1. Two experiments are reported in which the effect of the intragastric infusion of non-protein energy on fasting nitrogen losses was studied. Expt 1 was a preliminary trial with two 35 kg lambs given 0, 144, 288 or 432 kJ/kg live weight (W)0.75 per d as lipid or glucose infused into the abomasum for periods of 3 d. Expt 2 was of a 4 x 4 Latin square design with four sheep of about 30 kg live weight. The four treatments were control (fasted with water infusion), or the infusion of 144 W/kg W0.75 per d as glucose or lipid into the abomasum or as acetic acid into the reticulo-rumen.

2. Compared with the fasted control, glucose infusion reduced (P < 0.05) N excretion to about 0.6 of that of the control, increased (P < 0.05) plasma glucose, decreased (P < 0.05) plasma urea and β-hydroxybutyrate, and was without effect on plasma amino-N or creatinine excretion.

3. Lipid and acetate infusions were without statistically significant effect on N or creatinine excretion or any of the blood indices measured, with the exception of plasma glucose which was reduced (P < 0.05) with acetate infusion.

1. Three experiments were conducted with sheep given spring-harvested dried grass (SHG) and autumn-harvested dried grass (AHG). The first was a calorimetric trial to determine the metabolizable energy (ME) content of each grass and the efficiency with which sheep utilize their extra ME intakes above the maintenance level of intake. The second examined the relative amounts of extra non-ammonia-nitrogen (NAN) and individual amino acids absorbed from the small intestine per unit extra ME intake as the level of feeding was raised from energy equilibrium (M) to approximately 1.5 M. The third was a further calorimetric trial to investigate the effect of an abomasal infusion of 30 g casein/d on the efficiency of utilization of AHG.

2. The ME content of the SHG (11.8 MJ/kg dry matter (DM)) was higher than that of AHG (10.0 MJ/kg DM). The efficiency of utilization of ME for productive purposes (is. above the M level of intake; kf,) was higher when given SHG (kf 0.54 between M and 2 M) than when given AHG (kf 0.43 between M and 2 M).

3. As the level of intake of each grass was raised from M to 1.5 M there was a greater increment in the amounts of NAN (P < 0.001) and the total amino acid (P < 0.05) absorbed from the small intestines when sheep were given the SHG (NAN absorption, SHG 5.4 g/d, AHG 1.5 g/d, SED 0.54; total amino acid absorption SHG 31.5 g/d, AHG 14.3 g/d, SED 5.24).

4. Infusion of 30 g casein/d per abomasum of sheep given AHG at M and 1.5 M levels of intake increased (P < 0.05) the efficiency of utilization of the herbage from kf 0.45 to kf 0.57. Consideration is given to the possibility that the higher efficiency of utilization of ME in sheep given SHG may be related to the amounts of extra glucogenic amino acids absorbed from the small intestine which provide extra reducing equivalents (NADPH) and glycerol phosphate necessary for the conversion of acetate into fatty acids.

1. Lotus pedunculatus (cv. Grasslands Maku) grown on acid low-fertility soil and containing high concentrations of condensed tannin (76–90 g/kg dry matter (DM)) was grazed by growing sheep for 31–42 d periods in three experiments. In Expt 2 an additional group of lambs grazed areas oversown with white clover (Trifolium repens) and red clover (Trifolium pratense). Lambs were transferred from grazing ryegrass (Lolium perenne) – white clover straight on to lotus in all experiments (unconditioned sheep). In Expt 3 a second group was included which had grazed high-tannin lotus for a pre-experimental period of 8 weeks (conditioned sheep).

2. Effects of condensed tannin on body and wool growth were assessed by studying responses to daily oral administration of polyethylene glycol (PEG; molecular weight 3350, 75–100 g/d). PEG forms a complex with condensed tannin, which is assumed to be inert in its passage through the digestive system, and so effectively reduces the nutritional effects attributable to high condensed-tannin concentrations.

3. Live-weight gain (LWG) in the absence of PEG was low (27–125 g/d) for sheep grazing high-tannin lotus, and PEG administration increased LWG by 41–61 g/d and increased wool growth. In Expt 3, responses to PEG supplementation tended to be less with conditioned than with unconditioned sheep, indicating that conditioned sheep had partially adapted to the high-tannin diet.

