Preventing bloat on pasture

Preventing Bloat on Pasture

S. Ray Smith

University of Manitoba


The occurrence of bloat is a major limitation to greater use of alfalfa for grazing and to more effective use of red and white clover. Pasture bloat or frothy bloat is caused when the normal gases from fermentation cannot be released by belching (erutication) because a stable foam has developed in the rumen. This foam sometimes forms when ruminate livestock consume highly digestible forage legumes. In these forages soluble proteins and small particles are rapidly released into the rumen and attacked by slime producing rumen bacteria. In animals not yet accustomed to such rich feed  the slime builds up into a stable foam, fermentation gases build up and exert pressure on the diaphragm and bloat occurs. Often the animal simply stops eating at the onset of bloat and no further problems develop. In more severe bloat, the animal=s rumen is distended, it urinates and defecates frequently, bellows and staggers. If preventative action is not taken, death can occur due to restricted breathing and heart failure.


Historical Perspective on Bloat

Bloat is not a new problem. It has been around as long as livestock have been consuming highly digestable forages. In AThe Whole Art of Husbandry@ (published in 1716) J. Mortimer wrote about  Aclover-grass,@emphasizes  the care needed when cattle were first put into it, A. . . . Lest it burst them.@ Mortimer goes to add that this could be prevented by not letting them have too much, and by supplying straw; Abut the best way was to turn them into it the first day about noon, when the dew is off, and in a dry day, for about half an hour; the next day for an hour; . . . (gradually increasing each day) Then till four or five o=clock in the afternoon, and after that there will be no danger.@ He also states that Asome sow trefoil (birdsfoot) or ray-grass (ryegrass) with their clover, which very much prevents it doing of injury to cattle . . . .@


  1. Mortimer advice is still very relevant today. He emphasizes good grazing management to minimize the risk of bloat and this is still the best advice that I or anyone can give. We do have several other management options which I will mention in the following section. Also, progress is being made in the development of low bloat and potentially non-bloating alfalfa.


Reducing the Risk of Bloat on Pasture

The key to reducing the risk of bloat is to prevent animals from eating too much of a highly digestible legume too quickly. Also it is important to give their rumen microorganisms time to adapt to the new diet (just as Mortimer emphasizes above). The only way at present to totally prevent bloat without a special feed additive is to plant only grass pastures or to use only non-bloating legumes. Both are viable options, but grass only pastures means an annual N requirement and typically lower quality and the currently available non-bloating legumes (birdsfoot trefoil, sainfoin and cicer milkvetch) all have establishment and/or stand longevity problems.

For the remainder of this paper I will assume that you want to plant high digestible legumes like alfalfa and clovers in your pastures and you want management options that will reduce or prevent bloat.  There are a number of standard management options to reduce bloat on pastures that contain a high percentage of alfalfa, red or white clover. Most successful graziers use one or more of the following management strategies.

1)                  Do not turn hungry animals on fresh legume pasture.

2)                  Maintain at least 50% grass.

3)                  Do not start grazing when the pastures are wet from dew or rain.

4)                  Gradually introduce cattle to legume containing pastures (see Mortimer=s advice above).

5)                  Pre-fill with coarse hay before turning onto pasture.

6)                  Provide coarse hay at all times when cattle move onto a new pasture.

7)                  Delay grazing alfalfa until the bloom stage.

8)                  Cull frequent bloaters from your herd.

9)                  Feed the bloat preventative poloxalene (Bloat Guard7) mixed with a mineral or grain supplement or as a pasture block

(Note: effectiveness depends on required daily intake, therefore mixing with daily supplement is more effective than feeding in blocks on pasture).

10)              Check animals frequently for bloat when beginning grazing.


There are several new bloat management strategies that are being investigated in Canada. None of these eliminate bloat, but do provide other management options to reduce bloat. The first one is to mix a non-bloating legume with a bloating legume. Recent research showed that intake of 10 to 20% sainfoin with alfalfa reduced bloat by 45 to 93%. This is not a new strategy in that Mortimer suggested adding birdsfoot trefoil back in 1716. The difficulty is in maintaining a consistent mixture of the non-bloating legume. For example, both sainfoin and birdsfoot trefoil are slower to establish, have slower regrowth and are less persistent than alfalfa.


Another new strategy is to first windrow and wilt alfalfa before grazing. Just 24 hours of wilting increases sulfhydryl and disulfide content of alfalfa proteins which reduces the chances for bloating. In several studies, 48 hours of wilting almost completely eliminated the risk of bloat. The ionophone antibiotic monensin is now registered in Canada as a 120 day time release bolus.  Inserting this bolus into the rumen reduces the chance for bloat by 50%. There are attempts being made to register this product in the U.S. Research is also being conducted in Canada on a water soluble product from New Zealand that completely eliminates the risk of bloat.  Blocare 4511 has been available in use in New Zealand for 40 years, but the regulatory processes in the U.S. and Canada make its availability uncertain in the near future.


Non-Bloating Alfalfa?  

The ideal bloat preventative management strategy would be the availability of non-bloating alfalfa cultivars. While this is not likely in the near future steps are being made to develop cultivars with a reduced risk of bloat. Researchers at the Agriculture Canada Research Station in Saskatoon, Saskatchewan have been working for over 30 years to develop non-bloating alfalfa cultivars. They have recently released the cultivar >AC Grazeland= that shows a 60% reduction in bloating when grazed. This cultivar was developed by selecting for a lower initial rate of digestion to prevent the rapid buildup of stable foam causing bloat. Although AC Grazeland does not have the disease resistance necessary for Wisconsin conditions, U.S. breeding companies are hoping to develop similar low bloating cultivars in the future.

Another new strategy begin attempted by researchers to reduce the risk of bloat is to insert tannin expressing genes into alfalfa just as Roundup resistant genes have already been inserted. Tannins are one of the reasons that birdsfoot trefoil and sainfoin does not cause bloat. This process has not been as simple as it sounds because tannins are produced in plants by a very complicated series of chemical processes. This research is continuing at several centers in Canada, the U.S. and Australia. Hopefully, these researchers will be successful and you will one day have the option of buying seed of bloat free alfalfa cultivars.


Other Information

More detail on preventing bloat can be found in an article by Dan Undersander and Dave Combs in the summer 1998 Wisconsin Forager available at There is also very good information on grazing alfalfa at the America=s Alfalfa web-site


Acknowledgements: I want to especially acknowledge Bruce Coulman and colleagues for their very comprehensive article on preventing bloat and research on the development of low bloat alfalfa: Coulman, B.E., M. Gruber, T.A. McAllister, W. Majak, and D. Thompson. 2000. Future of alfalfa as a grazing crop: Bloat. Proceedings of the American Forage and Grassland Council. 16-19 July 2000. Madison, Wisconsin.


A series of other relevant papers on grazing alfalfa and bloat were recently published in the July 2000 issue of the Canadian Journal of Plant Science.