Rumen microbial production estimated either from urinary purine derivative excretion or from direct measurements of 15 N and purine bases as microbial markers: effect of protein source and rumen bacteria isolates

Microbial contribution to duodenal purine flow in fattening cattle given concentrate diets, estimated by purine N labelling (15N) of different microbial fractions

The origin of duodenal purine bases (PB) was studied in a digestion experiment with four heifers, cannulated in the rumen and duodenum, which received a basal concentrate (152 g crude protein (CP) per kg dry matter (DM)) together with barley straw (85: 15 fresh weight basis) or the same concentrate supplemented with soya-bean meal, carbohydrate-treated soya-bean meal, maize gluten meal or fish meal to increase its protein content to 192 g/kg DM. Tr eatments were assigned to the four animals in five experimental periods according to an incomplete Latin-square design. Each 30-day period included 20 days of change-over adaptation and 10 days of experimental measurements. The flow of digesta entering the duodenum was estimated using Yb and acid-detergent insoluble ash as indigestible markers according to a double-marker system and microbial nitrogen (N) and PB were labelled with15N infused into the rumen. The proportion of duodenal PB of microbial origin estimated from15N enrichment of PB-N averaged 0·66 (s.e. 0·029) and did not differ between treatments nor when protozoa or bacteria associated with liquid (LAB) and solid (SAB) fractions were used as a reference sample. On average microbial contribution to duodenal non-ammonia N was higher when estimated from the PB/N ratio than from15N (0·67 v. 0·55 (s.e. 0·015)) although differences were small and not significant when LAB was the reference sample (0·58 v. 0·52 (s.e. 0·018)) reflecting the higher PB/N ratio of this fraction compared with SAB and protozoa (2·04 v. 1·65 and 1·60 (s.e. 0·04) mmol/g). Considering only the duodenal PB of microbial origin resulted in estimates of microbial N synthesis from the PB/N ratio of SAB similar to those derived from15N enrichment of both bacterial fractions (12·9 v. 13·5 and 13·3 (s.e. 0·83) g/kg of organic matter apparently digested in the rumen OMADR)) but underestimated the values derived from LAB (9·9 g/kg OMADR). Regardless of the estimation method, neither the duodenal flow of microbial N nor the efficiency of microbial synthesis differed between treatments. These results suggest that a significant proportion of duodenal PB have a non-microbial origin which may lead to overestimation of microbial yield when PB are used as a marker. Differences in PB/N ratio between microbial fractions is another important factor to be considered.

The effects of synchronizing the rate of dietary energy and nitrogen supply to the rumen on the metabolism and growth of ram lambs given food at a restricted level

The effects of diets formulated to have two rates of organic matter (OM) release and to be either synchronous or asynchronous with respect to their hourly release of OM and nitrogen (N) in the rumen on N retention, microbial N production, growth and metabolism of ram lambs offered food at a restricted level was studied in two experiments. Four diets were formulated to differ in their rate and extent of OM and N release in the rumen based on the sum of in situ degradability data of the ingredients. All diets were formulated to have a similar metabolizable energy (10·4 MJ/kg dry matter (DM)), crude protein (140 g/kg DM) and daily ratio of N : OM released (34 g N per kg OM) and were either synchronous or asynchronous with respect to their hourly N : OM release. The four diets were slow energy, synchronous (SS), slow energy asynchronous (SA), fast energy, synchronous (FS) and fast energy asynchronous (FA). In both experiments the diets were offered at a rate of 1·75 maintenance energy requirements as two equal meals at 09:00 and 17:00 h. In experiment 1 there was no significant effect of diet on OM apparent digestibility or N retention. Lambs given diet FS had the highest daily production of allantoin (7·82 mmol per day; P < 0·05) and microbial N (7·80 g/day; P < 0Ό5). Hourly plasma urea and ß-hydroxy butyrate (3-OHB) concentrations exhibited a cyclical trend between meals with maximum concentrations occurring within 3 h of feeding and were higher in lambs given diet FA.

In experiment 2 the four diets were offered to 32 growing ram lambs. Animals given synchronous diets (SS and FS) had a significantly higher live-weight gain than those given asynchronous diets (SA and FA; (132 g/day v. 107 g/day respectively; P < 0·001). Food conversion efficiency (FCE; kg gain per kg DM intake) was improved proportionately by 0·23 in animals offered synchronous diets compared with asynchronous diets (P < 0·001). There was little effect of diet on carcass composition except kidney fat, which was greater in lambs offered the synchronous diets (P < 0·01). Plasma 3-OHB concentrations were higher throughout the growth period in lambs given diet FA whilst plasma urea concentrations were greater in lambs given the diet SS. In conclusion, greater attention to the formulation of diets to be synchronous for their hourly release of N : OM in the rumen can improve the growth rate and FCE of lambs. This effect may be due to an improvement in energy rather than N metabolism.

