The Absorption of Serum Albumin and Casein From the Mammary Gland of the Merino Ewe

Experiments have been carried out to determine the way in which 131I human serum albumin (131I HSA) and 131I casein are removed from the mammary gland when milk is allowed to accumulate in the gland. Lactating merino ewes with the mammary lymphatic duct cannulated were used in these experiments. The labelled proteins were introduced into the mammary gland through the teat duct and milk was allowed to accumulate in the gland. Lymph, plasma and urine samples were collected during the next 7–14 days. The results suggested that 131I HSA was absorbed from the mammary gland without being broken down and was removed largely by way of the lymphatics. It also appeared that casein was absorbed from the mammary gland and entered the interstitial pool without being broken down. However, the casein was rapidly transferred from the interstitial fluid into the blood stream. 131I casein when introduced intravenously into lactating ewes rapidly left the blood and entered the lymph, milk and urine suggesting that the casein in the blood existed as a small molecule. The significance of these results is discussed in relation to the physico‐chemical forms in which casein occurs in the body fluids.