Although we see a reduction in pH in March in the experimental group it is still above the critical pH of the rumen is 6 (Hutjens, 1998). The increased concentrations of VFA have probably resulted in changes in the milk composition. In this way, increases in ruminal butyrate and propionate concentrations could lead to an increased milk yield with butyrate acting as a source of energy and a lipid precursor, while sparing propionate from oxidation leaving it more available to conversion to glucose for lactose synthesis (Van Soest, 1982).