and rumen microbial populations in yearling beef steers

Sulfur (S) is a requisite part of the ruminant diet, but may sometimes be present in excess, leading to decreased animal performance and illness. In this experiment, 96 crossbred yearling steers (321 ± 29 kg BW) were used to determine the effects of dietary S concentration of a supplement fed to cattle on pasture and of the total diet in the finishing period. Steers were blocked by weight and allocated to smooth bromegrass-based pastures and supplemented with either a low S dried distillers grains with solubles (DDGS; 0.3% total dietary S; LS; n = 4 plots) or LS DDGS with additional S (0.45% total dietary S; HS; n = 4 plots). After 36 d on pasture, steers moved to the feedlot where half remained on the previous S treatment while half switched treatments, resulting in 4 treatments (LS-LS; LS-HS; HS-LS; and HS-HS; n = 6 feedlot pens). Steers were transitioned to the final finishing diet using a series of step up diets. Once fully transitioned, steers were receiving either 0.3% dietary S (LS) or 0.6% dietary S (HS). Plasma and liver mineral concentrations of half of the steers were determined at beginning of the trial (d 0), the end of the pasture period (d 35), and near the end of study (d 155). Plasma Mg was decreased (P = 0.05) in response to increased dietary S during the pasture period, however steers were not deficient. Copper concentrations in the plasma and liver were decreased (P < 0.05) in steers which had received increased dietary S when measured at the end of study (d 155). Average daily gain of steers did not differ (P = 0.50) between LS and HS during the pasture period, but was lower (P = 0.01) in HS vs. LS steers during the finishing period. Decreased gains translated to a tendency (P = 0.06) for hot carcass weight to be decreased in HS steers vs. LS steers. Fatty acid analysis of longissimus dorsi showed increased stearic and heptadecanoic acid (P = 0.04 and 0.01, respectively) in steers receiving increased dietary S. Cattle exposed to higher S diets during the pasture period did not show differences (P = 0.40) in performance based on the previous pasture treatment. However, cattle fed high dietary S on pasture had greater carcass fat cover (P = 0.01), suggesting S may have influenced lipid metabolism. Rumen H2S concentration was determined 6 hr post-feeding at multiple time points throughout transition and finishing (d 36, 45, 52, 59, 66, 91,125, and 155). Concentrations of rumen H2S did not differ while cattle were consuming a high forage diet (1733 and 1400 ppm for HS and LS, respectively; P = 0.54). During the feedlot period, rumen H2S concentration