Milk fever in cats is a dangerous drop in blood calcium that strikes nursing mothers, usually during the first few weeks after giving birth. The medical name is eclampsia (also called puerperal tetany), and while it’s more commonly discussed in dogs, it can happen in cats too. Left untreated, it can progress from restlessness to seizures within hours.
Why It Happens
A nursing queen loses significant amounts of calcium through her milk. Normally, the body compensates by pulling calcium from bone stores into the bloodstream. In milk fever, that process can’t keep up with demand. The result is a sharp decline in circulating calcium, a state called hypocalcemia. Normal blood calcium in cats falls between 9 and 11 mg/dL; eclampsia occurs when levels drop below 9 mg/dL.
Inadequate calcium intake during late pregnancy and early lactation compounds the problem. Queens with large litters face higher risk simply because more kittens mean more milk production and more calcium leaving the body. Cats that were poorly nourished before or during pregnancy are also more vulnerable.
When It Typically Occurs
Milk fever most often appears during early lactation, when the queen’s milk production is ramping up to meet her kittens’ needs. This usually means the first one to four weeks after birth, though cases can occasionally develop in late pregnancy or later in the nursing period. The condition is uncommon in cats overall, but when it does occur, the timeline tends to line up with peak milk demand.
Signs to Watch For
Symptoms tend to escalate quickly, sometimes over just a few hours. Early signs are easy to miss or misinterpret:
- Restlessness and panting: The queen may seem unusually anxious, pace around the nesting area, or breathe rapidly for no obvious reason.
- Facial twitching and rubbing: Muscle twitches around the ears and face are a hallmark early sign. Some cats rub at their faces repeatedly.
- Stiff, uncoordinated walking: You may notice a rigid gait, almost as if the cat’s legs aren’t bending properly.
- Loss of interest in kittens: A queen who was previously attentive may suddenly ignore or growl at her litter.
If calcium continues to fall, the signs become severe. The cat may develop full-body muscle spasms (tetany), collapse, or have seizures. Body temperature can spike dangerously high from sustained muscle contractions. Exercise or excitement can trigger or worsen symptoms at any stage, so keeping the environment calm matters.
How It’s Diagnosed and Treated
A veterinarian can confirm milk fever with a blood test measuring calcium levels, but in a nursing queen showing classic signs, treatment often begins immediately because speed is critical. Calcium is given intravenously under careful monitoring, since administering it too quickly can cause heart problems. Most cats respond rapidly once calcium reaches the bloodstream, with tremors and stiffness resolving within minutes to hours.
After the initial crisis, the queen typically goes home on oral calcium supplements and is monitored closely for recurrence. In many cases, the kittens need to be partially or fully weaned onto a milk replacer to reduce the calcium drain on the mother. If the kittens are old enough (usually around three to four weeks), the vet may recommend accelerating the transition to solid food. For younger kittens, bottle feeding with a commercial kitten milk replacer bridges the gap.
Recurrence is a real concern. Once a cat has had an episode, the underlying imbalance can return if she resumes full nursing duties too soon.
Preventing Milk Fever
Feeding a high-quality diet formulated for reproduction and lactation is the single most important preventive step. These diets are calorie-dense and contain the elevated calcium and phosphorus a pregnant or nursing cat needs. Phosphorus requirements are highest during growth, late gestation, and peak lactation because the mineral is essential for building the kittens’ skeletal tissue.
One counterintuitive point: supplementing extra calcium during pregnancy (before the kittens are born) can actually increase the risk. Excess calcium during gestation suppresses the hormonal system that mobilizes calcium from bone. Then, when lactation starts and calcium demand surges, the body is slow to respond. The safer approach is to feed a properly balanced diet rather than adding calcium supplements on your own. The calcium-to-phosphorus ratio matters too. A diet with too much phosphorus relative to calcium, or with highly absorbable forms of phosphorus, can throw off mineral balance and has been linked to kidney problems in cats over time.
During lactation, calcium supplementation may be appropriate, but only under veterinary guidance and typically only after the kittens are born. Queens nursing large litters benefit from free-choice feeding (food available at all times) since their caloric and mineral needs can be two to three times higher than normal.
What Recovery Looks Like
Most cats recover fully from an episode of milk fever as long as treatment comes quickly. The acute danger passes once calcium levels stabilize, which usually happens within the first day of treatment. The longer-term challenge is managing the rest of the nursing period without a relapse. This often means supplementing the kittens’ nutrition, continuing oral calcium for the queen, and weaning the litter as early as is safely possible. Cats that have had eclampsia with one litter are at higher risk with future litters, so planning ahead with your vet before the next pregnancy is worthwhile.