This invention relates to a novel strain of Megasphaera elsdenii and its uses. This invention further relates to preparations and methods incorporating such strain. This invention also relates to feedstuffs for ruminants and a preparation and method for the prevention and treatment of lactic acidosis in ruminants. This invention even further relates to a method of isolating a biologically pure culture of a superior ruminal microorganism in a relatively shorter time period than conventional methods. This invention yet further relates to a method of achieving any one or more of the following improvements in ruminants namely increased milk production; improved feedlot performance; improved growth rate; decrease in finishing time; lower digestive morbidity and mortality; lower incidence of lactic acidosis and related diseases; improved feed conversion efficiency; decrease in roughage content in feeds; and capability to feed on relatively higher concentrate diets.