1. The effect of the soya-bean protein isolate and casein, both given 200 g/kg diet for 3–4 weeks, on serum cholesterol was compared in male rats.

2. Soya-bean protein exerted a hypocholesteraemic effect only in a cholesterol-free low-fat (10 g maize oil/kg) diet, when the lowering action appeared independent of the strain of the rat or the feeding pattern. The results obtained with diets containing cholesterol or higher levels of fats or both showed no definite pattern of response.

3. Although the decrease in serum cholesterol appeared greater in α-lipoprotiens than in β-lipoproteins, the proportion of the former to total cholesterol remained almost unchanged. The concentration of serum apo A-I was significantly lower in rats given the vegetable protein.

4. Rats given soya-bean protein excreted significantly more neutral sterols.

5. The serum amino acid pattern did not reflect the difference in dietary protein. Addition of cholesterol to the diets modified the serum aminogarm, the decrease in threonine being most marked in both protein groups.

6. This study shows that the hypocholesteraemic action of soya-bean protein is easily modified by the type of diet.

1. All food was withdrawn from male weanling rats until a 40% loss of body-weight was attained. Another group of animals was treated similarly and then refed a stock diet until the original body-weight was attained.

2. The body-weight loss caused a significant reduction in the weight of the heart, kidney, liver and epididymal fat pads. Refeeding produced a return to the control weight of the heart and kidney, an increase in the weight of the liver and a deficit in the weight of the epididymal fat pads.

3. Body-weight loss caused a decrease in the weight of the three different muscles studied, and in the number and diameter of the fibres in each muscle. Refeeding restored the weight and cellularity of two of the three muscles to that of the control animals. The soleus muscle was heavier in the refed animals when compared to controls due to an increased fibre diameter.

4. It is concluded that the decrease in the number and diameter of muscle fibres during starvation in the rat can be restored on refeeding a stock diet.

1. The validity of the urinary excretion of Nτ-methyl histidine (Nτ-MH) in sheep as a measure of the breakdown of muscle protein in vivo was assessed from the urinary recovery of radioactivity following the intravenous administration of Nτ-[14CH3]methylhistidine.

2. Recoveries of radioactivity in urine from animals of 4 weeks to 7 years of age were incomplete in 7 d but progressively increased with the age of the animal, becoming almost quantitative (90%) in older animals after recovery for 3 weeks.

3. The incomplete urinary recoveries were not due to partial excretion of Nτ-MH in faeces or its oxidation and elimination in expired gases but were related to the presence in muscle of a pool of non-protein-bound Nτ-MH which was several times larger than the expected daily urinary excretion.

4. This pool in newly accreted muscle tissue was maintained by retention of some of the Nτ-MH released by breakdown of muscle protein. Hence, only a proportion of the Nτ-MH released from protein breakdown was available for excretion. This proportion increased with the age of the animal and was probably the main determinant of the improved recoveries of radioactivity obtained in urine from older animals.

5. The non-protein-bound Nτ-MH in muscle consisted of free Nτ-MH and a dipeptide containing Nτ-MH, the latter comprising on average approximately 82% of the total non-protein-bound Nτ-MH in muscle. This proportion did not change appreciably with the age of the animal.

6. The dipeptide appeared to be synthesized in muscle from free Nτ-MH and was not a terminal product of protein breakdown.

7. The results show that urinary excretion of Nτ-MH is not a reliable index of muscle protein breakdown in sheep.

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 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 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.

1. The effect of biotin supplementation of low-biotin practical diets during rearing and laying stages on performance was studied in White Leghorn-type laying hens.

2. Biotin supplementation during rearing did not have any apparent effect on the condition of the bird at point-of-lay or on subsequent laying performance.

3. Biotin supplementation during lay did not have any beneficial effect upon egg number, egg size or food intake or food conversion efficiency.

4. Internal egg quality, as reflected by albumen height, was slightly improved by biotin supplementation of layer's diet.

