Relationship of Certain Plant Polyuronides to Incidence of Pasture Bloat in Dairy Cattle1

Acid-soluble pectic substances, polyuronides, and pentosans were measured in plants from Ladino clover-alfalfa grass pasture plots grazed at 4-wk. intervals by dairy heifers and steers. The highest incidence of bloat occurred when Ladino and alfalfa were found to be highest in acid-soluble pectic substances. Daily changes in the polyuronide content and pentosans were less marked and were not associated with bloat. In an experiment with finely ground alfalfa clippings, one-third of the uronic acid equivalent was digested within one-half hour and accounted for most of the carbon dioxide produced. In vivo studies of rumen digesta revealed rapid disappearance of polyuronides within the rumen. Other studies showed (a) that phosphorus content of Ladino clover was unrelated to bloat, (b) that 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 content of pectic substances, and (c) that feeding grain once daily changed the diurnal pattern of bloating. 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.