scholarly journals The digestion by cattle of silage-containing diets fed at two dry matter intakes

1985 ◽  
Vol 53 (3) ◽  
pp. 691-708 ◽  
Author(s):  
J. A. Rooke ◽  
H. A. Greife ◽  
D. G. Armstrong
Keyword(s):  
Small Intestine ◽  
Dry Matter ◽  
Agricultural Research ◽  
Rumen Fluid ◽  
Soya Bean ◽  
Total N ◽  
Bean Meal ◽  
Soya Bean Meal ◽  
Microbial N

1. In a 4 × 4 Latin square experiment four cattle were given in two meals per d diets consisting of (g/kg dry matter (DM)) 500 barley, 400 grass silage and 100 soya-bean meal. The diets were given at either 1.15 (L) or 2.3 times (H) maintenance energy requirements and the soya-bean meal was either untreated (U) or formaldehydetreated (T).2. A 24 h collection of duodenal digesta and a 7 d collection of faeces were made using chromium sesquioxide for flow estimation and 35S as a marker of microbial nitrogen entering the small intestine. Samples of rumen fluid were also taken for estimation of lumen pH, ammonia and volatile fatty acid concentrations.3. Spot samples of duodenal digesta were obtained after administration of Cr2O3,-mordanted silage-fibre and soya-bean meal, to determine the rates of outflow of these markers from the rumen. Similar samples were also obtained after cessation of a continuous intraruminal infusion of ruthenium phenanthroline, 35S and CoEDTA.4. Incubations of each feedingstuff in porous synthetic fibre (psf) bags were carried out in the rumen and the rates of N disappearance from the bags determined.5. Increasing DM intake significantly ( P < 0.001) increased the quantities of organic matter (OM), total N and amino acid-N entering the small intestine and amounts subsequently voided in the faeces. Apparent digestibilities of OM and N were unaffected by DM intake; the proportions of total digestible OM digested in the rumen were significantly lower (P < 0.01) at the higher level of DM intake.6. Formaldehyde treatment of the soya-bean meal increased the quantities of N entering the small intestine; these increases were not significant.7. Increased DM intake increased the quantities of both microbial N (P < 0.001) and undegraded feed N (P < 0.01) entering the small intestine; HCHO-treatment also significantly (P < 0.05) increased the quantities of undegraded feed N entering the small intestine. The efficiency of microbial N synthesis within the lumen was not significantly affected by dietary treatments whereas apparent feed N degradability was reduced significantly ( P < 0.05) both by increasing DM intake and by HCHO-treatment of the soya-bean meal.8. Rates of disappearance of N from psf bags in the rumen were different for different feedingstuffs. However, for a given feedingstuff, the rate of N disappearance was not affected by the diets fed.9. The rates of decline in marker concentrations measured in duodenal digesta were significantly increased as DM intake increased with the exception of Cr2O2-soya-bean meal. The markers could be ranked (P < 0.05) in the following order of increasing outflow rate: ruthenium phenanthroline, 35S-labelled amino acids and Cr2O2-silage fibre < Cr2O3-soya-bean meal < CoEDTA.10. Estimates of the degradabilities of feedingstuffs were calculated from N disappearance rates from psf bags and either experimentally determined outflow rates or those proposed by the Agricultural Research Council (1984). Such estimates for the degradability of the whole diet were then compared with those determined in vivo using 35S as a marker.

scholarly journals The digestion by cattle of silage-containing diets fed at two dry matter intakes

1985 ◽  
Vol 54 (2) ◽  
pp. 483-492 ◽  
Author(s):  
H. A. Greife ◽  
J. A. Rooke ◽  
D. G. Armstrong
Keyword(s):  
Small Intestine ◽  
Amino Acid ◽  
Glutamic Acid ◽  
Amino Acid Composition ◽  
Acid Composition ◽  
Dry Matter ◽  
Soya Bean ◽  
Rumen Bacteria ◽  
Bean Meal ◽  
Soya Bean Meal

