ALTERATION IN RUMINAL FERMENTATION: THE EFFECT OF MEGASPHAERA ELSDENII INOCULATION ON SUBACUTE RUMINAL ACIDOSIS (SARA) IN VITRO

SARA is a serious herd problem in intensive dairy and beef operations because of triggering other metabolic disorders and causing lactation-fertility losses. SARA was induced in vitro to evaluate the effectiveness of Megasphaera elsdenii inoculation. Rumen fluid was collected from 2 ruminally cannulated Holstein heifers. Medium was prepared by mixing macromineral (200 ml), micromineral (0.1 ml), buffer (200 ml), reduction (40 ml) and resazurin (1 ml) solutions as well as distilled water (400 ml). The media were then added with 1) a test diet consisting (g/kg) of 550-soluble starch, 260- glucose, 60-cellulose, 70-cellobiose and 60-tripticase, 2) ground wheat and 3) ground corn, at levels of 10, 15, 20, 25, 30, 40, 50, 70 and 100 g/l. After determining their levels causing SARA as reflected by pH (~5.3) in preliminary experimentation, the substrates (test diet, 40 g/l; wheat, 30 g/l; corn, 50 g/l) were incubated with presence of 0, 105 , 107 , and 109 cfu M. elsdenii per ml at 39°C for 24 h. Rumen parameters were analyzed by 2-way ANOVA. There was substrate, but not inoculum level and substrate by inoculum interaction effects on measurements. The data confirm that increasing level of starch-rich feedstuffs leads to acidosis as reflected by decreased pH and the Ac:Pr ratio and increased lactate concentration. However, addition of M. elsdenii into media, one of the predominant lactate-utilizing bacteria failed to reverse SARA in vitro.