Trocar Cows

Short answer: Bloat, or ruminal tympany, is overdistension of the rumen and reticulum with the gases of fermentation. The Merck Veterinary Manual describes two forms.

In frothy (primary) bloat, gas is trapped in a stable foam mixed with the rumen contents, often on legume pasture, and the usual treatment is an antifoaming agent given by tube. In free-gas (secondary) bloat, gas collects above the contents because something, such as an esophageal obstruction, stops the cow from belching it up. Free-gas bloat is quickly relieved by passing a stomach tube or by inserting a trocar and cannula through the left flank into the rumen. A standard trocar is often too narrow to let stable foam escape, and a life-threatening case may need an emergency rumenotomy. The gas itself is mostly carbon dioxide: a 1974 review gives 45 to 70% CO2 and 20 to 30% methane, and a 1997 study of grazing dairy cows measured about 65 to 76% CO2 and 22 to 31% methane. The methane is why the escaping gas can be lit. The footage shows a cannula in a cow's flank with the gas burning as a blue flame. Lighting it is a demonstration, not part of the treatment.