Grazing activity and ruminal bacterial population associated with frothy bloat in steers grazing winter wheat

Two grazing experiments were designed to elucidate the shifts in rumen bacterial populations (Exp. 1) and grazing activities (Exp. 2) in wheat forage diet between bloated and nonbloated steers. In Exp. 1, the bacterial DNA density was greatest for Ruminococcus flavefaciens, Streptococcus bovis, and Eubacterium ruminantium among tested strains when steers were fed bermudagrass hay (d 0). Steers that grazed wheat forage, however, increased the bacterial density of 6 major rumen bacterial populations in bloated steers, indicating that frothy bloat may be associated with a species-specific bacterial population. In Exp. 2, overall time, total grazing, and ruminating time did not differ between bloated and nonbloated steers. In contrast, idling time was greater for bloated (P < 0.01) than for nonbloated steers (10.9 vs. 7.9 h/d, respectively). Bloated steers did not differ in total grazing activity patterns; however, grazing activity in bloated steers decreased (P < 0.05) from 0400 to 0700 h and 1400 to 1800 h. Ruminating activity in nonbloated steers peaked from 0200 to 0500 h and 1900 to 2200 h but was lower (P < 0.05) for bloated than for nonbloated steers from 0100 to 0600 h and 0700 to 1200 h. The data suggest that rumen bacterial populations and grazing activities changed when steers experienced frothy bloat.