Effect of forage to concentrate ratio in complete diets offered to sheep on voluntary food intake and some digestive parameters

Twelve mature ewes were used to study the effect of forage: concentrate ratio in complete diets on voluntary intake and some digestive characteristics. Diets consisted of four combinations of chopped lucerne hay and a concentrate (390 g cracked barley grains, 440 g cracked maize grains and 170 g soya-bean meal per kg of concentrate) in the following proportions (fresh matter basis): 0·8:0·2 (C20), 0·6:0·4 (C40), 0·4:0·6 (C60) and 0·2:0·8 (C80). Diets were offered over two 42-day periods and, in each of them, three sheep received one of the four diets, with the restriction that no animal received the same diet in both periods. Chromium Ill-mordanted fibre was used as a marker to estimate passage rate of digest a and microbial nitrogen supply (MNS) was estimated from the urinary excretion of purine derivatives. The increase in the proportion of concentrate affected linearly (P< 0·05) the voluntary intake of food, the mean values being 36·8, 37·9, 36·3 and 30·0 g dry matter (DM) per kg live weight per day for C20, C40, C60 and C80 diets, respectively. Apparent digestibility of DM, organic matter (OM) and crude protein increased linearly (P< 0·01) with the proportion of concentrate in the diet, whereas that of cellulose evolved auadratically (P< 0·05), reaching a minimum value in the C80 diet. Digestible OM intake was unaffected (P> 0·05) by the proportion of concentrate in the diet. Both particulate passage rate from the rumen and through the caecum and proximal colon decreased linearly (P< 0·05) as concentrate proportion in the diet increased. MNS (g/day) was not affected (P> 0·05) by the diet, whereas its efficiency (g/kg digestible OM intake) tended (P< 0·10) to increase with the proportion of concentrate in the diet.

Comparison of microbial markers (15N and purine bases) and bacterial isolates for the estimation of rumen microbial protein synthesis

The first objective of this experiment was to investigate the effect of using different bacterial isolates on the estimation of microbial protein production in semi-continuous fermenters (RUSITEC) given four diets, and to test whether a ‘mixed’ bacterial pellet was representative of the whole bacterial population in the fermenters. A second objective was to compare two different microbial markers (nitrogen-fifteen (15N) and purine bases (PB)). Diets consisted of neutral-detergent fibre from grass hay (10 g/day) and sugar-beet pulp (2 g/day) and 280 mg/day of one of four N forms (isolated soya-bean protein, soya-bean peptides, amino acids blended to profile soya-bean protein and NH4Cl). Two 14-day incubation runs were carried out and in each run each of the four different diets were given to two vessels. On days 12 and 13, total digesta (effluent plus nylon bags residues) was collected for analyses of non-ammonia N,15N enrichment and PB concentration, and for isolation of total mixed bacterial pellets (TB). On the last day of each incubation run, the system was stopped for isolation of liquid- (LAB) and solid-associated (SAB) bacteria. Microbial N flow was estimated from the15N enrichment and PB concentration in both total digesta and in the three different bacterial pellets (TB, LAB, and SAB). For all diets, LAB presented a greater (P < 005)15N enrichment and PB: N ratio than SAB, with TB having an intermediate value. For both markers, the use of LAB produced the lowest (P < 005) estimates of microbial N flow and the use of SAB produced the greatest (P < 005) estimates. The use of TB produced intermediate values with all diets, suggesting that TB consisted of SAB and LAB. For all bacterial pellets, PB produced greater (P 005) values of microbial N flow than15N. However, there was a positive relationship (r = 0·883; P 0001; no. = 15) between the values of microbial N flow determined with the two markers when TB were used as reference.

Effect of aα-galactosidase supplementation of cereal-soya-bean-pea diets on the productive performances, digestibility and lower gut fermentation in growing and finishing pigs

An experiment was carried out to study the effect of addingα-galactosidase to the diet on the performance and digestive parameters of growing-finishing pigs. Fifty-four gilts, average body weight (BW) of 43 (s.e. 0·4) kg, were allocated to 18 pens and used in a production experiment divided in two consecutive periods of 28 days each (growing and finishing). In each period gilts were given a diet based on cereals, soya-bean meal and peas, supplemented (Enzyme) or unsupplemented (Control) with 200 units per kg ofα-galactosidase. All diets included 2 g Cr2O3per kg as a digestibility marker. Food intake and body weight were recorded every 2 weeks and faecal samples by pen were collected at the end of each period. Average daily gain (ADG), food: gain ratio and faecal digestibility of dry matter (DM), crude protein (CP) and neutral-detergent fibre (NDF) were calculated. At the end of the production experiment nine gilts from each treatment were selected and given the finishing diet for a further 10 days before being slaughtered. Samples of digesta from the ileum and caecum were collected and ileal digestibility of monosaccharides determined. Short chain volatile fatty acids (SCVFA ) and purine bases (PB) in caecal digesta were analysed. The use ofα-galactosidase improved the ADG (P< 0·01) and the food: gain ratio (P< 0·01) simultaneous to increases in the faecal digestibility of DM (P< 0·05), CP (P< 0·05) and NDF (P= 0·07) in the finishing period. Alpha-galactosidase supplementation also improved the ileal digestibility of some monosaccharides (galactose, rhamnose, mannose and fucose) of the dietary fibre fraction (P< 0·05); and reduced total caecal concentration of SCVFA (P= 0·15), proportion of branched-chain VFA (P< 0·001), and concentration of total PB (P< 0·001). It is concluded that addingα-galactosidase to a cereal-soya-bean meal-pea diet improves ADG, food: gain ratio and digestibility in fattening pigs, and reduces the amount of fermentable substrate flowing to the large intestine.

