PSXVI-23 - The influence of trace mineral source on digestion, ruminal fermentation characteristics, and mineral solubility in beef cattle fed a high concentrate feedlot diet.

Twelve Angus steers (BW 530.9 ± 22.7kg) fitted with ruminal cannulae were used to determine the impact of trace mineral (TM) source on digestibility and ruminal VFA and soluble concentrations of Cu, Mn, and Zn. Steers were fed a high concentrate diet balanced to meet the requirement of finishing feedlot steers for 21d. Treatments consisted Cu, Mn, and Zn supplemented at 18, 40, and 90 mg/kg DM, respectively, from either sulfate (STM) or hydroxy trace mineral (HTM) sources (n = 6 steers/treatment; experimental unit = steer). Following a 21-d adaptation period total fecal output was collected for 5 d. Trace mineral sources had no impact on nutrient digestibility. On d 6, rumen fluid was collected at 0, 2, and 4 h post-feeding for VFA analysis. There were no treatment x time interactions for any VFA measured. However, HTM steers had greater (P < 0.05) ruminal molar proportions of propionate and tended (P < 0.07) to have greater molar proportions of valerate compared to STM steers. Steers fed STM had greater (P < 0.05) molar proportions of butyrate compared to HTM steers. Steers were then fed the same high concentrate diet without supplemental Cu, Zn, or Mn for 14 d. On d 15 steers received a pulse dose (via rumen cannula) from either STM or HTM. Ruminal samples were obtained at 2 h intervals starting at -4 and ending at 24 h relative to dosing. There was a treatment x time interaction (P < 0.05) for ruminal soluble Cu concentrations. Ruminal soluble mineral concentrations were greater (P < 0.05) for Cu at 4, 6, 8, and 16 h post-dosing in STM compared to HTM supplemented steers. Results indicate that ruminal solubility of Cu differs between STM and HTM sources and may impact rumen fermentation characteristics.