The degradation of nucleic acids in, and the removal of breakdown products from the small intestines of steers.

1. Nucleic acids and breakdown products were estimated in digesta taken from different sites in the small intestines of slaughtered steers given different diets. Amounts passing different sites were compared using cellulose as a non-digestible marker. The validity of this marker was checked with chromic oxide in some experiments. In other experiments, nucleic acids or derivatives were infused into the proximal duodenum of steers receiving diets of approximately equal proportions of flaked maize and hay. The amounts disappearing during passage through the small intestine were estimated using polyethylene glycol (PEG) as a non-absorbable marker. 2. In the slaughter experiments the amounts of nucleic acids entering the small intestine varied with the type of diet. RNA and DNA disappeared on average, to extents of 89% and 80% respectively between the abomasum and the terminal ileum, irrespective of the diet. RNA disappearance occurred almost entirely in the proximal quarter of the small intestine, whereas that of DNA extended further along the tract. 3. Nucleic acid degradation in the upper small intestine was accompanied by the transient appearance of adenosine, guanosine and pyrimidine nucleosides. These products were in greatest concentration in digesta from the first quarter of the small intestine and had generally completely disappeared by the terminal ileum. 4. Of the different substances infused into the smnall intestine, free nucleic acids were removed to extents greater than 97%, adenine, guanine and uracil had completely disappreaed, thymine and xanthine to approximately 80% and 95% and hypoxanthine and cytosine to only 51% and 48% respectively. The nucleosides adenosine and cytidine were also completely removed in the small intestine but were replaced, in part, by the catabolic products inosine plus hypoxanthine or cytosine respectively. Other nucleosides were removed to approximately half the extent of the correspoonding bases. 5. Serum and urine allantoin and uric acid levels were related to the amounts of purines entering the small intestines in free or bound form.

Changes in the composition of digesta during passage through the small intestines of steers.

1. Dry matter (DM), organic matter (OM), nitrogenous constituents, carbohydrate constituents and pH were estimated in digesta taken from eight different sites in the small intestines of slaughtered steers given different diets. Amounts of constituents passing different sites were compared using cellulose as a non-digestible marker. 2. Amounts of the different constituents entering the small intestines varied with the type of diet given but the patterns of removal of each constituent were similar regardless of diet. 3. DM and OM were uniformly down the length of the small intestines. Net digestibilities of 0.62 and 0.63 for DM and OM respectively of the amounts measured in segment 1 digesta (first 3 m post-pylorus) were found at the terminal ileum. DM and OM contents of segment 1 digesta were 5 and 8% higher respectively than in abomasal digesta. Significantly smaller amounts of digesta were found in the proximal quarter of the small intestines than in more distal sections. There was a 10% addition of water to digesta in segment 1 compared with abomasal digesta. Of the water entering the small intestines a net 65% was absorbed therein, most absorption occurring in the first half. 4. Ammonia nitrogen was removed uniformly down the length of the small intestines to a net extent of 75% of that in segment 1 digesta. There was an apparent increase of approximately 18% in the total N (TN) content of segment 1 digesta compared with abomasal digesta. There was an approximate net removal of 80% of the TN measured in segment 1 digesta during passage down the small intestines. Over 95% of the digestible TN was removed in the section of tract between 3 and 15 m from the pylorus. Net removal of nucleic acid N (NA-N) up to the distal ileum was 78% of that in segment 1 digesta, most removal occurred in the proximal quarter of the small intestine. Little or no net loss of diaminopimelic acid-N (DAP-N) occurred in the small intestine. 5. Of the carbohydrates entering the small intestines, there was little or no removal of rhamnose, arabinose or xylose. Net removal of ribose, mannose, galactose and 'starch' glucose up to the distal ileum was 82, 76, 54 and 70% respectively of the amounts found in segment 1 digesta. All disappeared uniformly down the length of the small intestine.

Effects of level of dietary intake and physical form of protein supplement on the digestibilities of different dietary carbohydrates between mouth and abomasum of young steers.