On the variation of urinary excretion of creatinine and purine derivatives in pregnant and lactating ewes given diets with different protein contents

The effect of the physiological state and dietary protein level on urinary excretion of creatinine (C) and purine derivatives (PD) was studied in two experiments carried out with pregnant and lactating ewes to evaluate whether the PD/C ratio in urine can he confidently used as an index of PD excretion. In both experiments ewes were given ammonia-treated straw and concentrates including different levels of fish meal and the excretion in urine and milk and the plasma concentration of C, allantoin (AL), xanthine, hypoxanthine and uric acid was measured.

Creatinine excretion (in urine and milk) was higher in pregnant ewes than in those lactating (492 and 420 (s.e. 10.0) μmol/kg maternal live weight0.75) and no significant differences were found due to number of foetuses and dietary protein level. The coefficient of variation was 0·10 in both pregnancy and lactation and individual variation accounted for proportionately 0·78 and 0·93 of total variation. The AL/C ratio in urine was highly correlated with daily AL excretion (r = 0·90 and 0·78 in pregnant and lactating ewes, respectively). Changes in PD excretion with experimental treatments were mainly reflected in AL, as the main component (0-83) of total PD. Most of the variation in AL excretion was explained by differences in rumen fermentable organic matter intake (RFOMI) (R2 = 0·79) and AL excretion did not differ between treatments when expressed per kg of RFOMI. In contrast to this the ratio AL/digestible organic matter intake decreased with increasing levels of fish meal in the diet. Urinary PD excretion was better related to estimated PD kidney tubular load (r = 0·76) than to PD plasma concentration (r = 0·64).

The results suggest that creatinine excretion is scarcely affected by the number of foetuses in pregnancy and dietary protein level but if the AL/С in urine is used instead of total collection as an index of purines absorbed in the duodenum, differences in urinary creatinine excretion due to physiological state must be accounted for.

Effect of sorghum tannins in sheep fed with high-concentrate diets

The aim of this study was to evaluate the nutritional value of three sorghum cultivars with different concentrations of condensed tannins in sheep diets. Six adult sheep (LW=56kg) with rumen and duodenal fistulas were assigned to experimental groups using two 3x3 Latin Square designs. The diets were formulated using three sorghum cultivars: LTC (low-tannin cultivar), MTC (medium-tannin cultivar) and HTC (high-tannin cultivar). Microbial nitrogen (MN) concentration in the duodenum was measured using a 15N trace technique. LTC, MTC and HTC diets presented values of 788, 722 and 747 (SE=20.6) g kg-1 for dry matter digestibility and 633, 535 and 530 (SE=35.8) g/kg for crude protein digestibility. The LTC diet was significantly different from the other diets (P<0.05). The nitrogen balance was 145.5, 94.8 and 83.8g kg-1 (SE=13.0) for LTC, MTC and HTC, respectively, with LTC showing greater nitrogen retention (P<0.05). Values obtained for MN in the digesta were 301, 364 and 469 (SE=30.6) g kg-1 for LTC, MTC and HTC, respectively, and there was no statistical difference (P>0.05) between the diets. The presence of condensed tannins in the sorghum interfered with the sheep's nitrogen retention; however, the microbial protein supply to the duodenum of the animals was not inhibited.

Net transfer of nutrients to the duodenum and disappearance ofn-alkanes in the reticulo-rumen and the hindgut of sheep fed grass/legume combinations

An experiment was carried out to examine the effect of increasing the proportion of Wimmera ryegrass hay in a lucerne hay-based diet on net transfer of nutrients to the intestine, and on the disappearance ofn-alkanes in the reticulo-rumen and the hindgut of sheep. Following a latin square design, four adult ewes were fed 1:0, 0·33:0·67, 0·67:0·33 and 0:1 proportions of legume and grass. Increasing the proportion of ryegrass in the diet linearly decreased the intake of DM (P= 0·017), organic matter (P= 0·021) and N (P= 0·001). However, neutral-detergent fibre intake was not affected (P= 0·148), nor was its digestibility coefficient (P>0·10). Diet had no effect on duodenal flows of nutrients (P>0·10), although the proportion of N intake (NI) recovered at the duodenum as non-NH3N (NAN) increased linearly withLolium rigidumin the diet (P= 0·002). Full recovery of NI as NAN was achieved at NH3concentrations in the rumen below 110 g/l. Microbial N contribution to NAN varied in a quadratic manner (P< 0·05) with the proportion of grass in the diet, although efficiency of microbial synthesis was not affected (P>0·10). Duodenal recovery of consumedn-alkanes was not affected by diet and was complete for those present in higher concentrations in the forages. Isolated rumen bacteria contained significant amounts ofn-alkanes, contributing to the duodenal flow of these hydrocarbons in variable proportions depending on the diet consumed.

