Grain poisoning of cattle and sheep
Grain poisoning, also known as grain overload or lactic
acidosis, is usually the result of stock consuming large quantities
of grain or pellets to which they are unaccustomed. Pasture-fed
cows or feedlot cattle not yet adapted to grain may become
acutely ill or die after eating only moderate amounts of grain,
whereas stock accustomed to diets high in grain content may
consume large amounts of grain with little or no effect. Some
circumstances under which grain poisoning can occur include:
accidental access to grain stores; stock access to stubble
paddocks containing excess grain after harvest; stock access
to standing crops; cattle and sheep on feedlot rations without
proper introduction; and grain feeding during drought without
proper introduction.
How is it caused? Grain and finely ground carbohydrate
(such as found in pellets) is rapidly fermented by bacteria in the
rumen, producing large quantities of lactic acid, which lowers the
pH in the rumen. The build-up of acid has effects on the animal
such as: there is a decrease in the numbers of useful bacteria in
the rumen and an increase in the amount of acid-producing
bacteria (causing further build-up of acid in the rumen), rumen
contractions cease, lactic acid draws fluid into the rumen from
the tissues and blood, resulting in dehydration, and, in severe
cases, the blood may become more acid, resulting in heart failure,
kidney failure and or even death.
Grains with a higher fibre content, such as oats and
sorghum, are safer to feed than, for example, wheat and barley,
since the fibre slows the rate of digestion. Cracking grain
increases the rate of digestion of the starch and consequently may
increase the risk of grain poisoning. Any factor that causes
variation in the intake of grain, or variation in the availability of
carbohydrate, may lead to grain poisoning problems. For
example, an unpalatable additive or inclement weather may put
cattle off their feed on one day, but then they gorge the next day.
The effects of grain poisoning may be worsened if the animal is
also suffering from cold stress. It is a wise precaution to increase
the proportion of roughage fed during particularly cold weather.
Other sources of carbohydrates, such as apples, grapes, bread,
baker’s dough and incompletely fermented brewer’s grain, can
also cause poisoning if eaten in excess.
Internet:<dpi.nsw.gov.au> (adapted).