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Effect of Various Levels of Calcium, Phosphorus and Vitamin D Intake on Bone Growth

I. Foxes

Six Figures

Bureau of Animal Industry, Agricultural Research Administration, United States Department of Agriculture, and Cornell University, Ithaca, New York^,2

In a factorially designed experiment the effects on bone growth of 4 levels of calcium, 4 levels of phosphorus, 4 levels of vitamin D, and of sex were investigated. One hundred and twenty-eight foxes were fed the experimental diets, beginning at a weaning age of 50 days and continuing to the time of pelting at an age of 254 days. X-ray photographs of the tibiafibula were taken at about 150 days of age.

At the close of the experiment the following measurements were taken on the isolated humeri: weight of ash, volume, weight of ether-extracted dried bone, length, bone thickness and degree of bending. Covariance analysis was used to adjust the ash content of each bone to an equal volume and an equal weight of ether-extracted dry bone. The ash per unit volume after covariance analyses best described the results on the humeri. Under the conditions of this experiment, the following conclusions are justified:

1. The calcium requirement of the growing fox at an age of 50 to 254 days is between 0.5 and 0.6% in the dry diet. The phosphorus requirement is between 0.4 and 0.6% in the dry diet. The vitamin D requirement is less than the amount which was supplied by the basal diet employed. It appears that a calcium to phosphorus ratio ranging from 1.0:1.0 to 1.7:1.0 is satisfactory.

2. In practice one could feed a range of 0.6 to 1.0% calcium and 0.6 to 0.8% phosphorus, provided the correct calcium to phosphorus ratio were maintained. The amount of vitamin D in the basal diet, 0.82 I.U. per gram dry food plus 200 I.U. per kilogram body weight, was not above the limit for best physiological efficiency.

3. If the diet does not contain enough calcium and phosphorus, or if the ratio is not correct, growing foxes about 50 to 100 days old will develop lameness, bent and crooked leg bones, recurrent spasms, enlarged joints, cranial enlargement, and malformed body bones.

4. The humeri of male foxes at the end of the experiment had more total ash and a greater volume, and the fresh and ether-extracted dried humeri weighed more than the humeri of the female foxes. There was no measurable difference between sexes in their requirement for calcium, phosphorus and vitamin D.

5. The time-saving value of the factorial design of the experiment is evident from its use here in arriving at these measurements of the calcium, phosphorus, and vitamin D requirements of the growing fox.

² At the time this work was conducted the research concerned with foxes was under the Fish and Wildlife Service, United States Department of the Interior. Effective June 30, 1946, all activities pertaining to fur farming were transferred to the United States Department of Agriculture.

Manuscript received 7 August 1950.