Effects of an extract of plant flavonoids (Bioflavex) on rumen fermentation and performance in heifers fed high-concentrate diets

To study the effects of an extract of plant flavonoids [Bioflavex (FL)] in cattle fed high-concentrate diets, 2 experiments were designed. In the first experiment, the effects of Bioflavex on the development of rumen acidosis was evaluated in 8 Holstein-Friesian crossbreed heifers (451 kg; SEM 14.3 kg of BW) using a crossover design. Each experimental period lasted 22 d; from d 1 to 20, the animals were fed rye grass, on d 21 the animals were fasted, and on d 22, rumen acidosis was induced by applying 5 kg of wheat without [

CONTROL

(CTR) heifers who did not receive Bioflavex] or with flavonoids [heifers who received FL; 300 mg/kg DM] through a rumen cannula. Rumen pH was recorded continuously (from d 19 to d 22). On d 22, average rumen pH was significantly (P < 0.01) higher in the FL animals (6.29; SEM = 0.031) than it was in the CTR heifers (5.98; SEM = 0.029). After the wheat application, the rumen VFA concentration increased (P < 0.01), the proportion of acetic acid decreased (P < 0.01), and lactate concentration (mmol/L) increased, but the increase was not as great (P = 0.09) in the FL as it was in the CTR heifers (0.41 to 1.35 mmol/L; SEM = 0.24). On d 22, Streptococcus bovis and Selenomonas ruminantium titers increased after the wheat application, but Megasphaera elsdenii titers increased (P < 0.05) only in the FL heifers. In the second experiment, the effect of Bioflavex on the performance and rumen fermentation in finishing heifers was evaluated. Forty-eight Fleckvieh heifers (initial BW = 317 kg; SEM = 5.34) were used in a completely randomized design. Heifers were assigned to 1 of 4 blocks based on their BW and, within each block, assigned to 1 of 2 pens (6 heifers/pen). In addition, 16 heifers (2/pen) were rumen cannulated. Individual BW and group consumption of concentrate and straw were recorded weekly until the animals reached the target slaughter weight. Supplementation with FL did not affect ADG, feed consumption, or feed conversion ratio. Rumen pH and molar proportions of propionate were greater (P < 0.01) and acetate proportion was less in the FL (P < 0.01) than they were in the CTR heifers. Flavonoid supplementation might be effective in improving rumen fermentation and reducing the incidence of rumen acidosis. This effect of flavonoids may be partially explained by increasing the numbers of lactate-consuming microorganisms (e.g., M. elsdenii) in the rumen.

Supplementation with non-fibrous carbohydrates reduced fiber digestibility and did not improve microbial protein synthesis in sheep fed fresh forage of two nutritive values

To determine whether non-fibrous carbohydrate (NFC) supplementation improves fiber digestibility and microbial protein synthesis, 18 Corriedale ewes with a fixed intake level (40 g dry matter (DM)/kg BW0.75) were assigned to three (n = 6) diets: F = 100% fresh temperate forage, FG = 70% forage + 30% barley grain and FGM = 70% forage + 15% barley grain + 15% molasses-based product (MBP, Kalori 3000). Two experimental periods were carried out, with late (P1) and early (P2) vegetative stage forage. For P2, ewes were fitted with ruminal catheters. Forage was distributed at 0900 h, 1300 h, 1800 h and 2300 h, and supplement added at 0900 h and 1800 h meals. Digestibility of the different components of the diets, retained N and rumen microbial protein synthesis were determined. At the end of P2, ruminal pH and N-NH3 concentration were determined hourly for 24 h. Supplementation increased digestibility of DM (P < 0.001) and organic matter (OM; P < 0.001) and reduced NDF digestibility (P = 0.043) in both periods, with greater values in P2 (P = 0.008) for the three diets. Daily mean ruminal pH differed (P < 0.05) among treatments: 6.33 (F), 6.15 (FG) and 6.51 (FGM). The high pH in FGM was attributed to Ca(OH)2 in MBP. Therefore, the decreased fiber digestibility in supplemented diets could not be attributed to pH changes. The mean ruminal concentration of N-NH3 was 18.0 mg/dl, without differences among treatments or sampling hours. Microbial protein synthesis was greater in P2 (8.0 g/day) than in P1 (6.1 g/day; P = 0.006), but treatments did not enhance this parameter. The efficiency of protein synthesis tended to be lower in supplemented groups (16.4, 13.9 and 13.4 in P1, and 20.8, 16.7 and 16.2 g N/kg digestible OM ingested in P2, for F, FG and FGM, respectively; P = 0.07) without differences between supplements. The same tendency was observed for retained N: 2.55, 1.38 and 1.98 in P1, and 2.28, 1.23 and 1.10 g/day in P2, for F, FG and FGM, respectively; P = 0.05). The efficiency of microbial protein synthesis was greater in P2 (P = 0.007). In conclusion, addition of feeds containing NFCs to fresh temperate forage reduced the digestibility of cell walls and did not improve microbial protein synthesis or its efficiency. An increase in these parameters was associated to the early phenological stage of the forage.