Steers fitted with simple rumen and abomasal cannulas were given isoenergetic diets of rolled barley and chopped straw, pelleted together with some tapioca alone (B) or with some tapioca replaced by coarse soyabean meal (M) or finely ground soyabean flour (F). The diets were given at two levels to support 0.5 (L) and 1.0 (H) kg/d live weight gain. Chromic oxide and PEG were given as digesta flow markers. Mouth to abomasum digestibilities of different dietary sugars at the low level of intake (LB) were 0.65, 0.68, 0.59, 0.56 and 0.94 for arabinose, galactose, xylose, cellulose-glucose and starch-glucose respectively. Corresponding values at the higher level of intake (HB) were 0.55, 0.66, 0.55, 0.44 and 0.93 respectively. Supplementation with either soya bean meal or flour had no significant effects on the mouth to abomasum of dietary carbohydrate digestibilities at either level of feeding.

The efficiency of microbial protein synthesis in the rumen and the degradability of feed nitrogen between the mouth and abomasum in steers given different diets.

Protozoa-free steers with simple rumen and abomasal cannulas were given basal diets consisting of a concentrate mixture of flaked maize and tapioca with barley straw (BS) or alkali-treated barley straw (BSA). Other diets were supplemented with urea (BSU and BSAU respectively) or with fish meal replacing the tapioca (BSF and BSAF respectively). The diets were isoenergetic and calculated to provide sufficient metabolizable energy (ME) to support a growth rate of 0.5 kg/d. Rumen-degradable nitrogen (RDN):ME values (g/MJ) were estimated to be 0.50, 1.20 and 0.80 for the basal diet, urea- and fish-meal-supplemented diets respectively. RNA and alpha,epsilon-diaminopimelic acid (DAP) were used as microbial markers. 103Ruthenium and polyethylene glycol (PEG) were given as flow markers and flows (g/24 h) at the abomasum of organic matter (OM) and nitrogenous constituents were calculated. Samples of mixed bacteria separated from rumen digesta from animals receiving N-supplemented diets contained significantly more N than those from animals receiving basal diets (approximately 74 and 62 mg/g dry matter (DM) respectively) but there were no other significant differences in total-N contents between treatments. RNA-N:total-N values were similar for all diets (approximately 0.13). DAP-N:total-N values were significantly lower in bacteria from animals receiving alkali-treated (AT) rather than untreated (UT) straw (approximately 0.008 and 0.011 respectively). The proportion of OM intake digested in the rumen (ADOM) was significantly higher for animals receiving AT straw rather than UT straw (approximately 0.54 and 0.43 respectively). N supplementation had no effect on OM digestibility.(ABSTRACT TRUNCATED AT 250 WORDS)

Factors influencing the digestion of dietary carbohydrates between the mouth and abomasum of steers.

Six protozoa-free steers with simple rumen and abomasal cannulas were given basal diets consisting of a concentrate mixture of flaked maize and tapioca with either barley straw (BS) or alkali-treated barley straw (BSA). Other diets used were supplemented with urea (BSU and BSAU respectively) or contained fish meal in place of tapioca BSF and BSAF respectively). The diets were given in a 6 X 6 Latin square design. Diets were isoenergetic and provided sufficient metabolizable energy (ME) to support a growth rate of approximately 0.5 kg/d. Basal diets, urea- and fish-meal-supplemented diets had estimated rumen-degradable nitrogen (RDN):ME values (g/MJ) of 0.5, 1.2 and 0.8 respectively. 103Ruthenium and polyethylene glycol were given as flow markers, and flows (g/24 h) at the abomasum of organic matter (OM) and carbohydrate components were calculated. True digestibility coefficients of OM between mouth and abomasum were significantly greater for diets containing alkali-treated straw (approximately 0.63) than for those containing untreated straw (approximately 0.55) but were not significantly affected by N supplementation. Digestibility coefficients of the neutral-sugar components of dietary polysaccharides between mouth and abomasum were 0.28, 0.34, 0.31, 0.23, 0.31 and 0.87 for mannose, galactose arabinose, xylose, cellulose-glucose and starch-glucose respectively for diet BS. Corresponding values were 0.37, 0.42, 0.56, 0.51, 0.40 and 0.88 for diet BSA. All but the mannose and starch-glucose values were significantly greater for the latter diet. N supplementation also led to increases in digestibility of all neutral sugars except mannose and starch-glucose. Fish meal produced a markedly greater effect than urea but only significantly so for cellulose-glucose. Thus, the highest digestibilities were seen for diet BSAF and were 0.68, 0.67, 0.74 and 0.64 for galactose, arabinose, xylose and cellulose-glucose respectively. Of all these sugars xylose consistently showed the greatest response in digestibility to sodium hydroxide treatment or N supplementation.

