1. The relationship between protein content of abomasal digesta and abomasal secretion of acid was studied in sheep fitted with re-entrant cannulas in the proximal duodenum.

2. A close relationship was found between the rate of passage of protein through the abomasum and acid secretion, both after varying the protein content of the rations supplied, and after direct introduction of proteins into the abomasum (infusion tube).

3. It is concluded that proteins stimulate abomasal secretion of acid.

1. Six experiments each involving two groups of six piglets, were designed to study the influence of environmental temperature on heat production, energy retention and protein and fat gain in early weaned piglets. Immediately after weaning, at a mean age of 25 d, the animals were raised in two open circuit respiratory chambers. Each chamber was equipped with a totally wired cage. The piglets were paired-fed and maintained at environmental temperatures of 20, 24 or 28°. Four replicates were used for each temperature. Metabolizable energy, heat production and nitrogen balance were measured during two consecutive periods (A and B), each of 6 d duration.

2. Heat production was higher at 20° than at 24 and 28° during periods A and B. Energy retention was negative during period A, it was positive during period B and increased with temperature.

3. Protein deposition was always positive and independent of environmental temperature. The net efficiency of protein utilization was 0.77.

4. Body fat was mobilized during period A at a higher rate at 20° than 28°. During period B, fat gain increased with increase in temperature.

5. The calculated ME requirement for maintenance amounted to 411 kJ/kg body-weight0.75 per d at 28°.

6. The critical temperature of early weaned piglets raised in intensive modern housing and fed at about 90% of the ad lib. intake is close to 28° during the first 12 d after weaning.

1. The rumen adapts to increased food intake by the hyperplasia of epithelial cells.

2. Volatile fatty acids (VFA) stimulate cell mitosis of sheep ruminal epithelium in vivo.

3. Since VFA generally inhibit cell proliferation in vitro insulin was proposed in this study as the possible mediator of the mitotic stimulation in vivo.

4. Infusions (6 h) of insulin (0.125 U/kg per h) plus glucose (300 mg/kg per h) (n 5), and glucose alone (300 mg/kg per h) (n 2) resulted in higher mitotic index of biopsied rumen epithelium (MI) during 3 or 6 to 24 h after the start of infusion, and higher plasma immunoreactive insulin (IRI) and higher plasma glucose (PG) during the infusion.

5. Insulin plus glucose infusion showed higher MI, higher IRI, and lower PG than glucose infusion.

6. Sheep infused with saline for 6 h (n 1) showed no marked changes in MI, IRI, and PG.

7. Increased IRI by insulin plus glucose or glucose alone infusion was considered to stimulate cell proliferation in rumen epithelium.

8. Other possible mediations were discussed.

1. Sheep were given four different diets which contained two types of forage and two types of concentrate. The forage portion of the diet consisted of either hay or silage, while the low-oil concentrate had high levels of starch and in the high-oil concentrate this starch was replaced by an isoenergetic amount of soya-bean oil.

2. The effects of these diets on various factors in the blood was measured.

3. The erythrocytes were more fragile in hypotonic solutions (6.0–8.5 g sodium chloride/l) of saline when they were eating a diet of hay and high-oil concentrates.

4. The levels of calcium, magnesium, phosphorus, glucose and β-hydroxybutyrate in the plasma were unaffected by dietary treatments.

5. Substitution of silage for hay in the diet increased the intake of all fatty acids, especially that of C18:3.

6. When the sheep had low intakes of oil, the change from hay to silage led to increases in the amounts of triglyceride (TG) and total lipid (TL) in their plasma, whereas with high intakes of oil this change of forage increased the plasma TG content by an even greater amount but did not alter the concentration of TL.

7. Increasing the intake of dietary oil raised the levels of both TG and TL in the plasma, irrespective of the type of dietary forage.

8. On silage diets the sheep had much greater amounts of 18:0 and 18:1 fatty acids but smaller quantities of 18:2 fatty acid in their plasma than on hay diets.

9. Changing the dietary forage from hay to silage or the concentrate from low- to high-oil enhanced the levels of all the trans isomers of C18 fatty acids in the blood of the animals.

10. These results imply that unsaturated fatty acids in silage-based diets are hydrogenated to a greater extent in the rumen than those in hay diets which results in an elevation in blood TG levels and that this in turn could profoundly alter such functions as milk fat synthesis and fat deposition in ruminants.

1. Expt 1. Five 150 kg steers with ruminal, abomasal and ileal cannulas were given 3000 g oaten chaff daily plus prelleted supplement with no added nitrogen (diet A) or 50 g N/d as urea (diet B), casein (diet C), casein and formaldehyde-treated casein (HCHO-casein) (50:50 w/w; diet D) and HCHO-casein (diet E), in a 5 × 5 Latin square design. The basal diet and supplement were fed in eight equal increments at intervals of 3 h. Proportions of dry matter and organic matter digested in the stomach and whole tract were greater for diets B, C, D and E than for diet A. Total volatile fatty acid levels in the rumen and the proportion of acetic acid were lower, and the proportion of propionic acid higher on diet A than on the other diets. Rumen ammonia levels were lower on diets A, D and E than on diets B and C. N flows at the abomasum, ileum and rectum were lower on diet A than on the other diets; abomasal flows and apparent intestinal absorptions of amino acids were higher on diets D and E than on diets A, B and C. Efficiencies of bacterial protein synthesis were 15, 15, 14, 13 and 12 g bacterial N/kg OM truly digested in the stomach on diets A, B, C, D and E respectively.