Metabolism of microbial nitrogen in ruminants with special reference to nucleic acids

Characteristically the metabolism of microbial nitrogen (N) compounds in ruminants involves the degradation of dietary N and synthesis of microbial protein (MP), compounds including a small amount of peptides and free amino acids, which may account for 75-85% of total N and the remainder are nucleic acids (NA: DNA and RNA). Generally rumen microbes contain 10-25% NA-N of the total N while 70-80% is in the form of RNA. This paper describes the degradation and synthesis of NA in the rumen and their fate in the lower digestive tracts. Their physiological and nutritional significance in different types of ruminant animals is also discussed. The research works on NA metabolism in ruminants has been mainly on metabolism of purines after rumen microbial digestion and absorption in the lower gut. Subsequently, the fate of absorbed purines has been intensively investigated to assess the extent of MP synthesis in the rumen. The method for predicting ruminal synthesized MP and subsequently digested MP has been proposed using urinary purine derivative (PD) excretion in sheep and cattle fed on ordinary feed. The latter approach has now been adopted for calculation of protein supply in some feeding standards, although there are still difficulties in predicting representative samples of rumen microbes, and also uncertainties in variations of non-renal and endogenous purine losses.

Microbial protein synthesis, ruminal digestion, microbial populations, and nitrogen balance in sheep fed diets varying in forage-to-concentrate ratio and type of forage

Six ruminally and duodenally cannulated sheep were used in a partially replicated 4 x 4 Latin square to evaluate the effects of 4 diets on microbial synthesis, microbial populations, and ruminal digestion. The experimental diets had forage to concentrate ratios (F:C; DM basis) of 70:30 (HF) or 30:70 (HC) with alfalfa hay (A) or grass hay (G) as forage and were designated as HFA, HCA, HFG, and HCG. The concentrate was based on barley, gluten feed, wheat middlings, soybean meal, palmkern meal, wheat, corn, and mineral-vitamin premix in the proportions of 22, 20, 20, 13, 12, 5, 5, and 3%, respectively (as-is basis). Sheep were fed the diets at a daily rate of 56 g/kg of BW(0.75) to minimize feed selection. High-concentrate diets resulted in greater (P < 0.001) total tract apparent OM digestibility compared with HF diets, but no differences were detected in NDF digestibility. Ruminal digestibility of OM, NDF, and ADF was decreased by increasing the proportion of concentrate, but no differences between forages were detected. Compared with sheep fed HF diets, sheep receiving HC diets had less ruminal pH values and acetate proportions, but greater butyrate proportions. No differences among diets were detected in numbers of cellulolytic bacteria, but protozoa numbers were less (P = 0.004) and total bacteria numbers tended (P = 0.08) to be less for HC diets. Carboxymethylcellulase, xylanase, and amylase activities were greater for HC compared with HF diets, with A diets showing greater (P = 0.008) carboxymethylcellulase activities than G diets. Retained N ranged from 28.7 to 37.9% of N intake and was not affected by F:C (P = 0.62) or the type of forage (P = 0.31). Microbial N synthesis and its efficiency was greater (P < 0.001) for HC diets compared with HF diets. The results indicate that concentrates with low cereal content can be included in the diet of sheep up to 70% of the diet without detrimental effects on ruminal activity, microbial synthesis efficiency, and N losses.

Effects of Different Protein Supplements on Omasal Nutrient Flow and Microbial Protein Synthesis in Lactating Dairy Cows

Eight ruminally cannulated Holstein cows that were part of a larger lactation trial were used in 2 replicated 4 x 4 Latin squares to quantify effects of supplementing protein as urea, solvent soybean meal (SSBM), cottonseed meal (CSM), or canola meal (CM) on omasal nutrient flows and microbial protein synthesis. All diets contained (% of dry matter) 21% alfalfa silage and 35% corn silage plus 1) 2% urea plus 41% high-moisture shelled corn (HMSC), 2) 12% SSBM plus 31% HMSC, 3) 14% CSM plus 29% HMSC, or 4) 16% CM plus 27% HMSC. Crude protein was equal across diets, averaging 16.6%. The CSM diet supplied the least rumen-degraded protein and the most rumen-undegraded protein. Microbial nonammonia N flow was similar among the true protein supplements but was 14% lower in cows fed urea. In vivo ruminal passage rate, degradation rate, and estimated escape for the 3 true proteins were, respectively, 0.044/h, 0.105/h, and 29% for SSBM; 0.051/h, 0.050/h, and 51% for CSM; and 0.039/h, 0.081/h, and 34% for CM. This indicated that CSM protein was less degraded because of both a faster passage rate and slower degradation rate. Omasal flow of individual AA, branched-chain AA, essential AA, nonessential AA, and total AA all were lower in cows fed urea compared with one of the true protein supplements. Among the 3 diets supplemented with true protein, omasal flow of Arg was greatest on CSM, and omasal flow of His was greatest on CSM, intermediate on CM, and lowest on SSBM. Lower flows of AA and microbial nonammonia N explained lower yields of milk yield and milk components observed on the urea diet in the companion lactation trial. These results clearly showed that supplementation with true protein was necessary to obtain sufficient microbial protein and rumen-undegraded protein to meet the metabolizable AA requirements of high-producing dairy cows.

