Composition of milk from red and grey kangaroos with particular reference to vitamins.

Analysis of milk from red and grey kangaroos confirmed that the composition of milk from individual mammary glands changes with advancing age of the associated suckled young. Although the proportion of particular components may change, concentration of solids, in particular fats and to a lesser extent protein and casein, increase throughout lactation. The results of analyses to determine the vitamin content of kangaroo milks are presented for the first time.

Concurrent studies of the flow of digesta in the duodenum and of exocrine pancreatic secretion of calves. 7. Influence of milk substitutes on abomasal lipolysis and biliary secretion.

1. The abomasal hydrolysis of lipids and the flow of endogenous (biliary) lipids was studied in two Friesian calves given four milk-substitute diets, by sampling the duodenal digesta. The diets were: reconstituted, mildly preheated, spray-dried skim-milk powder with (SKF) or without (SK) margarine fat or with 500 g/kg skim-milk powder in diet SKF replaced by soy-beran flour (ASKF) or fish-protein concentrate (BSKF) together with dried whey. The diets were given ad lib. twice daily from 13 to 37 d of age, each diet being given for six consecutive days. Collections of duodenal digesta from the re-entrant cannula situated caudal to the bile duct were made for 12 h after feeding the 6th and 12th meals for each diet. Samples from one collection only were subjected to detailed analysis of the lipid classes. 2. The inclusion of non-milk protein (ASKF and BSKF) not only increased the rate of passage of lipid through the abomasum but also the proportion of the lipid present as triglyceride particularly, in the first 2 h after feeding. 3. In a 12 h period, 2.3-6.3 g 'polar' lipids (mainly biliary phospholipids) were estimated to have been secreted. The rate of flow was high during the first hour after feeding and constant thereafter. The quantity of 'polar' lipid was not related to the type of milk fed or the duodenal flow of lipid. 4. When diet SK was fed, the small amounts of lipid present were extensively hydrolysed so that free fatty acids represented 700 g/kg lipid of dietary origin passing through the duodenum. When margarine fat was included in the diets (SKF, ASKF and BSKF), the free fatty acids represented only 210 g/kg lipid of dietary origin. 5. The quantities of lipid and nitrogen passing through the duodenum were poorly related to the quantities ingested at the beginning of the 12 h experimental period but were closely related to each other.

Studies on lipid digestion in the preruminant calf. 2. A comparison of the products of lipolysis of milk fat by salivary and pancreatic lipases in vitro.

1. A comparison has been made of the products of lipolysis of the fat in cow's milk by salivary and pancreatic lipases (EC 3-1-1-3) from a preruminant calf. 2. It was confirmed that salivary lipase releases short-chain acids preferentially, particularly butyric and caproic acids. This was not only true initially but also as the course of lipolysis progressed. Even after 60 min incubation the longer-chain acids were only released to about one-twentieth of the extent of butyric acid. 3. Although pancreatic lipase also initially released proportionately more butyric acid than other fatty acids, within 30 min the longer-chain acids were released to about half the extent of butyric acid. 4. Since the over-all extent of lipolysis by salivary lipase was limited by its inability to release long-chain acids, the release of these acids (which comprise two-thirds of the total fatty acids of milk fat) in the calf is likely to be dependent on the subsequent action of pancreatic lipase. 5. The release of fatty acids by pancreatic lipase was enhanced by pre-incubating milk fat with salivary lipase.

Studies on lipid digestion in the preruminant calf. The source of lipolytic activity in the abomasum.

1. Lipolytic and proteolytic activities and pH values were determined in secretions collected from innervated abomasal pouches and in abomasal contents from preruminant calves given liquid diets. 2. No lipolytic activity was detected in pouch secretions collected during 1 h after feeding, though lipolytic activity was present in abomasal contents; pepsin (EC 3.4.23.1) and renin (EC 3.4.23.4) were present in both pouch secretions and abomasal contents. The pH values of pouch secretions ranged from 1-2 to 1-8 and those of abomasal contents from 4-2 to 5-9. 3. When diet was placed directly into the abomasal pouch soon after feeding, the pH values of pouch and abomasal contents decreased similarly (i.e. from 6-3 to approximately 5). Protease activity (U/ml) of pouch contents ranged from 0-1 to 0-8 and that of abomasal contents from 0-1 to 0-2. No lipolytic activity was detected in pouch contents, though abomasal contents contained 0-6 to 1-2 U/ml and when the diet contained milk-fat as the dietary fat source considerable lipolysis of triglycerides containing shorter-chain fatty acids was found. 4. It is concluded that there is no significant secretion of lipolytic enzymes by the fundal mucosa and that the lipolysis of triglycerides in the abomasum of the preruminant calf is due predominantly to a lipolytic enzyme in saliva.

