AKC Breeder Newsletter
AKC Breeder Newsletter is a quarterly newsletter covering a wide range of topics of interest (nutrition, breeding techniques, health concerns, etc.) to the purebred dog breeder. You can sign up for AKC Breeder here. The following article appeared in the Winter 2015 issue.
Keeping calcium levels balanced will prevent “milk fever.”
By Jeff Grognet, DVM
Hypocalcemia, also known as milk fever, eclampsia, and puerperal tetany, is a depletion of calcium in the blood. Most breeders consider it a disease that only occurs during peak lactation, but hypocalcemia has been seen before whelping. It can kill, so prevention and early recognition is key.
With an average litter of pups, a Beagle bitch produces more than a liter of milk every day. Hypocalcemia is the result of a mismatch between loss of calcium in the milk produced for the puppies and inadequate calcium available to the bitch.
Calcium is in a dynamic balance in the bitch’s body. She absorbs calcium from the food through her intestinal wall into her bloodstream. If she consumes too much, the excess is excreted into her urine or stored in her bones. When her demand for calcium rises above the amount she gets from her diet, she draws calcium out of her bones into her bloodstream.
Calcium balance is controlled by hormones. As soon as blood-calcium levels start to fall, the parathyroid glands (small glands on each side of the windpipe) release parathyroid hormone (PTH). This hormone mobilizes calcium from the skeletal system, pushing calcium levels back into the normal range.
The opposite also occurs. If calcium levels rise above the range that the body prefers, PTH production drops to zero. The parathyroid gland goes into hibernation and calcium builds up in the bone.
This well-orchestrated calcium flow is maintained by specialized cells in the bone. Certain cells pull calcium out of the blood into the bone, while others push calcium out of the bone and back into the bloodstream. These cells are active during opposing periods of time.
If a bitch is given supplemental calcium, her blood-calcium level rises, and this activates the cells that transfer calcium into her bones. Her body goes into calcium-storage mode.
The problem occurs if she is in this mode when her calcium demand suddenly rises. During lactation, her mammary glands draw huge quantities of calcium out of her blood to produce the milk. The calcium in her diet or in supplements cannot meet this huge demand. She needs the calcium she has stored in her bones.
Unfortunately, the cells that move calcium out of the bones and into the bloodstream have been put to sleep by the calcium supplement she has been receiving. It takes several weeks to get them into action. During this time, the bitch’s blood-calcium level drops, sometimes low enough to cause clinical signs of hypocalcemia to appear.
Hypocalcemia is sometimes seen before whelping. The demands of colostrum production can boost calcium demands and the level drops. This can inhibit contractions of the uterus during whelping and stall labor. Most commonly, hypocalcemia appears when the bitch is at peak milk production about three weeks after whelping.
The bitches at the highest risk of developing this condition are toy-breed bitches and first-litter bitches. Less likely to develop hypocalcemia are large-breed bitches or bitches who have had several litters already (multiparous).
The symptoms of hypocalcemia are unmistakable. At the onset of clinical hypocalcemia, the bitch may be restless. She may whine, salivate, and be sensitive to stimuli. She may pant and pace around the room. Her gait may be stiff and ataxic. She will also be uninterested in her pups.
With too little calcium, the nerves become overexcited. They start sending repetitive impulses to the muscles they supply. The result: muscle twitching all over the bitch’s body.
Within minutes or hours, she exhibits the dramatic symptoms of hypocalcemia, including muscle tremors, muscle stiffness (also called tetany), and convulsions. The temperature may be elevated during hypocalcemia, not because of an infection, but because her active muscles are generating so much heat.
Treating Milk Fever
There are two things to do if hypocalcemia is suspected: Remove the pups and seek veterinary help immediately. Delayed intervention can result in death of the bitch.
Most veterinarians diagnose hypocalcemia based on clinical signs. It can be confirmed by a blood test to measure calcium levels. The advantage of a blood test is that it can also rule out concurrent hypoglycemia (low blood sugar).
The treatment for hypocalcemia is to give calcium. Because this condition can be a life-threatening, it is important to get calcium into the bitch as quickly as possible.
For this reason, most veterinarians go ahead and treat rather than wait for the results of blood tests.
The calcium is given intravenously, but it must be given slowly, with caution. If calcium is injected too quickly, it can trigger a potentially fatal heart arrhythmia.
Response to intravenous calcium is dramatic. Muscles relax almost immediately and the bitch is often normal within 15 minutes.
Once the low calcium has been corrected, the puppies are taken away and not allowed to nurse for at least 24 hours. This prohibition may need to be extended depending on the severity of the condition. During this time they are given milk replacer, either commercial or homemade. If they are old enough, they can be weaned. The bitch needs an oral calcium supplement to prevent recurrence. Once a bitch has had hypocalcemia, there is a strong possibility she’ll develop it again with future litters.
The key with hypocalcemia is to prevent it. Feed a well-balanced diet during pregnancy. A dietary ratio of calcium to phosphorus between 1:1 and 1.2:1 is suitable for pregnant bitches. This is designed to provide just enough calcium so that it does not slow the production of PTH. Many puppy-growth diets are higher in calcium and this can create a problem. Do not supplement with calcium when a bitch is pregnant.
If excessive calcium intake during pregnancy increases the incidence of hypocalcemia, can you prevent it by feeding a calcium-deficient diet to your pregnant bitch? The answer is no. Restricting calcium intake, below the recommended levels, does not seem to have any protective effect.
Once a bitch has whelped, a calcium supplement can be given safely because she is in calcium-utilization mode during lactation. Small-breed bitches are often given a calcium supplement, especially during their first lactation.
The recommended dose is 500 milligrams of calcium carbonate per five kilograms body weight per day throughout the rest of lactation. Calcium carbonate is a common antacid product.
Jeff Grognet is a veterinarian with a practice in British Columbia, Canada, and the regular nutrition and health columnist for akc family dog.