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The other morning, I examined a Holstein calf that was down in a super hutch. The temperature was around zero, and the wind was blowing out of the northwest at about 30 miles per hour. In other words, it was just another fine day in this paradise we call Minnesota winter. The calf was lying on its side and its body temperature was around 95 degrees. The owner and I chatted a bit about whether the prognosis was good enough on this bull calf to justify treatment. We decided to bring it inside a warm barn for a better look. I warmed up a bottle of lactated ringer's solution in a bucket of hot water. After placing a needle in the jugular vein, I used a Precision Extra meter and a glucose strip to test the blood glucose level. The reading was 20. This is extremely low. Why is this important, what caused it, and what should we do?
Glucose is really the most basic fuel of the mammalian body. While it is true that other substances can be used for fuel, certain cells in the body rely on glucose as the only source of energy. Some of these cells are erythrocytes (red blood cells), brain cells and kidney cells. Therefore, if the body cannot maintain blood glucose within a normal range, these cells cannot survive. Ruminants have a very interesting metabolic system for glucose. Adult cows typically have much lower blood glucose levels that non-ruminants and calves, who are essentially non-ruminants for the first few months of life. In addition, adult ruminants have a very tightly controlled glucose system, so it is quite unusual for blood glucose levels to be below or above the normal range. If one samples blood from ketotic cows, for example, one will find that the vast majority of them, even the pipe-licking, pie-eyed, rough-haired, skinny ones with feces as firm as horse manure, typically have normal blood glucose levels. (This is why, usually, routine administration of 50 percent dextrose, which is really just two glucose molecules bonded together, is typically not necessary, and may even be a bad idea.) Blood glucose is maintained because the major source of glucose is gluconeogenesis by the liver and kidneys, rather than from intestinal absorption from food. Calves, however, are much more like you or me, in that most of their glucose comes from intestinal absorption.
Our calf that cold day had suffered from pneumonia in the past, and had poor body condition as a result. It probably had not been eating as well as it should, and so the cold resulted in a low body temperature because it simply did not have enough insulation or enough caloric intake. When its blood glucose levels begin to drop, the calf likely became more depressed, and it probably ate even less. At this point, particularly when the weather is cold, the calf can suffer a hypoglycemic crisis, which results in cold extremities, reduced body temperature, recumbence, coma, and death. Calves that survive and perhaps never go down, may suffer from frostbite on their hooves, ears and tail.
Hypoglycemia, or low blood glucose, is likely to occur in calves that have had or are suffering from other diseases, and it is especially likely to occur in the winter. A hypoglycemic crisis is much more likely to occur when it is cold. This means that we should look for this in depressed young calves, especially in winter, and especially in calves with low body temperature. A Precision meter can be purchased for around twenty bucks and the glucose strips cost about one dollar, so the cost of testing is almost nothing. The same meter can also be used for testing BHBA (ketones) in blood of adult cows. The cost of a few ccs of 50 percent dextrose is only pennies.
We gave our calf some 50 percent dextrose in that bottle of warm fluids intravenously. When the bottle was empty, I rolled him onto his sternum, and he immediately tried to stand. This is a typical response to glucose therapy. This calf is not out of the woods by a long shot, but he almost certainly would have died within a few short hours without appropriate therapy. Survival will require staying warm, eating more calories, and resolution of the pneumonia. A useful tip for follow up of baby calves is putting one quarter cup of Karo syrup in the calf's mouth. It is pretty sticky stuff, so it stays there, and even if not swallowed, the glucose in the syrup will be absorbed by the tissues lining the mouth.
On some farms, 50 percent dextrose is probably overused as a treatment of adult dairy cows. However, on many more farms, 50 percent dextrose is underutilized as a treatment of hypoglycemic calves. It is likely that, for every cold snap in the winter, many calves that could survive, are found dead, especially in the morning. Glucose therapy is safe, inexpensive, and only requires a meter, some test strips, and the ability to give an IV injection. In fact, some calves may recover just from some warm milk and being moved to a warmer place. Your veterinarian can further explain glucose therapy and perhaps demonstrate how it is done on your farm. Glucose is the fuel the body needs.
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