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Rumen Conditions That Predispose Cattle to Pasture Bloat

Agriculture Canada Research Station, 3015 Ord Road, Kamloops, British Columbia V2B 8A9

R. E. Howarth

Agriculture Canada Research Station, 107 Science Crescent, Saskatoon, Saskatchewan S7N 0X2

K.-J. Cheng

Agriculture Canada Research Station, Lethbridge, Alberta T1J 4B1

J. W. Hall

Agriculture Canada Research Station, 6660 N.W. Marine Drive, Vancouver, British Columbia V6T 1X2

ABSTRACT

Rumen contents from the dorsal sac were examined before alfalfa ingestion to determine factors that predispose cattle to pasture bloat. Chlorophyll concentration, buoyancy of particulate matter, and rates of gas production were significantly higher in cattle that subsequently bloated than in those that did not. Higher chlorophyll in bloat cases indicated accumulation of suspended chloroplast particles in the dorsal sac, perhaps due to increased buoyancy of the particulate matter. The higher fermentation rates (in the presence of glucose) suggested that the latent capacity for gas production was due to microbial colonization of suspended feed particles. Chlorophyll 4 h after feeding was also higher in bloated as compared to unbloated animals. In short, the microbial colonization and retention of particulate matter provided active inocula for promoting rapid legume digestion. Consequently, gas production was enhanced when feeding commenced, but the fermentation gases were trapped by the buoyant, frothy ingesta, resulting in the condition of pasture bloat.