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In the present study, three primiparous lactating Holstein cows (260–285 d in lactation) were used in a 3 × 3 Latin square design to assess the effects of three doses (0·0, 0·4 and 0·8 μg/kg body weight) of lipopolysaccharide (LPS, Escherichia coli 0111:B4) on changes in ruminal microbiota and ruminal fermentation. Ruminal pH was linearly decreased (PPPP>0·10) the gene expression of Na+/K+-ATPase and monocarboxylic acid transporter-1, -2 and -4. A plot of principal coordinate analysis based on unweighted UniFrac values and analysis of molecular variance revealed that the structure of ruminal bacterial communities in the control was distinct from that of the ruminal microbiota in the cattle exposed to LPS. At the phylum level, when compared with the control group, LPS infusion in the tested cows linearly increased (PP

1. In Expt 1, fractional synthesis rates (FSR) of tissue protein were measured along the gastrointestinal tract (GIT) of six 1-week-old, milk-fed lambs by using a large amount of L-[3,4(n)-3H]valine.2. In Expt 2, eighteen lambs were used to determine the fractional growth rate (FGR) of gastrointestinal tissue protein.3. FSRMinimum(Min) and FSRMaximum(Max) were calculated assuming plasma or tissue homogenate free valine specific radioactivity was representative of the valine precursor pool for protein synthesis. There were no significant differences between FSR(Min) and FSR(Max) in any gastrointestinal tissue of lambs used in Expt 1 (P > 0.05). FSR gradually and significantly (P > 0.05) increased from the oesophagus (FSR(Max)26.5%/d). reticulo-rumen (30.1%/d), omasum (41.0%/d) and abomasum (56.1%/d) to small intestine (87.5%/d), and then declined significantly (P < 0.05) towards the caecum (45.2%/d) and the colon (38.4%/d). No significant differences were observed between FSR in the duodenum, jejunum or ileum (P > 0.05).4. FGR ranged from 2,6%/d in the oesophagus to 8,7%/d in the omasum. The ratio, FGR:FSR, which reflected the efficiency of protein deposition, was at a maximum in the stomachs and caecum and at a minimum in the small intestine.5. The relative contribution of the oesophagus, stomachs, small intestine and large intestine to GIT protein synthesis was 1, 13, 76 and 10% respectively. The GIT accounted for approximately 11.5% of whole-body protein synthesis.

1. Six closely shorn sheep were given brome grass (Bromus inermis) pellets at the rate of 59 or 98 g dry matter (dm)/h and maintained at ambient temperatures of 2–5° and 22–25° for 35 d. Measurements of digestion, rate of passage of digesta, and nitrogen transformations were made during the last 13 d of temperature exposure.2. Cold exposure at the lower level of intake reduced the apparent digestibility of dm and organic matter (om) approximately 0.055 units. Apparent digestibility of dm and om was further decreased approximately 0.03 units with the higher level of food intake in the cold. Apparent N digestibility was significantly depressed from 0.62 to 0.59–0.60 for sheep exposed to cold at both levels of intake.3. Exposure of sheep to cold resulted in a decrease in the turnover time of the particulate marker, 103Ru, from 19 h to 10.12 h in the rumen, a decrease in rumen volume, and a significant increase in dm and om which escaped digestion in the stomach. Volatile fatty acid and methane production in the rumen were highly correlated with the amount of om digested in the stomach. Methane production in the rumen comprised 0.81 of total production in warm sheep, and 0.68–0.74 of total production in cold-exposed sheep.4. More om and non-ammonia-N were apparently digested in the intestines of sheep exposed to cold than in warm sheep at the same food intake, but the apparent digestibilities in the intestines of dm, om and non-ammonia-N leaving the abomasum did not change significantly between treatments. The retention time of 103Ru in the intestines was 17.18 h in sheep given 59 g dm food/h at both exposure temperatures, but was reduced to 12 h for cold-exposed sheep given 98 g dm/h. Methane production in the postruminal tract was increased at the higher food intake, but there was no difference between warm and cold-exposed sheep at the same food intake.5. The rate of irreversible loss of plasma urea and rumen ammonia was measured by infusion of [15N]urea and [15N]ammonium chloride. Exposure to cold reduced the irreversible loss of plasma urea from 0.85 to 0.75–0.77 g N/g N intake, and the irreversible loss of rumen ammonia from 0.66 to 0.57–0.61 g N/g N intake. The transfer of plasma urea-N to the rumen ammonia pool was significantly greater (9.5 g N/d) in the cold-exposed sheep than the value (7.3 g N/d) in warm sheep.6. The efficiency of microbial synthesis in the rumen was increased in cold-exposed sheep, and was related to the amount of N recycled through the rumen ammonia pool from intraruminal sources. The effect of dilution rate and fermentation patterns on efficiency of microbial synthesis is discussed.

