Relationship of Certain Plant Polyuronides to Incidence of Pasture Bloat in Dairy Cattle

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Abstract
The highest incidence of bloat occurred in 8 dairy heifers and steers grazing Ladino clover-alfalfa-grass pasture plots during 3 seasons when the legumes were highest in acid-soluble pectic substances. Daily changes in the plant content of uronic acids, pentosans, and phosphorus, were less marked and were not associated with bloat. The polyuronides in finely ground alfalfa clippings were digested rapidly by rumen organisms in vitro, yielding significant quantities of carbon dioxide. In vivo studies of rumen digesta revealed rapid disappearance of polyuronides within the rumen. Water-to-plant dry matter ratios required to form a stable mass in vitro were relatively constant within species for alfalfa and Ladino clover and were unrelated to pectic substances. Feeding grain once daily changed the diurnal pattern of bloating as less attacks occurred during the next few hours. It was concluded that the polyuronides, precursors of rapid gas production in the rumen and including the acid-soluble pectins, are plant compounds contributing to pasture bloat.