|dc.description.abstract||A small pen study, a metabolic trial and a field observation study were conducted to evaluate sulfur (S) and thiamine metabolism, short chain fatty acid (SCFA) absorption, and mineral status in beef cattle fed high dietary S. In the small pen study, the effect of feeding corn (CDDGS), wheat (WDDGS) or a 50:50 corn:wheat blend (BDDGS) dried distillers grains with solubles (DDGS) on serum sulfate level of feedlot steers was evaluated using 288 crossbred steers (273.9 ± 18.5kg) in a completely randomized design. The steers were backgrounded and finished. The control backgrounding diet consisted of 34.3% barley grain, 26.0% brome grass hay, 10.3% barley straw, 22.8% barley silage, and 6.7% supplement (DM). For the three treatment diets, 17% of the barley grain was replaced with DDGS. Sulfur concentrations of control, BDDGS, CDDGS and WDDGS diets in the backgrounding phase were 0.2, 0.23, 0.31 and 0.33% (DM), respectively. The control finishing diet was 86.8% barley grain, 5.8% supplement and 7.4% barley silage (DM), and the three DDGS treatments included replacement of 40% of barley grain with an equal amount of DDGS. The corresponding sulfur concentrations for control, BDDGS, CDDGS and WDDGS diets in were 0.2, 0.33, 0.51 and 0.65% (DM), respectively. Corn DDGS or WDDGS cattle exhibited higher (P < 0.01) serum sulfate levels than BDDGS or control cattle in both backgrounding and finishing phases. Mean serum sulfate concentrations in cattle fed WDDGS and CDDGS were lower (P < 0.01) in finishing phase relative to backgrounding phase despite the higher S intake (P < 0.01).
In the metabolic study, effects of dietary S concentration and forage-to-concentrate ratio (F:C) on S and thiamine metabolism, SCFA absorption, and mineral status were evaluated using 16 ruminally cannulated heifers (initial BW 628 ± 48 kg) in a randomized complete block design with a 2 × 2 factorial treatment arrangement with main effects of dietary S (LS = 0.3% vs. HS = 0.67%, DM) and F:C (Low F:C = 4% vs. High F:C = 51% barley silage, DM). There was no interaction between S concentration and the F:C. The HS cattle had reduced DMI (P < 0.001) and SCFA (acetate, propionate and butyrate) absorption (P < 0.05) but greater concentrations of ruminal hydrogen sulfide (H2S) (P < 0.01), serum sulfate (P < 0.01) and urinary sulfate (P < 0.01), as well as greater urinary sulfate excretion (P < 0.01) than LS cattle. Free thiamine, thiamine monophosphate (TMP) and thiamine pyrophosphate (TPP) concentrations in blood and rumen fluid did not vary (P > 0.05) among HS and LS cattle. Concentration of TPP was increased by 9.2% (P = 0.10) but with a concomitant numerical decrease in free thiamine in HS brains than LS brains. The HS brains had greater TMP (P = 0.01) and total thiamine (free thiamine + TMP + TPP) (P < 0.01) than LS brains. The HS cattle had reduced (P < 0.05) ruminal cobalt (Co), iron (Fe) and manganese (Mn) but similar (P > 0.05) copper (Cu), magnesium (Mg), molybdenum (Mo), selenium (Se) and zinc (Zn) relative to LS cattle. There were reduced serum Mg (P = 0.003), Fe (P = 0.036) and Mn (P = 0.100) concentrations in HS cattle than LS cattle. Brain minerals except for Se did not differ (P > 0.05) among HS and LS brains. The F:C did not affect (P > 0.05) DMI, S metabolism, blood and brain thiamine and its phosphate esters, and brain mineral status. Ruminal pH, and serum Cu and Se were reduced (P < 0.05) and SCFA absorption, ruminal thiamine and its phosphate esters and serum Mg were greater (P > 0.05) for low F:C diet. No gross or microscopic changes indicative of PEM were detected in the brains of any experimental heifers.
In field observation, brain thiamine and its phosphate esters, and mineral status were evaluated from 4 naturally occurring S-induced polioencephalomalacia (PEM) affected feedlot steers. Data from PEM brains were compared with the brains of experimental heifers fed HS diet that were considered normal brains as they had no gross or microscopic changes indicative of PEM. The PEM brains had 36.5% lower TPP (P < 0.05) despite the 4.9 fold higher free thiamine (P < 0.01), and had reduced Cu (P = 0.058), Fe (P = 0.003) and Mo (P < 0.001) concentrations in comparison with normal brains.
The results indicate that serum sulfate levels in cattle fed DDGS supplemented diets reflect dietary S intake. Sulfur metabolism in beef heifers was not influenced by F:C but high dietary S inhibits SCFA absorption. Moreover, dietary S may increase metabolic demand for TPP. Failing to supply enough TPP may lead to the development of malacic lesions in animals affected by S-induced PEM. Reduced nutritional status of minerals such as Cu, Mo, and Zn associated with excessive S intake were not observed. Sulfur-induced PEM affected cattle exhibited reduced brain Cu, Mo and Fe.||en_US