1. Fistulated sheep given a concentrate diet were used to study the behaviour of solute ([51Cr]EDTA) and particle ([103Ru]phenanthroline) markers in the stomach under conditions of continuous feeding.2. An injection of a mixed dose of [51Cr]EDTA and [103Ru]phenanthroline was given into the rumen and the time course of marker concentrations in the rumen and the abomasum was recorded. The curves were analysed on the assumption that the stomach of the sheep could be represented as two mixing compartments (reticulo-rumen and abomasum) and a time delay (omasum). This model provided a very good description of the data.3. [103Ru]phenanthroline associated with small particles was retained in the rumen much longer than [51Cr]EDTA. Although exchange of [103Ru]phenanthroline occurred between large and small particle fractions, the results suggested that small particles may have been retained somewhat longer in the rumen than solutes. However, it was clear from the results that the mean retention times for particulate matter in the rumen could not be simply obtained using adsorbable markers.4. Cyclical fluctuations in the concentration of [51Cr]EDTA in the rumen indicated that there were daily variations in net water flux in the rumen.5. The presence of protozoa was associated with much shorter retention times of both solutes and particles in the rumen. Protozoa were also associated with reduced rumen volumes.

1. Expt 1. Forty 200 kg heifers were given wheat strawad lib. plus one of five pelleted supplements, each of which supplied 40 g/nitrogen as urea/d, Treatment A did not supply other sources of N, and other treatments supplied daily 40 g digestible N as casein and formaldehyde-treated casein (HCHO-casein) in the following proportions (w/w): 100:0 (B), 70:30 (C), 30:70 (D), 0:100 (E). After 5 weeks (period 1) all supplements were withdrawn from half (four) of the animals in each treatment group (NS) over a period of 8 weeks (period 2). At the end of period 2. N balances were measured in four animals on each of treatments E and NS.2. In period 1 the mean intake of straw by animals on treatments D and E was higher than the mean intake by animals on treatments A, B and C (3·32v. 2·83 k/d respectively,P< 0·01) and live-weight changes also differed significantly (+ 72 and – 126g/d respectively:P< 0·01). Intakes of straw in period 2 were 3·74 and 3·20 kg/d for animals with and without supplements respectively (P< 0·01) and live-weight changes were +110 and – 157 g/d on the respective treatments (P< 0·01). For animals receiving supplements in period 2, intakes of straw did not differ significantly between supplements; live-weight changes were −14 g/d on treatment A and +141 g/d on treatments B, C, D and E (P< 0·01).3. N balances on treatments E and NS were +11·4 and – 3·3 g/d respectively (P< 0·01), although digestibility of organic matter (OM) was similar on the two treatments.4. Expt 2. Four 185 kg steers with rumen and abomasal cannulas were given wheat strawad lib. plus one each of treatments A, B and E in a randomized block sequence. Dry matter (DM) intakes were 3·44, 3·89 and 4·05 kg/d on treatments A, B and E respectively (P< 0·05). N intakes were 29 and 37 g/d higher on treatments Band E respectively than on treatment A, but abomasal flows of N were only 4 and 14 g/d higher on the respective treatments. The latter value indicates that approximately 0·62 of HCHO-casein was degraded in the rumen. Efficiencies of bacterial protein synthesis were 31, 24 and 26 g bacterial N/kgOM apparently digested in the rumen (P> 0·05) on treatments A, B and E respectively.5. It was concluded that efficiency of bacterial protein synthesis in the rumen was not limited by the supply of peptides and amino acids, and that protein supplements do not consistently stimulate intake of low-quality roughages when requirements for rumen degradable N have been met. Higher flows of N to the intestines when HCHO-casein, and to a lesser extent casein, were given were associated with a shift from negative to positive live-weight changes. These live-weight changes were not significantly correlated with DM intakes from which it appears that effects of casein supplements on live weight may have been attributable to effects of absorbed amino acids on efficiency of tissue protein synthesis either directly or through gluconeo genesis.

