Acidosis in Dairy Cattle
Kung, Jr., Ph.D.
Ruminant Nutrition & Microbiology Laboratory
In a normal, healthy rumen, lactic acid
production equals lactic acid use.
Thus, lactic acid is rarely detectable in a healthy rumen.
However, a number of different factors can easily lead to an
imbalance in lactic acid metabolism (Table 1) resulting in acute or
1. Common factors leading to acidosis in dairy cattle.
too high in fermentable carbohydrates
high concentrate:forage ratio
fast a switch from high forage to high concentrate
fast a switch from silage to high levels of green chop forage
fiber content in diet
composed of very wet and highly fermented feeds
finely chopped forage
mixed TMR resulting in excess particle size reduction
One of the most common causes of
acidosis occurs when switching from a high fiber to high concentrate
diet that is rich in fermentable carbohydrates (starches and sugars). Large amounts of starch and sugar stimulate bacteria that make
lactic acid. In this
instance, bacteria that normally use lactic acid cannot keep up with
production. The amount of
acidity in the rumen is measured by pH readings.
The optimal rumen pH should be between 6.0 and 6.2, but there
is daily fluctuation below this level even in healthy cows.
Lactic acid is about ten times a stronger acid than the other
rumen acids and causes the rumen pH to decrease.
As the rumen pH drops below 6.0, bacteria that digest fiber
begin to die and thus, fiber digestion is depressed.
Because the end products of fiber digestion are used for milk
fat synthesis, a drop in milk fat test is a sure sign of acidosis.
In, addition, the accumulation of acid causes an influx of
water from the tissues into the gut and thus a common sign of acidosis
is diarrhea. If the rumen
pH continues to decline and falls below 5.5, many other normal healthy
rumen bacteria also begin to die.
As lactic acid accumulates, it is absorbed and lowers the pH of
the blood. High levels of
acid in the gut can also cause ulcers in the rumen resulting in
infiltration of bacteria into the blood that can cause liver
resulting from high acid production in the rumen also affects blood
capillaries in the hoof, causing them to constrict resulting in
acidosis is also characterized by cycling intake because animals eat
less during times of distress, then if the rumen adapts, their
appetite returns. If
blood pH drops too low, this can result in death of the animal in
Another common cause of acidosis is having diets too low in
effective fiber (see last newsletter) or too small particle size.
When animals donít chew their cud normally, lack of saliva
(that contains a natural buffer) contributes to low rumen pH.
Recently, researchers at the University of Wisconsin have found
that some mycotoxins can alter the metabolism of lactic acid causing
it to build up and cause acidosis. This may explain why acidosis and laminitis are also commonly
observed when mycotoxins are a problem.
can you tell if you have acidosis?
Observe cows for symptoms described Table 2.
2. Common symptoms of acidosis.
milk fat test; < 3.0 to 3.3%
rumen pH (< 5.8) in 30
to 50% of animals tested
and nutritionists also use a procedure called rumenocentesis to
measure rumen acidity. A
needle is pushed through the flank of the animal into the rumen and
ruminal fluid is withdrawn into a syringe.
The rumen fluid is then measured with a pH meter.
In my opinion, a low milk fat test (less than 3.3 to 3.0%) is
one of the best measures of acidosis.
Fat tests less than 2.7 to 2.8% will more than likely be
accompanied by cows with laminitis. In order to prevent acidosis good management practices are
needed to prevent the situations in Table 1 from occurring. Several pounds of long hay (or even straw) can go a long way
in helping cows but the root of the problem must be found and
corrected. Buffers can
also be useful in keeping rumen pH high, especially in corn
silage-based diets. Use common sense when changing diets and ensure that there is
effective fiber in your diets for production of saliva.