The removal of glucose, maltose and different starches from the small intestines of steers.

Four Friesian steers (103-150 kg) each equipped with simple abomasal and re-entrant ileal cannulas were used. Different amounts of glucose, maltose or one of several isolated starches or ground cereal grains, ranging from 80-400 g/8 h, together with polyethylene glycol were infused into the abomasums and absorption up to the ileum examined. The efficiency of removal of glucose remained high at all levels of infusion (greater than 80%) and at the highest level, 26.4 g glucose/kg body weight 0.75/d were calculated to be removed in the small intestines. At low levels of infusions, maltose was removed almost as efficiently as glucose, but the capacity of the small intestines to remove maltose was exceeded with infusions above 15 g/kg body weight 0.75/d. Soluble and isolated wheat starch were removed to similar extents and almost identically to maltose. Isolated maize starch, whilst being removed in the small intestines almost as rapidly as maltose at the lowest level of infusion, was less efficiently removed at higher levels. Rice and potato starches were poorly removed in the small intestines. Intestinal capacities for the removal of related wheat, soluble starch, maize, rice and potato starches were 102, 99, 80, 77 and 55% that of equivalent amounts of maltose. Starch in ground cereal grains (maize and wheat) were removed in the small intestines slightly less efficiently (75-90%) than the corresponding isolated starches.

Effect of dietary nitrogen source on carbohydrate metabolism in the rumen of the young steer.

1. Steers, fitted with simple rumen and duodenal cannulas, were given diets of approximately equal parts of flaked maize and hay (A) (containing 16 g nitrogen/kg dry matter (DM) or diets of flaked maize and straw supplemented with decorticated groundnut meal (B), fish meal (C), or heated (D) or unheated (E) soya-bean meal (containing 24 g N/kg DM). Chromic oxide was given as a marker with the feeds, and flows of different combined sugars at the duodenum estimated from the values for sugars:marker at this site. Contributions of bacterial constituents to these flows were estimated from amounts of RNA present. 2. Rumen bacteria from steers receiving diet A contained approximately 110 g alpha-dextran-glucose/kg DM and contributed about 60 g alpha-dextran-glucose/d at the duodenum; bacteria from steers receiving diets B, C, D or E contained 25-40 g alpha-dextran-glucose/kg DM and contributed about 20-30 g alpha-dextran-glucose/d at the duodenum. There were no significant differences between different N supplements. About half the alpha-dextran-glucose, varying amounts of the mannose and galactose, and nearly all the rhamnose and ribose in duodenal digesta were contributed by the bacteria. Almost all the arabinose, xylose and cellulose-glucose was of dietary origin. 3. For steers receiving diet A, mean coefficients of digestibility between mouth and duodenum, corrected where necessary for bacterial contribution, were 0-96, 0-73, 0-58, 0-22 and 0-53 for starch-glucose, galactose, arabinose, xylose and cellulose-glucose respectively. Corresponding mean values when diets B, C, D and E were given, which did not differ significantly amongst themselves, were 0-98, 0-79, 0-81, 0-59 and 0-58. Most values for galactose, arabinose and xylose were significantly higher than the diet A values.

Some effects of variation in carbohydrate and nitrogen intakes on the chemical composition of mixed rumen bacteria from young steers.

