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.

Summary(1) Lactating Large White sows were given an intravenous infusion of [U-14C]glucose (3 sows), or of triglycerides containing [1-14C]palmitic acid (1 sow) or [1-14C]stearic acid (1 sow).(2) The contribution of labelled plasma constituents to the synthesis of milk citrate, lactose, triglyceride glycerol, individual amino acids of the milk proteins and individual fatty acids of the triglyceride fraction was estimated by the ‘transfer quotient’ method. For the glucose infusions the mean values for the transfer quotients were: lactose, 70%; citrate, 42%; glyceride glycerol, 38%; protein, 3%; laurate, 6%; myristate, 12%; palmitate, 6%; palmitoleate, 4% and stearate, 2%. Palmitic acid of the plasma triglycerides made similar contributions of about 60% to the palmitic and palmitoleic acids of milk fat, whereas stearic acid made a major contribution (71 %) to the stearic acid of milk fat but a smaller contribution (42%) to oleic acid.(3) The results are compared with corresponding values for the goat and the cow.

I .Emulsions with egg phosphatides of nine synthetic triglycerides (tributyrin, tricaprylin, tripelargonin, tricaprin, trilaurin, trimyristin, tripahitin, triisostearin, triolein) and of rapeseed oil and a proprietary emulsion of cottonseed oil were given as continuous infusions into the jugular vein of lactating sows. The effects of the infusions on the concentration and composition of blood plasma lipids and on the composition of milk fat were determined.2. The infusions did not affect the concentrations in blood plasma of cholesterol, phospholipid or cholesterol esters, but there was a tendency for the concentration of plasma triglycerides to be increased which was most pronounced for the infusions of longer-chain triglycerides. The fatty acid composition of the plasma triglycerides was not altered by the infusion of tributyrin, except that there was an increase in the content of oleic and a decrease in that of linoleic acid. With other infusions the composition of the plasma triglycerides was altered towards that of the infused material and the effect was more marked for the longer-chain triglycerides, with the exception of triisostearin.3. The changes in the composition of the milk fat reflected those in the composition of plasma triglycerides, with two exceptions. The infusion of tripalmitin was associated with an increase not only in the palmitic acid content of milk fat but also in the palmitoleic acid content. Also, the changes in the content in milk fat of eicosenoic acid and, more especially of erucic acid during the infusion of rapeseed oil were much less than the corresponding changes in the plasma triglycerides.Studies of arteriovenous differences across the mammary glands of lactating sows (Linzell, Mepham, Annison & West, 1969; Spincer, Rook & Towers, 1969) have demonstrated an uptake of triglyceride fatty acids, which are incorporated largely into the triglycerides of milk fat (J. Spincer & J. A. F. Rook, unpublished). The fatty acids principally involved are palmitic, stearic and oleic, the major fatty acids of the plasma triglycerides. The present experiments were undertaken to study the extent to which these and other fatty acids are transferred to milk fat when infused as triglycerides into the blood plasma.Pharmacological and toxicological side-effects have been reported in a number of animal species following the infusion of vegetable oils in combination with a range of emulsifiers, but Schuberth & Wretlind (1961) found emulsions of soya-bean oil with egg phosphatides to be free of such effects. Emulsions with egg phosphatides of tripropionin, tricaproin, tricaprylin, tripelargonin, tricaprin, trilaurin and triolein (Storry, Tuckley & Hall, 1969) Animals and their management. Lactating Wessex/Landrace/Large White sows with piglets were taken as required from the University herd. Sows were confined in a holding crate and piglets to a separate pen. Suckling was permitted at 1.5 h intervals. Meal (5.5 kg/head per day) was offered to the sows twice daily and there was free access to water. ...