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Calcium Metabolism in Glucocorticoid-Treated Pony Foals

Cornell University, Ithaca, NY 14853

Pony foals were injected intramuscularly with 0, 0.5, or 5.0 mg dexamethasone per 100 kg body weight daily for up to 11 months. True absorption of dietary calcium was inhibited by treatment at 18 days (57% versus 14% of intake; P < .01) and 10 months (72% versus 55% versus 43%; P < .01), but not at 2 or 7 months, and was independent of age and treatment related decreases in intestinal calcium binding protein activities. Uninary excretion of calcium was increased by treatment through 7 months but decreased at 10 months. Treatment for 18 days resulted in total calcium excretions equivalent to 127% of dietary intake. All animals were in positive calcium balance thereafter. Endogenous fecal calcium excretion was not affected by treatment, age, or sex, averaging 18.0 mg per kg body weight per day. At 2 months, rates of calcium deposition into bone were 13.02, 7.01 and 6.83 g per 100 kg per day in ponies treated with 0, 0.5, and 5.0 mg per 100 kg, respectively. Corresponding rates of calcium removal from bone were 5.41, 1.88, and 2.69 g per 100 kg per day. These rates remained significantly inhibited in the treated ponies at 7 and 10 months. The net effect of dexamethasone treatment was an inhibition of bone turnover: calcium removal was suppressed more than calcium deposition.

KEY WORDS: • calcium metabolism • calcium kinetics • bone turnover • equine • glucocorticoid treatment

¹ Present address: Department of Animal Science, University of Maryland, College Park, MD 20742.

² To whom reprint requests should be sent.

³ Department of Pathology, New York State College of Veterinary Medicine, Cornell University, Ithaca, NY 14853.

⁴ Equine Research Program, New York State College of Veterinary Medicine, Cornell University, Ithaca, NY 14853.

⁵ Department of Animal Science, Morrison Hall, Cornell University, Ithaca, NY 14853.

Manuscript received 3 June 1981.