Efficiency Of Microbial Synthesis Research Articles

Effect of feeding level and substitution of barley grain by citrus pulp in ammonia-treated straw diets on digestibility and microbial synthesis efficiency in sheep

Because of its high pectin content, citrus pulp provides with readily fermentable energy for rumen microbial synthesis and promotes a more favourable environment for fibre digestion than starch supplements (Barrios et al., 1996). However, we are unaware of data comparing efficiency of microbial synthesis with cereals or citrus pulp. This work compares digestibility and efficiency of microbial synthesis of mixed straw diets with increasing substitution of barley by citrus pulp, at two feeding levels.Diets included equal parts of ammoniated barley straw (10.5 g N/kg DM) and a concentrate made up by different ratios of barley (18.2 g N/kg DM) and citrus pulp (11.1 g N/kg DM), namely M1 (100:0), M2 (66:33), M3 (33:66) and M4 (0:100).

Supplemental cracked corn for steers fed fresh alfalfa: II. Protein and amino acid digestion.

The effects of different levels of cracked corn on N intake, ruminal bacterial CP synthesis, and duodenal flows and small intestinal digestion of amino acids (AA) in steers fed fresh alfalfa indoors were determined. Angus steers (n = 6; average BW 338 +/- 19 kg) cannulated in the rumen, duodenum, and ileum were fed each of five diets over five periods in a Latin square design with an extra animal. Steers consumed 1) alfalfa (20.4% CP, 41.6% NDF) ad libitum (AALF); 2), 3), and 4) AALF supplemented (S) with three levels of corn (.4, .8, or 1.2% of BW, respectively), or 5) alfalfa restricted (RALF) to the average forage intake of S steers. Average N intake and duodenal flow of nonammonia N (NAN) were greater (P < .01) in S than in RALF steers. Greater duodenal flows of NAN in S compared with RALF were due to a trend toward higher (P = .06) flows of both bacterial and dietary N. Levels of corn decreased (P < .01) linearly N intake and increased (P < .01) linearly duodenal flow of NAN owing to a numerical linear increase in nonbacterial N (P = .15) with no increase in bacterial N flow. Duodenal NAN flows as percentages of N intake increased (P < .01) linearly (69.3 to 91.0%) as corn increased. Ruminal NH3 N concentration, ruminal CP degradability, and the proportion of bacterial N in duodenal NAN were decreased (P < .01) linearly as corn increased. Efficiency of net microbial CP synthesis was not affected (P > .05) by treatment (average 42.6 and 30.9 g N/kg of OM apparently or truly digested in the rumen, respectively). Small intestinal disappearance of total N and individual AA, except for threonine and lysine, and small intestinal digestibility of N and individual AA, except for methionine, histidine, and proline, increased (P < .01) linearly with level of corn and were greater (P < .01) in S than in RALF steers. Supplementing corn to steers fed fresh alfalfa reduced ruminal N losses and CP degradability and increased the duodenal flow and the small intestinal disappearance and digestibility of total N and total, essential, and nonessential AA.

Effect of forage particle size and intake level on fermentation patterns and sites and extent of digestion in dairy cows fed mixed diets

The aim of this study was to examine the effects and possible interactions between forage particle size and intake level on the site and extent of digestion and on ruminal fermentations in dairy cows fed mixed diets. Two forage particle sizes (chopped [C] or ground and pelleted alfalfa [G]) and two intake levels (ad libitum [H] and 80% of ad libitum [L]) were combined in a 2×2 factorial arrangement. Four mid-lactating cows equipped with ruminal and duodenal cannulas were used in a 4×4 Latin square design. On a dry matter (DM) basis, the four diets consisted of 18% maize silage, 25% dehydrated pelleted whole-crop maize, 25% dehydrated alfalfa and 32% concentrate. They were distributed twice daily with three hours access after each distribution. Dry matter intake averaged 21.9 kg day −1 for the H level. Feeding G rather than C diets reduced chewing time (22.1 vs. 27.7 min kg −1 DM). Feeding G diets sharply reduced organic matter (OM) and cell-wall constituents digestibilities ( P<0.01) with these effects being greater at H than at L intake ( P<0.10). Starch digestibility and the site of digestion of OM and carbohydrate were unaffected, but non ammonia nitrogen flow into the duodenum was increased ( P<0.05). Feeding G diets did not affect ruminal fermentation at the L intake level but the molar proportion of acetic acid was decreased and that of propionic acid was increased at the H intake level. When feeding GH diet, these changes in ruminal digestibility and fermentation patterns were associated with a reduced rumen retention time and lower cellulolytic activity which, in turn, were related to modifications in the ruminal environment. The range of pH during the day and hours below 5.6 were increased, whereas ruminal NH 3 was decreased compared to the three others diets. When cows were fed at H level the digestibilities of OM and cell-wall constituents were depressed ( P<0.01), along with the percentage of digestible materials disappeared in the rumen. Efficiency of microbial synthesis remained unaffected but the ruminal degradability of feed nitrogen tended to be lowered ( P<0.10). The H level increased ruminal content but did not change ruminal retention time. Lower ruminal digestibilities were mainly related to a depressed rate of digestion at H level. It is concluded that reducing the forage particle size can strongly affect the quantity and the nature of the digestive end-products by altering ruminal conditions. However, the magnitude of these digestive effects is dependent on the amount of fermentable OM ingested.