4. PEG supplementation had no effect on either LWG or wool growth of sheep grazing areas oversown with mixed clovers, confirming its effects as specific to forages containing condensed tannins. These experiments therefore conclusively show that high concentrations of condensed tannin induced by growing Lotus pedunculatus under low soil fertility conditions prevent maximum expression of LWG and wool growth in grazing sheep. These results contrast with high LWG (153–315 g/d) observed in growing sheep grazing the same lotus cultivar grown in high fertility soil and containing 20 g condensed tannin/kg DM, a level considered to be nutritionally beneficial.

1.Two experiments of Latin square design were made, each with four Friesian bull calves fitted with re-entrant duodenal and ileal cannulas at 4–10 d of age. The calves were used to studythe effect of giving milk-substitutes containing 0, 300, 500 and 700 g bacterial protein (Pruteen)/kg total protein on apparent digestibility of nitrogen fractions and amino acids and true digestibility of 3H-labelled milk protein and 35S-labelled bacterial protein in the small intestine. A third experiment of Latin square design with four intact Friesian calves was used to measure apparent digestibility of nutrients throughout the alimentary tract and retention of N, calcium and phosphorus.

2.At the duodenum, volume of outflow, its pH, and outflow of total-N (TN), protein-N (PN) and non-protein-N (NPN) decreased with time after feeding. At the ileum, volume of outflow and TN outflow were unaffected by time after feeding but PN outflow decreased; NPN outflow at the ileum increased to a maximum 6 h after feeding and then declined.

3.Increased inclusion of Pruteen did not affect the volume of outflow at the duodenum or ileum, but duodenal PN outflow increased. At the ileum, pH values were lower and TN, PN and NPN outflows were higher with increasing concentration of Pruteen in the diet. Apparent digestibility in the small intestine tended to decrease with greater amounts of Pruteen, but was only significant for NPN. Apparent digestibility from mouth to ileum significantly decreased for TN and PN as Pruteen inclusion increased.

4.Amino acid concentration in duodenal outflow, with the exception of that of arginine, reflected intake. The total amount of each amino acid in ileal outflow increased and the apparent digestibility of most amino acids decreased with greater amounts of Pruteen in the diet. Apparent digestibility of nucleic acid-N from Pruteen was very high.

5.True digestibility in the small intestine and between mouth and ileum of 3H-labelled milk protein was high and did not differ between dietary treatments. True digestibility of 36S-labelled Pruteen was low for the milk-protein diet and tended to increase linearly as more dietary Pruteen was included.

6.Dry matter concentration in faeces and a high apparent digestibility throughout the whole alimentary tract of carbohydrates did not differ between treatments. Apparent digestibility of dry matter, organic matter, crude protein and fat, apparent absorption of Ca, P and ash throughout the tract, retention of N, Ca and P and biological value of the protein decreased with inclusion rates greater than 300 g Pruteen/kg total dietary protein. The amount of N apparently absorbed in the large intestine was estimated as 0.9 g/d.

7.Comparison of intake of apparently absorbed essential amino acids with requirement suggests that histidine is likely to be the limiting amino acid, assuming that arginine is synthesized in the body.

8.Efficiencies of utilization of protein for tissue synthesis and to cover obligatory loss are estimated as 0.80, 0.75, 0.66 and 0.47 for diets containing 0, 300, 500 and 700 g Pruteen/kg total protein in the diet. Efficiencies of utilization of individual essential amino acids were also estimated.

1. The vitamin B12 in sows' milk is strongly attached to a specific ‘binder’ protein, which is present in excess. The influence of this ‘binder’ on the uptake and retention of cyanocobalamin and two natural analogues(cobinamide and Co-α-[2-methyladenyl]cobamide) was investigated with neonatal piglets.

2. Retention of a single oral dose of cyano[58Co]cobalamin given before 7 d of age was consistently higher with suckled than with early-weaned piglets, as determined by measurement of whole-body radioactivity.

