Vitamin deficiency in dogs: symptoms, causes and treatment

Overview

Vitamins have different functions

Vitamins are divided into fat-soluble A, D, E and K and water-soluble B and C vitamins. Many water-soluble vitamins help enzymes function. Vitamin A is needed for vision and epithelial health, among other functions. Vitamin D regulates calcium and phosphorus absorption and deposition in bone. Vitamin E acts as an antioxidant, protecting cells from oxidative injury. Vitamin K deficiency impairs clotting.

Nutritional deficiency diseases are rare with appropriate complete food or professionally balanced home-made diets. However, dietary adequacy and vitamin absorption are separate issues.

Low blood B12 has been found in 19–61% of dogs with chronic inflammatory intestinal disease. Low folate, or vitamin B9, has occurred in 1–47% of the same disease group. These figures concern dogs with intestinal disease rather than vitamin status across all dogs.

Fat-soluble vitamins can accumulate in the body. Excess water-soluble vitamins generally leave more readily because less is stored. B12 is also stored in the liver.

Causes

Dietary imbalance

Food made from few ingredients can lack nutrients. An assessment of 200 home-made recipes found 95% deficient in at least one essential nutrient. More than 83% had multiple deficiencies. These were calculated recipe deficiencies rather than equivalent proportions of dogs developing disease.

Thiaminase enzymes in raw freshwater fish and shellfish can destroy thiamine, or vitamin B1. Excessive processing heat can also destroy thiamine. Raw egg white contains avidin, which binds biotin and prevents absorption. Nevertheless, naturally occurring biotin deficiency is very rare in dogs.

Impaired absorption and metabolism

Vitamin B12, or cobalamin, is mainly absorbed in the final small intestinal section. Absorption requires intrinsic factor, produced mainly in the canine pancreas. More than 80% of dogs with exocrine pancreatic insufficiency, or EPI, are B12-deficient. Chronic intestinal disease can also reduce absorption. A rare inherited disorder can impair B12 absorption or metabolism.

Availability of different vitamins

Dogs can also use plant beta-carotene as a vitamin A source. They can form niacin from the essential amino acid tryptophan, making deficiency rare with balanced feeding. Dogs need dietary vitamin D because their skin has little of the precursor needed to use sunlight.

Intestinal microbes also affect vitamin K availability, and microbial changes can predispose to deficiency. A shortage therefore does not always result from one food ingredient.

Dietary B12 comes particularly from animal ingredients, while unfortified plant products contain very little or none.

Risk factors

Growing puppies need balanced food suited to their growth stage and nutritional needs. Vitamin D or mineral deficiency can damage growth plates. Rickets therefore does not always mean vitamin D deficiency alone.

Home feeding is risky when a recipe is unbalanced or supplements and ingredients are changed without guidance. Longstanding gastrointestinal disease particularly predisposes dogs to B12 and folate deficiency. Inherited B12 malabsorption has been described in Giant Schnauzers, Border Collies and Beagles. This concerns that rare disorder rather than every vitamin deficiency.

Typical symptoms

Signs depend on the missing vitamin and the disease causing deficiency.

• Your dog loses weight or appetite.
• Diarrhoea persists or gastrointestinal signs worsen.
• A puppy grows poorly or fails to develop as expected.
• Muscles are weak or movement becomes clumsy.
• Your dog limps or bones are painful to touch.
• Dim-light vision declines or inflammatory eye changes develop.
• Bleeding lasts longer or occurs more readily.

Oral inflammation and bloody diarrhoea can accompany rare niacin, or vitamin B3, deficiency. Folate or biotin deficiency can cause skin and coat changes, for example.

Severe vitamin E deficiency can also impair reproduction, including sperm formation or puppy viability.

Complications and consequences

Organ injury and growth problems

Severe B12 deficiency can cause anaemia and permanent neurological injury. Rickets can cause long bone or vertebral fractures. Vitamin A deficiency can damage the cornea and retina. Vitamin K deficiency can cause excessive bleeding.

Acute thiamine deficiency can injure the nervous system, while prolonged deficiency can alter heart muscle and peripheral nerve function. Low B12 is associated with a poorer outlook in chronic inflammatory intestinal disease.

Excess vitamins can also cause harm

Vitamin D overdose can raise blood calcium and phosphorus and cause permanent soft tissue calcification. Excess vitamin A can also cause skeletal changes, fractures and internal bleeding. Confirmed deficiency is therefore corrected specifically, rather than combining supplements randomly.

Very high vitamin E intake can disrupt absorption of other fat-soluble vitamins and cause A, D or K deficiency signs. High vitamin C supplementation raises concerns in dogs with calcium oxalate urinary stones because its breakdown increases urinary oxalate.

Diagnosis at the vet

The whole diet is reviewed

Dietary assessment considers the recipe, ingredients and whether feeding differs from the original plan. Every component of a home-made recipe matters: changing an oil, for example, can alter nutrient balance. In systems using these labelling categories, packaging identifies 'complete feed' or 'complementary feed' intended to supplement other food.

