In frothy bloat, gas fails to rise to form a dorsal gas layer because:

• A. Gases are retained in the mass of ingesta due to froth
• B. Gases are absorbed into the bloodstream
• C. The rumen stops producing gas
• D. The animal stops swallowing

Answer: (A)

In frothy bloat the key idea is that gas cannot separate out of the rumen contents because it is trapped in a stable foam formed by the ingesta. The bubbles are coated by surface-active substances from the feed, creating a frothy mass that holds gas bubbles within the liquid/solid mixture. Because the gas is dispersed and stabilized in this foam, it cannot coalesce and rise to form the dorsal gas layer that you would see in simple, free-gas bloat. This explains why no visible gas cap develops and distension comes from the foam-filled rumen rather than a separate gas layer.

So the gas is retained within the mass of ingesta due to froth, which is the mechanism behind frothy bloat. The other options don’t fit because gas production continues and isn’t removed by absorption into the blood, the rumen still ferments, and the problem isn’t caused by the animal stopping swallowing; it’s the presence of stable foam that prevents gas from escaping via eructation.