The compressive strength and persistence of protein foams produced from extracts of legume leaves were measured. The presence of foliar proanthocyanidin (PA, condensed tannin) in species such as Onobrychis and Lotus correlated with foams of negligible compressive strength and persistence and also with a reputation for bloat safety in the field. PA purified from forage legume leaves significantly decreased the compressive strength of protein foams produced from purified red clover leaf protein. The decrease in the compressive strength was related to the concentration of added PA in a dose-dependent manner. A ratio of PA to protein of 0 . 1 reduced the compressive strength by approximately half relative to the strength of the PA-free control. Purified PAS with different chemical structures had similar effects on the compressive strength of protein foams. The significance of these observations to pasture bloat and forage legume improvement is discussed.

Results are reported from three experiments conducted at the Dairy Research Institute, Ellinbank, Australia during 1992/93 which examined the composition and kinetics of the gas in the rumen headspace of lactating dairy cows grazing white clover/perennial ryegrass pastures. Before grazing, rumen headspace gas was composed of carbon dioxide 65%, methane 31% and nitrogen 4% whereas, after one hour of active grazing, the headspace gas was composed of carbon dioxide 76%, methane 22% and nitrogen 2%. The composition of headspace gas was not affected by antibloat capsules (which release 250 mg/day of monensin). The headspace gas from bloated cows contained slightly less (P<0·01) carbon dioxide and slightly more nitrogen than that from non-bloated cows.A novel technique which employs ethane as a tracer to measure rumen headspace volume and the kinetics of the rumen headspace gases is described. The tracer technique was used in two experiments in which the influence of grazing, antibloat capsules and bloat on the rumen headspace volume and the kinetics of the headspace gases were examined. It is concluded that our ethane tracer technique provides a simple and inexpensive way to estimate methane production by grazing ruminants.

A general purpose controlled release (CR) intra-ruminal device (CRD) containing chromium sesquioxide (CrrO.) was used to measure mean daily fecal dry matter excretion (FE) For personal use only.

ABSTRACf Four quantities which assist in characterising persistent strong foams produced from proteins, plant extracts, or rumcn liquor are described. Two are derived from foam drainage data by applying the second order relation dv = k2 (voo-v)2. They are drainage constant, k 2 , and foam dt retention volume, Vo-Voo. The remaining two quantities are physic .. l properties determined by the effect of the foam on a sensing disc connected to a strain gauge. They are compressive strength and stress relaxation. The reproducibility and variation of these quantities within a range of experimental conditions are given, and their possible interdependence and relationship to foam persistence are considered.

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