Effect of increasing dietary vitamin A on bone density in adult dogs.

Abstract

There has been an increase in vitamin A fortification of livestock feeds resulting in increased residual vitamin A in organ meats, which are often used in canned dog foods. The effect on bone density of feeding various concentrations of vitamin A in a canned dog food product was investigated. Thirty-two random-source dogs were assigned to four treatments in a randomized complete block design. The diets contained 15,000, 50,000, 116,000, or 225,000 IU vitamin A/1,000 kcal ME. Diets were fed up to 1 yr. Computed tomography was used to determine bone density of the right tibia at 0, 3, 6, 9, and 12 mo. Computed tomography is a more sensitive technique for determining bone density in vivo than conventional x-rays. There were no differences (P > .10) in tibia bone or marrow density in any of the dogs fed the various concentrations of vitamin A. There was no interaction of time x diet on bone density (P > .05) or bone marrow density (P > .05). In addition, there were no changes in serum alkaline phosphatase, calcium, or phosphorus. These results indicate that concentrations of vitamin A three times the recommended maximum safe amount (71,429 IU/1,000 kcal ME) are not detrimental to normal bone health in dogs. Therefore, these data support the hypothesis that canines are less sensitive to excess vitamin A in the diet than some other mammals.

The distribution of vitamin A and retinol-binding protein in the blood plasma, urine, liver and kidneys of carnivores

“…The high levels of lipoprotein bound retinyl esters in carnivores are not homeostatically regulated as is retinol, but depend greatly on actual vitamin A intake in food [24,26]. Notwithstanding, the occurrence of retinyl esters in the blood plasma of canines and mustelids is not associated with any sign of vitamin A intoxication [5,19,23]. This reduced susceptibility of carnivores to high levels of retinyl esters in blood plasma raises questions concerning the possible regulatory mechanisms protecting carnivores.…”

Vitamin and Mineral Requirements

“…Experimental vitamin A deficiency results in abnormal bone growth and neurological disorders in young animals. 8,9 The cat differs from the dog because it cannot use carotenoids and must consume all of its vitamin A as preformed retinyl palmitate or free retinol from animal tissues. If the deficiency persists, shortening and thickening of the long bones occur, along with abnormal development of the bones of the skull.…”