There are three types of bloat;
- Frothy bloat affects cattle (and occasionally sheep) grazing succulent, lush feed. It is the only bloat of any consequence to graziers, and is discussed in detail below.
- Feedlot bloat affects feedlot cattle that are fed very finely ground rations. The problem requires a detailed appraisal of the feedlot ration. Professional advice from an experienced feedlot vet is recommended.
- Secondary bloat occurs when there is damage to the rumen or oesophagus, which prevents the belching mechanism from working properly. This form of bloat occurs sporadically, one animal at a time, and is uncommon. The appropriate treatment and prospects for recovery depend on the cause and severity of the initial injury.
What is Frothy Bloat?
Frothy bloat is a common problem with cattle grazing lucerne or succulent clover-dominant pastures, especially if white or red clover is the dominant species. Bloat can also occur in cattle on a green cereal crop or lush grass-dominant pasture, but is much less common.
With frothy bloat, gas produced during fermentation in the rumen is not belched up as normal, but instead remains in the rumen as small bubbles suspended in foam. Cattle cannot belch up foam. Pressure builds up in the rumen as the foam accumulates.
The most obvious sign of bloat is a tight, distended abdomen, especially on the left flank. Affected cattle stop eating, separate from the rest of the mob and become restless. They often get up and down, look at their flanks and kick their bellies. Severely affected cattle have difficulty breathing, and stand panting with their tongues hanging out.
Death can occur within 30 minutes of the first signs of bloat. Death is a result of pressure from the rumen pushing forward and up, compressing the lungs (which makes breathing difficult) and the major blood vessels (which restricts blood flow around the body). Many cattle with bloat are simply found dead in the paddock.
A diagnosis of bloat is based on the signs shown by affected cattle, and the history of grazing a high risk pasture. When cattle are found dead in the paddock, a post-mortem examination is necessary to rule out other diseases such as blackleg.
After death from frothy bloat, the foam in the rumen breaks down, and after 6-12 hours the rumen contents may look normal. After death from other causes, fermentation continues in the rumen and the carcass can distend and “bloat” with gas.
In severe cases, where a bloated animal is panting to breathe, treatment is a matter of great urgency. A half hour’s delay is likely to be fatal. Use a sharp knife with a guarded blade. Stab through the upper left flank into distended rumen, then twist the knife. This produces an explosive release of rumen contents and immediate relief for the cow. Try to keep hold of the rumen wall, to prevent it from changing position relative to the cow’s side, and the abdomen filling with rumen contents. If the abdomen is not too contaminated with rumen contents, the cut is sewn up, and antibiotics are given to help fight infection, there is a good chance the animal will survive.
With less severe cases, the best treatment is vegetable oil, given as a drench or injected directly into the rumen. The oil helps to disperse the foam. Tiny droplets of gas within the foam coalesce into larger bubbles, which are belched out. The type of oil is not critical - peanut oil, cotton seed oil, paraffin oil and linseed oil are all suitable. Cream can be used in an emergency. 250millilitres of oil per cow is recommended.
Death from bloat can occur so quickly that the emphasis must be on prevention rather than treatment. For beef herds, there is a number of bloat control options.
- Bloat blocks - these contain a chemical which limits foam production in the rumen. Blocks are relatively cheap and easy, but only moderately effective. Many cows do not lick blocks, and so are not protected. To improve block consumption, cattle can be taught to lick molasses blocks at or soon after weaning. Bloat blocks need to go out 2 weeks before the start of the bloat season, so the cattle get accustomed to licking the blocks.
- Bloat licks - roller drum licks are effective against bloat, but like blocks, cattle must be trained to lick them. The drums should be located in the shade, near watering points. When training cattle to use a lick, use molasses and water alone (3:5 mix), then add an anti-foaming agent at the start of the bloat season. There are a number of anti-foaming agents commercially available. For a 200 litre (44 gallon) roller drum, a suitable recipe is: molasses 72 litres, water 115 litres, anti-foaming agent 5 litres. One 200 litre drum should last 35 cattle for 1 week.
- Medicated capsules - these are inserted into the rumen, where they slowly release the drug Rumensin over a period of 3 months. This reduces foam production in the rumen, and hence the risk of bloat, but does not prevent all cases. Bloat may still occur in some animals grazing high risk pastures. The capsules are relatively expensive, but work well and give good peace of mind.
- Medicated water supply - this system can only be used where cattle have no access to creeks or dams. Even then there is a problem; when the risk of bloat is greatest, cattle get most of their water requirements from the pasture. The anti-foaming agent can be added to the reservoir tank, or added with an automatic dispensing device attached to the trough. The anti-foaming agent should be added to the water 2 weeks before the bloat season, to give the cattle time to get accustomed to the taste.
- Pasture spraying - pasture spraying with paraffin, tallow or peanut oil is an effective method of preventing bloat, but only practical for small intensive operations. The pasture needs to be sprayed daily.