Pasture management strategies for reducing the risk of legume bloat in cattle.

Results from two decades (1973-1993) of bloat research at Kamloops are reviewed. The trials were conducted with groups of ruminally fistulated cattle either grazing or fed daily fresh-cut alfalfa (Medicago sativa) herbage. Studies were conducted during the growing season (May to September) and in the fall (October and November). The alfalfa was usually in the vegetative to early bloom stages of growth. Visual assessments of bloat severity on a scale of 1 to 5 were made .5 to 2 h after feeding started, at which time ruminal cannulas were opened to relieve ruminal pressure. Every cultivar of alfalfa tested caused bloat, but sainfoin (Onobrychis viciifolia), birdsfoot trefoil (Lotus corniculatus), and cicer milkvetch (Astragalus cicer) did not. This confirms the bloat-safe features of these alternate legume forages. Bloat was positively associated with the level of Fraction 1 protein and total soluble protein in alfalfa, supporting the concept of a decreased probability of bloat with advancing stages of plant maturity. There was no association between alfalfa saponins and bloat. Prefeeding ruminal chlorophyll levels were higher and ruminal clearance rates were lower in cattle that were susceptible to bloat. Cattle that bloated on a given day consumed 18 to 25% less alfalfa immediately before bloat than non-bloaters did in the same time period. Ruminal cations were associated with bloat incidence but cation manipulation through supplementation did not prevent bloat. Of all the feed additives tested, only poloxalene (Bloat Guard) completely prevented bloat.(ABSTRACT TRUNCATED AT 250 WORDS)