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.

1) Two wether sheep fitted with ruminal and duodenal re-entrant cannulas were used to study the influence of the physical form of a barley grain and barley straw diet and intraruminal addition of ammonium salts (mainly acetate) on digestibility of dietary constituents, the flow of digesta to the duodenum and the composition of digesta from the rumen and duodenum.(2). Grinding and pelleting of the diet depressed the digestibility of crude fibre and increased that of the nitrogen-free extract and addition of ammonium salts increased the digestibility of crude fibre. The effects of the physical form of the diet on the composition of the short-chain fatty acids of rumen liquor were not consistent and the addition of ammonium salts produced changes over and above those attributable to the small amounts of acids in the mixture. The extreme values observed for the molar proportion of propionic acid were 12-3 and 38-1% and the corresponding values for w-butyric acid were 28-1 and 9-0%.(3). Variations in the flow of nitrogenous materials to the duodenum were related more to the pattern of fermentation established in the rumen than to the experimental treatments. There was a highly significant relationship between the molar proportion of propionic acid and the abomasal output of nitrogen and also the abomasal output of a-e-diaminopimelic acid and a-linked glucose polymers. The amino acid composition of duodenal digesta differed from that of the diet-in particular the proportion of glutamic acid was decreased and the proportions of aspartic acid, alanine, lysine and histidine were increased-but differences in composition between treatments and between animals were small.(4). The faecal output of nitrogen differed little between animals and between treatments, but nitrogen retention was significantly increased during the intraruminal infusion of ammonium salts.Alteration of the physical form of a diet, by grinding and pelleting, is known to influence the digestion of food materials in the rumen, and effects can be especially marked with diets containing a high proportion of concentrated foods. There are reports of effects on the composition of short-chain fatty acids in rumen liquor and the rate of passage of food particles (for references, see Moore, 1964;Shaw, 1961),

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. ...