Supply of nutrients and productive responses in dairy cows given diets based on restrictively fermented silage

The objective of this paper is to review research which has evaluated the feeding of dairy cows with diets containing large proportions of grass silage. In Finland, milk production systems evolved are based on the use of restrictively fermented silages. Higher potential yields, smaller production risks than with cereal grains, short grazing period and high digestibility of grasses grown in northern latitudes have facilitated this development. Factors affecting nutrient supply from these diets are discussed. Digestibility is determined mainly by the stage of maturity at harvesting and it is not markedly affected by the level of energy and protein supplementation. Intake of grass silage is influenced both by digestibility and fermentation characteristics. Efficiency of microbial synthesis is high in animals given diets based on restrictively fermented silage but rumen fermentation pattern is characterised by low molar proportions of propionate. Production responses to additional concentrate are relatively small, especially when the amount of concentrate exceeds 10 kg day-1. High substitution of silage dry matter (DM), negative associative effects on digestion and partitioning of energy towards body tissues account for small production responses. Protein supplementation has consistently increased milk protein yield but responses do not appear to be related to the level of milk production, silage crude protein content, amount of concentrate or stage of lactation. The new protein evaluation system provides an accurate prediction of protein yield with the typical Finnish dairy cow diets. The high slopes (ca. 0.5) between protein supply and milk protein yield within experiments suggest that protein supply is suboptimal and protein supplements are used with a high efficiency.

Effect of Ruminal Degradability of Crude Protein and Nonstructural Carbohydrates on the Efficiency of Bacterial Crude Protein Synthesis and Amino Acid Flow to the Abomasum of Dairy Cows

Four lactating Israeli Holstein cows that were ruminally and abomasally cannulated were used in an experiment with a 4 x 4 Latin square experimental design to study the effects of different amounts of ruminally degradable crude protein (CP) and ruminally degradable nonstructural carbohydrates on ruminal fermentation and efficiency of bacterial CP synthesis. Four diets were formulated to contain the following percentages (percentage of respective fraction) of ruminally degradable protein (RDP) and ruminally degradable nonstructural carbohydrates, respectively: 1) 73.8 and 85.3%, 2) 72.4 and 75.3%, 3) 67.7 and 86.0%, and 4) 66.3 and 76.0%. The 2 × 2 factorial effects of high and low concentrations of RDP or nonstructural carbohydrates were examined. Intakes of DM and organic matter (OM) were similar among treatments, and apparent and true ruminal digestibilities of OM were also similar. Apparent digestibility of CP in the total tract was higher for diets containing high concentrations of ruminally degradable nonstructural carbohydrates. Efficiency of microbial CP synthesis was higher for diets supplemented with low concentrations of RDP and averaged 196g of microbial CP/kg of OM truly digested in the rumen. Total and bacterial CP flows were higher for diets containing low concentrations of RDP. Therefore, greater amounts of amino acids (AA) of bacterial origin reached the abomasum. The abomasal flow of AA was higher for diets containing low concentrations of RDP. Most of the profiles for essential AA in the abomasum were influenced and balanced by profiles for bacteria. When diets contained a high concentration of RDP (73% of total dietary CP), the supplementation of a high concentration of ruminally degradable nonstructural carbohydrates had no positive influence on bacterial yield or efficiency of bacterial CP synthesis. Other factors, such as AA and peptides included in the RUP fraction, may be important to maximize the efficiency of bacterial CP synthesis.