1. In a 4 x 4 Latin square experiment four cows were given, twice daily, diets consisting of (g/kg dry matter (DM)) 500 barley, 400 grass silage and 100 soya-bean meal. The diets were given at either 1.15 (L) or 2.3 (H) times maintenance energy requirements and the soya-bean meal was either untreated (U) or formaldehyde (HCH0)-treated (T).2. The passage of digesta to the duodenum was estimated using chromic oxide as a flow marker;35S was used to estimate the amount of microbial protein entering the small intestine. A microbial fraction was prepared by differential centrifugation from duodenal digesta. Samples of bacteria and of protozoa from rumen digesta were also prepared.3. The total amino acid contents of feedingstuffs, duodenal digesta, duodenal microbial material, rumen bacteria and rumen protozoa were determined by ion-exchange chromatography. The D-alanine and D-glutamic acid contents of the samples were determined by gas–liquid chromatography.4. The quantity of each amino acid entering the small intestine was significantly (P < 0,001) increased by increasing DM intake and tended to be increased by formaldehyde-treatment of the soya-bean meal. There were net losses of all amino acids across the forestomachs except for lysine, methione, o-alanine and D-glutamic acid for which there were net gains.5. There were significant (P < 0.05) differences in amino acid composition between rumen bacteria and duodenal microbial material; differences in amino acid composition between rumen bacteria and rumen protozoa were also observed.6. D-Alanine and D-glutamic acid were present in the silage but not in the barley or either of the soya-bean meals. All samples of microbes and digesta contained D-alanine and D-glutamic acid.7. The use of D-ahine and D-glUtamiC acid as markers for microbial nitrogen entering the small intestine was assessed. Estimates of the quantities of microbial N entering the small intestine based on the D-alanine or D-glutamic acid contents of rumen bacteria or duodenal microbes were significantly higher than those determined using 35S as a marker.

scholarly journals The effect of formaldehyde treatment before ensiling on the digestion of wilted grass silage by sheep

1979 ◽  
Vol 42 (3) ◽  
pp. 535-545 ◽  
Author(s):  
R. C. Siddons ◽  
R. T. Evans ◽  
D. E. Beever
Keyword(s):  
Amino Acids ◽  
Small Intestine ◽  
Soya Bean ◽  
Apparent Digestibility ◽  
Fatty Acid Production ◽  
Protein Nitrogen ◽  
Gross Energy ◽  
Bean Meal ◽  
Soya Bean Meal ◽  
Microbial N

1. Wilted perennial ryegrass (Lolium perenneL. cv. Endura) was ensiled without additive or after addition of a mixture of equal volumes of formic acid (850 g/kg) and formalin (380 g formaldehyde/kg) applied at a rate of 35 g formaldehyde/kg herbage crude protein (nitrogen × 6.25). The digestion of the two silages and the effect of supplemental N as urea or urea plus soya-bean meal on the digestion of the treated silage was studied using sheep fitted with a rumen cannula and re-entrant cannulas in the proximal duodenum and distal ileum.2. The additive markedly reduced carbohydrate fermentation and protein degradation in the silo.3. There were no significant differences between diets in rumen pH, dilution rate, volatile fatty acid production and the molar proportions of acetate, propionate and butyrate. However, rumen ammonia levels and the apparent digestibility of organic matter (OM), gross energy (GE) and cellulose in the stomach were significantly depressed (P< 0.05) by the additive. It also reduced (P< 0.05) the extent to which the N of the silage was degraded in the rumen and, with the treated silage, more microbial N was synthesized in the rumen than food N degraded, resulting in a net gain of N between mouth and duodenum, as compared to a net loss with the untreated silage.4. Supplementation of the treated silage with urea or urea plus soya-bean meal significantly increased (P< 0.05) the amount of food N degraded in the rumen and rumen ammonia levels but had no effect on the apparent digestibility of OM, GE and cellulose in the stomach or on the amount of microbial N reaching the duodenum.5. The quantity of microbial amino acids entering the small intestine and the apparent digestibility of amino acids in the small intestine were similar for all four diets. However, the quantity of food amino acids reaching the small intestine was significantly higher with the three diets containing the treated silage and consequently the apparent absorption of amino acids from the small intestine was substantially higher with these diets than with the untreated silage.

scholarly journals Estimation of the degradability of dietary protein in the sheep rumen by in vivo and in vitro procedures

1985 ◽  
Vol 54 (2) ◽  
pp. 545-561 ◽  
Author(s):  
R. C Siddons ◽  
J Paradine ◽  
D. L. Gale ◽  
R. T. Evans
Keyword(s):  
Rumen Fluid ◽  
Flow Measurements ◽  
Fractional Rate ◽  
Outflow Rate ◽  
Bean Meal ◽  
Sheep Rumen ◽  
Soya Bean Meal ◽  
Microbial N