Urinary excretion of purine derivatives as an index of microbial protein synthesis in the camel (Camelus dromedarius)

Five experiments were carried out to extend knowledge of purine metabolism in the camel (Camelus dromedarius) and to establish a model to enable microbial protein outflow from the forestomachs to be estimated from the urinary excretion of purine derivatives (PD; i.e. xanthine, hypoxanthine, uric acid, allantoin). In experiment 1, four camels were fasted for five consecutive days to enable endogenous PD excretion in urine to be determined. Total PD excretion decreased during the fasting period to 267 (se 41·5)?μmol/kg body weight (W)0·75per d. Allantoin and xanthine+hypoxanthine were consistently 86 and 6·1?% of total urinary PD during this period but uric acid increased from 3·6?% to 7·4?%. Xanthine oxidase activity in tissues (experiment 2) was (μmol/min per g fresh tissue) 0·038 in liver and 0·005 in gut mucosa but was not detected in plasma. In experiment 3, the duodenal supply of yeast containing exogenous purines produced a linear increase in urinary PD excretion rate with the slope indicating that 0·63 was excreted in urine. After taking account of endogenous PD excretion, the relationship can be used to predict purine outflow from the rumen. From the latter prediction, and also the purine:protein ratio in bacteria determined in experiment 5, we predicted the net microbial outflow from the rumen. In experiment 4, with increasing food intake, the rate of PD excretion in the urine increased linearly by about 11·1?mmol PD/kg digestible organic matter intake (DOMI), equivalent to 95?g microbial protein/kg DOMI.

Determination of reticulo-rumen and whole-stomach digestion in lactating cows by omasal canal or duodenal sampling

Four ruminally and duodenally cannulated multiparous Finnish Ayrshire cows were fed on diets consisting of grass silage (0·6 kg/kg DM) and one of four concentrates: barley, barley + urea, barley + rapeseed meal and barley + rapeseed cake. The objective of the present study was to compare omasal canal and duodenal digesta flows. Values for digesta flow into the omasal canal and duodenum were determined using a triple-marker method based on Co-EDTA, Yb-acetate and indigestible neutral-detergent fibre (NDF) markers. Microbial non-NH3 N (NAN) flow was assessed by purine flow. Microbial samples to determine the bacterial purine: N ratio were harvested from the rumen, omasum and duodenum. Organic matter flow was significantly lower into the omasum than the duodenum, indicating an endogenous organic matter secretion into the abomasum. In contrast, NDF and acid-detergent fibre flows were significantly higher into the omasum indicating digestion of fibre in the omasum. Microbial NAN flows were significantly different (P < 0·001) when estimates were based on bacterial samples harvested from different sites. Differences in total NAN, microbial NAN and dietary NAN flows entering the omasal canal and duodenum were non-significant. The results indicated that the omasal sampling technique provides a promising alternative to the duodenal sampling technique to investigate forestomach digestion in dairy cows and offers an alternative means to study rumen N metabolism.

Purine quantification in digesta from ruminants by spectrophotometric and HPLC methods

The method of Zinn & Owens (1986;Canadian Journal of Animal Science66, 157–166), based on release of purine bases by HClO4followed by their precipitation with AgNO3, was used to study recovery of purines from lyophilized rumen microbial orEscherichia colipreparations added to matrices such as cellulose, starch and neutral-detergent fibre. The recovery of purines was poor (approximately 50 %). Under the hydrolysis conditions (12 M-HClO4, 90–95° for 1 h) used in the method of Zinn & Owens (1986), the recovery of purines from the rumen microbial preparations added to matrices measured using an HPLC method was 95–102 %, suggesting that the lower recovery of purines in the method of Zinn & Owens (1986) was not due to incomplete hydrolysis of nucleic acids. Using the HPLC method, adenine and allopurinol (an internal standard) were found to be heat-labile as substantial destruction was observed on heating at 121°. On the other hand, another commonly used internal standard, caffeine, was stable at 121°. A complete hydrolysis of nucleic acids from the rumen microbial preparation was observed with 2·5 ml 0·6 M-HClO4in a total volume of 3 ml (0·5 M-HClO4during hydrolysis) at 90–95° for 1 h, and under these conditions adenine, guanine, allopurinol and caffeine were stable. Moreover, under these milder hydrolysis conditions, the recovery of purine bases from the rumen microbial orE. colipreparations added to matrices ranged from 92 to 108 % using the method of Zinn & Owens (1986). Based on the results, changes in hydrolysis conditions have been proposed for accurate determination of purine bases using spectrophotometric or HPLC methods.

