Understanding bloat in a cow, causes, prevention and treatment
Bloat causes severe losses in the major dairying areas of Africa each year. Cow deaths and lower milk production are the result of an excessive accumulation of gas in the rumen (paunch) which can not be belched away by the cow. Bloat is generally associated with cows grazing pastures with a high legume content (clover or lucerne) in spring and autumn. A clover content of over 50% is considered dangerous, however problems have been seen at levels below this when new succulent growth is abundant. Occasionally young grasses can cause bloat if they contain large amounts of soluble protein. Farmers have found that hungry cows which gorge themselves when introduced to the pasture are particularly at risk. Mornings with dew on the grass or overcast, windy days are frequently associated with outbreaks.
Researchers have found that heifers are three times more likely to die of bloat than mature cows. Jerseys are three times more susceptible than Friesians and crossbreds are twice as susceptible.
Treatment and prevention are costly and it is important to remember that, apart from restricting access to dangerous pastures, there is no single method which will guarantee 100% protection from bloat. Many farmers use two or more of the following techniques to reduce the incidence of bloat on their farms.
Signs of bloat
Cattle with bloat may display the following signs:
- no longer grazing;
- a reluctance to move;
- distended left abdomen;
- appear distressed — vocalise, eyes bulging;
- strain to urinate and defaecate;
- rapid breathing — mouth may be open with tongue protruding;
Legumes should be introduced into the diet gradually over several days. Avoid cows gorging new pastures by feeding them before letting them out to graze. Silage, hay or more mature pasture can be used to reduce the cow’s appetite. Initially, cows should only be allowed access to the pasture for short periods (one hour or so) and monitored closely during grazing and immediately after removal.
Cows will become accustomed to dangerous pastures over several days and will modify their intake to reduce bloating. Some farmers claim that mowing or slashing the pasture and allowing it to wilt for 2 – 3 hours will reduce the risk of bloat.
Three types of medication can be used to control bloat in cows.
- Fermentation modifiers eg Anti-bloat capsule
- Detergents eg Teric – there are over 300 different types of Teric (alcohol ethoxylate) on the market!
- Anti-foaming agents eg Paraffinic oil and tallow.
The systems used to administer these chemicals aim to provide a continuous supply of medication over the whole grazing period. Movements within the gut ensure that the chemical is thoroughly mixed with the contents of the rumen, preventing the formation of a stable gas foam. As with any chemical, dose rates should be checked on the label and any withholding periods strictly adhered to.
Directly drenching cows with a detergent is perhaps the most successful way of controlling bloat and is widely practised in New Zealand. Teric 12A23B is one of the more effective and less bitter tasting detergents and is used after milking. Cows readily accept being drenched with 100% Teric after a 3 – 4 day training period using a molasses and Teric mixture (1 part Teric to 1 part molasses). Cows require 20 mls of Teric 12A23B or Teric PE64 at 12 hourly intervals for protection. Other detergents (and other types of Teric) may be less concentrated and higher doses may be required. Check the label carefully when comparing products.
Bloat oils may also be directly drenched, however larger volumes are required and the duration of action is significantly shorter than for the detergents.
Anti-bloat capsules are a longer lasting alternative to aid in the control of bloat in cattle. Administered as a large plastic pellet down the throat (into the rumen), they provide a continuous supply of chemical for 80 – 100 days. The capsules have been found to reduce bloat deaths by about 80%. Trials have shown that cows with capsules have an increase in milk and protein production. Butterfat test (%) may be depressed but the total fat yield for the season is unaffected.
Spraying the pasture with oil
Spraying the whole day’s grazing with anti foaming agents, such as paraffinic oil, is a very reliable method of bloat control if carried out properly. It is best suited to ‘strip grazing’ systems that provide small, fresh areas for intensive grazing at least once per day. Oils only give 2 – 4 hours protection in the rumen and so need to be consumed over the entire grazing period. Spraying the total area of each day’s grazing (24 hours) at a rate of 85 mls of oil per cow is recommended. It is important that the grazing area is not over estimated or the oil may be spread too thinly and some cows may not eat enough. Make sure the oil will emulsify with water prior to purchase. Do not spray more than 2 – 3 days grazing at a time. Respraying may be required after heavy rain. Boom spraying equipment and fencing must be in good condition to avoid failures.
Feeding in the bail
Anti bloat medications can be mixed with concentrates and fed through the bloat season. Detergents and oils have been added to supplementary feeds (pellets or grain) with good results, providing that the cows eat sufficient amounts twice daily. Feed companies sell pre-mixed feeds with added Teric. Powdered Teric or bloat oil can be used for those with home mixing systems. Cows will only eat liquid Teric voluntarily if it is mixed with molasses in equal proportions. Each cow requires 57 mls of this mixture twice daily for protection. Rumensin (monensin) mixed with supplementary feed is not registered for bloat control in dairy cattle in Australia. It is not known whether it will control bloat when used in bail feeding systems and is not recommended for this purpose.
Between 30 and 70 mls of thick bloat oil can be applied to the flank of each cow with a brush or automated spraying system. Most, but not all cows will lick this off during grazing. Adding molasses or tallow increases palatability but encourages some cows to lick it off others. Wet weather and variable consumption reduce the effectiveness of this control method.
Water trough application
Detergent can be added to troughs if it is the only source of water available to the herd. Detergents are bitter tasting and need to be gradually introduced into the water supply over a week or two, until the herd becomes accustomed to the taste. Teric 12A23B at 40 mls per 15 litres of trough water is recommended for bloat control. The fresh water supply must be disconnected unless a metering device can supply a measured amount of Teric as the water flows in. Trough Add is registered for use in troughs and includes a dye so the concentration of the chemical in the water can be monitored. Troughs must be replenished with the concentrate at regular intervals to maintain protection. Despite this, the daily water consumption of individual cows can fluctuate greatly leading to variable control within the herd.
These are generally used on beef properties where more effective control methods are not feasible. A regular daily intake by all cows is required for adequate protection.
If the cow is still standing
There are a number of products specifically registered for the treatment of bloat in cattle. Tympanyl and Berg Oil are two examples. If these are not available, bloated cows should be drenched immediately with 60 – 120 mls of bloat (paraffinic) or vegetable oil. Teric and other detergents are less effective in these situations. Cows should be removed from the pasture as soon as possible to prevent losses.
If the cow is down and in extreme distress
If treatment with oil has not been successful and the cow is likely to die before a veterinarian can attend, the pressure in the rumen should be relieved surgically. Often a wide bore (14G) milk fever needle or trocar and cannula is sufficient for this purpose. The site for stabbing is on the left flank, an open hand’s width behind the last rib and a similar distance below the ends of the short ribs (spinal vertebrae). If a needle or cannula is not available, or they become blocked with foam (and the cow is in severe distress) a sharp narrow bladed knife can be used as a last resort. A 2.5 cm stab wound is ample and the knife should be left in the incision and twisted until gas and foam have ceased escaping.
A veterinarian will be required to suture the wound and administer antibiotic therapy if the rumen wall has been punctured during treatment.
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