THE RELATION BETWEEN THE FAT AND CARBOHYDRATE METABOLISM OF LACTATION, AS INDICATED BY THE RESPIRATORY QUOTIENT OF THE MAMMARY GLAND

Abstract

The respiratory quotient of the mammary glands of goats in various physiological states was detd. by analysis of arterial and mammary-venous blood samples. Samples drawn from lactating, unanesthetized goats resulted in a mean R.Q. of 1.17 [plus or minus] 0.036, as compared to a mean of 1.15 [plus or minus] 0.034 when the blood vessels were anesthetized locally. Under nembutal anesthesia the variation was reduced, as shown by the mean value of 1.09 [plus or minus] 0.0115. Correction for the synthesis of urea in the lactating gland increased the R.Q. to 1.18. Non-lactating pregnant goats had a mammary R.Q. identical to that of lactating goats, while 0.81 was found for a non-lactating non-pregnant goat. Results indicate that the active mammary gland normally synthesizes a portion of the milk fat from carbohydrate. Since the value declines below unity during fasting, at which time it is known that there is also a marked decrease in the lower fatty acids of milk fat, the synthesis is probably concerned with these acids and the higher fatty acids are derived directly from the neutral fat of the blood.