BLOAT INVESTIGATIONS. THE pH OF RUMEN CONTENTS AND ITS ROLE IN LEGUME BLOAT

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Abstract
Severe bloat occurred only when the pH of the rumen contents (rumen pH) of four fistulated cows was in the range 5.2 to 6.0. The bloat-producing legumes, alfalfa (Medicago sativa) and Ladino clover (Trifolium repens ’Ladino’), produced lower rumen pH than orchardgrass (Dactylis glomerata) which does not produce bloat. When rumen pH was depressed to the range obtained with the legumes by adding grain to the orchardgrass ration, there was no bloat.Although the change in rumen pH was the same in both years of the experiment, the pH was lower in the first year. The bloat frequency in a milking herd on similar feed was also greater in the first year. In both years, clover produced lower pH and more bloat than alfalfa.The duration of bloat symptoms tended to increase with severity, but there was no relationship between either the length of the feeding period or the rumen pH and severity. Cattle might recover while the pH was still in the optimum bloat-producing range because the supply of foaming agent had been depleted.It was concluded that four important conditions were necessary to produce bloat: vigorous gas production, to produce the foam gas phase and rumen pressure, adequate 18S protein to produce and maintain the foam, sufficient acid to lower the rumen pH below 6, and cations to bind the protein molecules in the surface film.

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