1. Samples of rumen digesta were taken at different times after giving calves various dried forage or hay and cereal diets and mixed bacteria were separated. 2. For calves receiving dried forage only, the carbohydrate content of mixed bacteria varied with time after feeding, reaching a maximum of approximately 140 g/kg dry matter (DM) after 0-5-1h, decreasing to about 60 g/kg DM after 4 h. 3. Replacement of part of the dried forage with glucose to give a similar metabolizable energy intake but approximately half as much nitrogen, produced a similar pattern of change with time after feeding but resulted in a markedly increased maximum bacterial carbohydrate content (approximately 230 g/kg DM). Addition of urea to this diet reduced the bacterial accumulation of carbohydrate to approximately the same level as was found in samples from calves receiving forage only diets. For the forage diets the carbohydrate content fell to 60-100 g/kg DM 4 h after feeding. For the hay and cereal diet the value was 170 g/kg DM at this time. 4. Changes in bacterial carbohydrate content were largely a result of changes in storage polysaccharide (alpha-dextran) content. 5. Crude protein (N X 6-25) and ash contents of mixed bacteria decreased after feeding with all-forage diets, but returned to approximately fasting levels within 4 h. At this time samples from calves receiving dried forage and glucose diets contained less CP and more ash (approximately 450 and 220 g/kg DM respectively) than those from calves given diets of dried forage only (approximately 525 and 180 g/kg DM respectively). 6. CP, total carbohydrate and ash content of mixed rumen bacteria contributed approximately 0-80 g/g DM. 7. Sodium, potassium, calcium, magnesium and phosphate accounted for approximately 0-50 g/g bacterial ash.

A comparison of the chemical composition of mixed bacteria harvested from the liquid and solid fractions of rumen digesta.

Steers, equipped with simple rumen cannulas, were given diets of approximately equal parts of rolled barley and straw supplemented with urea. The diets provided sufficient estimated rumen degradable nitrogen (RDN; RDN:metabolizable energy values of 1:3) to maintain maximum microbial synthesis. In some experiments Na235SO4 was introduced into the rumen to label microbial protein. Rumen digesta samples were taken before feeding and mixed rumen bacteria were separated from the solid (solid-associated bacteria; SAB) and liquid (liquid-associated bacteria; LAB) fractions of digesta. The most effective method of removing SAB from the fibre was a combination of homogenizing and pummelling. This process did not affect the physical form or chemical composition of the bacteria. Samples of SAB contained significantly (P less than or equal to at least 0.05) less ash, total N, RNA and diaminopimelic acid (DAP) and significantly (P less than or equal to 0.01) more lipid than samples of LAB. Concentrations (g/kg dry matter) of ash, total N, RNA, DAP and lipid in SAB were approximately 87, 70, 35, 2.2 and 245 respectively. Corresponding values for LAB were 157, 80, 50, 3.8 and 124 respectively. RNA-N:total N and DAP-N:total N values in SAB were significantly lower than those in LAB (P less than or equal to 0.05 and 0.02 respectively). 35S:total N values were similar in both groups of bacteria. The importance of differences in constituent:total N values in the two groups of bacteria in relation to their use as indices of microbial protein synthesis is discussed.

Glycosyl ureides in ruminant nutrition. 1. Preparation and estimation of lactosyl urea and other glycosyl ureides.

1. Glucosyl urea, lactosyl urea and galactosyl urea were prepared from pure sugars and urea and their purity confirmed by determination of their melting points, specific rotations and by mass spectrometry. 2. Using whey as a lactose source, a range of conditions were examined for the preparation of lactosyl urea on a laboratory scale. Yields of 60% were achieved when lactose and urea (molar ratio, urea: lactose 0:6) were reacted for 15 h in sulphuric acid at pH 2.0 and a temperature of 70 degrees. 3. Methods of detection and estimation of all three ureides in whey preparations and ruminant digesta samples were developed. Two quantitative methods, one involving acid-hydrolysis, the other ion-exchange chromatography, were used. The latter method enabled determination of individual quantities of ureides in mixtures.

Glycosyl ureides in ruminant nutrition. 3. In vivo studies on the metabolism of glycosyl ureides and corresponding mixtures of their free component molecules.

