Effects of supplement sulfate (Dynamate) and thiamin-HCl on passage of thiamin to the duodenum and site of digestion in steers

Effects of dietary supplementation of thiamin-HCl (1 g daily) and a feed grade double sulfate of magnesium and potassium (Dynamate, added at 1.8% of diet dry matter; referred to as sulfate) on ruminal passage of thiamin and site of digestion in dairy steers (464 kg initial weight) fed a 77% concentrate diet were determined in a 4 X 4 Latin square experiment. Sulfate supplementation tended to reduce duodenal thiamin flow with (P less than .08) and without (P greater than .10) added thiamin. Supplementation with thiamin alone decreased ruminal disappearance of fed organic matter and nitrogen (P less than .03) and total tract disappearance of starch (P less than .06) and nitrogen (P less than .02), and increased ruminal microbial efficiency (P less than .04). Sulfate addition to the high thiamin diet alleviated these effects but depressed microbial efficiency (P less than .05). Sulfate included in the diet without added thiamin affected plasma thiamin positively, whereas sulfate added to the diet with supplemental thiamin changed plasma thiamin negatively (interaction, P less than .06). In conclusion, a marked depression of ruminal digestion induced by dietary thiamin-HCl supplementation disappeared upon dietary addition of sulfate and sulfate depressed the quantity of thiamin passing from the rumen. Because preventing thiamin deficiency and optimizing site of digestion in feedlot cattle are desired, these changes deserve further study.