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 .
. . .@
J. 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 www.uwex.edu/ces/forage/wfc/summer98.htm. There is also very good information on grazing alfalfa at the Americas Alfalfa web-site www.americasalfalfa.com.
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.
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