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Effect of Vitamin A Depletion on Liveweight, Plasma and Liver Levels of Vitamin A and Microanatomy in Young Dairy Calves

Animal Industries and Animal Diseases Departments, Storrs Agricultural Experiment Station, University of Connecticut, Storrs

L. A. Moore

Bureau of Dairy Industry, Agricultural Research Administration, U. S. D. A., Washington, D. C.

ABSTRACT

The effect of a vitamin A-depletion ration on liveweight, carotene and vitamin A levels in the blood and liver, clinical appearance and microscopic anatomy was studied in 21 young calves beginning at 106 days of age. All calves were fed a vitamin A-depletion ration of 2.67 lb. per 100 lb. of liveweight, with six of the calves receiving in addition a daily equivalent of 107,143 USP units of vitamin A. Observations on the daily feed intakes, clinical appearance, weekly liveweight, plasma carotene and vitamin A were made and tissue samples for histological study and liver samples for carotene and vitamin A analyses were obtained at slaughter. The experimental period was terminated for those calves fed only the depletion ration when the blood plasma level was less than 4 per cent for 2 consecutive wk., and for those calves fed the supplemental vitamin A at average ages comparable to those fed only the depletion ration.

Until the blood plasma level decreased to 4 per cent, all calves readily consumed the vitamin A-depletion ration. At this level of plasma vitamin A, seven of the calves fed only the depletion ration began refusing some feed. Liveweight was not affected and both the gain in liveweight and rate of gain were not significantly different between groups of calves.

Blood plasma carotene decreased in all calves with successive weeks on experiment and was characterized by a relatively rapid decrease early in the experimental period with a marked decline in rate of decrease occurring during the middle and end of the experimental period. In contrast, plasma vitamin A values decreased in a uniform manner regardless of the level and, therefore, indicated a possible means of measuring vitamin A stores by prediction, using this relatively uniform rate of decrease as a standard. The liver stores of vitamin A were considered depleted in those calves receiving only the vitamin A depletion ration.

Spinal fluid pressures at the termination of the experimental period were elevated in the calves receiving only the depletion ration, while those receiving the supplemental vitamin A remained essentially the same as at the start of the experiment. Exophthalmos was observed in six calves, muscular in coordination in five, diarrhea in four and convulsions in one, all symptoms occurring toward the termination of the experiment for the individual calves.

Squamous metaplasia of the interlobular and main ducts of the parotid gland was observed in eight of nine depleted calves and in none of the six controls.