5. Input-output relationships were calculated for the incorporation of biotin in egg yolk.

6. Metabolic measurements suggested that biotin concentration in egg yolk was the best criterion of biotin status in the hen.

7. It is concluded that practical diets contain sufficient biotin to support optimum egg-laying performance in hens.

1. Spray-dried diets were prepared containing (g/kg): dried skim-milk 665, dried whey 65, soya-bean oil 270 (diet U); or single-cell protein (Pruteen; SCP) 308, dried whey 440, soya-bean oil 252 (diet X). The diets had a crude protein (nitrogen × 6·25) content (g/kg) of 250 (diet U) and 240 (diet X), excluding nucleic acids (36 g/kg) in diet X.

2. The diets were reconstituted (200 g dry matter/l) and mixtures of diets U and X prepared to give diets supplying 0 (diet U), and approximately 400 (diet V), 600 (diet W) and 800 (diet X) g crude protein from SCP/kg total protein. All diets were supplemented with vitamins, and minerals to equalize the calcium, phosphorous, sodium and potassium concentrations.

3. Pigs weaned at 2 d of age were given the diets at hourly intervals on a scale based on live weight. At 28 d age the experiment was terminated and pigs killed 1 h after a feed for a study of protein digestion. Polyethylene glycol (PEG) was fed in the diets (0.5 g/l) for 24 h before slaughter.

4. Performance of pigs fed on diet V was as good as on the all-milk diet U. Greater levels of replacement by SCP (diets W and X) reduced performance. Mortality was greater on the all-milk diet, but protein source had no effect on the incidence of scouring. N retention (g/d per kg live weight) was similar for all diets but declined with age.

5. SCP appeared to stimulate secretion of pepsin and chymotrypsin, and reduced the pH value in digesta in the stomach. Enzyme adaptation may have been insufficient to digest high levels of SCP in the diet, and together with the decreased transit time observed using PEG as a marker, may account for the poorer performance when 600 or 800 g/kg milk protein was replaced.

6. Nucleic acids from SCP were metabolized and not retained for tissue synthesis. Allantoin excretion accounted for 75% of the theoretical maximum for complete excretion of nucleic acids, and uric acid excretion was also increased.

1. Pigs (twenty-one/diet) were weaned at 2 d of age and given liquid diets (200 g dry matter/l) at hourly intervals during a 26 d experiment. The pigs were fed on a scale based on live weight. The diets contained (g/kg DM): dried skim-milk 730 (diet A), dried whey 508·5, isolated soya-bean protein 218, DL-methionine 3·5 (diet S), and soya-bean oil 270 (diets A and S). Diet T contained equal proportions of diets A and S. Soya-bean supplied 0, 370 and 740 g crude protein (nitrogen × 6·25)/kg total crude protein in diets A, T and S respectively.

2. Performance was similar for both diets A and T (P > 0·05). Pigs given diet S scoured severely, and fourteen died. The survivors grew very poorly. Nitrogen retention (g/d per kg live weight) was greater for diet A compared with diet T (P < 0·0r), and decreased with age (P < 0·01).

3. Protein digestion was examined in the pigs killed at 28 d of age. The amount of soya-bean protein in the diet did not affect the amount of digesta in the stomach, but soya-bean protein decreased the pH, DM and total N content of the digesta (P < 0.01), and increased, though not significantly (P < 0·05), pepsin activity in the digesta and stomach tissue. Acid secretion into the stomach appeared to be enhanced in pigs given a diet containing soya-bean protein.

4. Amounts of trypsin, chymotrypsin, total N and proportion of non-protein-N in the digesta from the small intestine were similar for both diets A and T. The amounts for both diets were greater in the distal compared with the proximal region of the small intestine (P < 0·05). Chymotrypsin activity in the pancreas was reduced (P < 0·05) in pigs given diet T, although this reduction did not seem to impair digestion in 28-d-old pigs. Trypsin activity in the pancreas was similar for both diets A and T.

