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The Fat Metabolism of the Mammary Gland of the Normal Cow and of the Cow in Ketosis

Department of Dairy Industry, Storrs Agricultural Experiment Station, University of Connecticut, Storrs, Connecticut

ABSTRACT

1. In severe ketosis, characterized by ketonemia, hypoglycemia, and varying degrees of inanition, the short chain fatty acids of milk fat were considerably below normal. Consequently ß-hydroxybutyric acid cannot be considered the precursor of these fatty acids.
   
2. On the basis of the present evidence it appears that ß-hydroxybutyric acid is one of the chief sources of energy for the active mammary gland.
   
3. The administration of large quantities of glucose to cows with ketosis was followed by a significant increase in the water-soluble steam-volatile fatty acids of milk fat within 36 to 48 hours. This was accompanied by an increase in the unsaturation of the fatty acids. The water-insoluble steam-volatile fatty acids were not immediately affected, but increased following the recovery of the animal.
   
4. The short chain fatty acids of milk fat are not decreased nearly as much by ketosis as by short periods of fasting, although the blood glucose is usually lowered at least 50 per cent more by severe ketosis than by a few days of fasting.
   
5. The percentage of short chain fatty acids in the milk fat are much more closely associated with food intake than with the level of blood glucose, lactic acid, or acetone bodies.
   
6. The low R. Q. of the mammary gland of the fasted cow is probably due, in part, to the oxidation of ß-hydroxybutyric acid.
   
7. In five experiments the total amount of blood traversing the mammary gland in a period of 24 hours was calculated from the utilization of calcium and phosphorus per 100 cc. of blood and the total amounts of calcium and phosphorus secreted in a 24-hour period. Each unit of volume of milk required 494 volumes of blood. Similar analyses indicated that the blood fat removed would account for 92.8 per cent of the milk fat secreted, and that the blood glucose removed would account for 105.5 per cent of the lactose.