Eclampsia has many names: you may know it as “milk fever,” but in the veterinary field, it’s referred to as “puerperal hypocalcemia,” and in later stages, as “puerperal tetany.”

Mostly seen in dams weighing 25 pounds or less, the potentially fatal condition can, however, occur in any nursing canine, according to Margret L. Casal, D.V.M., Ph.D., an associate professor at the University of Pennsylvania School of Veterinary Medicine, who specializes in veterinary genetics, pediatrics and reproduction. While it’s more common in small breeds, it can happen in “any breed of dog, with any size litter, and at any time during lactation,” according to the Merck Veterinary Manual.

Hypocalcemia is most often seen three to five weeks after whelping, Casal says, “at the peak of lactation.” It typically occurs because the dam loses too much calcium through her milk, due to a larger-than-normal litter or unusually big puppies. Inadequate nutrition prior to or after whelping can also cause hypocalcemia. When this happens, the dam’s body will do everything it can to produce milk with enough calcium for the puppies.

“There’s a lot of calcium in milk, and there has to be,” Casal says. “Normally it comes from the diet. If there’s not enough, it comes from the bones.” At some point, calcium will come from the bloodstream, where it is a naturally occurring mineral. “If the calcium drops in the serum [blood], things like muscles don’t work properly.” Not just large muscles, like those in the legs, are affected. Any muscle, including the heart, as well as nerve conduction, can suffer, Casal says.

She points out that eclampsia in humans is the other way around. Women usually get it before birth or right around the birth because “calcium demand is larger in humans before birth. In dogs it’s after birth.”

Rarely, canine hypocalcemia will happen late in gestation. When it does, the bitch has a hard time giving birth, Casal says, because the uterine muscle has difficulty contracting. However, she warns – repeatedly – that supplementing with calcium during gestation is not an option. “That’s a really bad thing,” she says. In fact, it can actually lead to eclampsia, according to Merck, because “excessive calcium intake during pregnancy causes down-regulation of the calcium regulatory system and subsequent clinical hypocalcemia when calcium demand is high.” In layman’s terms, giving calcium supplements can trigger the body to stop making the supply of calcium it normally would, and later, when it is most needed, there isn’t enough in the system. This can lead to eclampsia.

Eclampsia, or puerperal hypocalcemia, a life-threatening calcium deficiency in postpartum bitches, is most commonly seen in breeds weighing 25 pounds or less. It can, however, occur in any dam of any size. Photo © Can Stock Photo Inc.

Signs of Trouble

In the early stages of hypocalcemia post-whelping, the dam will appear nervous and restless. She will pant and seem stiff in her movements. “Dogs realize something’s wrong, but they don’t know what it is,” Casal says. “They just don’t feel right. Calcium is so important for so many things. It might even change how the brain functions.”

The dog may provide some behavioral cues that all is not well, such as aggression, whining, salivation and pacing. She may be hypersensitive to stimuli and seem disoriented.

“You need to treat right away when you see those kinds of things,” Casal says.

If a dog’s breeder hasn’t yet recognized a potential problem, the next clinical sign, twitching, should say, “Get me to the emergency clinic!”

Casal explains: “Calcium is required for stabilizing the interplay between other molecules that sit at the junctions between muscle and the nerve cells. If you remove the calcium, these cells lose their stabilization, and the nerves are able to fire over and over and over again. That’s what causes those muscle twitches. The nerves keep firing, telling the muscles to contract without provocation.”

Tremors are “very fine – fine, fine – muscle movements that don’t make the dog fall over or anything like that,” Casal says. “You have to really look at the animal to see that. It’s a very quick shake. Spasms are more violent and last longer,” but are not as extreme as convulsions or seizures.

At this point, some breeders might consider administering corticosteroids because of the apparent nervous system involvement. “That’s a bad idea,” Casal says. “That can make it a lot worse.” Corticosteroids are contraindicated, she says, because they lower serum calcium. “They may interfere with intestinal calcium transport and increase urinary loss of calcium.”

Testing for a Diagnosis

As long as the dog’s veterinarian is experienced in caring for postpartum bitches, he or she will know how to test for hypocalcemia. It is not, however, as simple as measuring the calcium in the blood. The concentration of free calcium ions, or ionized calcium, will determine whether a dog is actually hypocalcemic. Normal serum calcium concentration – that of calcium bound to phosphates – cannot be used to judge whether a dog has hypocalcemia.

In addition, the equilibrium between ionized calcium and protein-bound calcium is affected by pH, according to Merck. “Acidosis increases the ionized fraction, whereas alkalosis decreases ionized calcium; total calcium concentration is not affected by changes in pH.” So, an animal with an acidic chemistry can have no clinical signs of hypocalcemia, despite having a lower-than-normal ionized calcium level. A dog with an alkaline chemistry may have clinical signs of hypocalcemia, but have a normal ionized calcium test result.

Another consideration in testing for hypocalcemia is the level of albumin in the blood. A water soluble protein, albumin aids in the transport of molecules of calcium and other elements through the bloodstream. Mild hypocalcemia, in conjunction with low albumin, usually “does not indicate a disorder of calcium metabolism,” according to Merck.

