Grain Overload

Gerald Hauer, DVM
Bison Production Specialist
Alberta Agriculture, Food and Rural Development
Bison Centre of Excellence, Leduc, Alberta.
Phone: (780) 986-4100

Reprinted form The Tracker, volume 3, issue 5, May 1999


Many people believe that bison are not susceptible to grain overload (carbohydrate engorgement) and do not take precautions when introducing their bison to grain.  Bison are not as susceptible as other farm species but they will eat too much grain if given the opportunity and this can cause digestive upsets.  Introducing grain to ruminants slowly is the key to avoiding this problem.

Grain Overload

When a ruminant eats too much of a carbohydrate rich feed they are susceptible to a condition known as rumen overload (carbohydrate engorgement, or more commonly grain overload).  In Western Canada grain is usually the cause of this disease but interestingly enough in other parts of the world the same condition can be caused by feeds such as apples, grapes, bread, or any other feed that is high in starch (I have heard of a bottle raised moose that died after stealing several loaves of bread).  Elk and deer seem to be quite susceptible to the condition.  It is one of the more common causes of death in farmed elk in Alberta.  Bison appear to less susceptible but they will overload if they are hungry and are given unlimited access to grain.

The reason that ruminants (animals like cattle, sheep, bison, deer and elk) are susceptible to this condition is that they rely on micro-organisms like bacteria and protozoa to breakdown feed and release nutrients in their large first stomach, the rumen.  There is a mixed population of these organisms in the rumen at any one time and the relative percentages of each type depend on what the animal is eating.  For example, if an elk is on a hay diet then the bacteria that break down hay will predominate.  If the elk has been getting a lot of grain then the number of bacteria that digest grain will be higher.  The percentages of these microorganisms will change as the animal’s diet changes and if the change occurs over a long period of time there is generally no problem.

Problems arise when a ruminant is given a large amount of a high carbohydrate feed that it is not accustomed to and therefore the bacteria and protozoa in the rumen are not able to properly digest it.  In this situation a bacteria called Streptococcus bovis grows very rapidly and produces large quantities of lactic acid.  The acid is absorbed into the blood stream through the rumen wall causing a decrease in the blood pH and causes water to be drawn back into the rumen leading to dehydration.  The combination of these events can lead to weakness and death.

If the lactic acid is produced very quickly, the chance of the condition being fatal increases.  The speed of acid production is determined by the type of grain that is consumed (wheat is the fastest, barley is intermediate, and oats is the slowest), by the amount of processing that the grain has undergone ( finely ground grain will have a much faster acid build up than whole grain because the bacteria can break it down much faster), and how accustomed the animal is to grain (if the rumen is already used to getting some grain in the diet then there will be a slower build up of the lactic acid).

This condition can be very hard to treat because the lactic acid acts very much like a toxin and the build up of the acid is difficult to reverse.  In cattle, emergency slaughter is often recommended if the animal is too sick to save because the meat is still OK to eat.  Heroic treatments such as surgery to empty the rumen, flushing out the rumen contents, and IV fluids can be attempted on valuable animals but these only achieve moderate success.  If an animal lives through an episode of grain overload, the lactic acid can cause other damage such as a disturbance of hoof growth known as laminitis or founder, liver abscesses, and scarring of the rumen.   It is better to prevent this disease rather that have to treat it!

There are two main causes of grain overload.  One is accidental unlimited  access to grain in animals whose rumens are not adapted to it.  Examples of this are grain bins breaking open, animals gaining access to spilled grain at harvest time, self feeders that have run out and then refilled several days later when the animals are very hungry, animals breaking into a pen where another group is on self fed grain, or insufficient trough space at feeding time (dominant animals overeat). Elk and deer will overload much more readily if they have been fed the ration in the past and have acquired a taste for it. The second cause is farmers trying to get their animals onto a high grain ration too quickly.  To prevent this type of grain overload the ration of any ruminant should be changed slowly to allow the rumen and the micro-organisms time to adapt.  Grain should be introduced slowly and in small increments.  A minimum of 4-6 weeks should be used to get the animals onto a higher grain ration (adding 10% more grain every 4-5 days is a good rule to follow).

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