The incidence of polioencephalomalacia and concentrations of ruminal hydrogen sulfide ([H2S]) in feedlot cattle appear to be greatest during the first 30 days of being fed a high sulfur (S) finishing diet. It was hypothesized that delaying exposure to high-S until cattle are fully adapted to a high-concentrate diet would reduce the peak [H2S], thus reducing potential for S-induced polioencephalomalacia. Sixty Angus crossbred-steers were moved into the feedlot and fed a moderate S (0.3% S) step-up diet for 7 days. Then steers were weighed (443 +/- 12.8 kg), blocked by weight, and randomly assigned to one of three dietary treatments: (1) two moderate-S (0.3% S) step-up diets fed for 7 d each (days 1-14) followed by a moderate S finishing diet (days 15-98; MS), (2) two high-S (0.6% S) step-up diets fed for 7 d each (days 1-14) followed by a high S finishing diet (days 15-98; HS), or (3) two moderate-S (0.3% S) step-up diets fed for 7 d each (days 1-14) followed by a moderate S finishing (0.3% S) diet for the first 28 days of the finishing period (days 15-42), followed by the high-S diet (0.6% S) for the remainder of the trial (days 43-98; Delayed S; DS). Ruminal [H2S] and pH were measured 6 h post-feeding on days 15, 21, 28, 42, 49, 56, 70, 84, and 98. The numerically greatest [H2S] (4948 mg/L) occurred in HS-steers on day 42 (28 d on the finishing ration) and on day 70 (28 d after starting high-S) for DS-steers (3690 mg/L). The maximum [H2S] of HS-steers tended to be greater (P=0.09) than DS-steers, despite S intake not differing (P=0.75). The elevated ruminal [H2S] of HS-steers on day 42, was likely not due to a decreased ruminal pH during adaptation to the finishing diet as pH did not differ due to treatment (P=0.40) or day (P=0.16). Overall, HS-steers had a 15% decrease (P=0.02) in average daily gain compared to MS-steers whereas gain of DS-steers was intermediate, not differing from MS (P=0.13) or HS (P=0.26) steers. These findings suggest that there may not be any additional increase in steer gains by delaying S inclusion in the diet until after the first 28 days of finishing, though it may decrease the maximum ruminal H2S concentration. (C) 2013 Elsevier B.V. All rights reserved.