1. Steers and sheep were given basal diets of barley and straw (1:1, w/w), usually containing urea, which for certain experimental periods were supplemented with pure glucosyl urea (GU), pure lactosyl urea (LU) or a product prepared from whey concentrate (EW) which contained 65-80% of the lactose in the form of LU. 2. On the morning of an experiment ureide (or EW) was omitted from the feed and a dose of either ureide (or EW) or equivalent amounts of free lactose and urea (L + U) was added to the rumen within 30 min of feeding, together in some experiments with polyethylene glycol (PEG) as a fluid-phase marker. Samples of rumen contents, and in some experiments abomasal contents, were taken at intervals for up to 8 h. 3. For both steers and sheep given GU and LU for the first time (unadapted animals) there was little or no accumulation of ammonia in the rumen or cleavage of the sugar-urea bond. Galactose was, however, slowly liberated from LU. 4. For steers and sheep which had been given GU, LU or EW for approximately 7-10 d or more (adapted animals) some accumulation of ammonia occurred after adding GU or LU to the rumen, but for LU it occurred less rapidly and to a lower peak concentration than when L + U was added. In adapted animals cleavage of the sugar-urea bond in LU was virtually complete in 2-4 h. Degradation of the components of L + U was virtually complete within 1 h. 5. Recovery at the abomasum of ureide (present either as GU or LU) estimated from ureide: PEG values, appeared to be complete in experiments with unadapted sheep given a dose of EW. In adapted sheep only very small amounts of ureide in an EW dose (on average 6%) entered the abomasum undegraded. Amounts lost in this way appeared to be positively correlated with the rate of fluid turnover in the rumen.

Glycosyl ureides in ruminant nutrition. 2. In vitro studies on the metabolism of glycosyl ureides and their free component molecules in rumen contents.

1. The fate of glucosyl urea (GU), lactosyl urea (LU) and corresponding mixtures of the free sugars and urea and their degradation products were examined during in vitro incubation of the compounds with rumen contents taken from donor sheep and steers at various stages of adaptation to these compounds. 2. The sugar-urea bond was virtually unattacked in rumen contents from unadapted sheep and steers but generally a slow release of the galactose moiety occurred. After feeding LU or GU to animals for a period of approximately 10 d, the rates of disappearance of both bound urea and sugar had increased, but were still markedly slower than those of the corresponding free sugars and urea. In vitro rates of degradation of both free lactose and urea also increased in response to the feeding of lactose and urea to rumen content donor animals. 3. Ammonia accumulation in rument contents when GU or LU were the substrates was notably lower than when equivalent amounts of glucose and urea or lactose and urea were the substrates. 4. Bacterial growth was estimated using an vitro method based on incorporation of 32P into bacterial nucleic acids. Markedly different patterns of bacterial growth were observed depending on whether LU or lactose and urea were the substrates.

The effect of free and protected oils on the digestion of dietary carbohydrates between the mouth and duodenum of sheep.

Sheep fitted with rumen and re-entrant duodenal cannulas were given diets of approximately 200 g hay and 400 g concentrate mixture alone, or supplemented daily with 40 g linseed or coconut oils free or protected with formaldehyde-casein in a 5 x 5 Latin-square arrangement. Chromic oxide paper was given as a marker at feeding time and passage to the duodenum of neutral-detergent fibre (NDF) and different sugars were estimated from the values for constituent:marker at the duodenum. Contributions of microbial carbohydrates to these flows were estimated from amounts of RNA present. The carbohydrate composition of mixed rumen bacteria from sheep rumen digesta were similar regardless of diet. Of the sugars entering the duodenum all the rhamnose and ribose and 0.51, 0.24 and 0.35 of the mannose, galactose and starch-glucose respectively, were contributed by the microbes. Virtually all the arabinose, xylose and cellulose-glucose were contributed by the diet. For sheep receiving the basal ration, coefficients of digestibility between mouth and duodenum, corrected where necessary for microbial contribution, were 0.95, 0.66, 0.67, 0.62, 0.45 and 0.51 for starch-glucose, mannose, arabinose, galactose, xylose and cellulose-glucose respectively. Corresponding values when free-oil-supplemented diets were given were 0.95, 0.55, 0.38, 0.55, 0.01 and -0.02 respectively. Values for diets supplemented with linseed oil or coconut oil did not differ significantly. Addition of protected oils to the basal feed also resulted in depressed digestibilities of dietary structural sugars but to a far lesser extent than those observed with the free oils. Apparent digestibility of NDF was altered in the same direction as those of the main structural sugars, averaging 0.50, 0.17 and 0.29 in animals receiving the basal, free-oil-supplemented or protected-oil-supplemented diets respectively. The reasons for the difference between NDF and discrete carbohydrate analytical totals are discussed.

