Grazing Legumes and Bloat - Frequently Asked Questions

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 What legumes can cause bloat?
The legumes that are well known to cause bloat are alfalfa and clover (Alsike, Yellow & White Sweet, Red, Dutch White, Crimson, Kura, Berseem, and Persian). Some legumes are higher risk than others. Alfalfa, Red, White, Alsike and Kura clovers are high risk, whereas Persian, Berseem, and Arrow-leaf clovers are considered moderate bloat-risk.

Are there legumes that do not cause bloat?
There are several legumes that are considered "non-bloating." These are Sainfoin, Cicer Milkvetch, Fenugreek, Hairy and Crown Vetch, and Bird's-Foot Trefoil. Purple Prairie Clover, a lesser-known native legume, is also non-bloating.

Are there other forage plants to know that can cause bloat?
There are some other forage species to take note that have potential for causing bloat: Young, green cereal crops, brassicas (rape-seed, kale, turnips), and legume vegetable crops (field peas, beans, lentils, and chickpeas).

What makes legumes like alfalfa high risk for bloat?
These legumes are highly digestible plants, especially when they are growing rapidly and in the pre-bloom stage. Weak cell structure (low fibre, thin cell walls) and high soluble protein composition make these plants highly digestible. As plants mature, cell walls thicken, fibre levels increase, and soluble protein levels decrease. The rate of digestion decreases as plants become more mature. Bloat risk drops substantially when alfalfa plants are at the 15 to 20% bloom stage.

What makes non-bloating legumes non-bloating?
Legumes such as sainfoin, fenugreek and birds-foot trefoil have condensed tannins that mitigate bloat by binding to proteins that are rapidly released in the rumen during fermentation, and destabilizing bubbles that are formed when rumen fluid and rumen gases mix. Tannins binding to soluble proteins reduce the risk of bloat and protects them from degradation by rumen microbes, which increases the amount by-pass protein entering the lower digestive tract.

Cicer milkvetch is the only non-bloating legume that does not contain condensed tannins. Instead, it contains cell structures in the leaves and stems called "mesophylls" which are tougher compounds than what is found in alfalfa and clover. These structures are more difficult for rumen microbes to degrade. Mesophyll cells are not easily broken when the chewed either during ingestion or rumination. As a result, the rate of digestion is reduced and nutrients including protein are released more slowly into the rumen. Gas production is also reduced.

What is the type of bloat caused by legumes like alfalfa and clover and what causes it?
Frothy bloat is commonly associated with legumes such as alfalfa and clover. The cause of frothy bloat is rapid digestion of plant material, which encourages a sudden release of cell contents.

Animal and plant factors relating to the cause of frothy bloat include saliva production and plant cell structure. When livestock eat dry feeds, saliva is produced in large quantities. Saliva contains a substance called "mucin" that acts as an anti-foaming agent. Growing plants/legumes at the early bloom and vegetative stages contain 80 to 90% water. These plants tend to have thin cell walls that break down easily with little chewing. Less saliva is produced under these conditions thus less mucin is added to the forage.

Rapid degradation of plant material causes a sudden release of cell contents for microbes to digest. With high nutrient availability, microbial populations increase dramatically; further increasing the rate of digestion. Soluble proteins and carbohydrates make up a large part of these cell contents, as do small particles which microbes attach themselves to. Excess carbohydrates that microbes do not digest are stored as "slime" outside of their bodies, or inside as energy-dense globules.

Microbial slime has high viscosity and is very stable in rumen contents. The slime prevents gas bubbles from escaping, causing rumen pressure to increase, making it more difficult for the animal to breathe. If this "bloat" condition is not corrected, eventually the animal cannot breath and it dies from suffocation, or a lack of oxygen.

What factors pose the highest risk for bloat?
A variety of factors pose great risk for bloat in livestock: soil moisture, plant factors, time of day, weather or environmental factors, and animal susceptibility.

Soil moisture & type
When soil moisture levels are favorable for the growth of alfalfa, so are conditions for bloat problems. Plants become quite fleshy and less fibrous; leaves become soft and are easily crushed between the fingers. Bloat potential is reduced when soil moisture levels are insufficient due to drought or soil salinity.

Pasture bloat has been found to be more frequent in moist soil zones of the Parkland regions especially in the Grey Wooded soil zones; bloat issues become less frequent in Dark Brown to Brown soil zones.

Environmental Conditions
Conditions with moderate daytime temperatures (20 to 25ºC) seems to coincide with bloat incidence. Cool overnight temperatures have also found to induce bloat in both spring and autumn. These cool temperatures delay growth and maturation of forage plants, creating optimum conditions for bloat. On the other extreme, temperatures that get high enough to create moisture stress and desiccation may reduce bloat potential.

