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Details: Created on Tuesday, 04 August 2009 13:56; Last Updated on Thursday, 29 November 2012 11:52; Hits: 3930

In the normal cow’s rumen, the gases that are produced by microbes breaking down the feed are belched up. Under certain conditions these gases form a stable foam, that cannot be belched, but rather traps the gas, quickly building up pressure in the rumen. This pressure is transferred to the blood supply and the lungs, and the cow can die.

The first thing you will see in a bloating cow is an enlarged abdomen, especially in the upper left flank. As the cow becomes uncomfortable she may stand with her head up hill, get up and lie down frequently, kick at her belly or roll over. In severe distress she will have difficulty breathing, arch her back and extend her head, drool green saliva and stick out her tongue.

If the cow is in non-life-threatening distress, first check that there are no other cows in the paddock in a similar or worse condition. Then walk her back to the shed for drenching – use a bloat remedy if you have one (preventatives can also be used as treatment), otherwise a cup of paraffin or vegetable oil. It may be possible to mix the drench through the rumen contents by gently kneading the left abdominal wall. Be careful to put the drench down her throat – she may be reluctant to swallow and it can easily go in to the lungs. Go back, and shift the rest of the herd to a new paddock.

If the cow is down and the condition is life threatening, stab through the skin and in to the rumen of the cow. Stab a handspan behind the last rib, and a handspan below the backbone on the left side. The hole must be just big enough to let the pressure out. Keep the cow on her feet, treat her with antibiotics, and call the vet to assess the wound.

Bloat prevention

The formation of stable foam arises from a complex interaction of plant, animal and microbe factors. The threat of bloat is always present, and so preventing bloat requires manipulation of these factors.

Some cows are more predisposed to bloat by the size and structure of their rumen, the rate at which it empties, the rate of saliva production, the composition of their saliva. Some of these traits have a genetic component, so not keeping replacement heifers that are the daughters of bloat-prone cows is one strategy. However bloat prone cows are also high producers.
Some pasture species (especially legumes) or conditions (succulent, rapidly growing, lush and leafy pre-bloom) contribute to bloat. Unfortunately, these are also the pastures that support the highest milk production. Newly sown and recently fertilized paddocks are also higher risks. Knowing which paddocks and weather conditions stimulate bloat will forearm you against it. Topping the paddock and leaving it to wilt may help. High pre- and post-grazing residuals also help reduce bloat
Rumensin, as well as enhancing cow production, has been shown to alter the community of microbes in the rumen away from bloat producers, and towards safe ones.
Hungry cows having a large, rapid feed on the lushest parts of the pasture contributes. Consider holding cows back after milking so that more cows get to the paddock at the same time, and you go to shut them in sooner after the first ones arrive. While you’re holding them back, let them eat hay or balage. Another alternative may be to let cows go back from milking to their old break, and let the fence down mid-morning.
Chemical treatments act by breaking down any foam that may form. They can be added to in-shed drench, water troughs, or sprayed on pasture. The appropriateness of these depends on your farm, equipment and labour set-up. A preventative dose must reach the rumen of every cow every day. In all instances, the manufacturer’s instructions must be closely followed.

Drenching. This must be done twice a day, but may integrate well in some sheds with mineral drenching. The dose rate can be increased if bloat problems are encountered.

Trough treatment. Not as reliable as drenching, as some cows drink more than others, and the amount drunk will depend on climate, pasture conditions and other water available. A different metering device to that used for minerals is put in the trough to release a set volume of bloat treatment each day. It may be necessary to allow animals time to adjust to the taste. Some chemicals require a higher loading dose in newly treated troughs.

Pasture spraying. Each break must be evenly sprayed a few hours before the cows go on to it, the cows then eat the cause and the cure together. Wind and rain can decrease the reliability of this method.

Effective bloat control will require combining good pasture management, herd observation, chemical preventatives, treatment and pasture and cow genetics.

Rob Mills, Feb 2003