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Free gas bloat is excessive accumulation of free gas in the dorsal sac of the rumen.
Aetiology
Any condition causing oesophageal obstruction or interference with normal eructation can result in accumulation of free gas in the rumen.
Common causes include lesions of the oesophageal groove, physical obstruction/choke and pressure on the oesophagus and/or vagus nerve by either enlarged mediastinal and bronchial lymph nodes or a thoracic mass (thymic lymphosarcoma).
Chronic recurrent bloat is seen as a sporadic problem in weaned calves and may be related to previous bouts of bronchopneumonia that lead to enlarged bronchial lymph nodes or damage to the thoracic portion of the vagus nerve.
Neurogenic causes include tetanus and vagus indigestion. Cereal overfeed and acidosis result in rapid gas production within the rumen.
Clinical Presentation
Free gas bloat appears as distension of the left sublumbar fossa with progressive discomfort/distress.
Management
An orogastric tube is passed to relieve accumulated gas. Atrocar/canula can be inserted or a fistula created surgically if the problem recurs several times per day over the following 4–5 days.
For chronic/recurrent bloat associated with tetanus or abscessation along the oesophagus, placing a surgical fistula in the rumen allows time to treat the primary condition.