Effects of Feeding Formate-Treated Alfalfa Silage or Red Clover Silage on Omasal Nutrient Flow and Microbial Protein Synthesis in Lactating Dairy Cows

Eight ruminally cannulated Holstein cows that were part of a larger lactation trial were blocked by days in milk and randomly assigned to replicated 4 x 4 Latin squares to quantify effects of nonprotein N (NPN) content of alfalfa silage (AS) and red clover silage (RCS) on omasal nutrient flows. Diets, fed as total mixed rations, contained 50% dry matter from control AS (CAS), ammonium tetraformate-treated AS (TAS), late maturity RCS (RCS1), or early maturity RCS (RCS2). Silages differed in NPN and acid detergent insoluble N (% of total N): 50 and 4% (CAS); 45 and 3% (TAS); 27 and 8% (RCS1); 29 and 4% (RCS2). The CAS, TAS, and RCS2 diets had 36% high-moisture shelled corn and 3% soybean meal, and the RCS1 diet had 31% high-moisture shelled corn and 9% soybean meal. All diets contained 10% corn silage, 27% neutral detergent fiber, and 17 to 18% crude protein. Compared with RCS, feeding AS increased the supply of rumen-degraded protein and omasal flows of nonammonia N and microbial protein, which may explain the improved milk yield observed in the companion lactation trial. However, omasal flow of rumen-undegraded protein was 34% greater on RCS. Except for Arg, omasal flows of individual AA, branched-chain AA, nonessential AA, essential AA, and total AA did not differ between cows fed AS vs. RCS. Within AS diets, no differences in omasal AA flows were observed. However, omasal flows of Asp, Ser, Glu, Cys, Val, Ile, Tyr, Lys, total nonessential AA, and total AA all were higher in cows fed RCS1 vs. cows fed RCS2. In this trial, there was no advantage to reducing NPN content of hay-crop silage.

Effect of Varying Dietary Ratios of Alfalfa Silage to Corn Silage on Omasal Flow and Microbial Protein Synthesis in Dairy Cows

Eight ruminally cannulated multiparous Holstein cows that were part of a larger production trial were used to study the effects of varying dietary ratios of alfalfa silage (AS) to corn silage (CS) on omasal flow of nutrients and microbial protein. Cows were blocked by DIM and randomly assigned to 2 replicated 4 x 4 Latin squares (28-d periods). Diets fed contained (dry matter basis): A) 51% AS, 43% rolled high-moisture shelled corn (HMSC), and 3% solvent soybean meal (SSBM); B) 37% AS, 13% CS, 39% HMSC, and 7% SSBM; C) 24% AS, 27% CS, 35% HMSC, and 12% SSBM; or D) 10% AS, 40% CS, 31% HMSC, and 16% SSBM. Crude protein (CP) contents were 17.2, 16.9, 16.6, and 16.2% for diets A, B, C, and D. All 4 diets were high in energy, averaging 49% nonfiber carbohydrates and 24% neutral detergent fiber. Total microbial nonammonia nitrogen flow was lower on diet D (423 g/d) compared with diets A (465 g/d), B (479 g/d), and C (460 g/d). A significant quadratic effect indicated that microbial protein synthesis was maximal at 38% AS. Supply of rumen-degraded protein decreased linearly from 3,068 g/d (diet A) to 2,469 g/d (diet D). Omasal flow of rumen-undegraded protein did not differ among diets and averaged 1,528 g/d. However, when expressed as a percentage of dry matter intake, rumen-undegraded protein increased linearly from 5.59% (diet A) to 6.13% (diet D), probably because CP from SSBM was more resistant to degradation than CP from AS. Essential AA flow was lowest on diet D, and Lys flow tended to be lower on diet D, which may explain the lower milk and protein yields observed on that diet.

Comparison of four markers for quantifying microbial protein flow from the rumen of lactating dairy cows

Eight ruminally cannulated lactating cows from a study on the effects of dietary rumen degraded protein (RDP) on production and N metabolism were used to compare 15N, total purines, amino acid (AA) profiles, and urinary excretion of purine derivatives (PD) as microbial markers for quantifying the flow of microbial protein at the omasal canal. Dietary RDP was gradually decreased by replacing solvent soybean meal and urea with lignosulfonate-treated soybean meal. The purine metabolites xanthine and hypoxanthine were present in digesta and microbial samples and were assumed to be of microbial origin. The sum of the purines and their metabolites (adenine, guanine, xanthine, and hypoxanthine) were defined as total purines (TP) and used as a microbial marker. Decreasing dietary RDP from 13.2 to 10.6% of dry matter (DM) reduced microbial nonammonia N (NAN) flows estimated using TP (from 415 to 369 g/d), 15N (from 470 to 384 g/d), AA profiles (from 392 to 311 g/d), and PD (from 436 to 271 g/d). Averaged across diets, microbial NAN flows were highest when estimated using TP and 15N (398 and 429 g/d), lowest when using PD (305 g/d), and intermediate when using AA profiles (360 g/d) as microbial markers. Correlation coefficients between 15N and TP for fluid-associated bacteria, particle-associated bacteria, and total microbial NAN flows were 0.38, 0.85, and 0.69, respectively. When TP was used as the microbial marker, ruminal escape of dietary NAN was not affected by replacing solvent soybean meal with lignosulfonate-treated soybean meal in the diets. The direction and extent of response of dietary and microbial NAN flow to dietary treatments were similar when estimated using 15N, AA profiles, and PD, and were in agreement with previously published data and National Research Council predictions. Microbial and dietary NAN flows from the rumen estimated using 15N appeared to be more accurate and precise than the other markers. Caution is required when interpreting results obtained using TP as the microbial marker.

