Vitamin D is a collective term for a class of open-ring steroidal compounds derived from the cyclopentane polyhydrophenanthrene ring, which possess anti-rickets properties. The main components of vitamin D are cholecalciferol (vitamin D3) and ergocalciferol (vitamin D2). Vitamin D3 is a product of dehydrocholesterol in animal skin after exposure to ultraviolet light, collectively known as calciferol.
Vitamin D is crucial for cats. Studies have found that cats with higher vitamin D levels during hospitalization have a greater chance of recovery. Researchers at the Royal Veterinary Research School at the University of Edinburgh discovered this phenomenon, and the findings could help veterinarians provide better advice to pet owners regarding their pets' prognosis.
Researchers also tested blood samples from 99 critically ill cats treated at the university's small animal hospital. With the owners' consent, the team examined the cats' vitamin D levels. They found that cats with higher levels of vitamin D in their blood were more likely to survive 30 days after admission compared to cats with the lowest levels. This can help veterinarians predict which animals are more likely to recover.
Researchers say this study highlights the need to understand more about whether vitamin D affects cats' susceptibility to certain diseases and what impact it has on the consequences of those illnesses. Therefore, ensuring your cat receives adequate vitamin D can potentially extend its lifespan. 
I. Clinical symptoms of vitamin D deficiency in cats
Young pets may exhibit rickets symptoms, initially manifesting as pica, digestive disorders, a tendency to lie down, lameness, slow growth and development, cartilage hypertrophy, swelling of the limb joints, and bending of the limbs when standing; in severe cases, the pet may stand in an "X" or "O" shape. Bone hardness is significantly reduced, fragility increases, and fractures are common. Serum alkaline phosphatase activity is elevated, while blood calcium and phosphorus levels are decreased. Adult pets, on the other hand, may exhibit osteomalacia and osteoporosis. Early symptoms include digestive disorders primarily characterized by pica, followed by motor impairment, stiffness in the lower back and legs, lameness in one or more limbs, or alternating lameness in different limbs, and a tendency to lie down and refuse to stand. Subsequently, skeletal swelling and deformities will appear, with swollen and painful limbs, swelling at the costochondral junctions of the ribs, and easy fractures. Serum calcium levels show no significant change, serum phosphorus levels are significantly decreased, and serum alkaline phosphatase levels are significantly elevated.
II. Causes of Vitamin D Deficiency in Cats
Insufficient sunlight exposure over a long period can lead to vitamin D deficiency. Young pets experience rapid growth and development during weaning and early sexual maturity, resulting in significantly increased calcium and phosphorus deposition. Adult pets are also prone to losing large amounts of calcium and phosphorus during late pregnancy and lactation. These factors can all increase the body's need for vitamin D, and insufficient supplementation can easily lead to deficiency. Gastrointestinal diseases affect vitamin D absorption, liver diseases affect the conversion and storage of vitamin D in the liver, and kidney diseases can affect the hydroxylation of vitamin D. Additionally, strontium and cynomorium in feed can interfere with vitamin D utilization, and excessive vitamin A content can also hinder the body's use of vitamin D, causing relative deficiency.
III. Treatment of Vitamin D Deficiency
Vitamin D deficiency often reduces the body's absorption and storage of calcium. Because the disease progresses slowly, by the time typical symptoms appear, the cat not only lacks vitamin D but also suffers from osteoporosis due to severe calcium deficiency. Therefore, treatment for vitamin D deficiency usually involves a two-pronged approach: supplementing both vitamin D and calcium. Initially, 5-10 mL of cod liver oil and 2-3 g of calcium can be administered daily for 5-6 days, followed by a 2-3 day break with the cod liver oil, then continued until recovery. If the cat has developed severe skeletal deformities, an intramuscular injection of 100,000-200,000 IU of vitamin D3 and an intravenous injection of 2-3 g of calcium chloride or calcium gluconate are necessary before continuing the above treatment. During treatment, the cat's eating and digestive status should be closely monitored. If digestive problems occur, stomachic agents should be used as appropriate.
IV. Vitamin D Requirements, Symptoms of Poisoning, and Treatment in Pets
The minimum vitamin D requirement for a cat during its growth period is 750 IU per kilogram of dry matter in its diet, while the minimum requirement for adult cats during the maintenance period is 500 IU per kilogram of dry matter in their diet, with a maximum of 10,000 IU.
Vitamin D poisoning can occur from long-term feeding of feed containing excessive amounts of vitamin D or from feeding pets animal liver or cod liver oil. The main clinical manifestations of poisoning include anorexia, diarrhea, elevated serum calcium levels, normal or slightly elevated serum phosphorus levels, and bone decalcification. Long-term high calcium levels can also cause multiple peripheral calcifications, such as kidney stones and osteoporosis. Upon discovering poisoning, immediately adjust the diet. In addition to symptomatic treatment, administer prednisolone injections, or subcutaneous injections of furosemide or calcitonin.