1. Estimates of degradability of nitrogen in the sheep rumen for a basal hay diet and for soya-bean meal (SBM), groundnut meal (GNM) and fish meal (FM), when given together with the hay, were determined from measurements of (1) duodenal N flow, (2) ammonia kinetics and (3) rumen N disappearance from polyester bags and rumen outflow rate. The ability of various in vitro procedures to predict in vivo N degradability was also examined.2. Four sheep were given a basal hay diet (800 g dry matter (DM) and 19 g N/d) either alone or supplemented with isonitrogenous amounts (15 g N/d) of SBM, GNM or FM. Duodenal non-ammonia-N flow (g/d) was increased more by FM (8.0) than by GNM (5.9) and SBM (5.8), whilst microbial N flow (g/d) was increased more by SBM (3.9) than by GNM (2.3) and FM (1.6). N degradability values calculated from these results were 0.88, 0.76 and 0.57 for the SBM, GNM and FM respectively. The corresponding value for hay was calculated to be 0.76.3. The irreversible loss of ammonia in the forestomachs (g N/d) was increased more by SBM (11.9) than by GNM (7.2) and FM (5.8) whilst ammonia outflow from the rumen (g N/d) was increased to a similar extent by all supplements ( I.1, 0.9 and 0.8 respectively), as was the amount of microbial N (g/d) synthesized from sources other than rumen ammonia (1.8, 2.0 and 1.9 respectively). N degradability values calculated from these results were 0.84, 0.54 and 0.45 for the SBM, GNM and FM respectively.4. The fractional rate of N disappearance (/h) when the feedstuffs were incubated in polyester bags in the rumen of sheep receiving the basal hay diet (800 g DM/d) was the highest for SBM (0,145) and lowest for FM (0.037), with the hay (0.082) and GNM (0.071) intermediate, whilst the fractional outflow rates from the rumen (/h) of the three supplements were similar (0.034, 0.038 and 0,030 for SBM, GNM and FM espectively). N degradability values calculated from these results were 0.82, 0.67 and 0.60 for the SBM, GNM and FM respectively; the value for the hay was 0.73.5. Of a number of in vitro procedures tested, only N solubility in sodium hydroxide and ammonia or total non-protein-N (NPN) production during incubation with rumen fluid in the absence of hydrazine sulphate ranked the supplements, although not the hay, in the same order as the in vivo degradability procedures. In terms of absolute values, N solubility in NaOH, at room temperature, gave estimates similar to those derived from the duodenal flow measurements; estimates derived from ammonia and total NPN production were lower.

scholarly journals Digestion of concentrates in sheep

1971 ◽  
Vol 25 (2) ◽  
pp. 225-233 ◽  
Author(s):  
E. R. Ørskov ◽  
C. Fraser ◽  
I. McDonald
Keyword(s):  
Small Intestine ◽  
Terminal Ileum ◽  
Crude Protein ◽  
Dry Matter ◽  
Daily Intake ◽  
Latin Square ◽  
Soya Bean ◽  
Bean Meal ◽  
The Mean ◽  
Soya Bean Meal

1. Four sheep were given four diets containing proportions of rolled barley and soya-bean meal varied to provide 10.3, 13.3, 16.1 and 19.9% crude protein in the dietary dry matter; the treatments were given according to a 4 x 4 Latin square design. The mean daily intake was 989 g dry matter. The apparent disappearance of protein, ash, ether extractives and carbohydrate before the abomasum, between the abomasum and terminal ileum and between the terminal ileum and rectum was measured.2. The amount of non-ammonia crude protein (Y1, g/d) disappearing from the small intestine increased with protein intake (X, g/d) according to the equation Y1 = 2.12X – 0.0057X2–83, reaching a maximum when there was about 19% crude protein in the dry matter of the diet.3. The treatments had no significant effects on the disappearance of starch, ether extractives or ash. About 93% of starch disappeared in the rumen and 6% in the small intestine. The total mean daily intake of ether extractives was 21 g; 9 g were added in the rumen, 24 g disappeared from the small intestine and 6 g were excreted in the faeces. The total mean daily intake of ash was 67 g; 26 g were added in the rumen, 37 g disappeared from the small intestine, 9 g from the large intestine and 47 g were excreted in the faeces.

