In Vitro Digestion of Bloat-Safe and Bloat-Causing Legumes by Rumen Microorganisms: Gas and Foam Production

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Abstract
Leaves of 3 bloat-safe legumes, birdsfoot trefoil (Lotus corniculatus L.), sainfoin (Onobrychis viciaefolia Scop.), cicer milkvetch (Astralagus cicer L.), and of 3 bloat-causing legumes, alfalfa (Medicago sativa L.), red clover (Trifolium pratense L.) and white clover (T. repens L.), were incubated with strained rumen fluid or with mixed rumen fluid and solids. Gas released was measured during the early period (0-22 h) of this in vitro digestion. Gas volume was greater with a 1:1 (wt/vol) mixture of solid and fluid rumen contents than with rumen fluid alone. It was greater with whole and chewed leaves from bloat-causing legumes than with whole leaves from bloat-safe legumes. When leaves were homogenized, volumes of gas from bloat-causing and bloat-safe legumes were similar. More gas was released from homogenized leaves than from the same weight of whole leaves. Amount of foam produced on chewed herbage and homogenized leaves of bloat-causing legumes was greater than on those of bloat-safe legumes. These results are consistent with the rate of disintegration and digestion of legumes by rumen bacteria being an important determinant in pasture bloat. Measurement of gas produced early in in vitro digestion may provide a useful bioassay for evaluating bloat-causing potential of legumes in breeding selections if variability of the method can be reduced.

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