Concurrent studies of the flow of digesta in the duodenum and of exocrine pancreatic secretion of calves. 3. Further studies on the addition of fat to skim milk and the use of non-milk proteins in milk-substitute diets.

1. The flow of digesta through the duodenum and the concurrent secretion of the pancreas were studied in four Friesian calves given four milk-substitute diets. The diets were: reconstituted, "mildly" pre-heated, spray-dried skim-milk powder with (SKF) or without (SK) margarine fat or with 5o percent of the skim-milk powder in diet SKF replaced by soya-bean flour (ASKF) or fish-protein concentrate (BSKF), together with dried whey. The diets were given ad lib. twice daily from 13 to 37 d of age, each diet being given for 6 consecutive days. Collections of duodenal digesta and pancreatic secretions, from cannulas, were made for 12 h after feeding the 6th and 12th meals ("experimental" meals) for each diet. 2. The diets fed as "experimental" meals contained polyethylene glycol (PEG) as a fluid (whey) marker and goat's milk containing (3H)lysine as a marker for total protein; beta-carotene was added as a lipid marker to the three diets containing margarine fat. 3. Over the 12 h postprandial period, the patterns of duodenal digesta flow and secretion of pancreatic fluid did not differ markedly between the four diets. The abomasal outflow of both nitrogen and lipid in a 12 h postprandial period was related to their intakes from the "penultimate" (5th and 11th) meals for diets SKF and SK BUT TO THEIR INTAKES AT THE "EXPERIMENTAL MEALS" FOR DIETS ASKF and BSKF. Secretion of pancreatic enzyme activity was highest during the 1st hour after feeding but the main outflow from the abomasum of total N and lipid occurred 5-10 h after feeding. 4. The time required for all the whey marker (PEG) to pass through the duodenum was similar for diets SKF and SK, but only 53 and 42 percent respectively of the ingested protein marker passed through the duodenum in the 12 h after feeding. More acid appeared to be secreted by the abomasum when diet SK was given; also less undigested protein passed out of the abomasum after giving this diet. It is concluded that the physical absence of fat globules in the abomasal clot increases the degree of proteolysis. 5. The secretions of pancreatic fluid and pancreatic enzyme activity were all markedly lower for diet SK than for diet SKF. 6. With diets containing non-milk proteins (ASKF and BSKF), abomasal proteolysis was less efficient and the ingested protein passed out of the abomasum more rapidly than for diet SKF. There was no difference in the rate of abomasal outflow of the whey fluids between diets SKF, ASKF and BSKF. 7. In comparison with diet SKF, diets ASKF and BSKF tended to induce less pancreatic enzyme secretion over a 12 h postprandial period, with the exception of lipase. 8. There appeared to be no direct relationship between the quantities of any of the pancreatic enzymes secreted during a postprandial period and either the concurrent flow of duodenal digesta or the total quantities of dietary constituents passing through the duodenum.

Studies on metabolism of vitamin A. The effect of vitamin A status on the secretion rates of some steroids into the ovarian venous blood of pregnant rats.

1. Rats raised on a vitamin A-deficient diet supplemented with either retinyl acetate or retinoic acid were mated and became pregnant. 2. The rates of secretion of progesterone, 20alpha-hydroxypregn-4-en-3-one, oestradiol-17beta and oestrone into the ovarian-venous blood of rats in these two groups were measured on days 9 and 15 of pregnancy. 3. Rates of secretion of progesterone and 20alpha-hydroxypregn-4-en-3-one, both on days 9 and 15, were lower for the rats given retinoic acid. No such differences were found in ovarian oestrogen secretion. 4. The implications of these results are discussed in the light of the previous demonstration that the activity of ovarian 3beta-hydroxy-Delta(5)-steroid dehydrogenase was markedly less in pregnant rats given retinoic acid.