Trace Mineral Source Impacts Volatile Fatty Acid Profile and Rumen Trace Mineral Solubility in Feedlot Steers

Two experiments were conducted to evaluate the effects of trace mineral (TM) source on: (1) nutrient digestibility and rumen fermentation characteristics, (2) rumen TM solubility, and (3) TM binding strength on ruminal digesta. In experiment 1, twelve cannulated Angus steers were adapted to a high-concentrate diet, blocked by body weight, and randomly assigned to dietary treatments consisting of 18, 40, or 90 mg of supplemental Cu, Mn, and Zn/kg DM, respectively, from either sulfate (STM) or hydroxy (HTM) sources. Following diet adaptation, total fecal and rumen fluid were collected over a 5 d period. Nutrient digestibility was not affected (p > 0.15) by TM source. Steers supplemented with HTM had greater (p < 0.05) ruminal molar proportions of propionate and lower (p < 0.05) molar proportions of butyrate compared to STM-supplemented steers. In experiment 2, steers received a single pulse dose of their respective TM treatments via the cannula. Ruminal samples were obtained at 2 h intervals from -4 to 24 h post-dosing. Ruminal-soluble Cu concentrations were greater (p < 0.05) for STM-dosed steers. Steers receiving HTM had greater (p < 0.01) Cu and Zn and lower (p < 0.01) Mn released from digesta compared to those receiving STM.