The digestion by cattle of barley and silage diets containing increasing quantities of soya-bean meal

1986 ◽  
Vol 107 (2) ◽  
pp. 263-272 ◽  
Author(s):  
J. A. Rooke ◽  
P. Alvareza ◽  
D. G. Armstrong
Keyword(s):  
Small Intestine ◽  
Amino Acid ◽  
Latin Square ◽  
Basal Diet ◽  
Soya Bean ◽  
Meal Intake ◽  
Bean Meal ◽  
The Mean ◽  
Soya Bean Meal ◽  
Microbial N

SummaryA 4 x 4 latin-square design experiment was carried out to determine the effects of increasing nitrogen (N) intake by feeding diets containing increasing amounts of soyabean meal upon the digestion of organic matter (OM) and N by cattle equipped with rumen and duodenal cannulae. A basal diet (B) containing 600 g ground barley and 400 g grass silage/kg diet and three diets (BS1, BS2 and BS3) in which increasing amounts of the barley were replaced by soya-bean meal were fed. The mean daily intakes of OM and N when each diet was fed were 4·56, 4·55, 4·30 and 4·52 kg OM and 920, 114·7, 138·3 and 164·1 g N for diets B, BSl, BS2 and BS3 respectively.Neither the amounts of OM entering the small intestine nor those voided in the faeces were altered by the diets fed. Thus the mean apparent OM digestibility for all the diets fed was 0·74 + 0·013 and the proportion of digestible OM intake apparently digested in the rumen was 0·77 + 0048.Mean daily concentrations of ammonia N in the rumen were significantly (P < 0·001) increased from 38 mg N/l (diet B) to 129 mg N/l (diet BS3) as N intake increased.The quantities of non-ammonia N and of amino acid N entering the small intestine were not significantly (P >0·05) increased as more soya-bean meal was added to the diet, although diet BSl supported the greatest flows of N to the small intestine. Thus as more soya-bean meal was added to the diet there were increasing net losses of nonammoniaN(P < 0·01) and amino acid N (P < 0·01) prior to the small intestine. Faecal N excretion was not increased (P > 0·05) as soya-bean meal intake increased and thus apparent N digestibility was significantly (P < 0·01) increased by increasing soyabean intake.Both the quantities of microbial N entering the small intestine daily and the apparent efficiency of microbial N synthesis within the rumen were increased when diet BSl was fed in comparison with the basal diet (B) and then declined when diets BS2 and BS3 were fed; these increases were not significant. The quantities of feed N entering the small intestine daily were not significantly (P > 0·05) increased as soya-bean meal intake increased; thus apparent feed N degradability in the rumen was significantly (P < 0·01) increased as soya-bean meal intake increased. In contrast, the rates of disappearance of N from each of the components of the diets fed, when incubated in the rumens of the cattle in porous synthetic fibre-bags, were not increased (P > 0·05) as soya-bean meal intake increased.

scholarly journals The importance of the form of nitrogen on microbial protein synthesis in the rumen of cattle receiving grass silage and continuous intrarumen infusions of sucrose

1989 ◽  
Vol 61 (1) ◽  
pp. 113-121 ◽  
Author(s):  
J. A. Rooke ◽  
D. G. Armstrong
Keyword(s):  
Fatty Acids ◽  
Small Intestine ◽  
Volatile Fatty Acids ◽  
Synthetic Fibre ◽  
Soya Bean ◽  
Grass Silage ◽  
Rumen Ph ◽  
Bean Meal ◽  
Soya Bean Meal ◽  
Microbial N

1. In a 4x4 Latin square design experiment, four cattle were given grass silage in two meals per d to satisfy maintenance energy requirements. In addition, sucrose (170 g/kg silage dry matter (DM)) was infused intraruminally at a constant rate with no nitrogen supplementation; with the infusion intraruminally of either casein (23 g/kg silage DM) or urea (8 g/kg silage DM); or with soya-bean meal (64 g/kg silage DM) fed in two equal portions.2. Samples of duodenal digesta representative of a 24 h period were obtained using chromium-EDTA and ytterbium acetate for flow estimation and35S as a marker of microbial N entering the small intestine. Samples of rumen fluid were also taken for estimation of rumen pH and concentrations of ammonia-N and volatile fatty acids. Estimates of apparent organic matter (OM) and N digestibility and of the rates of silage DM and N disappearance from porous synthetic-fibre bags incubated in the rumen were also made.3. The N supplements had no significant effects on rumen pH, concentrations of volatile fatty acids, their molar proportions or the disappearance of DM or N from porous synthetic-fibre bags. N supplementation increased rumen ammonia-N concentrations (urea,P< 0.05; casein, soya-bean meal, not significant).4. N supplementation had no significant effects on the digestion of OM, acid-detergent fibre or soluble carbohydrate.5. Infusion of casein increased the quantities of total non-ammonia-N (not significant) and microbial N (P< 0.05) entering the small intestine daily and the efficiency of rumen microbial N synthesis (not significant). Giving soya-bean meal twice daily resulted in marginal increases in the quantities of non-ammonia-N and microbial N entering the small intestine, while infusing urea intraruminally had no effect.

