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Physiological Studies of the Rumen with Emphasis on the Animal Factors Associated with Bloat¹

Department of Animal Husbandry, University of California, Davis

ABSTRACT

Several physiological processes were compared between animals with known bloat susceptibility fed a ration of fresh alfalfa tops.

Only stable IVI (ingesta volume increase) and salivary secretion and composition differed significantly between susceptible and nonsusceptible cows.

A second, more extensive study showed that the susceptible cows secreted significantly less saliva during rest and during feeding, with a significantly higher concentration of bicarbonate than the nonsusceptible animals. Whole ingesta from susceptible cows normally was higher in dry matter content and less dense (due to foaminess) than ingesta from nonsusceptible cows. No differences were found in salivary potassium, phosphate, sodium, and mucin; frequency and amplitude of rumen contractions; rate of gas production; total-, soluble-, and ammonia-nitrogen of rumen liquor; buffering capacity of ingesta and saliva; rumen pH and water consumption.

When fed chopped alfalfa hay, a nonsusceptible cow appeared to secrete significantly more saliva during rest, with a significantly lower concentration of potassium than the susceptible cows. Salivary bicarbonate, phosphate, sodium, mucin, and water consumption did not differ significantly. Whole ingesta dry matter content was normally greatest in the susceptible cows.

The physical nature of the ingesta is the most important characteristic distinguishing bloating from nonbloating animals. Saliva added to the rumen during periods of rest may exert an influence on this characteristic, we suggest, by preventing stable foam formation through reduced ingesta surface tension, and by reducing the concentration of agents responsible for foam stabilization through more complete fermentation.

¹ In cooperation with the Animal Disease and Parasite Research Division, Agricultural Research Service, USDA.

² Present address: Department of Animal Science, University of Alberta, Edmonton, Alberta, Canada.