The fall bloat-peak may be caused by heavy dew or frost periods. Though alfalfa has a reputation for being "bloat-safe" after fall frost, there still is risk of bloat. First frost can cause the rupture of plant cells, and production of these small cell fragments can increase bloat risk. A killing frost (-5 to -9ºC or lower) must persist for at least a week plus a few days for dry down is needed before bloat potential is reduced.

Plant Factors
The most significant contributor to bloat with regards to plants is maturity level. The younger the plants, the more likely bloat problems will occur. As plants mature, the risk of bloat declines. Mature plants have higher fiber content, and a slower digestion rate. However plants that have high moisture content as affected by environmental conditions can still pose a bloat issue. Plants hit by frost with ruptured cells and frozen contents can also pose a bloat problem even if they have reached bloom stage.

Animal Factors
Bloat potential tends to be influenced by heritability, which determines the speed that the rumen can clear out small feed particles. The faster these particles can be passed, the less likely these animals will be to bloat. The best management practices are to cull out those animals that bloat, regardless if they are chronic bloaters, or have bloated only once. A study in New Zealand had shown there was no easily measurable physiological trait that could be selected against in a practical on-farm breeding program.

What management practices can be used to reduce risk of bloat?
There are several management practices you can use to reduce bloat risk in your livestock:
  • Never turn out or introduce hungry animals onto an alfalfa pasture. Fill them up with hay in the morning before turning them out onto a new alfalfa stand, or move them when they are not looking too interested in moving to the next paddock.
  • Maintain a uniform and regular intake of legume forages. Do not allow for intermittent grazing, such as moving them off at night and putting them back on in the morning, because this will encourage bloating outbreaks. Once animals have started grazing legumes, leave them on these legumes no matter the time of day or night.
      o Outbreaks of pasture bloat may occur when grazing is interrupted by adverse weather (such as thunderstorms), or by biting insects. These can alter normal grazing habits, resulting in more intensive and shorter feeding periods that may increase the incidence of bloat.
  • Reduce the length of the grazing period by using a rotational-grazing system where livestock are moved to a new paddock every 2 or 3 days, or less. This decreases the chance for animals to selectively graze plants that may be both more palatable and higher bloat risk. It also allows for plant residue to be left behind in a take-half-leave-half grazing system.
      o When it is time to change paddocks, move animals when they are not hungry, preferably in late afternoon. Do not move in the morning because this is when animals will eat the most and when heavy dew increases rate of digestibility.
      o A rotational-grazing system will allow you to leave plant residue behind after each move. You can never have too much residue left behind; this is a sign that animals are being moved when there may still be a little more to eat, and that they are not going to be overly hungry when moved to a fresh pasture.
  • Defer grazing until plants are in full bloom. Plants in vegetative stage are more likely to cause bloat than plants in full bloom.
Graze alfalfa pastures that have been swathed and wilted for 24 to 48 hours. This reduces the moisture content of the legume and has been found to reduce incidence of bloat.
  • Establish high-legume (at least 60% legume and 40% or less of grass) stand with non-bloating legumes. For example, an alfalfa-sainfoin mix stand where sainfoin makes up 25% of the legume component is enough to reduce bloat by 95 to 98%. Also consider a legume stand that is largely made up of non-bloating legumes.

What products are available to prevent bloat in livestock?
Products marketed for bloat control such as Bloat Guard are ideal, since they contain active ingredients that are anti-foaming detergents. Bloat Guard contains poloxalene, which can be given to cattle at doses of 4 to 8 g of Bloat Guard (2 to 4 g of poloxalene) per 100 kg of body weight per day in twice-daily feedings. It comes in a form to be mixed with feed supplement such as grain. Bloat prevention, however, isn't guaranteed when the product is offered free choice because intake can be extremely variable based on period of time between visits and amount the animal will eat.

Alfasure is another product available for bloat control, but is offered on a prescription-basis from a practicing veterinarian.

Use of trace mineral salt blocks with selenium may also reduce incidence of bloat.

Feeding Legumes to Cattle
Bloat in Cattle
Bloat in Ruminants – Merck Veterinary Manual
Prevention of Pasture Bloat in Cattle Grazing Alfalfa – Manitoba Ag

Prepared by Karin Lindquist, Ag-Info Centre, Alberta Agriculture and Forestry
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For more information about the content of this document, contact Karin Lindquist.
This document is maintained by Marie Glover.
This information published to the web on August 28, 2003.
Last Reviewed/Revised on November 16, 2018.