The digestion of untreated and formaldehyde-treated soya-bean and rapeseed meals by cattle fed a basal silage diet

1983 ◽  
Vol 100 (2) ◽  
pp. 329-342 ◽  
Author(s):  
J. A. Rooke ◽  
I. M. Brookes ◽  
D. G. Armstrong
Keyword(s):  
Small Intestine ◽  
Amino Acid ◽  
Soya Bean ◽  
Protein Supplements ◽  
Formaldehyde Treatment ◽  
Bean Meal ◽  
Low Efficiency ◽  
Soya Bean Meal ◽  
In Sacco

SUMMARYThe effect of pretreating soya-bean and rapeseed meals with formaldehyde was studied. Soya-bean and rapeseed meals, both untreated and formaldehyde-treated, were fed to cattle receiving a basal diet of silage in a 4 × 4 latin square. Formaldehyde treatment of both meals significantly reduced apparent N digestibility. All four protein supplements increased the amounts of non-ammonia N and amino acid N entering the small intestine over those obtained when silage was fed alone. Formaldehyde treatment of the meals increased the amounts of non-ammonia N and amino acid N entering the small intestine; this effect was significant, however, for only the formaldehyde treatment of the soya-bean meal. The low efficiency of microbial N synthesis observed when silage was fed alone was increased by the inclusion of both of the soyabean meals in the diet but not by the inclusion of the rapeseed meals. Formaldehyde treatment reduced the apparent degradability of the soya-bean meal N, determined in vivo, from 0·90 for the untreated meal to 0·40 for the formaldehyde-treated meal; similarly the degradability of the untreated rapeseed meal was reduced from 0·77 to 0·41 by the formaldehyde treatment. The in sacco technique gave values for degradability for the protein supplements which ranked them in a similar manner as did the in vivo technique; however, for any one meal the in sacco value for degradability was lower than that determined in vivo.

Evaluation of the nutritive value of single-cell protein (Pruteen) for lactating dairy cows

1986 ◽  
Vol 106 (3) ◽  
pp. 593-599 ◽  
Author(s):  
E. Teller ◽  
J.-M. Godeau
Keyword(s):  
Milk Production ◽  
Dry Matter ◽  
Nutritive Value ◽  
Agricultural Research ◽  
Latin Square ◽  
Soya Bean ◽  
Metabolizable Energy ◽  
Cell Protein ◽  
Bean Meal ◽  
Soya Bean Meal

SummaryTwo experiments were conducted with four lactating cows in a latin-square design. The rations were composed mainly of maize silage plus concentrates, supplemented with urea, Pruteen, or soya-bean meal supplying 25% of total dietary N. Nitrogen and energy balances were measured, and milk production recorded.Dry-matter digestibility, intake of metabolizable energy (ME) and ME concentration in dietary dry matter were not significantly altered when Pruteen was substituted for soya-bean meal. However, mean nitrogen digestibility for all the treatments was significantly lower than expected from published relationships.The substitution of Pruteen for soya-bean meal did not significantly affect the nitrogen balance of the animals or milk production, but the latter tended to be higher than that recorded with urea.The responses to the different N supplements are discussed in relation to the feeding systems of the Agricultural Research Council and the French Protéines Digestibles dans l'lntestin Grêle, and are compared with predictions made from statistical relationships developed in our laboratory.

