Dietary sulfur concentration affects rumen hydrogen sulfide concentrations in feedlot steers during transition and finishing.

摘要

Angus steers (n=96; 321+or-29 kg BW) were used to determine how previous exposure to increased dietary S would affect ruminal hydrogen sulfide concentrations ([H₂S]) in the feedlot, to investigate the effects of dietary S on ruminal [H₂S] during transition and finishing, and to determine if dietary S affects the glutathione status of finishing cattle. Steers were strip-grazed on smooth bromegrass (Bromus inermis L.) over a 35 d period and received a dry distillers grains plus solubles (DDGS) supplement at 1% of BW (DM basis) that contained either 0.50% S (LS; n=4 plots) or the DDGS supplement with an additional 0.30% S from sodium sulfate (0.80% S in supplement; HS; n=4 plots). On d 36 steers were moved from the pastures to feedlot pens with one-half of the steers on each treatment in the pasture period remaining on the same treatment during the feedlot period and half being switched to the other treatment (n=6 pens). For the first 10 d in the feedlot, steers were fed hay ad libitum and 1% BW of the DDGS supplement representing their new treatment, followed by transition to finishing diets. Dietary S of transition and finishing diets were 0.2% to 0.3% S for LS and 0.5% to 0.6% S for HS. No interaction between pasture and feedlot treatment was observed (P>=0.50), so data for the feedlot period were pooled by feedlot treatment (n=12 pens). Rumen [H₂S] were measured on d 35 of the pasture period and on d 46 while receiving ad libitum hay and supplement at 6 h after the feeding of the supplement and after 7 d on each of the 3 transition diets (d 53, 60, and 67) and on d 93, 126, and 155 of the study after receiving the finishing diet for 26, 59, and 88 d at 6 h after feeding. Ruminal [H₂S] did not differ between treatment while steers were fed the supplement on forage-based diets. However, ruminal [H₂S] of HS-fed steers was greater (P<0.05) than LS-fed steers when transition diets and the finishing diets were fed. Relative to S intake, ruminal [H₂S] increased disproportionally after 26 d on the finishing diet. This was followed by a decrease in [H₂S] on d 59 of finishing, although S intake was increased (P<0.05) compared with d 26 of finishing. It appears that factors other than S intake alone contribute to ruminal [H₂S]. The amount of glutathione in the liver of steers did not differ (P=0.47) because of dietary S, but the concentration of oxidized glutathione increased (P=0.03) in HS-fed compared with LS-fed steers, suggesting that the potential for oxidative stress in cattle fed high-S diets may warrant further investigation.