Short answer: Vitamin D (calciferol) is an essential fat-soluble vitamin in dogs and cats with two principal dietary forms: D2 (ergocalciferol) from plant and fungal sources and D3 (cholecalciferol) from animal sources. Per Mellanby 2011 (Vet Rec) canine vitamin D physiology review and How 1994 (Endocr Res) canine cutaneous vitamin D synthesis work, dogs and cats cannot synthesize adequate cholecalciferol from cutaneous UVB exposure — the hair coat blocks UVB penetration and the 7-dehydrocholesterol-to-cholecalciferol pathway in canine and feline skin is far less efficient than in humans. Dogs and cats therefore depend on dietary vitamin D throughout life. Per AAFCO 2024 Official Publication Dog Food Nutrient Profiles, canine formulas require a minimum 500 IU vitamin D per kg dry matter and a maximum of 3,000 IU vitamin D per kg dry matter; feline formulas require a minimum of 280 IU per kg dry matter and a maximum of 30,080 IU per kg dry matter. Per FDA-CVM 2018–2024 vitamin D toxicity advisories, multiple commercial dry kibble lines have been recalled following formulation errors that produced batches exceeding the AAFCO maximum by 10–70 fold, with subsequent clinical hypervitaminosis D in pets per Crossley 2017 (J Am Anim Hosp Assoc). Per Galler 2012 (J Vet Intern Med) and Selting 2016 (J Vet Intern Med), vitamin D status is also linked to canine renal disease management and immunoregulatory pathways. The KibbleIQ rubric scores vitamin D positively when present at AAFCO-substantiated levels in any AAFCO-complete formulation; the rubric does not deduct credit for the supplement-form presence of vitamin D because every AAFCO-complete formulation requires it.

D2 vs D3 forms and dog or cat biological activity

Per Tripkovic 2012 (Am J Clin Nutr) D2 vs D3 bioequivalence review and Hurst 2020 (J Steroid Biochem Mol Biol), the two dietary forms of vitamin D are ergocalciferol (D2) derived from UV-irradiated ergosterol in plants and fungi (mushrooms, yeast, lichen-derived commercial supplements) and cholecalciferol (D3) derived from 7-dehydrocholesterol in animal-source ingredients (fish liver oils, fatty fish, egg yolk, animal liver, lanolin-derived commercial supplements). Both forms are biologically inactive precursors that must undergo two enzymatic hydroxylation steps: 25-hydroxylation in liver to 25-hydroxyvitamin D (calcidiol) — the principal circulating storage form measured in plasma testing — and 1α-hydroxylation in kidney to 1,25-dihydroxyvitamin D (calcitriol) — the active hormonal form binding the vitamin D receptor (VDR).

Per Mellanby 2011 (Vet Rec) and Hurst 2020, D3 cholecalciferol has approximately 2–5 times greater biological activity than D2 ergocalciferol in dogs on an IU-equivalent basis because D3 maintains higher plasma 25-hydroxyvitamin D levels and longer biological half-life. AAFCO 2024 ingredient definitions accept both D2 and D3 sources for canine and feline vitamin D requirement substantiation, but commercial pet food formulations almost universally use D3 cholecalciferol due to the bioequivalence advantage. The cholecalciferol cluster overlaps with our cod liver oil explainer (a primary natural D3 source) and our vitamin D3 sourcing controversy page for synthetic vs natural source debate.

Pet food source ingredients and AAFCO range

Per AAFCO 2024 Official Publication Dog Food Nutrient Profiles, the canine vitamin D requirement is set at a minimum 500 IU per kg dry matter (12.5 mcg per kg dry matter) and a safe upper limit (SUL) of 3,000 IU per kg dry matter (75 mcg per kg dry matter). Per AAFCO 2024 Cat Food Nutrient Profiles, the feline vitamin D requirement is set at a minimum 280 IU per kg dry matter (7 mcg per kg dry matter) and a safe upper limit of 30,080 IU per kg dry matter (752 mcg per kg dry matter) — an order of magnitude higher SUL than canine reflecting greater feline tolerance per NRC 2006 Nutrient Requirements of Dogs and Cats.

Pet food meets the vitamin D requirement through three principal source classes: (1) direct supplement-form D3 premix (the most common source — vitamin D3 powder coated on dicalcium phosphate or other inert carrier), (2) fish-source ingredients (cod liver oil at ~10,000 IU per teaspoon, salmon oil at ~400–600 IU per teaspoon, fatty fish meal), and (3) egg yolk and animal liver at modest contribution. The peer fat-soluble vitamin cluster overlaps with our vitamin A explainer, mixed tocopherols explainer (vitamin E), vitamin E forms explainer, and vitamin K menaquinones explainer.

