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A Study of the Blood Carotene in Relation to Lipolytic Activity of Milk

Dairy Industry Division
Animal Husbandry Division University of California, Davis, California

ABSTRACT

Six cows, 5 Jerseys and 1 Guernsey, were kept for various periods, extending up to 269 days, on a very low-carotene diet of bleached alfalfa hay and concentrates. On this diet the depletion of carotene in blood and milk fat was most rapid in the first 20 days; after about 40 days the carotene values of both the blood and milk fat leveled off at the values between 0.25 and 0.05 mg. of carotene per 100 cc. of blood plasma. The relation between the amount of carotene in blood and that in milk fat approached a factor of a direct proportionality when considered for each cow separately. The numerical values of carotene, moreover, are nearly the same in blood and in milk fat if expressed on the basis of mg. of carotene per 100 cc. of blood plasma and mg. of carotene per 100 cc. of milk fat.

With 4 cows, the depleted carotene was restored to normal by feeding either crystalline ß-carotene (up to 1000 mg. daily, dissolved in cottonseed oil) or green alfalfa.

The data on the extent of lipolysis of fat in aged milk, measured by surface tension of milk and acid degree of fat, failed to reveal any consistent relation between the level of carotene in the blood or the milk fat of a cow and the extent of spontaneously developed hydrolytic rancidity in her milk.

This study has fully confirmed that the advanced stage of lactation is a contributing or major factor in the secretion of milk high in the concentration of a naturally active lipase. In this experiment every cow in a late stage of lactation and gestation on the diet of bleached alfalfa hay and concentrates secreted milk that spontaneously developed strong rancid flavor.

The limited data obtained in the present study support the observations made by other workers: the ingesting of green feed prevents the secretion of milk high in a concentration of a naturally active lipase and generally improves the flavor of milk.

A critical examination of the results obtained in this study warrants two conclusions: 1) that the principle responsible for the beneficial effect of green feed in preventing spontaneous lipolysis of the milk fat is not its high carotene content and 2) that the hydrolytic rancidity occurring in the milk of cows near the end of gestation on a dry-feed diet cannot be attributed to the low-carotene content of the ration.