The effects upon rumen microbial protein synthesis of giving sheep diets of rolled barley and hay supplemented with increasing quantities of soya-bean meal

1986 ◽  
Vol 106 (3) ◽  
pp. 635-638 ◽  
Author(s):  
J. A. Rooke ◽  
M. A. Overend ◽  
D. G. Armstrong
Keyword(s):  
Protein Synthesis ◽  
Rumen Fluid ◽  
Soya Bean ◽  
Microbial Protein ◽  
Microbial Protein Synthesis ◽  
Bean Meal ◽  
Soya Bean Meal ◽  
Basal Ration ◽  
Degradable Protein

A ruminant animal is largely dependent upon microbial protein synthesized within the reticulorumen for amino acids to meet its requirements for maintenance and production. The major precursor for rumen microbial protein synthesis is ammonia arising both from degradation of feed proteins within the rumen and from nitrogen recycled to the rumen. The concentration of rumen ammonia-N required to sustain maximal rates of microbial protein synthesis in vivo has been variably reported to range from 22 to 235 mg ammonia-N/1 rumen fluid (Miller, 1982). Most experiments which have investigated the concentrations of rumen ammonia-N required for maximal rates of microbial protein synthesis have used the addition of urea to the diet as the means of increasing rumen ammonia-N concentrations. However, little attention has been paid to the effects upon rumen ammonia-N concentrations and upon the efficiency of rumen microbial protein synthesis of supplying increasing amounts of a readily degradable protein in the diet, although Beardsley et al.(1977) found that as increasing amounts of soya-bean meal were fed to sheep, net losses of N across the forestomachs of the sheep were increased. In this paper, two experiments are described in which increasing amounts of soya-bean meal were fed to sheep receiving a basal ration of rolled barley and hay; the digestion of organic matter (OM) and of amino acid N (AAN) within the rumen, the net quantities of microbial AAN entering the small intestine and the efficiency of rumen microbial AAN synthesis were measured.

scholarly journals Estimation of flows of organic matter and nitrogen components in postruminal digesta and effects of level of dietary intake and physical form of protein supplement on such estimates

1983 ◽  
Vol 49 (1) ◽  
pp. 119-127 ◽  
Author(s):  
A. B. Mcallan ◽  
R. H. Smith
Keyword(s):  
Organic Matter ◽  
Rumen Fluid ◽  
Soya Bean ◽  
Metabolizable Energy ◽  
Diaminopimelic Acid ◽  
Total N ◽  
Bean Flour ◽  
Physical Form ◽  
Bean Meal ◽  
Soya Bean Meal

1. Steers fitted with simple rumen, abomasal and sometimes duodenal cannulas were given isonitrogenous and isoenergetic diets consisting of pellets containing equal amounts of rolled barley and chopped straw together with tapioca alone (B), or with some tapioca replaced by coarse soya-bean meal (M) or finely ground soya-bean flour (F). Diet B had an estimated rumen degradable nitrogen (RDN): metabolizable energy (ME) value of approximately 0·8 g/MJ. The corresponding value for each of the supplemented diets was 1·3–1·4. Diets were given at two levels of intake designed respectively to provide ME intakes to support weight gains of 0·5 kg/d (L) and 1·0 kg/d (H). Chromic oxide and polyethylene glycol were given as indigestible markers. Values were calculated for flows (g/24 h) at the abomasum of organic matter (OM), non-ammonia-N (NAN) and microbial (bacterial)-N (MN). Estimates of MN were based on RNA and α-ε;-diaminopimelic acid (DAP) measurements. The steers had low rumen protozoal counts throughout the whole experiment with fewer than 8000 ciliate protozoa/ml of rumen fluid.2. Proportions of OM apparently digested between the mouth and abomasum were significantly lower for H than for L intakes but showed no other significant differences. Mean estimated efficiency of microbial protein synthesis was approximately 17 g N/kg OM apparently digested in the rumen for the LB diet, but was significantly greater at approximately 26 g N/kg OM apparently digested for the HB diet. The protein-supplemented diets gave values of 31–32 which were significantly greater than the value for the LB but not the HB diet.3. Amounts of feed nitrogenous constituents surviving between the mouth and the abomasum were estimated from NAN minus MN corrected for endogenous N. Values for the proportions of feed N degraded, derived from these estimates, were 0·71, 0·66, 0·72, 0·69, 0·67 and 0·70 for diets LB, HB, LM, HM, LF and HF respectively. There were no significant differences due to level of feeding, supplementary protein or the physical form of that protein.4. Estimates of MN flows at the abomasum based on RNA determinations in fresh samples did not differ significantly from estimates based on DAP determinations. However, storage of aqueous suspensions of mixed rumen bacteria by deep-freezing or freeze-drying resulted in significant losses of RNA. No such losses were observed for abomasal digesta. This meant that if samples were stored by these means before analysis, the use of RNA as a microbial marker was vitiated.5. In some experiments digesta samples were taken from the duodenum as well as the abomasum. Estimates of total N flows did not differ significantly between these sites.

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