Vitamin D toxicity history and pet food recall context

Per FDA-CVM 2018 advisory on excess vitamin D in dry dog food and FDA-CVM 2020/2022/2024 follow-up advisories, multiple commercial dry kibble lines have been recalled following formulation errors that produced batches exceeding the AAFCO 3,000 IU per kg dry matter safe upper limit by approximately 10–70 fold. Documented affected brand-product-year pairs include the Blue Buffalo 2010 recall (per our Blue Buffalo 2010 vitamin D recall page), Fromm 2016 and 2021 recalls (per our Fromm 2016 recall page and Fromm 2021 recall page), Hill’s Science Diet 2019 canned line recall (per our Hill’s 2019 recall page), and Purina Pro Plan Veterinary Diets 2023 recall (per our Purina Pro Plan veterinary 2023 recall page).

Per Crossley 2017 (J Am Anim Hosp Assoc) canine hypervitaminosis D clinical review and Mellanby 2005 (Vet Rec), clinical hypervitaminosis D in dogs presents with polydipsia, polyuria, hypercalcemia, soft-tissue mineralization (kidney, lung, heart, vasculature), and renal injury. The dose threshold for acute toxicity in dogs is approximately 0.1 mg/kg cholecalciferol orally (~4,000 IU per kg body weight) per Rumbeiha 2000 (J Am Vet Med Assoc) canine cholecalciferol toxicosis review. The pet food formulation error context is that supplement-form D3 is a potent input at small quantities, and premix-mixer calibration errors or duplicate-addition errors can produce 10–70x overage with downstream toxicity. The broader toxicity framework lives at our vitamin D toxicity controversy page.

Vitamin D in canine kidney disease and immunoregulation

Per Galler 2012 (J Vet Intern Med) canine vitamin D and renal disease work and Polzin 2017 (Vet Clin North Am) IRIS staging of canine CKD, vitamin D status is a clinically relevant marker in canine chronic kidney disease management. Renal 1α-hydroxylase activity (the kidney enzyme that converts 25-hydroxyvitamin D to active calcitriol) declines in progressive CKD, producing functional vitamin D deficiency despite adequate substrate. The Polzin 2017 IRIS protocol includes calcitriol replacement therapy in IRIS Stage 2–4 canine CKD with confirmed secondary hyperparathyroidism. Dietary phosphorus restriction is the cornerstone of canine CKD management; vitamin D supplementation is selective and case-dependent.

Per Selting 2016 (J Vet Intern Med) canine vitamin D and immunology review, vitamin D status modulates innate and adaptive immune function through VDR signaling in macrophages, T-cells, and B-cells. Selting 2016 documented an inverse association between 25-hydroxyvitamin D status and infection risk, neoplasia risk, and immune-mediated disease risk in dogs, though the causal direction is unsettled and intervention trial evidence is limited. The kidney disease framework overlaps with our best dog food for kidney disease guide. Phosphorus, calcium, and vitamin D form a tightly coupled regulatory triad — see our calcium explainer for the calcium side of the equation, and our Ca:P ratio controversy page for adult-dog calcium:phosphorus management context.

How KibbleIQ scores vitamin D

The KibbleIQ Dry Kibble Rubric treats vitamin D as a required nutrient supplied universally in AAFCO-complete formulations. Every AAFCO-substantiated canine or feline complete-and-balanced formula must meet the AAFCO 2024 vitamin D minimum (500 IU/kg DM canine, 280 IU/kg DM feline), so vitamin D presence does not differentiate formulations on a positive-credit basis. Formulations using cholecalciferol (D3) rather than ergocalciferol (D2) match the dominant commercial pet food practice and the Tripkovic 2012 / Mellanby 2011 bioequivalence preference for D3 in dogs; the rubric does not score this distinction.

The rubric does negatively flag formulations that have been subject to FDA-CVM vitamin D recall actions; the rubric’s recall-history overlay (under development per ROADMAP_v2 §R9) will apply a temporary score penalty to actively-recalled formulations during the recall window. For non-recalled formulations within the AAFCO range, vitamin D is treated as scoring-neutral but compliance-required. To check whether your dog’s food meets AAFCO substantiation, paste the ingredient list into the KibbleIQ analyzer. For methodology context, see our published methodology. For peer essential-nutrient context, see our calcium explainer and vitamin A explainer.