PSI-24 - Trace mineral source, diet type, and Rumensin influences ruminal fermentation characteristics

Abstract: Sixteen Angus crossbred steers (531 ± 22.7 kg), fitted with rumen canulae, were used to determine the impact of trace mineral (TM) source, diet type, and Rumensin (R) or Rumensin + Tyolsin (RT) supplementation on rumen fermentation characteristics. Experiment 1: Steers were individually housed and fed a high concentrate finishing diet for 21 d. Steers were then blocked (n=4 steers/block) based on mean dry matter intake (DMI) over the acclamation period. Steer blocks were then randomly assigned to 4 dietary treatments for 28 d. A 2 x 2 factorial arrangement of treatments was used. Factors included: 1) TM source (Sulfate or Hydroxy Cu, Mn, and Zn TM supplemented at 18, 40, and 90, mg/kg DM, respectively) and 2) with or without RT (supplemented at 36.3 and 11 g/metric ton DM, respectively). Following the 28 d feeding period, rumen samples were collected at 0, 2, and 4 h post-feeding. Experiment 2: All steers were then transitioned to a lactating dairy diet for 21 d. Steers were then blocked and assigned to treatments for 28 d. Treatments included: 1) TM source (Sulfate or Hydroxy Cu, Mn, and Zn TM supplemented at 10, 50, and 60, mg/kg DM, respectively) and 2) with or without R (0.0 or 24.2 g of Rumensin/metric ton DM). Following the 28 d feeding period, rumen samples were collected as described previously. Rumen fluid samples from both experiments were analyzed for short chain fatty acids (SCFA), pH, and ammonia concentrations. Within an experiment, data over the three time periods (0, 2, and 4 h) were averaged for each parameter measured prior to statistical analysis. Experiment 1: Molar proportions of acetate were lesser (P < 0.04) and propionate greater (P < 0.01) in steers receiving Hydroxy TM compared to steers receiving Sulfate TM. All other rumen fermentation characteristics measured in this experiment were similar across TM source. Rumen molar concentrations of acetic acid were lower in steers receiving RT compared to steers not receiving RT. Steers receiving RT and Hydroxy TM tended (P < 0.10) to have lower rumen ammonia concentrations compared to steers receiving RT and Sulfate TM. Experiment 2: There were no TM source impacts on the rumen fermentation characteristics measured. Supplementation of R reduced molar concentrations (P < 0.02) and proportions (P < 0.01) of acetate and increased molar concentrations and proportions of propionate (P < 0.01, P < 0.01, respectively) and butyrate (P < 0.02, P< 0.04, respectively). These data indicate that TM source, R, and RT may modulate rumen fermentation characteristics but their impacts on rumen fermentation may be diet dependent.