A Study of Lipid Absorption in Young Milk-Fed Calves with the Use of a Lymphatico-Venous Shunt for the Collection of Thoracic Duct Lymph

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Abstract
A technique has been described for the collection of thoracic duct lymph from the young milk-fed calf. The establishment of a recirculating lymphatico-venous shunt permitted the repeated sampling of lymph from three calves for periods of 9-17 days, during which the animals remained in good health. The pattern of absorption of lipid was studied by determining the changes in the output of lipid in lymph of the calves fed whole milk either twice or once daily. When the calves were fed twice daily it was found that the mean hourly flow of lymph and output of neutral lipid, free fatty acid, and phospholipid changed relatively little with time after feeding, compared with a definite pattern of change observed over the first 12 hr. after feeding when the calves were fed once daily. With once daily feeding the flow of lymph reached a peak 4-5 hr. after feeding. The concentration of neutral lipid was at its lowest level at this time but subsequently increased sharply to reach its highest level at about 10 hr. The output of neutral lipid, free fatty acid, and phospholipid also reached their highest levels at about 10 hr. after feeding. There was a sharp decrease in the output of the lipids between 10 and 12 hr. with relatively constant values over the 12-24-hr, period after feeding. The mean hourly output of lipid in the lymph over this latter period was found to be similar to that in the first 12-hr, period, emphasizing the continuous nature of lipid absorption. The ingestion of approximately 140-190 g/24 hr of longer-chain fatty acid (>C12) in one or two feeds of milk resulted in the transport of an estimated 100-160 g/24 hr. of neutral lipid fatty acid in the thoracic duct lymph. Since the concentrations of neutral lipid and triglyceride were found to be similar, the estimate for the output of neutral lipid would represent approximately the output of chylomicron triglyceride. The lipid composition of the lymph was found to be similar for samples collected before feeding and at the time of maximum lipid absorption.

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