1. Net flux of volatile fatty acids (VFA), D-β-hyroxybutyrate (BOHB) and L-lactate across post-stomach (anterior mesenteric-drained viscera (MDV)), stomach and total hepatic portal-drained viscera (PDV) tissues was measured in two beef steers (mean live weight 390 kg).2. Net flux was measured while steers were fed, in sequence, on (1) chopped lucerne (Medicato sativa) (twelve meals/d), (2) chopped lucerne (two meals/d) and (3) a pelleted concentrate diet containing 780 g ground maize/ kg (two meals/d).3. Five hourly net flux measurements were obtained on 2 d for each dietary regimen, beginning 0.5 h before a meal delivered at 08.00 hours. Net flux was calculated as venous-arterial concentration differences (VA) multiplied by blood flow (measured by downstream dilution ofp-aminohippurate (PAH)).4. Stomach tissues accounted for 85 to over 100% of net VFA and BOHB appearance across PDV. Net appearance across stomach tissues represented 74% of net PDV L-lactate appearance.5. When lucerne was given, there was net utilization of arterial acetate and BOHB across MDV. This MDV utilization may reflect acetate and BOHB use as an energy source or their incorporation into mesenteric fat.6. When concentrate was given, moren-butyrate andn-valerate and less L-lactate appeared across PDV and less 3-methylbutyrate appeared across stomach tissues than when lucerne was given. Postprandial increases in VFA, BOHB and L-lactate net flux across PDV followed meal-feeding of lucerne.7. On a net basis, the relative contribution of MDV tissues to total PDV net appearance of VFA and BOHB was small (< 15%) in these steers.

1. Six sheep, three animals per diet, were prepared with rumen fistulas and fed on frozen grass or grass–maize pellets to give magnesium intakes of 1·79 and 2·23 g/d respectively. The mean apparent availabilities of Mg in sheep fed on frozen grass and grass–maize pellets were 0·31 and 0·36 respectively.2. The rumen contents were fractionated by straining the digesta through linen cloth and then differentially centrifuged to give 20 000gand 100 000gsupernatant fractions.3. In all sheep, regardless of diet, at 4 and 16 h after a meal, 50 and 60% respectively of the total Mg in the rumen contents was found in strained rumen fluid while 30 and 38% respectively of the total Mg was found in the 100 000gsupernatant fraction.4. The net absorption of Mg from the temporarily isolated and washed reticulo-rumen was studied using either 100 000 g supernatant fractions of rumen contents from sheep fed on one or other of the two diets, or inorganic buffers containing the same concentration of Mg and other macroelements.5. The Mg was readily absorbed from the 100 000gsupernatant fraction placed in the rumen with the rate of absorption being 7·3 μmol/1 per min (505 mg/d) from the supernatant fraction obtained from sheep fed on frozen grass and 11.3 μmo/1 per min (781 mg/d) from the supernatant fraction from sheep fed on grass–maize pellets. In the same sheep, the previously described rates of Mg absorption from the 100 000gsupernatant fraction were similar to those obtained from the comparable inorganic buffers.6. The effects of varying concentrations of potassium and sodium on the net absorption rate of Mg (as24Mg) and on the one-way efflux of Mg (as28Mg) from supernatant fractions or rumen fluid and inorganic buffers were investigated using the temporarily-isolated and washed rumen in three sheep. Although the net absorption rate of24Mg from supernatant fractions or buffers containing similar K concentrations varied significantly between sheep, a similar percentage decrease in the absorption rates of both24Mg and28Mg was found for each sheep as the K concentration was increased.7. One pair of sheep was fed on the frozen grass and the other pair was fed on the grass–maize pellets. Their daily intakes of K were then increased to 50 g/d for 14 d by intrarumen infusion of potassium chloride. In three of the four sheep the plasma Mg concentration fell within 12 h of the start of the KCl administration. In all sheep urinary excretion of Mg decreased and its faecal output increased. The increased intake of K had no effect on the distribution of Mg in the rumen contents.8. Gel-filtration chromatography of the 100 000gsupernatant fractions, regardless of the diet, showed that over 90% of the Mg in the 100 000gsupernatant fractions was associated with a low-molecular-weight fraction of about 200 Da which corresponded to the elution volume of magnesium chloride in 0·1 M-sodium chloride.9. It is concluded that any binding of Mg ions to small organic molecules in the 100 000gsupernatant fraction of rumen contents played no significant role in the restriction of Mg absorption from the reticula-rumen. The depressent effect of increased K concentration in rumen contents on the net absorption of Mg is via a reduction in the absorptive flux rather than by increased secretion of Mg into the rumen fluid.