Use of Odd and Branched-Chain Fatty Acids in Rumen Contents and Milk as a Potential Microbial Marker

The objectives of this study were: 1) to determine if a correlation exists between rumen odd and branched-chain fatty acids (OBCFA, i.e., C(15:0), iso C(15:0), anteiso C(15:0), C(17:0), iso C(17:0), anteiso C(17:0), and C(17:1)), uracil, and purine bases (PB), 2) to evaluate the potential of milk OBCFA secretion to predict duodenal flow of microbial protein in lactating cows, 3) to evaluate the accuracy of the latter prediction equations using an independent data set, and 4) to determine whether these predictions were more accurate than predictions based on dry matter intake (DMI) and dietary characteristics. In the first experiment, 4 lactating dairy cows arranged in a 4 x 4 Latin square were offered diets based on grass silages of different botanical composition and a standard concentrate. The relationship between rumen pool size of OBCFA and microbial matter was investigated. Rumen pool size of microbial matter (g), determined 4, 12, and 17 h after feeding, using uracil and PB as microbial markers, was closely related to OBCFA (g) [r(2) = 0.716, root mean square error (RMSE) = 4.45]. To correct for differences in marker concentrations among strains of rumen microbes, C(17:0) was included in the regression equations, resulting in an increased predictive power (r(2) = 0.780, RMSE = 3.92). The relationship between microbial flow to the duodenum and milk OBCFA yield was evaluated in a second experiment with lactating dairy cows offered diets based on grass silage and concentrates differing in starch source. Similar to observations in the rumen, milk OBCFA yield was closely related to microbial flow to the duodenum (RMSE = 4.28), but predictive power of equations did not increase when straight-chain C(17)-fatty acids were included in the regression equations (RMSE = 4.92). Evaluation of the current prediction equations with 3 independent datasets resulted in a root mean square prediction error of 20.5 and 13.4% of the observed mean for equations based on milk secretion of total OBCFA and straight-chain C(17)-fatty acids, respectively. Comparison of the accuracy of the latter equations with 2 previously published equations based on DMI and dietary characteristics suggest the former to be more accurate. This first evaluation suggests that milk OBCFA could be used as a marker for duodenal flow of microbial matter, especially when accurate measurements of DMI are not available.

A comparison of purine derivatives excretion with conventional methods as indices of microbial yield in dairy cows

Three multiparous, ruminally and duodenally cannulated Holstein-Friesian milking cows (558 +/- 14 kg BW) with a mean milk yield of 19.9 +/- 1.4 kg/d in their 4th mo of lactation were fed a mixed diet of forage and concentrate at 100, 85, and 75% of ad libitum intake in a 3 x 3 Latin square design. Duodenal digesta flow was estimated using the dual-phase technique in which Cr-EDTA and Yb-acetate were used as liquid and solid markers, respectively. Microbial N (MN) was estimated using the duodenal flow of purine bases (PB); bacterial isolates from the rumen liquid and solid phases were used as references. Additionally, duodenal flow of PB and MN were estimated indirectly using the excretion of purine derivatives (PD) in urine and milk. Duodenal flow of PB and derived MN tended to decrease with feed restriction (from 258 to 154 mmol/d and 123.5 to 74.4 g/d, respectively). Estimates of PB and MN based on urinary PD showed the same trend, and decreases in PB (from 314 to 266 mmol/d, using LAB) were statistically significant. Using LAB, efficiencies of microbial protein synthesis in the ad libitum treatment were 12.9 and 17.0 g of MN/g of organic matter apparently digested in the rumen when estimated using duodenal PB and urinary excretion of PD, respectively. Urinary excretion of PD closely reflected changes in duodenal flow of PB as a result of feed restriction.

Large bowel fermentation of maize or sorghum-acorn diets fed as a different source of carbohydrates to Landrace and Iberian pigs

Twenty-four finishing pigs (twelve Iberian and twelve Landrace) were used in a growing and slaughtering experiment. Animals were fed two diets differing in their ingredients, maize (diet C) or sorghum-acorn (diet A). At an average weight of 107.0 kg pigs were slaughtered and hindgut digesta sampled to study the effect of breed and diet on large bowel fermentation. Flows of digesta to the hindgut compartment were estimated based on an indigestible flow marker (Cr2O3) and were higher in Iberian than in Landrace pigs (P<0.001), and higher in animals fed diet A than diet C (P=0.07). The higher flows in Iberian pigs were mainly associated with a higher voluntary feed intake (3.50 v. 2.70 kg/d, P<0.01) and lower ileal digestibility of NSP (-12.8 v. 47.8, P<0.01). Differences between diets were mainly associated with a lower ileal digestibility of starch from diet A (89.2 v. 96.9 %, P=0.06), although no differences in the resistant starch content were observed in vitro. Fermentation of different carbohydrates through the large bowel showed that NSP-glucose had lower digestibility in Iberian than in Landrace pigs (62.5 v. 94.2 %, P<0.001), but no differences were observed in starch, or other NSP-fibre fractions (arabinose, xylose and galactose). The type and amount of carbohydrates reaching the large bowel were related to the diet but also to breed, and promoted differences in the fermentative activity associated with different volatile fatty acid patterns and changes in microbial enzymic activity.