Vitamin tests and underlying disease

With prolonged intestinal signs, B12 measurement helps assess severity and concurrent problems. B12 near the lower reference limit can already involve intracellular deficiency. Metabolic markers such as methylmalonic acid, or MMA, or homocysteine can refine functional adequacy assessment when needed. Folate is interpreted alongside other tests because dysbiosis or B12 deficiency can raise it.

A TLI blood test can investigate pancreatic insufficiency. Suspected rickets needs skeletal and biochemical assessment alongside diet. X-rays may show growth plate and bone abnormalities. Poor coat condition or tiredness alone cannot establish a particular deficiency: these occur with many deficiencies.

Inherited B12 malabsorption can involve anaemia, low neutrophils and abnormally enlarged marrow cells.

Checking food composition

Laboratory nutrient analysis can help check the practical delivery of a long-term home-made diet when needed. This distinguishes calculated recipe contents from the actual ration.

Treatment

Correct both deficiency and its cause

Your vet plans replacement according to the deficient vitamin and whether the cause is diet or malabsorption. Inadequate food is balanced for life stage and health. A vet with nutritional expertise can formulate an individual home-made recipe. Adding an occasional ingredient does not replace calculating the whole diet.

Malabsorption also requires treatment of intestinal disease or another underlying problem. EPI treatment includes pancreatic enzyme replacement and B12 supplementation. B12 deficiency can itself worsen digestive signs, so correction forms part of overall care.

B12 can be replaced through different routes

With chronic inflammatory intestinal disease, low or low-normal B12 is replaced orally or by injection. Four randomised studies included 126 dogs with intestinal disease receiving oral or subcutaneous B12. Blood B12 normalised in every dog in these studies. Functional deficiency markers improved or normalised in 3 studies. This evidence concerns intestinal disease, and the same approach does not automatically suit every inherited malabsorption disorder.

B12 status is reassessed after treatment. Folate or vitamin D replacement may be considered for confirmed deficiency, particularly with D deficiency and hypocalcaemia, meaning low calcium.

Nutritional treatment of rickets

Rickets treatment corrects dietary deficiencies and nutrient imbalance. The outlook is good if bones have not fractured and growth plates have no permanent damage. Large amounts of vitamins A or D are not used as a precaution because excess can cause serious injury.

Prevention

The main diet should be complete food appropriate for life stage or a professionally formulated, balanced home-made diet. Under these labelling categories, complete feed is intended to cover all daily nutritional needs. Complementary feed supplements other feeding and is not equivalent on its own.

Follow a home-made recipe, including supplements and ingredients, without substitutions of your own. Simply rotating recipes may not correct deficiencies because several recipes lack the same nutrients. Dogs can produce vitamin C in the liver from glucose, so no equivalent dietary requirement has been defined as for essential dietary vitamins.

Cooking fish destroys thiaminase enzymes that break down thiamine. This differs from losing thiamine itself through excessive food processing.

Important for dog owners

Bring names and labels for every food and supplement, plus the exact home-made recipe. Record portions and what has actually been substituted or omitted. Departing from the recipe can change nutritional balance. Agree response monitoring: B12 status is rechecked after replacement.

Weight, appetite, stools, movement and puppy growth provide information about changing signs. Coat appearance alone cannot determine a need to supplement a vitamin already supplied adequately. In intestinal disease, deficiency risk may involve absorption rather than food originally lacking vitamins.

Frequently asked questions

Can a dog eating complete food develop vitamin deficiency?

Nutritional deficiency diseases are rare with appropriate balanced complete food. However, B12 deficiency can develop if intestinal disease impairs absorption. Pancreatic insufficiency is another important example because dogs need pancreatic intrinsic factor to absorb B12.

Is dietary variety enough to balance home-made food?

Variety alone may not help if different recipes share the same deficiencies. In an assessment of 200 recipes, 95% lacked at least one essential nutrient. The whole daily home-made diet therefore needs nutritional calculation tailored to your dog.

Are vitamin supplements always harmless?

Excess vitamins A or D can cause serious injury. Fat-soluble vitamins can accumulate. Combining supplements is therefore not automatically safe: assess their need through the whole diet, confirmed deficiency and your dog's disease.

Can B12 deficiency be treated without injections?

With chronic inflammatory intestinal disease, B12 can be replaced orally or by injection. In 126 dogs across 4 randomised studies, blood levels normalised with both routes. Your vet selects delivery and monitoring individually, and intestinal disease treatment is not generalised to every inherited metabolic disorder.

Will sunlight correct vitamin D deficiency?

Vitamin D is an essential dietary vitamin for dogs. Canine skin contains very little of the substance ultraviolet light would convert into vitamin D3. More outdoor time alone therefore does not correct dietary deficiency: nutrition and any other disease need investigation.