The possibility was examined of supplying vitamin A to chickens from the first days of life as carotene in green plants. Growth experiments were carried out with chickens till the age of 8 weeks. Different kinds of forage (horse-beans, Berseem clover, green oats, sweet potato leaves, cow-peas, corn-leaves) were given in quantities calculated to supply 300 μg. carotene per 100 g. feed; control groups received fish-liver oil, given at the level of 500 i.u. per 100 g. feed. Weight gains and extent of vitamin A storage in liver served as an indication of the utilization of carotene from different sources. The utilization of carotene from all the plants examined was sufficient to support normal growth, only in the groups receiving clover was growth found to be somewhat slower. Remarkable differences were found in the extent of liver storage, and that was taken as an indication of differences in activity of the carotene from the different sources.

Attempts to determine the reasons for these differences in liver storage capacity of the carotene from the various plants did not reveal the presence of any plant components enhancing or depressing vitamin A storage.

Similarly, no correlation could be found between digestibility coefficients of carotene in the different plants and liver vitamin A storage. This correlation seemed likely in sweet potato leaves only, the rather low digestibility coefficient found in these leaves may account, at least partially, for the low activity of this plant.

The stereoisomeric composition of the β-carotene of the different plants and the xanthophyll/carotene ratio are very similar in all plants tested and cannot account for differences in carotene activity of the plants studied.

The results of this work show that it is possible to satisfy the requirements of chicks for vitamin A from the first days of life by supplying certain forage plants. In practice, because of the variability of the carotene content in such plants, care has to be taken when estimating the amounts to be given. Green plants should be given to chickens freely or at least in liberal amounts.

Four Israeli-Friesian cows, two at peak and two at mid lactation, were fitted with duodenal cannulas. They were given proline or water infusions for 8-day periods to evaluate the effect of duodenal infusion of proline on arginine uptake by the mammary gland and on milk yield and composition of dairy cows. Milk fat content and 40 g/kg fat-corrected milk yield increased for all cows due to proline infusion. Milk protein concentration during either early or mid lactation and milk protein yield during early lactation, were not affected by proline infusion. Milk protein yield during mid lactation was increased due to proline infusion. Arginine uptake by the udder dropped by one-half during proline infusion. Results suggest that post-ruminal administration of supplemental proline reduced requirements for arginine by the udder and improved efficiency of dietary energy utilization.

Multiparous dairy cows were allotted at the beginning of the dry period to two groups, each of about 75 cows. In addition to a basal diet containing a very low concentration of carotene and a normal concentration of retinyl ester, the carotene group was given a daily supplement of 500 mg carotene during the dry period and 750 mg carotene during lactation, and the retinol group was given an equivalent amount of retinyl ester. Plasma carotene concentrations were much higher in the carotene group (ca. 4·2 mg/1 v. ca.. 0·35 mg/1), but plasma retinol did not differ. Neither peripheral plasma progesterone concentration nor the interval between calving and first insemination were affected by carotene supplementation. Conception rate was greatly improved by carotene supplementation in the younger cows (second and third lactation) during the first part of the experiment (cows calving in September to December): conception rates at first insemination were 0·70 v. 0·33 (P < 0·05); for all inseminations, conception rates were 0·71 v. 0·38 (P < 0·01). However during the second part of the experiment (cows calving in January to April) no significant differences were found between the two groups.

Plasma tocopherol concentration in cows given carotene was significantly higher during the dry period and the 1st weeks of lactation, but these differences disappeared in the later stages of lactation. Plasma cholesterol concentration in the carotene group was highly correlated with plasma carotene concentration (r = 0·52 to 0·59, P < 0·001); however even higher correlation coefficients were found between plasma cholesterol and plasma tocopherol in both the carotene and the retinol groups (r = 0·61 to 0·80, P < 0·001). Plasma concentrations of triglycerides, glucose, urea and aspartate aminotransferase were not affected by the treatment.

A high plasma carotene concentration is not a prerequisite for conception; however, under certain conditions which need defining, the carotene concentration appears to be a limiting factor.

1. The changes in the concentration of some enzymes and their metabolites were studied in the first stages of vitamin A deficiency in chicks.

2. Kidney arginase (EC 3.5.3.1) and liver xanthine dehydrogenase activities had increased even before complete disappearance of vitamin A from the plasma. Similarly, an increase was found in plasma uric acid, and plasma urea also increased but to a lesser extent. Liver proteolytic activity also was slightly increased by vitamin A deficiency.

3. Kidney D-amino acid oxidase (EC 1.4.3.3) activity and plasma concentrations of total protein and free amino acids were not affected, at least in the first stages of the deficiency.

