Effect of Two Levels of Intake of a Vitamin a Depletion Ration on Some Blood Constituents and Deficiency Criteria in the Dairy Calf

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Abstract
Ten pairs of 36-day-old calves were fed a vit. A depletion ration at 2 levels of intake, low and high, until the blood plasma vit. A values decreased to less than 4.0 [mu]g.% for 2 consecutive 7-day periods. This resulted in a 7-day increase in body wt. of 7.1 [plus or minus] 1.5 and 11.0 [plus or minus] 0.4 lb. for the low and high levels of intake, respectively. Over-all, plasma carotenoids and vit. A decreased while whole blood and plasma ascorbic acid exhibited no change. None of these constituents were affected by level of intake of the depletion ration. Hemoglobin decreased in calves on the low level of intake of the depletion ration but no change was found for calves on the high level. Heart rates of animals on the high level of intake averaged 20 beats/min. higher than those on the low level of intake, whereas rectal temps. and terminal spinal fluid pressures were unaffected. Among the histological changes, only the frequency of occurrence of squamous metaplasia in the interlobular ducts of the parotid gland was significantly greater in the high level group.