Blood work: revelations, limitations for cattle - DVM
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Blood work: revelations, limitations for cattle


DVM360 MAGAZINE


If diarrhea is absent, renal disease and a urinary obstruction or ruptured bladder should be suspected. Hyperkalemia is not a consistent finding in ruminants with a ruptured bladder.

Chemical element measurements

Calcium, phosphorus and magnesium measurements also are useful. Mild hypocalcemia is common in sick cattle, and an addition of extra calcium to fluids usually is indicated. Clinical hypocalcemia is easily recognized during physical examination, and blood work usually is unnecessary. However, in cases that relapse or with unusually high numbers of cases in a herd, blood work might be helpful to make sure phosphorus and magnesium problems are not contributing to the signs.

Beef cattle with hypocalcemia along with hypomagnesemia usually will have signs of hypomagnesemic tetany. These animals might not respond as well to magnesium administration as pure hypomagnesemia, or they might relapse. Remember that acid-base status and albumin levels will influence ionized levels of calcium, but this will not be reflected in a total calcium measurement.

Hypercalcemia is rare and usually caused by excessive administration of intravenous calcium.

Hypophosphatemia usually is due to prolonged anorexia or dietary problems. The condition is uncommon and often related to hemolysis. However, renal disease should be investigated if hemolysis is ruled out.

Blood urea nitrogen (BUN) and creatinine are indicators of dehydration and/or renal disease. Since urea is recycled in saliva and utilized in the rumen, increases in BUN do not always occur, so increases in creatinine are more sensitive.

The most common cause of azotemia is dehydration, which can be detected clinically. But renal disease and dehydration can occur concurrently so urine-specific gravity is indicated for azotemic animals.

In most species, if the urine-specific gravity is less than 1.025 in an azotemic animal, renal disease should be suspected. However, since cattle with other disease processes can have azotemia and a low urine-specific gravity with no evidence of renal disease, this needs to be a repeatable finding.

The problem comes in that these animals usually need fluid therapy, and once fluid therapy is instituted, a urine-specific gravity is not reliable. So if fluid therapy is instituted, and the BUN and creatinine return to normal in about 24 hours, the azotemia is probably prerenal. If the BUN and creatinine stay elevated, renal disease should be suspected.

Interpreting enzyme tests

Enzyme tests must be interpreted with caution because many are not specific for one disease system. The most useful enzyme is gamma-glutamyltransferase (GGT).

Elevations in GGT can occur with cholestasis and hepatocellular membrane damage in cattle. Chronic liver disease is more common and usually involves some degree of cholestasis. Also, GGT stays elevated longer than other enzymes. So elevations in GGT can indicate active or recent hepatocellular damage or chronic liver disease.

Other enzyme elevations might indicate one type of disease or another, but most indicate that the liver should be further investigated. The caveat to this is that in the face of normal enzymes, liver disease cannot be ruled out. Increases in bilirubin occur more frequently with hemolytic diseases than liver disease.

Many times, the bilirubin is normal with liver disease. High bilirubin in association with liver disease usually is a poor prognosis.

Dr. Navarre works as an extension veterinarian with Louisiana State University's Department of Veterinary Science.


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Source: DVM360 MAGAZINE,
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