During normal digestion, healthy cows will produce large volumes of gas in their stomachs. This gas rises above the liquid stomach contents and then escapes when the cow burps (technically termed “eructation”). Bloat occurs when this gas cannot be released and instead accumulates, causing distension of the first sections of the cow’s stomach – the rumen and reticulum. Left untreated or in extreme cases this can prove fatal. However, bloat in a cow is a sign of an underlying abnormality rather than a diagnosis in itself.
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What causes bloat?
There are two main types of bloat, referred to as free gas bloat and frothy bloat.
Free gas bloat
Gas collects above the liquid stomach contents as normal, but then cannot be released; either due to a physical obstruction to the route between stomach and mouth, or due to a problem with eructation (the cow’s ability to burp).
Physical obstruction is most commonly due to food matter that has become stuck in the oesophagus (tube that connects mouth to stomach). Cows fed root vegetables such as potatoes are particularly at risk of this. A milder form of bloat can also be seen in conditions such as pneumonia in young calves where the glands (lymph nodes) inside the chest are thought to be enlarged and due to their positioning alongside the oesophagus, restrict passage of gas out of the stomach.
Disorders of eructation (burping) can also cause free gas bloat. This may be associated with any condition affecting muscle function in cattle; for example milk fever (low calcium levels) which can be easily treated, or conditions such as tetanus which can be much more difficult to manage.
Frothy bloat
This is more complex, and occurs when a stable foam layer forms on top of the normal liquid rumen contents. This traps the small gas bubbles that are produced during normal digestion and prevents them from joining together to form larger gas caps which can be released by burping.
The foam forms due to nutritional imbalance, typically when cows have had access to large amounts of rich, rapidly growing spring grasses such as clover and alfalfa, or young green cereal crops, rape, kale, turnips, and legume vegetable crops. As such, frothy bloat is often seen seasonally in Spring and Autumn. Although it can also occur when cattle have access to high volumes of concentrate feeds; usually due to a feeding error when cattle are housed or an unauthorised late-night raid of the feed stores!
Diagnosis
Cows with bloat will become visible distended at the left side behind the ribs; and will often stop eating and have breathing difficulty. Understanding this recent management history will aid in diagnosis; e.g. a recent move onto rich grazing may suggest frothy bloat whereas recent root veg feeding may indicate free gas bloat is more likely. A vet or farmer may pass a tube via the mouth into the stomach both as part of the diagnosis and to provide treatment.
Treatment
As a vet, frothy bloat cases can be a challenge to deal with simply due to the large numbers of cattle potentially involved in an outbreak. Whereas free bloat cases tend to be seen more commonly in individual animals.
Free gas bloat
There are several options. It may involve passing a stomach tube to dislodge the physical obstruction (e.g. a potato) or simply the treatment of the underlying disease, for example pneumonia, low calcium (milk fever) or tetanus. If the buildup of gas is severe and longer-term management is required (for example in the case of tetanus which may take weeks to resolve completely) a trochar device can be fitted. This rigid tube holds the stomach and flank together and allows gas to escape through the hollow centre of the tube. Once the underlying condition has been resolved, the trochar can be removed.
Frothy bloat
This is usually by passing a stomach tube to relieve any available gas (often only a small amount). And to deliver anti foaming agents such as oils combined with surfactants to disperse the foam. This process may need to be repeated until the causative food has passed through the digestive system. Dietary management must be altered to prevent recurrence of the bloat. In rare cases the foodstuff may be removed from the stomach surgically. But this would only be undertaken in severely affected, high value animals.
Prevention
As is often the case with animal health, prevention is better than cure. In the case of free gas bloat, this would be by maintaining good general herd health and making early detection and treatment of bloat cases.
With frothy bloat, farmers may be able to avoid using high risk pastures at high-risk times of year. If this cannot be done, allowing livestock limited area access for very short periods each day, whilst also buffer feeding with high fibre diets may reduce the risk of bloat. In some countries, milking cows will be dosed at each milking (twice daily) with an antifoaming agent when high risk pasture is being grazed. It may also be possible to spray the grass itself with antifoaming agents, providing that grazing access can be restricted.NADIS, the National Animal Disease Information Service, provide more information on bloat in cattle here and further detail on prevention can be found here
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