Vitamin B12, or **cobalamin**, is one of the most important micronutrients in your dog’s body. It plays a critical role in red blood cell formation, nerve function, intestinal health, and energy metabolism. Yet despite its importance, B12 deficiency in dogs is **underdiagnosed and frequently overlooked** — often presenting as vague symptoms that resemble other common conditions.
In this comprehensive guide, we’ll explore what causes B12 deficiency in dogs, how to recognise the signs, how it’s diagnosed, and what nutritional strategies can support recovery and long-term health.

Why Is Vitamin B12 So Important for Dogs?

Vitamin B12 is a water-soluble vitamin that must be obtained from the diet. In dogs, it’s absorbed in the ileum (the final part of the small intestine), with the help of intrinsic factor — a protein secreted by the pancreas (unlike in humans, where it’s produced in the stomach).

Once absorbed, B12 supports several essential functions:

DNA synthesis
Red blood cell production
Neurological integrity and brain function
Fat and carbohydrate metabolism
Intestinal cell regeneration (enterocyte health)
Immune system regulation

Even subclinical deficiencies (not yet showing up on basic bloodwork) may interfere with digestion, reduce nutrient absorption, and sap your dog’s energy over time.

Symptoms of Vitamin B12 Deficiency in Dogs

Signs of B12 deficiency are non-specific and often confused with other conditions like food intolerances or IBS. Common symptoms include:

Weight loss or failure to gain (especially in puppies)
Chronic diarrhoea or soft stools
Lethargy and general weakness
Inappetence or fussy eating
Intermittent vomiting
Flatulence or digestive discomfort
Poor coat condition or dull fur
Neurological signs (e.g., tremors, confusion, ataxia)
Low folate or folate imbalance on bloodwork

In puppies or young dogs with genetic B12 absorption issues, growth may be stunted, and immune function may be compromised.

Common Causes of B12 Deficiency in Dogs

B12 deficiency can result from malabsorption, chronic disease, or poor dietary intake. Key causes include:

1. Inherited Malabsorption Syndromes

Certain breeds — including Border Collies, Beagles, and Giant Schnauzers — may carry genetic mutations that impair B12 absorption via the cubam receptor in the ileum. This condition, known as Imerslund-Gräsbeck Syndrome, requires lifelong supplementation.

📖 Study: Kook et al. (2012). JVIM 26(2):304–10

2. Exocrine Pancreatic Insufficiency (EPI)

Dogs with EPI lack intrinsic factor, which is required for B12 absorption. Supplementation is critical in managing EPI alongside enzyme therapy.

📖 Study: Batt et al. (1991). Res Vet Sci 51(2):180–7

3. Chronic Inflammatory Bowel Disease (IBD)

Inflammation of the ileum and disruption of the gut barrier can significantly reduce B12 absorption. These dogs may also suffer from gut dysbiosis and poor nutrient uptake.

4. Small Intestinal Bacterial Overgrowth (SIBO)

Excess bacteria in the small intestine compete for available B12, leading to deficiency. High folate levels are often a clue.

5. Liver Disease

Because the liver stores B12, chronic hepatic dysfunction may reduce B12 reserves, especially in combination with poor dietary intake.

6. Unbalanced Diets

Though rare in dogs fed complete commercial foods, deficiencies can occur in those fed:

Home-prepared diets without supplementation
Vegan or vegetarian diets (no natural B12)
Poor-quality raw diets
Meals lacking organ meats or animal products

7. Intestinal Surgery or Cancer

Surgical removal of the ileum or GI tumours can impair B12 uptake and long-term nutritional status.

How Is B12 Deficiency Diagnosed?

Diagnosis typically includes:

Serum cobalamin (B12) – levels should ideally be >350 ng/L
Methylmalonic acid (MMA) – elevated in cellular B12 deficiency
Folate testing – helps differentiate between dysbiosis and malabsorption
Pancreatic function testing – to check for EPI
Breed history and clinical signs

Note: Dogs may have normal serum B12 but still experience cellular deficiency. That’s why MMA testing is increasingly recommended.

Study: Toresson et al. (2015). JVIM 30(3):678–82

Nutritional and Medical Management of B12 Deficiency

1. Cobalamin Supplementation

There are two primary routes:

Parenteral (Injection)

250–1,000 µg subcutaneously once weekly for 4–6 weeks
Followed by monthly maintenance if required

Oral (Cyanocobalamin or Methylcobalamin)

High-dose oral B12 (e.g., 250–500 µg/day) can be effective — even in dogs with malabsorption — due to passive diffusion
Methylcobalamin may be more bioavailable, though veterinary research is still emerging

2. Therapeutic Diet

Dogs with B12 deficiency typically benefit from:

Highly digestible proteins (e.g., turkey, chicken, white fish)
Moderate fat levels (especially in GI or pancreatic cases)
Soluble fibre (e.g., pumpkin, psyllium) to aid gut healing
Probiotics and prebiotics to restore the microbiome
Digestive enzymes (if needed in EPI)

Foods to Avoid in B12-Deficient Dogs

Unbalanced homemade meals without supplementation
Raw bones or overly fatty meats (hard to digest with EPI or IBD)
Grain-free, high-legume kibbles (may worsen gut inflammation)
Vegan diets – contain no natural B12
Raw fibrous vegetables – may irritate an already inflamed gut

Long-Term Management & Monitoring

For chronic or genetic B12 deficiency, lifelong management may be needed. This includes:

Monitoring B12 levels every 3–6 months
Addressing underlying conditions (IBD, EPI, dysbiosis, etc.)
Ongoing dietary support with a complete, gut-friendly meal plan
Routine gut support – including probiotics, fibre, and deworming

Case Example: Giant Schnauzer with Imerslund-Gräsbeck Syndrome

A 6-month-old Giant Schnauzer presented with poor weight gain, chronic diarrhoea, and low energy. Serum cobalamin was 110 ng/L. Genetic testing confirmed a cubam receptor mutation. Following a 6-week course of weekly B12 injections, followed by monthly maintenance, the dog made a full clinical recovery.

📖 Reference: Fyfe JC et al. (2004). JVIM 18(4):463–6

Final Thoughts

Vitamin B12 deficiency in dogs is more common than many owners realise — and it’s often a sign of something deeper like IBD, EPI, or inherited malabsorption. With early detection, the right supplementation, and evidence-based dietary support, most dogs can enjoy a dramatic improvement in energy, digestion, and overall wellbeing.

Need Help Managing B12 Deficiency?

At The Canine Dietitian, we provide expert 1:1 consults, tailored diet plans, and long-term support for dogs with gastrointestinal or metabolic conditions.

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Peer-Reviewed References

Toresson L, Steiner JM, et al. (2015). JVIM, 30(3):678–82.
Kook PH, et al. (2012). JVIM, 26(2):304–10.
Fyfe JC, et al. (2004). JVIM, 18(4):463–6.
Batt RM, et al. (1991). Res Vet Sci, 51(2):180–7.
Simpson KW, et al. (2001). Vet Clin N Am Small Anim Pract, 31(5):1019–35.

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Vitamin B12 Deficiency in Dogs: Causes, Symptoms, and Long-Term Nutritional Management