Effect of different levels of phosphorus on rumen microbial fermentation and synthesis determined using a continuous culture technique.

A continuous culture technique was used to study the phosphorus requirements of rumen micro-organisms. Solutions of artificial saliva containing 120, 80, 40 and 0 mg inorganic phosphorus (Pi)/l were infused into the reaction vessels previously inoculated with rumen contents, resulting in Pi concentrations in the vessel contents of 48, 28, 4 and less than 1 mg/l respectively. Various fermentative and synthetic characteristics were examined. In the vessel contents, concentrations of protozoa (about 0.9 X 10(5)/ml) were not significantly affected by Pi concentration. Total volatile fatty acids (VFA) produced averaged about 6.83 mmol/h with Pi levels of 48 and 28 mg/l. Reduction in Pi concentrations to 4 and less than 1 mg/l resulted in significant reductions in total VFA to approximately 6.25 and 3.75 mmol/h respectively, accompanied by a rise in pH from 6.5 to 7.3. Ammonia-nitrogen values, which averaged about 131 mg/l at the higher Pi concentrations, also increased with the lowest level of Pi to about 240 mg/l. ATP concentrations averaged about 14 mumol/l at the highest Pi concentration and fell progressively with each reduction in Pi concentration to a final value of 2.5 mumol/l with the Pi level less than 1 mg/l. At Pi concentrations of 48 and 28 mg/l, the digestibilities of xylose, arabinose and cellulose-glucose were maintained at about 0.90, 0.62 and 0.70 g/g input respectively. At lower Pi concentrations these digestibilities fell significantly and corresponding values at Pi less than 1 mg/l were 0.73, 0.41 and 0.31 respectively. Starch digestion was unaffected by Pi concentration and remained at about 0.90 g/g input. The amount of microbial-N synthesized averaged 0.48 g/d and was maintained with Pi concentrations down to 4 mg/l. There was, however, a significant reduction to 0.26 g/d with Pi concentrations of less than 1 mg/l. The efficiency of microbial protein synthesis was variable but averaged approximately 25 g N/kg total carbohydrate fermented. It was estimated that the minimum Pi concentrations required in rumen fluid in vivo to maintain maximum degradative and synthetic microbial activities was in the range 75-100 mg/l and that over-all P requirement of the microbes was of the order of 5.1 g/kg apparently digested organic matter intake.

The effects of frequency of feeding on some quantitative aspects of digestion in the rumens of growing steers.

Three steers with simple rumen and abomasal cannulas were given ground and pelleted diets containing predominantly dried grass meal (DG) or rolled barley (RB). Diets were given at frequencies of two or eight feeds/d in a simple changeover design. Chromic oxide and polyethylene glycol were given as flow markers and flows (g/24 h) of organic matter (OM), nitrogenous and carbohydrate compounds were calculated. Ribonucleic acid and 35S were used as microbial markers and diaminopimelic acid (DAP) as a bacterial marker. Frequency of feeding had no significant effect on mean rumen pH, ammonia levels or liquid outflow rates with either diet. Rumen volume was decreased and abomasal digesta flow increased on Diet DG with more feeds but these parameters were unaffected with Diet RB. Increased feeding frequency with both feeds resulted in increased numbers of protozoa. There were no significant effects of feeding frequency of Diet DG on the abomasal flows of any of the nitrogenous constituents measured. However, there was a significant increase in microbial-N flow from 33 to 43 g/d with more frequent feeding of diet RB which was not reflected in bacterial-N flow as measured by DAP. The apparent digestion of OM in the rumen, expressed as g/g intake with diet DG was 0.41 and 0.31 for two feeds and eight feeds/d respectively. Corresponding values for diet RB were 0.56 and 0.63 respectively. The reduction in OM digestion with frequent feeding of diet DG was reflected in similarly reduced rumen digestibilities of all dietary carbohydrate components whereas the increase in OM digestion with diet RB was reflected only by the component sugars of the dietary fibre. The efficiencies of microbial protein synthesis (expressed as gMN/kg ADOM) increased from 36 to 46 when the feeding frequency of diet DG was increased from two to eight times/d. No significant effect of frequency of feeding was found for diet RB. Mouth to abomasum degradation of feed-N (expressed as g/g intake) of 0.64 was unaffected by the number of feeds of diet DG but was significantly increased from 0.55 to 0.82 when eight rather than two feeds/d of diet RB were given.