5. It seems likely that the neonatal pig does not have the digestive capacity to tolerate the large daily intakes of soya-bean protein when dried skim-milk was totally replaced in the diet (diet S). When half the dried skim-milk was replaced, protein digestion was not impaired in 28-d-old pigs.

1. Female rats were undernourished from birth through replacement for 12 h/d of the lactating mother by a nipple-ligated mother. This resulted in slow growth so that at 22 d of age the body-weights equalled those of well-nourished animals at 14 d.

2. At 14, 17, 20 and 22 d groups of eight to ten animals each of undernourished and well-nourished rats were autopsied, serum follicle-stimulating hormone (FSH) concentration was determined by radioimmunoassay, utersuses were weighed and ovaries examined by light microscopy.

3. Undernutrition caused a 3–4 d delay in the third-week drop in serum FSH and in ovarian development as indicated by the number of antral follicles and by the maximal diameter of the ovaries and of the largest follicles.

4. It is postulated that the effect of undernutrition on serum FSH may be due to delayed increase in ovarian feedback effectiveness, which may be the result of either the retardation in ovarian development or a continued high level of serum oestrogen-binding protein. It remains uncertain through which mechanism(s) undernutrition brings about delayed onset of puberty.

1. A combination of a mineral balance and a radioisotope technique has been used to study the relationship between dose rate of 1-α-hydroxycholecalciferol (1α-OH-D3) and the magnitude and duration of its effect on the various processes of calcium and phosphorous metabolism in adult wether sheep.

2. The rate of absorption of Ca was markedly increased by treatment and maximum response occurred at the lowest dose rate.

3. Although sheep were already Ca-replete, the extra Ca absorbed was all retained and increased retention was brought about by a combination of an increase in bone accretion and a decrease in bone resorption. This finding conflicts with the generally-held belief that bone resorption is increased by cholecalciferol treatment.

4. The rates of absorption and retention of P were increased by 1α-OH-D3 treatment and maximum response occurred at the lowest dose rate.

5. That P absorption could be increased by treatment suggests that not all the available dietary P was absorbed in the control period.

6. Although the loss of endogenous P in the faeces was unaltered by treatment, the secretion of P into the gut was increased, and the increase was directly related to increased serum inorganic P concentration.

7. Nearly all the extra P absorbed was retained and increased retention was achieved by a combination of an increased incorporation into and a decreased loss from the non-exchangeable pools of bone and soft tissues.

8. The time interval taken for absorption rates of Ca and P to return to normal after the end of each treatment was related to the dose rate of 1α-OH-D3. Although higher dose rates had little effect on the magnitude of response, they did prolong slightly the duration of response.

1. Neonatal hypoglycaemia is a relatively common clinical problem in children but ethical constraints limit the investigations that may be made in the newborn.

2. As a preliminary step to assess the suitability of the piglet as a model for glucose metabolism in man, whole-body glucose turnover and glucose pool size were measured using [2-3H]glucose in forty piglets from ten litters.

3. Glucose pool size was linearly related to brain weight. However, multiple regression showed that the most useful predictors of pool size were body-weight and resting plasma glucose concentration.

4. Glucose turnover was related to both brain weight and body-weight alone, but multiple regression showed that better predictors of turnover were liver weight, spleen weight and pancreas weight.

5. Similarities between our own results in piglets and those obtained in human neonates by Bier et al. (1977) extend not only to glucose turnover, but also to its relationship with body-and brain weight. These findings suggest that the piglet may be a useful model for the study of glucose metabolism in babies.

The metabolism of [1-C14]linolenic acid (18:3ω3) by the foetal rat was studied in vivo and in vitro. It is suggested that foetal brain has the capacity to convert linolenic to docosahexaenoic (22:6ω3) acid to meet its requirements for docosahexaenoic acid.