Abstract
Feline vitamin D status is based on dietary consumption but metabolism of this essential nutrient and the efficacy of supplementation forms are poorly described in cats. The aim of this study was to further elucidate the metabolites of vitamin D2 in cats and to compare the effectiveness of vitamin D2 and 25(OH)D2 for increasing feline vitamin D status. Eight adult male castrated domestic shorthair cats received vitamin D2 or 25(OH)D2 in a single crossover design. Vitamin D2 was dosed daily in a molar equivalent dosage to vitamin D3 ingested in the diet while 25(OH)D2 was provided at a daily dose of 20% molar equivalent intake of dietary vitamin D3 based on its expected higher potency. Plasma concentrations of 25-hydroxyvitamin D epimers were evaluated at baseline then every 2 weeks for a total of 10 weeks. Analysis of multiple vitamin D metabolite concentrations was completed at the end of each supplementation period, followed by a washout period preceding the second phase of the crossover trial. Results showed that supplementation with 25(OH)D2 more effectively and rapidly raised circulating 25(OH)D2 levels in cat plasma compared to vitamin D2. Formation of C-3 epimers of 25(OH)D3, 25(OH)D2, and 24,25R(OH)2D3, but not 24,25(OH)2D2, were observed in feline plasma. The abundant concentrations of epimeric forms of vitamin D metabolites found in circulation suggest that these metabolites should be considered during vitamin D analyses in cats. Further studies using 25(OH)D and vitamin D2 forms are needed to conclude safety and efficacy of these vitamers for supplementation in this species.
Highlights
Unlike some mammals, cats cannot synthesize adequate vitamin D from UV light and have a dietary requirement for this nutrient [1]
The aims of this study were: [1] to identify vitamin D metabolites present in cats, including epimeric forms of vitamin D2 and D3 metabolites that have been previously identified in other species, and [2] to compare the effectiveness of vitamin D2 and 25(OH)D2 for increasing vitamin D status in cats
While vitamin D3 intake varied slightly with adjustments to food intake, this did not appear to have a substantive effect on D status as there was no significant crossover phase effect on plasma 25(OH)D3 concentrations
Summary
Cats cannot synthesize adequate vitamin D from UV light and have a dietary requirement for this nutrient [1]. Cholecalciferol (vitamin D3) is found in animal tissues and is provided in most commercial feline diets through ingredients or supplementation [2]. Ergocalciferol (vitamin D2) is a fungal and plant source of vitamin D [3] that is currently found in feline supplements for homemade diets. This may offer an alternative for cats that must avoid specific animal protein sources due to adverse food reactions or food allergies. Vitamin D2 is less likely to induce toxicity in cats when provided at an equivalent dose to D3 [4]. Knowledge regarding vitamin D metabolism, including utilization of vitamin D2, in cats is extremely limited
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