Barring involvement of these other variables, a concentration of ionized calcium under 7 milligrams per one-tenth of a liter requires treatment.

It’s best, of course, to find this out before a dog enters the subsequent stages of hypocalcemia, with these progressive clinical signs: poor muscle coordination, inability to stand, fever, convulsions in which the dog is conscious, seizures in which the dog is not conscious, then death. Dogs may also have tachycardia, a fast heart rate; polyuria, large production of urine; polydipsia, excessive thirst; and vomiting.

Ultimately, the heart can be affected, because nerves “innervate the heart and tell it to beat,” Casal explains. “Once the first nerve pulse comes in, there are nerves in the heart that have to be very concordant when they release their electricity to make the heart beat in a concordant fashion. With low calcium, electrical signals can go through to the heart before they’re supposed to.”

Veterinarians use numerous tools to diagnose hypocalcemia, particularly if the dam is in the early stages. The first is known as “signalment,” the dog’s age, breed and sex. Again, Casal stresses that this condition can develop in any dog, regardless of breed or size. Obviously, clinical signs reported by the breeder or observed under veterinary examination are key. So is the dam’s history: how many puppies are in the litter, how much they weigh, what kind of diet she ate prior to whelping and her current diet, Casal says.

A blood test, revealing an ionized calcium level under 7 milligrams per one-tenth liter, contributes to the diagnosis. A veterinarian will also order a serum chemistry profile to rule out hypoglycemia and other electrolyte imbalances, which the dam may also have.

However, Casal says she wouldn’t necessarily wait for the calcium test results to start treatment. The arrival at the university’s Ryan Veterinary Hospital of a smaller dog with a litter of puppies at home, showing clinical signs of hypocalcemia, would be enough for her to begin treating the dog.

Time to Drip the Calcium

Treatment consists of 10 percent calcium gluconate given intravenously, about 0.5 to 1.5 milliliters per kilogram of body weight over 10 to 30 minutes, then repeated for a total dose of 5 to 20 milliliters. This depends on the size of the dog and her response to the treatment, Casal says.

During treatment, the dog should be hooked up to an EKG monitor or her heart rate listened to “carefully,” Casal says. Too much calcium given too quickly can cause tachycardia; bradycardia, a slow heart rate; or arrhythmias, irregular heartbeats. Monitoring is paramount to the dog’s survival. “You can kill the dog because its heart will stop,” Casal says.

If any cardiac effect develops during the treatment, it will be stopped until the heart rate and rhythm return to normal. At resumption of treatment, administration is at half the original rate.

Introduction of the calcium gluconate “usually results in rapid clinical improvement within 15 minutes,” Casal says. “Muscle relaxation should be immediate. It’s very fast. It’s one of those things where they come in with a dog that can’t even stand anymore, and it’s got all these twitches. You give it the calcium, and you see very rapid improvement.”

The associate professor says the most effective and least dangerous treatment is calcium gluconate. Other forms of calcium, such as calcium chloride, cannot replicate the results demonstrated with the gluconate version.

When the dam is stabilized with an ionized calcium level of at least 7 milligrams per one-tenth liter, “we send them home as soon as possible,” Casal says, usually within a few hours. “If the heart’s been seriously affected, we might keep them longer. If they’re really bad, we’ll have them bring the puppies in to stay” with the dam.

Any cerebral edema – swelling of brain tissue from excess water – or hypoglycemia – low blood sugar – resulting from the bout with hypocalcemia will be treated as well.

Merck advises breeders not to let puppies nurse for 12 to 24 hours after the dam’s stabilization. The puppies can be fed a milk substitute during this period, or, if reasonable, they can be weaned. If hypocalcemia reoccurs while the litter’s still nursing, Merck recommends removing the pups from the dam and hand-raising them or weaning them as appropriate based on their age.

Once the dam goes home, Casal prescribes an oral calcium supplement with vitamin D for a total daily dosage of 25 to 50 milligrams. It’s best to maintain the dam at an ionized calcium level of 8 to 9.5 milliliters per one-tenth liter.

Toward the end of the nursing period, the dog is weaned off the calcium. Again, Casal stresses that long-term calcium supplementation is discouraged as it can predispose the bitch to hypocalcemia with subsequent litters.

However, simply because a dog has had hypocalcemia does not mean she will necessarily have it again, Casal says. This is especially true if the next litter is smaller. If the bitch has another large litter, consider supplementing the puppies with milk replacer. Casal also recommends supplementing the bitch’s regular food with puppy food toward the second half of gestation. And, she says, don’t feed a homemade diet to breeding bitches. “High quality nutrition is very important,” she says. “Stay away from the raw foods if possible. You never know what the calcium levels are.”

However, with proper nutrition, the dam can be expected to nurse the next litter without a recurrence.

Casal says there may also be an as-yet-unproven hereditary component to puerperal hypocalcemia.

In the meantime, breeders who know the clinical signs can get affected dams to the vet in plenty of time to treat them with little or no aftereffect.