The effect of trace mineral source and fiber source on total-tract nutrient digestion

Abstract Text: Excess rumen soluble Cu and Zn can reduce fiber digestion and alter rumen microbial populations. Substitution of forage with non-forage fiber sources (NFFS) can be economically beneficial, but the reduction in particle size can decrease rumen pH, increase fiber passage rates, and decrease fiber digestion. Eighteen multiparous cows were used in a split-plot replicated Latin square with two 28 d periods to evaluate the effects of Cu, Zn, and Mn source (sulfates or hydroxy; Micronutrients Inc., Indianapolis, IN) and dietary neutral detergent fiber (NDF) source (forage diet = 26% NDF vs NFFS = 36%) on total-tract nutrient digestibility. We hypothesized that hydroxy trace minerals, which are soluble at a lower pH compared to sulfates, would increase digestibility regardless of fiber source. During the entire experiment (56 d) cows remained on the same fiber treatment but source of supplemental trace mineral was different for each 28 d period so all cows were exposed to both mineral treatments. During each of the two 28 d periods cows were fed no supplemental Cu, Zn, or Mn for 16 d followed by 12 d of feeding supplemental Cu, Zn, and Mn from either sulfates or hydroxy sources. Basal Cu, Zn, and Mn concentrations for the forage diet were 9, 30, and 38mg/kg, respectively; while basal concentrations were 11, 50, and 47mg/kg, respectively for the NFFS diet. Supplemental concentrations of Cu, Zn, and Mn fed were approximately 9, 30, and 30mg/kg, respectively. No mineral source x fiber interactions were observed for production measures or digestibility. Treatment had no effect (P≥0.38) on DMI (24.2kg) or milk production (34.9kg). Mineral source had no effect on macronutrient intakes (P≥0.63), but feeding hydroxy Cu, Zn, and Mn increased NDF digestibility (48.5 vs 46.4%). Cows fed NFFS had decreased DM digestibility (65.9 vs 70.2%), OM digestibility (67.4 vs 71.7%), CP digestibility (58.8 vs 62.1%) and starch intake (4.3 vs 8.8kg), and increased starch digestibility (97.5 vs 96.3%), NDF intake (8.6 vs 6.0kg) and NDF digestibility (50.5 vs 44.4%) compared with cows fed forage treatment. Digestible organic matter (DOM) was reduced (62.0 vs 66.8%) for cows fed NFFS compared to those fed forage, indicating reduced concentration of digestible energy. Mineral source did not affect DOM (P=0.32). Replacing dietary forage with NFFS reduced dietary energy and although hyroxy minerals increased NDF digestibility the effect was not great enough to influence DOM.

Keywords: fiber, total-tract nutrient digestion, trace minerals