ABSTRACT: 1. Measurements were made of arterial and coccygeal concentrations of plasma constituents and of arteriovenous differences across the mammary gland in two anaesthetized lactating sows, and of coccygeal-mammary-venous differences in three conscious sows when lactating and again later when ;dry'. 2. With the possible exception of acetate concentration, the compositions of arterial and coccygeal plasma were similar, and arteriovenous differences in the anaesthetized lactating sow corresponded closely to coccygeal-venous differences in the conscious animal. 3. In the ;dry' sow coccygeal-venous differences were in all instances small. 4. In the lactating sow there were large arteriovenous (or coccygeal-venous) differences (mean value as a percentage of arterial or coccygeal concentration) in glucose (31%), acetate (46%), arginine (27%), glutamate (42%), histidine (26%), isoleucine (36%), lysine (25%), leucine (39%), methionine (38%), phenylalanine (32%), proline (31%), threonine (22%), tyrosine (32%) and valine (27%), and in palmitate (19%), oleate (23%), linoleate (21%) and stearate (16%) of the plasma triglycerides. The values for the following constituents were in all instances small: beta-hydroxybutyrate, acetone+acetoacetate, citrate, lactate, alanine, glycine, aspartate, palmitoleate of the plasma triglycerides, phospholipids, cholesterol, cholesteryl esters and free fatty acids. 5. Of the total recorded uptake of plasma constituents by the lactating gland, 59% was accounted for by glucose, 28% by amino acids, 11% by plasma triglycerides and 2% by acetate. The relative uptakes of glucose and amino acids were higher in the sow than values reported previously for the goat, and the relative uptakes of acetate and triglycerides much less.
