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To compare the effects of short-term dietary supplementation with vitamin D3 and 25-hydroxyvitamin D3 (25[OH]D3) on indicators of vitamin D status in healthy dogs.


13 purpose-bred adult dogs.


20 extruded commercial dog foods were assayed for 25(OH)D3 content. Six dogs received a custom diet containing low vitamin D concentrations and consumed a treat with vitamin D2 (0.33 μg/kg0.75) plus 1 of 3 doses of 25(OH)D3 (0, 0.23, or 0.46 μg/kg0.75) once daily for 8 weeks followed by the alternate treatments in a crossover-design trial. In another crossover-design trial, 7 dogs received a custom diet supplemented with vitamin D3 or 25(OH)D3 (targeted content, 3,250 U/kg [equivalent to 81.3 μg/kg] and 16 μg/kg, respectively, as fed) for 10 weeks followed by the alternate treatment. In washout periods before each trial and between dietary treatments in the second trial, dogs received the trial diet without D-vitamer supplements. Dietary intake was monitored. Serum or plasma concentrations of vitamin D metabolites and biochemical variables were analyzed at predetermined times.


25(OH)D3 concentrations were low or undetected in evaluated commercial diets. In the first trial, vitamin D2 intake resulted in quantifiable circulating concentrations of 25-hydroxyvitamin D2 but not 24R,25-dihydroxyvitamin D2. Circulating 25(OH)D3 concentration appeared to increase linearly with 25(OH)D3 dose. In the second trial, circulating 25(OH)D3 concentration increased with both D vitamer–supplemented diets and did not differ significantly between treatments. No evidence of vitamin D excess was detected in either trial.


Potency of the dietary 25(OH)D3 supplement estimated on the basis of targeted content was 5 times that of vitamin D3 to increase indicators of vita-min D status in the study sample. No adverse effects attributed to treatment were observed in short-term feeding trials. (Am J Vet Res 2021;82:722–736)

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in American Journal of Veterinary Research