Objective: 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.
Animals: 13 purpose-bred adult dogs.
Procedures: 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.
Results: 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.
Conclusions and clinical relevance: 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 vitamin D status in the study sample. No adverse effects attributed to treatment were observed in short-term feeding trials.