J. Anim Sci.
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J. Anim Sci. 1979. 48:882-886.
© 1979 American Society of Animal Science
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Effect of Vitamin D and Sunlight on Growth and Bone Development of Young Ponies1

W. M. El Shorafa2, J. P. Feaster, E. A. Ott and R. L. Asquith

University of Florida, Gainesville 326113

Abstract

Twelve Shetland ponies were allotted equally to three treatments in a 2 x 3 factorially designed experiment to determine the effect of deprivation of sunlight and dietary vitamin D on growth and bone development: T1—ponies deprived of dietary vitamin D and sunlight; T2—ponies without sunlight but receiving 1,000 IU supplemental vitamin D per day; T3—ponies kept outdoors, without supplemental vitamin D. The ponies were maintained on experiment for 5 months after a period of 1 month on a vitamin D-deficient diet in a closed, windowless barn to reduce vitamin D stores. Two of the ponies in each of three treatment lots were 3 months old when assigned (group I) and two were 9 months (group II). The calcium-to-phosphorus ratio in the diet was 1.3:1.

No external signs of rickets were apparent in T1 ponies, but loss of appetite, discomfort on standing and decreased growth were noted. Feed conversion did not differ among treatment lots.

Bone ash concentration (percentage of dry, fat-free bone) was lower (P<.01) in ponies of T1 than in T2 and T3, and lower (P<.01) in group I than group II. Calcium, phosphorus and magnesium (percentage of bone ash) were normal with no difference due to treatment. Bone water concentration was higher (P<.05) for T1 ponies than for T2 or T3; an age effect was also noted, with group I higher than group II (P<.05).

Bone density was lower (P<.01) as was cortex area (P<.07) in T1 ponies than in T2 or T3, and group II ponies had greater (P<.05) bone cortex area than group I. Bones of T1 ponies within group I had lower breaking strength (P<.01) than those of T2 or T3 but differences were not significant within group II. In all treatments, group II ponies had higher (P<.05) breaking strength than group I.

Radiographs revealed that the epiphyseal plates at the distal end of the metacarpal bone and proximal ends of the first and second phalanges of T1, group I ponies were irregular, widened and poorly defined, and the epiphyses late in closing.

Results indicate that ponies fed adequate calcium and phosphorus need dietary vitamin D for normal bone development if they have no sunlight; dietary vitamin D is not needed with abundant sunlight.

Footnotes

1 Florida Agricultural Experiment Station Journal Series No. 1420.

2 Present address: University of Guam, Agana, Guam 96910.

3 Department of Animal Science.






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