| Summary: | Ketosis in dairy cattle is now universally recognized as a clinical syndrome causing appreciable monetary loss to the dairy industry. It has been established as a definite pathological state within the area studied in the present work. No completely adequate specific therapy has been suggested for the treatment of the various recognized forms of ketosis.
Present methods for the rapid detection of uncomplicated and complicated ketosis in the field are not entirely satisfactory.
However, sufficient data has been published to provide a reasonable picture of the blood and urine changes that occur in ketosis; and the necessary laboratory procedures are available for its detection. The present work has added to this information and has afforded a first comparison of ketosis as recognized here, with the condition observed elsewhere.
Information was obtained from the University herd of Ayrshire cattle permitting the establishment of normal levels for blood and urine constituents under winter and summer feeding conditions. It has been demonstrated that, under the feeding and management conditions prevailing in the University herd, a subclinical avitaminosis A exists not only in the winter, but probably in the summer months.
From the information published elsewhere, as well as from the present data, it would appear that the heavy drain on the maternal energy reserve and on certain of the vitamins following parturition, is sufficiently great to cause a physiological derangement of pathological significance. The possibility is suggested that vitamin A might play a critical role, in the induction of this derangement. It seems likely that the fundamental metabolic disorder is concerned with the energy metabolism of the animal. It is not yet established whether this is solely within the carbohydrate cycle, the lipid cycle or within both. Nor is it established whether vitamin A is involved in this derangement.
In the present Investigation, no experimental work has been carried out relative to ketosis in other domestic animals. A review of the current literature concerning ketosis in other domestic animals has been made and the various conditions have been compared to the ketotic state in dairy cattle. These observations confirm, in part, the tentative conclusion that ketosis is a disturbance of energy metabolism.
The mechanisms involved in normal energy metabolism have been' discussed in relation to the energy picture in the ketotic state. A brief outline has been given of the various theories which have been suggested to account for the formation of ketone bodies.
The experimental work was planned on the assumption that the basic cause of ketosis is a deficiency of available carbohydrate and as a result the animal's energy requirements are not satisfied. This deficiency may arise through a dietary inadequacy or through the inability of the animal to metabolize carbohydrate arising from protein and lipid precursors.
A working hypothesis was advanced proposing that the inability of an animal to make use of its energy resources through normal pathways is due to a deficiency of vitamin A. On the basis of this hypothesis, it was assumed that animals suffering from avitaminosis A would be unable to metabolize administered carbohydrate in the normal manner. The experimental results obtained indicate that in young animals deprived of vitamin A, a hypoglycemia of clinically significant proportions develops as the vitamin A deficiency progresses. The data suggests further that this hypoglycemia is one of the earliest symptoms of avitaminosis A and arises despite an adequate Intake of dietary energy.
The development of a hypoglycemia on adequate energy intake followed by a characteristic loss in body weight is offered as supplementary evidence that vitamin A may have a role in carbohydrate metabolism. Other experiments have been conducted that demonstrate the inability of the vitamin A deficient animal to utilize glucose administered per os. Work is proceeding in order to confirm this finding.
In conclusion, results have been presented to suggest that vitamin A may possess, in addition to its other established functions, a specific role in carbohydrate metabolism. The experimental data is not yet sufficiently complete to assign the properties of a coenzyme to vitamin A. Moreover, the possibility of vitamin A affecting the hormonal balance and thus indirectly, carbohydrate metabolism, cannot be precluded on the basis of the present investigation.
Final proof that vitamin A may possess this coenzyme activity must await further studies. It is suggested that subsequent work might well exploit the advantages of "in vitro" tissue slice techniques.
Related experiments have been carried out and are appended to the thesis for future reference. === Land and Food Systems, Faculty of === Graduate
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