Effect of altering the non-structural: structural carbohydrate ratio in a pasture diet on milk production and ruminal metabolites in cows in early and late lactation

AbstractThe effect on digestibility, ruminal metabolites, microbial protein synthesis and milk production of manipulating the non-structural (NSC): structural (SO carbohydrate ratio in a predominantly pasture diet was investigated in cows in early (trial 1) and late (trial 2) lactation. Twenty-four cows in trial 1 and 15 cows in trial 2 were offered pasture only (P), 0·85 P plus 0·15 NSC/protein mixture (PR), and P plus an additional 0·1 (trial 1) or 0·15 (trial 2) NSC (PE) in a Latin-square arrangement. All diets were isonitrogenous and P and PR were isoenergetic. PE but not PR increased microbial protein synthesis and decreased ruminal ammonia and milk urea levels, compared with P. Efficiency of microbial synthesis (g N per kg digestible organic matter intake) was not altered by treatment. Treatments had minor effects on ruminal pH and no effect on volatile fatty acid concentrations. PE and PR did not affect milk yield or protein yield and decreased fat yield compared with P in trial 1. Milk yield was increased on PE and PR compared with P and was greater on PE than PR, in trial 2. Yields of fat and protein were higher on PE than on P and yield of protein was higher on PR than on P. The results suggest that increasing the ratio of NSC: protein by increasing total carbohydrate intake was more effective in improving nitrogen utilization in the rumen than was increasing the NSC: SC ratio without increasing carbohydrate intake.

Quantitative review of ruminal and total tract digestion of mixed diet organic matter and carbohydrates

The mean response and main factors of variation (level of concentrate, nature of carbohydrate in the concentrate and level of intake) for organic matter, cell wall material, starch digestion and microbial synthesis in the gastrointestinal tract of ruminants were quantitatively reviewed using a data base involving 157 papers. The ruminal digestion (mean +/- SE%) of organic matter, cell wall material, and starch were 45.2 +/- 11.2 (n = 553), 47.7 +/- 17.7 (n = 348), and 74.1 +/- 16.2 (n = 140), respectively and the proportion of each component digested in the rumen in relation to total tract digestibility was 64.7 +/- 12.3, 78.8 +/- 18.5 and 80.5 +/- 16.3, respectively. The efficiency of microbial synthesis (g of microbial protein/kg of organic matter truly fermented in the rumen) and the proportion of microbial nitrogen in the total amount of nitrogen leaving the stomachs (%) were, 23.6 +/- 9.3 (n = 320) and 55.1 +/- 16.5 (n = 289), respectively. The ruminal digestion of organic matter increased by 2 points for every 10 percent increase in concentrate incorporation. The ruminal digestion of cell wall material was maximal when the concentrate incorporation in the diet was 30%. When the ruminal digestion of cell wall decreased, the substitution of ruminal digestion by intestinal digestion was partial (10%). The efficiency of microbial synthesis was optimal when the level of concentrate incorporation was 40%. The nature of the carbohydrates in the concentrates had a significant effect on the efficiency of the microbial synthesis, which was higher (+6.6 g of nitrogen/kg of fermentable organic matter in the rumen) with slowly degradable starch (SS) or digestible fiber (DF) than with rapidly degradable starch (RS). Moreover, the mean depression of cellulolysis in the rumen was higher with RS (-13 points) comparatively to SS (-7 points) or DF (-5 points).