2. Expt. 2. Forty 300 kg steers were fed oaten chaff ad lib. plus twice the amount of the same pelleted supplements as in Expt 1. Intake of oaten chaff was 23% higher with N supplements (diets B, C, D and E) than without (diet A). Live-weight gains were 356, 798, 843, 842 and 805 g/d on diets A, B, C, D and E respectively.

3. It was concluded that efficiency of bacterial protein synthesis was not limited by the supply of peptides and amino acids in the rumen and that increases in amino acid availability in the intestines from feeding HCHO-casein did not increase food intake or live-weight gain.

1. An experiment was conducted with goat kids to determine the effect of zinc injection on Zn binding in cytosols of several tissues of kids.

2. Following the Zn load, plasma Zn increased for 8 h then decreased. Zn injection significantly increased the Zn contents of the liver and kidney.

3. Injection of Zn into kids stimulated the production of Zn in a fraction with an apparent molecular weight of approximately 10000 in the cytosols of the liver, kidney and small intestinal mucosa. It is suggested that these fractions probably correspond to metallothioneins, Rumen papilla did not synthesize Zn-containing protein in response to an acute administration of Zn.

4. Zn injection significantly decreased the Cu content of the liver and affected the distribution of Cu in hepatic cytosol fraction, suggesting an interaction between these two elements.

5. The volume of bile collected in the gall bladder and its Zn content were markedly increased by Zn injection, suggesting that bile is one of the Zn excretion routes in kids.

1. Hepatocytes isolated from vitamin B12-deficient and vitamin B12-supplemented rats were maintained in primary culture and were used to study the effect of methionine on the metabolism of [3H]folic acid and [5-14C]methyltetrahydrofolic acid.

2. Vitamin B12 levels were reduced by approximately 75% in the hepatocytes from the deficient animals. Total folate and methyltetrahydrofolic acid concentrations were also significantly reduced.

3. There was no significanct difference in the uptake and retention of added [3H[folic acid and [5-14C]-methyltetrahydrofolic acid between the hepatocytes of the two groups. The incorporation of 14C into phospholipids was reduced by approximately 60% in the vitamin B12-deficient hepatocytes (P < 0.001).

4. The addition of methionine to the culture medium doubled the uptake and retention of 3H in both groups, but it did not change the amount of water-soluble 14C Compounds. In the vitamin B12-deficient hepatocytes mainly methylated folate increased, whereas non-methylated folate increased in the hepatocytes of the control animals. A tenfold increase of 14C incorporated into phospholipids was found in both groups after methionine was added.

5. Demethylation of methyltetrahydrofolic acid, the intracellular retention of folate and the utilization of liberated methyl groups, for example in the methylation of phospholipids, were highest in the presence of both methionine and vitamin B12 suggesting an intimate co-ordination between these two substances in the regulation of folate metabolism.

1. A method for producing a standard low-fluoride diet from a green alga and yeast is described. Chlorella pyrenoidosa was grown in a culture medium prepared with distilled water and analytical grade chemical salts. The spent culture medium from the alga culture was reclaimed and replenished with salts and sucrose for the production of yeast, Saccharomyces cerevisiae.

2. The single-cell organisms were separated by centrifugation from their culture media and the dried cells were blended with sucrose, maize oil, cellulose and a salt mix to produce diet pellets for rats and mice.

3. The diet was readily accepted as food by rats and mice and it was found to contain 100–300 μg fluoride/kg dry weight. Two generations of rats and four generations of mice were bred on this diet.

4. The use of hydroxyapatite to reduce the fluoride content of the chemicals used in the production of the alga and yeast biomass was investigated. Diet pellets prepared with this biomass contained 45–60 μg fluoride/kg dry weight.

1. Rats were fed for 14 d on diets containing 50, 150 or 250 g/kg casein as the protein source. The daily excretion of Nt-methylhistidine (His(τMe)), a non-re-utilized amino acid, was determined.

2. His(τMe) excretion/100 g body-weight appeared to be unaffected by increasing the concentration of dietary protein from 150 to 250 g/kg. Assuming no change in the proportion of muscle in the animals these results are indicative of no change in myofibrillar protein catabolic rate. The excretion rate/100 g body-weight of the animal given 50 g/kg casein was lower than the other two treatments, especially towards the end of the 14 d treatment period. Thus at this time the myofibrillar-protein catabolic rate was lower than in the animals fed on the higher protein diet.

3. In the animals fed on the high protein diet there was a tendency for this (τMe) excretion rate/100 g body-weight to increase with age.

4. Nitrogen balance and creatinine excretion results are also presented.