4. Oral dosing of deficient chicks with retinyl palmitate to provide 300 μg retinol, 24 h before killing, brought about a decrease in the activities of both enzymes and of plasma uric acid, and an increase in plasma urea.

5. Dietary levels of vitamin A were reflected not only in the liver concentrations of the vitamin but also in the plasma concentrations.

1. The distribution of vitamin A esterase activity for vitamin A acetate, palmitate, and alcohol was studied in various tissues of the chick.

2. Liver and kidneys were highly active in the hydrolysis of acetate, and showed only slight activity in the hydrolysis of palmitate or in the synthesis of vitamin A esters.

3. Pancreas was highly active in both acetate and palmitate hydrolysis and in the synthesis of vitamin A esters.

4. The small intestine showed a moderate and equal activity in all three reactions.

5. Sodium taurocholate enhanced the hydrolysis of vitamin A palmitate by pancreas and small intestine. It also enhanced the hydrolysis of vitamin A acetate by pancreas, but had no effect on the hydrolysis of acetate by liver, and even inhibited this reaction in kidneys and intestine. It also inhibited the synthesis of vitamin A esters by pancreas and small intestine.

1. The efficiency of absorption of and liver storage from a single oral dose of 10000 i.u. vitamin A palmitate decreased in chicks reared on a diet containing 10% protein as compared to the efficiency in chicks reared on a diet in which the protein level was adequate. When the chicks were given orally an equivalent dose of vitamin A alcohol, the absorption was equally efficient at both dietary protein levels.

2. The vitamin A alcohol content of this intestine, plasma and liver of chicks dosed with vitamin A palmitate was decreased by protein restriction. The physiological change responsible for this decrease seems to be the lowering of the hydrolysing activity for vitamin A palmitate in pancreas and in the duodenal mucosa.

3. The importance of the enzymic step in the absorption of an oral dose of vitamin A palmitate is shown by the finding that protein malnutrition reduced only slightly the final liver stores when vitamin A in its different forms (palmitate, acetate or alcohol) was injected directly into the blood stream.

4. The uptake of injected vitamin A from the blood was much delayed when the vitamin was injected as palmitate, i.e. the ester of a long-chain fatty acid, instead of the acetate ester of the free alcohol.

5. When vitamin A was injected, the liver content did not rise continuously with time, but showed a temporary decrease after a certain period. The phenomenon was apparently due to changes in the rate of the two inverse processes of uptake of the vitamin by the liver and liberation from it.

1. The effect of dietary protein level and supplementation with thyroxine on the liver storage of vitamin A, on the fraction of liver vitamin A in the alcohol form, and on the plasma levels of vitamin A and proteins has been studied in chicks.

2. Liver storage was reduced by lowering the dietary protein level.

3. Protein restriction lowered the percentage of vitamin A found in the liver as retinol.

4. Thyroxine increased both vitamin A storage and the fraction of the total vitamin A as retinol, this effect being dependent on dietary protein level.

5. Plasma vitamin A and plasma protein contents were lowered to a highly significant extent by protein restriction. This drop was essentially caused by reduction of the albumin fraction in chicks fed on a 5% protein diet and by a reduction of β- and γ-globulins in chicks fed on a 10% protein diet.

6. Thyroxine supplementation of the diet lowered to a highly significant extent plasma protein content; this reduction was caused by a dramatic fall in the level of plasma albumin. The β- and γ-globulins were concomitantly increased.

1. The effect of dietary protein level and supplementation with thyroxine and thiouracil on depletion of liver stores of vitamin A, on the percentage of liver vitamin A in the alcohol form and on the plasma level of vitamin A and protein has been studied in chicks. In an experiment with cockerels the relation was investigated between the vitamin A level of plasma and the electrophoretic pattern of its proteins.

2. Liver vitamin A depletion was considerably reduced by lowering the dietary protein level.

3. Protein malnutrition lowered the percentage of vitamin A found in the liver in the alcohol form.

4. Depletion of vitamin A from the liver was related to the percentage of vitamin A in the alcohol form.

5. Thyroxine increased both vitamin A depletion from the liver and the percentage of vitamin A in the alcohol form, whereas thiouracil had the opposite effect.

6. Plasma vitamin A, and plasma protein contents were significantly lowered in cockerels receiving a 5% protein diet. The drop in plasma protein level was essentially caused by a reduction of the albumin fraction. No significant change in the levels of globulins was observed even after a 4-week period of protein malnutrition.

7. When the dietary protein level was restored to normal both the albumin and vitamin A levels in plasma increased.