Utilization and Excretion of Ingested Ascorbic Acid by the Dairy Cow

Abstract

Summary A Holstein cow was maintained in normal physical condition for a period of 15 months on a ration containing very little ascorbic acid. During this period a normal male calf was born. Blood plasma ascorbic acid values ranged from 0.28 to 0.59mg. per 100ml. but usually fluctuated between 0.30 and 0. 45mg. per 100ml. As the lactation period progressed the total daily ascorbic acid excretion in the milk diminished in a manner paralleling the decrease in milk volume. During this time the urinary ascorbic acid excretion appeared to be erratic with values ranging from 14.1 to 97.8mg. per 24 hours. The ingestion of large amounts of ascorbic acid increased the urinary excretion of the vitamin very slightly and then only temporarily. The rate of urinary excretion of the vitamin appeared to be greater during the daytime than during the night. In vivo and in vitro rumen studies, made possible with the aid of a rumen fistula, showed that crystalline ascorbic acid in amounts of 150g. was rapidly destroyed in the rumen. Ascorbic acid supplied in a natural form as Cerograss Chops, was also destroyed in the rumen but at a slower rate owing, presumably, to the slower dissolution of ascorbic acid from the natural grasses. These studies also indicated that the destruction of ascorbic acid in the rumen was a result, at least in part, of the action of microorganisms. The results of these experiments may be summarized, in support of the probable synthesis of ascorbic acid by the dairy cow, as follows: 1) ascorbic acid either in the crystalline form or as a part of a natural product ( Cerograss Chops ) is destroyed rapidly in the rumen; 2) the apparent independence of the cow for dietary ascorbic acid is reflected by normal concentrations of ascorbic acid in the blood and milk in spite of a low ascorbic acid intake over a prolonged period of time; and finally, 3) the ingested intake of ascorbic acid on this lowascorbic acid ration is exceeded by the combined output of the vitamin in the milk and the urine.