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

Agriculture Canada Research Station, Lethbridge, Alberta T1J 4B1

R. E. Howarth

Agriculture Canada Research Station, Saskatoon, Saskatchewan S7N 0X2

J. W. Costerton

Department of Biology, University of Calgary, Calgary, Alberta T2N 1N4

ABSTRACT

Leaves of three bloat-safe legumes — birdsfoot trefoil (Lotus corniculatus L.), sainfoin (Onobrychis viciaefolia Scop.), and cicer milkvetch (Astralagus cicer L.) — and of three bloat-causing legumes — alfalfa (Medicago sativa L.), red clover (Trifolium pratense L.), and white clover (Trifolium repens L.) — were incubated with strained rumen fluid or with mixed rumen fluid and solids. Gas released was measured during the early period (0 to 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 the bloat-causing legumes than with whole leaves from the bloat-safe legumes. However, 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. The 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 the bloat-causing potential of legumes in breeding selections if variability of the method can be reduced.

¹ Fellow of the Consejo Nacional de Investigaciones Cientificas y Téenicas de la República Argentina on transfer of work.