1. The abilities of cattle, sheep, goats, equines and rabbits to digest mature timothy (Phleum pratense) hay were compared. Apparent digestibilities were partitioned into true digestibility, metabolic faecal output (MFO) and fibre digestibility. The aim of the study was to determine the relative effects of fermentation site (among groups) and of body-weight (within groups) on the efficiency of digestion.2. The ruminants were superior to equines, which were in turn superior to rabbits, in digesting fibre components of the hay. A large individual variation in digestibility was noted only for the equines. Increasing body-weight was associated with higher digestibility in ruminants, but no such trends were seen in the non-ruminants.3. The MFO expressed as a proportion of dry matter intake gave similar values for all groups (0·085–0·118). As a proportion of available microbial substrate originating from the feed, the values were found to be 0·167 for the ruminant, 0·425 for the equines and 2·13 for the rabbits. The value for the rabbits shows that their lower tract microflora must obtain energy from non-fibre components of the feed. No appreciable digestion of the generated microbes by the host was suggested by the values obtained for the equines.

1. Sheep prepared with a rumen cannula and with re-entrant cannulas at the proximal duodenum and terminal ileum were given diets of dried grass, and dried grass supplemented with formalin-treated or untreated casein. They were fed either continuously or once daily. Paper impregnated with chromic oxide was given once daily via the rumen fistula.2. The observed daily flows of magnesium at the duodenum and ileum were highly correlated with the corresponding flows of Cr.3. There was a net absorption of Mg from the stomach as well as the intestinal region of all sheep.4. Protein supplementation had no effect on the extent or sites of Mg absorption, but altering the feeding regimen changed the proportions of the net absorption of Mg occurring in the stomach and intestinal regions.

1. Four wether sheep, each fitted with re-entrant duodenal cannulas and a rumen cannula, were used to determine the relative quantitative importance of digestion in the stomach compared with that in the intestines when diets of low (HM1) and high starch (CM1) content were fed at 0.9 times maintenance and when the high-starch diet was fed at 1.7 (CM2) and 2.3 (CM3) times maintenance. Paper, impregnated with chromic oxide, and polyethylene glycol (PEG) were administered.2. An apparatus is described which allowed one operator to collect, record, sample and return the duodenal digesta from two sheep simultaneously.3. Total digestion was determined by faeces collections over 7–10 day periods, and digestion in the stomach by measuring the total flow of digesta from the abomasum to the duodenum over two 24 h periods with two or three sheep on each ration. Flow values were adjusted to give 100% recovery of chromic oxide.4. The recoveries of chromic oxide and PEG were similar and it was concluded that either marker was satisfactory for adjusting 24 h flow values. Disadvantages of using PEG are discussed.5. There was relatively little difference between rations HM1 and CM1 in the proportion of digestible organic matter and energy digested in the stomach. Only 57.1% of the total dry-matter digestion occurred in the stomach for ration HM1 compared with 65.0% for ration CM1 reflecting a smaller net gain in ash for ration CM1. Doubling the level of intake (ration CM2) resulted in a decrease in the proportion of digestible dry matter, organic matter and energy digested in the stomach. When the level was increased still further with ration CM3, the proportion continued to decrease with one sheep but increased with the other.6. All but 5–11% of the digestible starch (measured as α-linked glucose polymer) was fermented in the stomach, the lowest proportion being with ration HM1.7. The amount of nitrogen reaching the duodenum was approximately equal to the amount ingested with rations HM1 and CM1 but considerably greater with the other two rations. All rations contained approximately 2% nitrogen.8. Calculation of the estimated loss of energy as methane and heat of fermentation suggested that 50–54% of the digestible energy was absorbed as volatile fatty acids.

1. When rumen fluid together with small quantities of (15NH4)2S04[1-14C]sodium acetate and polyethylene glycol (PEG) was introduced into the emptied rumen of a sheep, no significan change occurred in the ratio15N:14C during a period of 30–60 min. The ratio15N:PEG, however, declined by 22–53%. when(15NH4)2SO4, [1-14C]sodium acetate and PEG were introduced into the normal rumen of a sheep fed on lucerne hay the ratio15N:14C in the whole rumen contents showed no appreciable change in a period of 1 h, but the ratio15N:PEG declined by 25–41%. It was therefore concluded that the rate constants for removal of ammonia nitrogen (NH2-N) and volatile fatty acid (VFA) from the rumen were very nearly equal.2. In sheep fed at 1 h intervals on lucerne hay chaff or lucerne hay pellets VFA production, VFA and NH3-N concentration in the rumen fluid and the volume of fluid passed from the rumen to the omasum were determined. From these results and the information previously gained on the relative rates of removal of NH2-N and VFA from the rumen, the amounts of NH3-N produced in the rumen and absorbed there or at lower levels of the digestive tract were calculated to be equivalent to 23–27% of the dietary N in lucerne hay chaff and 17% of that in lucerne hay pellets; 59–66% of the NH3-N was absorbed from the rumen and the remainder passed to the omasum.