Effect of Proline on Arginine Uptake and Nitrogen Metabolism of Lactating Goats

The hypothesis that addition of proline may save dietary protein for milk production was tested by administration of proline to two goats through a duodenal cannula. Because proline is synthesized by the mammary gland in vitro from arginine, the effect of proline supplementation on arginine uptake by the gland was tested in vivo. Arginine uptake, calculated from arterio-venous difference, dropped significantly in both animals, especially in the morning 1 h after milking, when a low-protein diet was fed. Milk production and total nitrogen in milk were not affected significantly by proline supplementation. A trend was toward decrease of milk orotic acid and an increase of milk fat due to proline supplementation.