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Milk Production of Cows Fed Diets Deficient in Vitamin A

University of Tennessee, Knoxville

Abstract

Lactation response of dairy cows fed diets high in concentrates and low in roughage to vitamin A supplementation has been investigated in three experiments utilizing 52 cows on normal feeds and 32 cows fed a vitamin A depletion diet. Cows fed normal feeds, including alfalfa hay and corn silage along with excessive allowances of concentrates for complete lactations, did not develop signs of vitamin A deficiency, and maintained high to normal levels of vitamin A in blood and liver. Time required to produce vitamin A deficiency on the depletion diet varied from 4 to 14 mo. according to level of initial liver storage of vitamin A. Average rate of depletion of liver stores was 34.8% per month. Providing 50,000 I.U. vitamin A daily to depleted cows which had started lactation in reasonably good condition, did not produce a significant change in milk yields in comparison with deficient pair mates. When vitamin A depletion, determined by liver analyses, was not reached until midlactation, there was no change in the lactation curve to indicate that provision of adequate supplemental vitamin A influenced milk yields. Vitamin A intakes on the depletion and deficient diets were not high enough to prevent edema and reproductive problems indicative of vitamin A deficiency. Since no lactation response to supplementing such diets with adequate vitamin A was observed, it is concluded that provision of adequate vitamin A for successful reproduction will provide ample intakes for normal lactation.

¹ Present address: Agricultural Extension Service, DeLand, Florida.

² Present address: Department of Dairy Science, Clemson State University, South Carolina.

³ The authors gratefully acknowledge donations of stabilized vitamin A by Distillation Products Industries, Rochester, N. Y., and irradiated dry yeast type 178F by Clinton Corn Processing Co., Clinton, Iowa.