Effect of Cobalt Chloride on Fermentation of Alfalfa and Smooth Bromegrass Hays by Horse Cecal Microorganisms

Abstract

Effects of Co on fiber digestibility in horses are largely unknown. Our objective was to evaluate effects of Co chloride on in vitro gas production, VFA production, and dry matter (DM) disappearance (IVDMD) using cecal fluid from 4 cannulated Quarter Horses. Five grams DM of alfalfa or smooth bromegrass hay were provided as substrate with Co added at 0.0, 0.5, 5.0, 25.0, or 50.0 mg/kg substrate DM. Ten milliliters cecal fluid and 140 mL McDougall's buffer were incubated in duplicate, and pH, VFA concentrations, and IVDMD were measured after 48 hours. Gas production, used as an indicator of fermentative activity, was recorded every 15 minutes. Terminal pH was not affected by Co or forage type (P > .19). There was greater IVDMD in cultures containing alfalfa (29.2%) compared with smooth bromegrass hay (19.4%; P < .01). There was a forage × Co interaction (P < .05) in which gas production was greater in cultures containing alfalfa, and 5 mg Co/kg substrate DM led to greater gas production than 50 mg Co/kg substrate DM in cultures containing brome (P < .05). Gas production was affected by forage, Co, and time (P < .01). Production of individual and total VFA, as well as acetate:propionate (A:P) ratio were increased in cultures containing alfalfa (P < .05); however, there were no effects of Co on VFA concentrations (P > .05). While gas production was influenced by Co in cultures containing brome, no effects of Co were observed for pH, VFA, or IVDMD.

Keywords: Cecal microbiota; Cobalt; Equine; In vitro digestibility.