Increasing dietary neutral detergent fiber concentration decreases ruminal hydrogen sulfide concentrations in steers fed high-sulfur diets based on ethanol coproducts

Authors

S. J. Morine, Iowa State University
M. E. Drewnoski, University of Nebraska-LincolnFollow
S. L. Hansen, Iowa State UniversityFollow

Document Type

Article

Date of this Version

2014

Citation

J. Anim. Sci. 2014.92:3035–3041 doi:10.2527/jas2013-7339

Comments

Used by permission

Abstract

Cattle feedlot diets commonly contain ethanol coproducts that are high in S. This dietary S is reduced in the rumen by sulfate reducing bacteria, resulting in an accumulation of hydrogen sulfide (H2S), increasing the risk for S toxicity. A negative correlation between H₂S and ruminal pH has been observed previously. The objective of this study was to determine the effect of varying dietary NDF from chopped bromegrass hay (66% NDF) on performance, ruminal pH, and ruminal H2S gas concentration of steers fed a high-S finishing diet. One hundred fifty crossbred steers (359 ± 51 kg BW) were blocked by BW into pens of 5 steers and randomly assigned within block to 1 of 5 treatments (n = 6 pens per treatment) and fed for 84 d. Dietary treatments included 3.5, 5.7, 7.9, 10.1, or 11.4% roughage NDF (rNDF) from bromegrass hay and contained 0.46% dietary S from a combination of dried distillers grains with solubles and condensed corn distillers solubles. In all diets, hay was added at the expense of dry-rolled corn. Effective NDF increased linearly (P < 0.01) with increased inclusion of rNDF. Final BW was not affected by rNDF (P ≥ 0.12). The addition of roughage did not affect ADG (P ≥ 0.13) or gain efficiency (P ≥ 0.12). Dry matter intake increased linearly (P < 0.01) as rNDF concentration increased. There was a treatment × month interaction for S intake (P < 0.01), explained by steers fed 3.5 or 11.4% rNDF increasing S intake each month whereas the middle rNDF inclusions had similar S intake between months 1 and 2 and increased in month 3. Ruminal H₂S concentrations and ruminal fluid pH were measured at 6 h postfeeding on d 7, 14, 21, 29, and 84. Ruminal pH increased linearly (P < 0.01; 5.48, 5.61, 5.71, 5.74, and 5.80 ± 0.041 for 3.5, 5.7, 7.9, 10.1, and 11.4% rNDF, respectively) and ruminal H2S concentrations decreased linearly (P < 0.01; 1.00, 0.86, 0.76, 0.70, and 0.62 ± 0.037 g/m3 for 3.5, 5.7, 7.9, 10.1, and 11.4% rNDF, respectively) as rNDF inclusion increased. Using mixed model regression analysis, ruminal pH had a strong negative relationship with ruminal H₂S concentrations (β = –0.63; P < 0.01). Under conditions of this study, increasing roughage did not affect cattle gains but helped maintain greater ruminal pH and decreased H₂S concentration, suggesting that this dietary strategy may lessen the risk of S toxicity in feedlot cattle.