3. Efficiency of retention declined with age, more rapidly in early-weaned than in suckled animals; when the dose was given at 14 d approximately 30% was retained by both groups.

4. Distribution of the retained cyano[58Co]cobalamin within the body of the piglets was the same in both groups; about half was present in the liver.

5. Foraging piglets may ingest adventitious vitamin B12 and its analogues, which are present in the sow's faeces and in contaminated litter. The influence of the vitamin B12-binder in sows' milk on the uptake and retention of two non-cobalamin analogues, and the effects of the analogues on the uptake and retention of vitamin B12 from 2 to 14 d after parturition, were investigated with early-weaned piglets.

6. The analogues were detected in the liver but not in the body organs. They were also present in blood plasma, urine and bile, in high concentration relative to that of vitamin B12. The content of analogues in the liver was very small in relation to the amounts ingested, and much less than that of vitamin B12. There was no indication that the vitamin B12-binder in sows' milk influenced uptake and retention of the analogues, or that ingestion of analogues affected the content of vitamin B12 in the body organs and fluids examined.

1.It has been postulated that the vitamin B12-binding protein in the sows' milk may facilitate the intestinal absorption of vitamin B12 in the piglet. This implies that the binder is not rapidly and completely degraded by gut proteases, and the present experiments were devised to test this assumption.

2. Piglets aged 7 and 28 d were given a test feed of sows' milk whey both with and without cyano[3H]cobalamin to saturate the binder, and with 14C-labeHed polyethylene glycol (PEG) as a marker. Control piglets were given a milk substitute containing no vitamin B12-binder. At 80 min after the test meal the piglets were killed and the contents of the stomach and small intestine were removed for analysis.

3. Recovery of [14C]PEG, mainly from the middle and distal portions of the small intestine, ranged from 49 to 78%. Apparent loss of vitamin B12-binder from the intestine was calculated from the ratio, PEG: binder. In both 7- and 28-d-old piglets, the content of saturated binder in the middle and lower small intestine was about 20% depleted relative to that in the test feed. With the unsaturated binder the loss was more variable and generally greater, at about 50%.

4. At slaughter the stomach was nearly empty and the high unsaturated binding capacity of the contents was attributed to endogenous binders. However, in the middle and lower small intestine, the binding capacity was derived mainly from sows' milk given with the test meal. No free cyano[3H]cobalamin was found in the intestinal contents of piglets given sows' milk to which enough cyano[3H]cobalamin had been added to saturate the binder.

5. There was no change in the molecular weight of the vitamin B12-binder during its passage down the intestine, as judged by its behaviour on filtration in Sephadex gel G-150.

6. The results indicate that a high proportion of saturated binder, and a smaller proportion of unsaturated binder, survived unchanged in the intestine of piglets at both ages.

1. The influence of the vitamin B12-binding protein isolated from sows' milk on the uptake of vitamin B12 was investigated using microvillus membrane vesicles prepared from the small intestine of 7- and 28-d-old piglets. Uptake of radioiodinated purified binder was also examined.

2. The binder strongly promoted uptake of vitamin B12 at both ages; in the absence of the binder there was little uptake. The uptake mechanism was specific and operative in vesicles prepared from all regions of the small intestine. Uptake was a rapid process, exhibiting saturation kinetics, with a pH optimum at about 7.0, and dependent on the presence of magnesium or calcium ions for maximum activity. Atfinity constants of the binding sites for the milk binder were determined.

3. Competition experiments using complexes of the binder with vitamin B12 and with non-cobalamin analogues (cobinamide and Co-α-[2-methyladenyl]cobamide) showed that the bound analogues competed with bound vitamin B12 for uptake but with lower efficiency.

4. Intrinsic factor also promoted vitamin B12 uptake by the vesicles but it did not compete with the milk binder for the same binding sites. It promoted uptake only in microvilli isolated from the lower third of the small intestine, and was more effective with preparations from 28-d-old piglets, whereas the milk binder was more effective with the 7-d-old piglets. Porcine gastric cobalophilin competed with the milk cobalophilin, but with lower efficiency.

