GRAZING MANAGEMENT AND PASTURE COMPOSITION ON PAIRED FARMS WHICH DIFFERED IN THE INCIDENCE OF BLOAT

Farm practices, pasture species, and pre- and post-grazing herbage mas ses were monitored monthly from June 1990 to April 1991 and from Augus t to November in 1991 and 1992 on 16 pairs of dairy farms. Each pair i ncluded one farm with a history of bloat despite routine use of preven tatives (bloat-prone) and one farm which historically rarely observed bloat in the absence of chemical use (bloat-free). Farms within a pair were on similar soil types and herds had similar genetic backgrounds. The incidence of bloat during spring was low in all years. Bloat-free farms averaged less ryegrass (58 versus 66%) and more grasses other t han ryegrass (25 versus 17%) in pasture and higher pre- and post-grazi ng herbage masses than bloat-prone farms in 1990 and 1991. Bloat-free and bloat-prone farms did not differ in white clover content, soil fer tility, milksolids production, or stocking rate. The differences in pa sture species and herbage mass suggested that differences in managemen t between bloat-free and bloat-prone farms may be associated with inci dence of bloat under mild bloat conditions, but their role in influenc ing the occurrence of severe bloat could not be assessed.