Studies of rumen function in an in vitro continuous culture system.

An in vitro continuous culture system to simulate processes in the rumen is described. This comprises a culture vessel (Fig. 2) fed continuously with pelleted solid feed (Fig. 1); artificial saliva also enters the vessel while effluent leaves it continuously in two streams, one is filtered and the other simply overflows (Fig. 1). In this way liquid and solid turnover times may be manipulated independently; in a trial experiment the former and latter were 6.3% and 3.4% per hour respectively. In four replicated experiments a steady-state was achieved in 5-6 days with a feed of barley, tapioca, fishmeal, urea and straw and maintained for a further 7 to 14 days. During a steady-state period, rumen characteristics in terms of protozoal count, pH, redox potential, total volatile fatty acid concentration and ammonia concentration were stable and similar to those found in the rumens of animals given similar diets. Flows of microbial N compounds were assessed by infused Na2H32PO4 with the artificial saliva and estimating the 32P label incorporated in bacterial fractions. The system demonstrably provided a satisfactory means for studying many aspects of rumen function.

The degradation of different protein supplements in the rumen of steers and the effects of these supplements on carbohydrate digestion.

1. Four steers with simple rumen and abomasal cannulas were given diets consisting of ground and pelleted alkali-treated straw, rolled barley and tapioca supplemented with urea (diet U) or containing single-cell protein (diet SCP), maize-gluten meal (diet MGM) or rapeseed meal (diet RSM) in place of some of the tapioca. The isoenergetic diets were given in a 4 x 4 Latin square design in eight feeds/d at 3-h intervals and provided sufficient metabolizable energy to support a growth rate of approximately 0.5 kg/d. Chromic oxide and polyethylene glycol were given as markers and appropriate samples taken from the rumen and abomasum. Flows (g/d) at the abomasum of organic matter and nitrogenous and carbohydrate constituents were calculated. 2. Rumen ammonia levels were similar with all three protein supplements at about 9 mmol/l, which was significantly lower (P less than 0.05) than that in animals on diet U (16 mmol/l). Rumen liquid outflow rates (/h) were 0.099, 0.139, 0.125 and 0.160 for diets U, SCP, MGM and RSM respectively; the difference between diet U and diet RSM was significant (P less than 0.05). Corresponding values for Cr2O3 outflow rates were 0.027, 0.032, 0.027 and 0.030/h respectively, which did not differ significantly from each other. 3. RNA, 35S and diaminopimelic acid (DAP) were used as microbial markers. Efficiencies of microbial-N (MN) synthesis, expressed as g MN/kg apparently digestible organic matter, truly digestible organic matter or carbohydrate fermented, were generally not significantly affected by the diet and averaged 29, 22 and 29 respectively based on mean RNA and 35S markers. Corresponding values derived from DAP of 22, 16 and 21 g MN/kg respectively were all significantly (P less than 0.001) lower. Using 35S as microbial marker, MN flows at the abomasum as a proportion of non-ammonia-nitrogen flow were 0.78, 0.64, 0.51 and 0.78 for diets U, SCP, MGM and RSM respectively. Derived true rumen degradability values (g/g intake) of the total dietary N were 0.91, 0.79, 0.69 and 0.90 for diets U, SCP, MGM and RSM respectively. Protein supplement degradabilities for single-cell protein, maize-gluten meal and rapeseed meal were 0.73, 0.51 and 0.98 respectively. 4. Mouth-to-abomasum digestibility coefficients of the main neutral-sugar components of dietary polysaccharides were 0.68, 0.63 and 0.61 for arabinose, xylose and cellulose-glucose on diet U.(ABSTRACT TRUNCATED AT 400 WORDS)

Nutrient supply and growth of cattle offered straw-based diets.