5. It was concluded that a specific transport mechanism for absorption of vitamin B12, mediated by the vitamin B12-binder in milk, exists at the intestinal brush border of neonatal piglets and strongly reinforces the developing intrinsic factor-mediated mechanism during the early days or weeks of life.

6. It is suggested that the binder in the milk has a wider physiological significance and acts also as a ‘host protective’ factor and as a scavenger of adventitious vitamin B12.

1. Continuous infusion and single-shot administration of 15NH4Cl into the caecum of the conscious rabbit was used to measure caecal ammonia flux.

2. Continuous infusion of 15NH4Cl and sampling from both the caecal ammonia and blood urea pools indicated that 0.27 of plasma urea-nitrogen was derived from caecal ammonia-N.

3. Values from intravenous [15N]urea and intracaecal 15NH4Cl infusions were used to produce two models of the movement of N between these two metabolic pools.

4. Further analysis of the results suggested an alternative model involving a third pool associated with the caecal mucosa and values for this model are also presented.

1. Oxygen consumption and ouabain-sensitive respiration was measured for liver biopsies from lactating and non-lactating ewes and for hepatocytes isolated from mature, dry ewes. O2 consumption, ouabain-sensitive respiration and 86Rb+ uptake were also measured for hepatocytes isolated from lambs, fed adult sheep and adult sheep starved for 5 d.

2. Ouabain-sensitive respiration in the liver of ewes at peak lactation accounted for 45% of the total liver O2 consumption. This percentage was 24–37% higher (P > 0.05) than measurements made during late lactation and during the non-lactating period.

3. Total O2 consumption and ouabain-sensitive respiration rates of lamb hepatocytes were greater ( P > 0.05) than similar measurements for hepatocytes isolated from adult sheep.

4. Ouabain-sensitive 86Rb+ uptake by hepatocytes from fed sheep was up to six times greater (P > 0.05) than that by cells from starved sheep.

5. The magnitude of ouabain-sensitive respiration of hepatocytes from starved sheep was 62% lower (P > 0.05) than that for hepatocytes from fed sheep.

1. The development of gastric secretory capacity of hydrochloric acid and pepsin (EC 3. 4. 23. 1) was studied in thirty-eight Large White x Landrace pigs from the litters of six sows (three pairs of two), 9–38 d of age. The pigs of each pair of sows were born within 24 h of each other. The pigs of a litter were paired according to sex and size and cross-fostered, i.e. one pig from each pair was allocated to each sow.

2. One litter from each pair was reared entirely by the sow (milk-fed, MF) whereas the other litter was reared by the sow for 21 d, but was allowed access to solid food (210 g crude protein (nitrogen x 6.25)/kg) at 12 d and was entirely dependent on solid food after 21 d (creep-fed, CF).

3. Following a 14–18 h fast, pigs were anaesthetized (Halothane–sodium pentobarbitone) and their stomachs perfused a a constant rate with Ringer solution. Gastric secretion was stimulated by intravenous infusion of betazole hydrochloride (Histalog) at 3 mg/kg per h for 2 h. Hydrochloric acid and pepsin were measured in the perfusate which was collected at 15-min intervals.

4. There were significant positive correlations between stomach weight and body-weight for both MF and CF pigs. The slope of the regression line for CF pigs was significantly greater than that for MF pigs (P < 0.01).

5. There were significant positive correlations between maximal acid output and stomach weight for both MF and CF pigs.

6. There were significant positive correlations between maximal pepsin output and stomach weight for both MF and CF pigs. The slope of the regression line for CF pigs was significantly different from that for MF pigs (P < 0.01). There were also significant positive correlations between maximal pepsin output per unit stomach weight and stomach weight for both MF and CF pigs.

7. The pattern of development of pepsin secretory capacity in both CF and MF pigs was different from that for acid secretion. Maximal outputs of acid per unit stomach weight for MF and CF pigs remained relatively constant. Maximal outputs of pepsin per unit stomach weight and per unit body-weight increased with age for both MF and CF pigs.

8. The results indicate that pigs given access to solid food before weaning and weaned on to solid food have heavier stomachs and greater acid and pepsin secretory capacity than pigs fed entirely on sows' milk.