Short communication: Serum and tissue concentrations of vitamin D metabolites in beef heifers after buccal dosing of 25-hydroxyvitamin D ₃

Sixteen crossbred (British x Continental; average unshrunk body weight = 507.9 kg; SD = 45.6 kg) beef heifers fed a steam-flaked corn-based finishing diet with melengestrol acetate (0.4 mg/heifer daily) included to suppress estrus were used in a completely random design to evaluate the efficacy of buccal administration of 0, 10, 100, or 1000 mg of 25-hydroxyvitamin D₃, (25-OH D₃). Serum Ca, P, Mg, 25-OH D₃,1,25- dihydroxyvitamin D [1,25-(OH)₂ D₃], albumin, and protein were measured 24 h before dosing (-24 h), at dosing (0 h), and 6 and 24 h after dosing, after which the cattle were slaughtered at a commercial facility. Samples of kidneys, liver, longissimus lumborum, and triceps brachii were collected and evaluated for concentrations of 1,25-(OH)₂ D ₃. With -24 and 0 h as baseline covariates, a significant time x treatment interaction was observed for serum 25-OH D₃ and Ca concentrations, but not for serum 1,25-(OH)₂ D₃. Supplemental 25-OH D₃ doses of 100 and 1000 mg significantly increased serum 25-OH D₃ at 24 h after dosing, 1,25-(OH)₂ D₃ at 6 and 24 h after dosing, and serum Ca at 24 h after dosing. Similarly, buccal dosing of 1000 mg of supplemental 25-OH D₃ significantly increased (approximately 2- to 3-fold) concentrations of 1,25-(OH)₂ D₃ in the kidney, liver, and longissimus lumborum relative to the other 3 treatments but not in triceps brachii. Serum albumin, protein, P, and Mg were not affected by treatment. Based on these results, buccal administration of 100 and 1000 mg 25-OH D₃ increased vitamin D₃ metabolites in serum and tissues, and it should be an effective method of delivering the vitamin.