Pasture bloat is a serious and unpredictable condition of grazing cattle. Despite years of research into bloat prevention, it is still a common problem in New Zealand, largely as a side effect of improved pastures and the push for high production.
Spring and autumn tend to be the most dangerous seasons when young, lush pastures are high in protein, water and starch and low in fibre. Fermentation of this feed in the rumen produces excess gas that becomes trapped in the rumen contents. This forms stable foam that cannot be belched out.
Cattle can bloat within 15 minutes of being put onto high risk feeds. Outbreaks of bloat commonly occur, however individual cattle can die of bloat with little sign of bloat in the rest of the herd.
Cattle suffering from bloat will have a distended abdomen - most obvious in the upper left-hand flank. Initially the cow is restless, stops eating and tries frequently to urinate and defaecate. As the distention becomes worse, the animal shows severe respiratory distress and may have its tongue out and head and neck extended. Cattle eventually die from heart or lung failure due to the pressure of the distended abdomen on these organs.
If you notice an animal with early signs of bloat, drench them with bloat oil or 100ml of vegetable oil if this is not available. Remove the herd from the offending pasture and feed hay or mature grass/silage. Animals in severe distress will need to be stabbed in the upper left-hand flank to relieve the pressure. If you are unsure of how to do this, speak to your vet now so that you will be prepared.
There are a number of other conditions that can cause a cow to appear bloated. If the animal does not respond to initial treatment, call a vet.
There is no one bloat control measure that will be 100% effective on its own, however the risk of bloat can be significantly reduced by a combination of management practices and bloat prevention products. An extra bonus is that most of these strategies improve production/profitability in addition to controlling bloat and include:
- Avoid gorging of high-risk pastures by hungry cows. This is more likely to happen on fast spring rounds when feed is tight. Options are to offer hay or silage; avoid high-risk paddocks as the first feed after morning milking; alternatively graze high-risk pastures with poorer quality pastures.
- Ensure the diet contains adequate fibre. Higher pre- and post-grazing residuals lower the incidence of bloat as the pasture is more mature. Adding hay or straw to the diet will provide additional fibre with the added benefit of improving rumen function and reducing the risk of sub-clinical acidosis.
- Rumen modifiers. These are oral products that alter the rumen flora make-up by increasing the population of efficient energy-producing bacteria and reducing the population of less efficient gas-producing bacteria. Rumensin is an example of a rumen modifier and is available in powder, liquid and capsule form.
- Bloat detergents. Modern bloat detergents (e.g. Bloatenz) act by breaking down the stable foam in the rumen. They can be administered via drinking water or directly drenched. Dose rate may need to vary with the level of risk.
