EFFECTS OF COBALT ON IN-VITRO FIBER DIGESTION OF FORAGES AND BY-PRODUCTS CONTAINING FIBER

Cobalt glucoheptonate as a source of Co to enhance ruminal fiber diges tion was evaluated in two in vitro digestibility experiments. In Exper iment 1, Co supplementation (0, 5, and 10 ppm) of five substrates (lea f and stem fractions of alfalfa and orchardgrass hays and ground corn) was evaluated under two dietary conditions (ruminal fluid taken from steers fed alfalfa hay or a high concentrate diet) for 24 or 48 h of f ermentation in a 3 x 5 x 2 x 2 factorial arrangement. In Experiment 2, four concentrations of Co (0, 10, 20, and 30 ppm) were added to five substrates (alfalfa hay, orchardgrass hay, corn cobs, recycled newspri nt treated with HCl, and cellulose casings) and were incubated with ru minal fluid from steers fed alfalfa hay for 24 or 48 h of fermentation in a 4 x 5 x 2 factorial arrangement. No interactions among treatment s were observed for digestibilities of DM, OM, or NDF in both experime nts or for VFA concentrations in Experiment 1. Supplementation with Co did not increase digestibilities of DM, OM, or NDF in either experime nt or concentrations of VFA in Experiment 1. In Experiment 1, in vitro digestibilities of DM, OM, and NDF were higher for inoculum from stee rs fed alfalfa versus concentrate. In Experiment 2, digestibilities of DM, OM, and NDF were highest for alfalfa hay and lowest for recycled newsprint treated with HCl. Cobalt concentrations that were above mini mum requirements did not improve digestion of DM, OM, or fiber.