An experiment was conducted using steers cannulated at the rumen, duodenum and ileum to study the effects of increasing the levels of barley and fishmeal in straw-based diets. Diets A, B, C and D contained ammonia-treated straw, barley and fishmeal in the ratios, 67:33:0, 66:23:11, 53:47:0 and 52:36:12 (by weight) and were offered in daily amounts of 3.9, 3.9, 4.8 and 4.8 kg dry matter. The effects of barley were attributable to increased intakes of digestible organic matter and consequently to increased flows of microbial matter to the duodenum. There were no modifications in the balance of energy to nitrogen-yielding nutrients available for absorption. Introducing fishmeal into diets improved digestibility of cellulose and xylose by up to 6.7 and 4.7% respectively, and shifted digestion towards the large intestine. Second, it increased amino acid N supply to the small intestine which averaged 52.2, 63.2, 68.8 and 84.0 g/d with diets A, B, C and D. Some changes were also noted in the balance of amino acids absorbed. Consequently, the contribution of amino acids to metabolizable energy intake increased with the proportion of fishmeal in diets (0.17, 0.20, 0.18 and 0.21 for diets A, B, C and D). Growth rates measured in heifers amounted to 259, 431, 522 and 615 g/d for diets A, B, C and D. They appeared to be related to intestinal amino acid supply.

The effects of different sources of nitrogen supplementation on the post ruminal flows of organic matter and different nitrogenous constituents in steers.

Friesian steers, virtually protozoa free, were equipped with simple rumen and abomasal cannulas. They were given diets consisting of approximately equal proportions of ground, pelleted alkali treated straw and a rolled barley, tapioca mixture supplemented with urea + casein (UC), soybean meal (SBM), 'normal' white fishmeal (NDF) or white fishmeal designated as being of 'low' rumen degradability (LDF). The diets were isoenergetic (the protein sources replacing part of the tapioca) and they were given in amounts to supply sufficient metabolizable energy (ME) to support an average growth rate of 0.5 kg/d. Rumen degradable nitrogen (RDN): ME values were estimated to be 2.08, 1.40, 1.90 and 1.66 for diets UC, SBM, NDF and LDF respectively. RNA, alpha-epsilon-diaminopimelic acid and 35S (added as sulphate) were used as bacterial markers. Chromic oxide and polyethylene glycol (PEG) were given as flow markers and flows (g/24 h) at the abomasum of organic matter (OM) and nitrogenous constituents were calculated. Rumen volumes and ruminal liquid fractional outflow rates were measured using PEG. Samples of mixed rumen bacteria separated from strained rumen digesta from animals receiving diet UC contained significantly less DAP-N (0.322 g/kg DM) than those from animals receiving diets SBM, NDF or LDF (0.530 g/kg DM). Mean rumen volume (approximately 15 l) and liquid fractional outflow rates (approximately 0.105/h) were similar on all diets but there was appreciable variation between animals. The proportion of OM intake digested in the rumen was similar on all diets. The proportional contribution of bacterial-N to the total non-ammonia-N passing the abomasum based on mean values derived from DAP and 35S as markers was 0.57, 0.47, 0.39 and 0.31 for diets UC, SBM, NDF and LDF respectively. Corresponding values based on RNA were 0.71, 0.50, 0.48 and 0.35 respectively. Bacterial-N (RNA) flows at the abomasum were 31, 25, 26 and 20 g/d for diets UC, SBM, NDF and LDF respectively. Corresponding values for 35S and DAP were 26, 24, 21 and 18 g/d respectively. Values derived from RNA flows were consistently and significantly higher (P less than 0.01) than those based on DAP or 35S. Mean estimated efficiencies of bacterial protein synthesis (g bacterial-N/kg OM truly digested) were 15, 15, 14 and 12 for diets UC, SBM, NDF and LDF respectively.(ABSTRACT TRUNCATED AT 400 WORDS)