LAUSR

This presentation will discuss mineral requirements of ruminal microorganisms, and the effect of trace mineral source on ruminal fermentation. Sulfur and phosphorus are required in relatively large amounts by ruminal microorganisms, and dietary deficiencies of these minerals have been related to impaired ruminal fermentation. A number of trace minerals are required in low concentrations by ruminal microorganisms. With the except of cobalt (Co) minimal trace mineral requirements of the host ruminant appear to be considerably greater than that needed for rumen microbial requirements. It is well known that certain bacteria can synthesize vitamin B12 from inorganic Co. Some bacteria require vitamin B12 as a growth factor, and adequate dietary Co is needed to allow sufficient ruminal B12 synthesis to meet their requirement. Vitamin B12 is needed as a cofactor for ruminal microorganisms to convert succinate to propionate. Dietary Co deficiency results in decreased ruminal propionate in ruminants fed high concentrate diets, and decreased fiber digestion in ruminants fed high fiber diets. Attempts have been made to use high concentrations of certain trace minerals to favorably manipulate ruminal fermentation. For example, attempts have been made to increase rumen protein bypass by feeding high dietary zinc (Zn). However, studies have indicated that high concentrations of copper (Cu), Zn, and iron reduce cellulose digestion in vitro. Recent studies have indicated lower fiber digestibility in cattle supplemented with sulfate sources of Cu, Zn, and manganese compared with those fed similar concentrations from hydroxy or certain organic sources. Additional research is needed to elucidate the mechanism(s) whereby trace mineral sources affect fiber digestibility differently.