Effet du niveau et de la nature de l'azote dégradable sur la digestion ruminale d'un régime à base d'ensilage de maïs chez la vache laitière

Four diets differing in level and source of nitrogen were given in a 4 x 4 latin square design using four dairy cows canulated in the rumen and duodenum. A low N diet (T-, 17.4 g N/kg DM) with only 17 g of degradable N per kg of fermentable OM (FOM) (covering 73% of microbial requirements) was supplemented with up to 21.6 g/kg DM and 22 g/kg FOM (covering 95% of microbial requirements) of increasing levels of preformed amino acids. Three mixtures of urea and casein [100:0 (U); 50:50 (UC) and 0:100 (C)] were used in order to supply 30, 15 and 0% of the total N of the diet as urea-N. The four diets (66% maize silage) were isoenergetic and were offered 95% of ad libitum twice daily. OM and NDF digestibilities in the total digestive tract and in the rumen did not differ between T- and U diets. These digestibilities increased linearly with the proportion of casein-N in the diet but the response remained low. The levels and the source of degradable N did not affect the non ammonia nitrogen (NNA) flow into the duodenum, the microbial N flow and the efficiency of microbial synthesis. NNA flow exceeded N intake for all diets but the net recycling into the rumen was markedly higher for the LN diet (+110 vs +31 g/day). This is related to a lower excretion of urea-N in urine (22 vs 80 g/day). These results suggest that in cows fed at 95% of ad libitum, the shortage of degradable N hardly affects the digestion of the diet and that the supply of preformed amino acids is not an important limiting factor for bacterial growth when maïze silage based diets are fed. Therefore, the supplementation with such preformed carbon chains is not of practical interest.

The effect of stage of harvest on the process of digestion in cattle fed winter oats indoors. II. Nitrogen digestion and microbial protein synthesis

The effects of dates of harvest of winter oats ( Avena sativa L.) on the sites of nitrogen (N) digestion and ruminal microbial CP synthesis were studied in cattle fed indoors. The forage was cut from randomly selected areas of a single field at five dates from autumn to spring: A (25 May, autumn); EW (25 June, early winter); W (9 August, winter); ES (22 September, early spring); LS (20 October, late spring). The trial was arranged as a completely randomized design considering dates of harvest as treatments. Two heifers weighing 567 ± 17.8 kg fitted with cannulas in the rumen, proximal duodenum and distal ileum were given ad libitum access to feed. Animals were dosed with chromic oxide and Co-EDTA as external markers. The N content of the forage (g kg −1 dry matter) varied between 37.2 in A and 16.5 in LS ( P < 0.0001) and N intakes (NI, g kg −1 live weight (LW)) ranged from 0.81 to 0.23 with the lowest value in LS ( P < 0.02). Mean ruminal ammonia (NH 3-N) concentration ranged ( P < 0.0005) from 32.5 mg dl −1 in A to 5.1 in LS. Non-ammonia N (NAN) flow to the small intestine ranged from 0.46 to 0.25 g kg −1 LW ( P < 0.001). For A, EW, and W forages the NAN flows in relation to NI ( NAN NI , g g −1) were lower ( P < 0.05; mean: 0.69) than in the ES and LS forages (mean: 1.12). The NAN NI was negatively related to NI kg −1 digestible OM intake (DOMI), NAN NI = 1.63 − 0.015 g NI kg −1 DOMI; ( r = −0.94; P < 0.001). Microbial CP synthesis (g N kg −1 OM apparently digested in the rumen, OMADR) ranged from 31.5 to 46.0, tended to be lower in A ( P < 0.15) than in other forages and averaged 0.69 of the duodenal NAN. Ruminal CP degradability (g g −1 NI) tended to be higher ( P < 0.13) in A (0.81) than in ES (0.65). The date of harvest of winter oats can influence ruminal N digestion and intestinal supply of N. Duodenal NAN flow is dependent on NI and NAN NI depends not only on NI, but also on OM digestibility of winter oats. A high ruminal ammonia concentration in winter oats with high N content may be due to inefficient microbial capture of ruminally degraded CP, even when the efficiency of microbial synthesis (g N kg −1 OMADR) may be high.

Digestion of 14C-labelled condensed tannins from Desmodium intortum in sheep and goats.

An experiment was conducted to investigate the metabolism of condensed tannin (CT) in sheep and goats offered a mixture of Digitaria decumbens (700 g/kg) and Desmodium intortum (300 g/kg) hay. Radioactive 14CO2 was used to label CT in young growing desmodium plants, [14C]CT was extracted, purified and infused intraruminally, and the metabolism of [14C]CT was followed in the rumen and lower digestive tract of both species. Digestion of DM, organic matter (OM), cell-wall constituents (CWC), N and the efficiency of rumen microbial synthesis were determined using a continuous intraruminal infusion of 51Cr EDTA, YbCl3 and Na235SO4. The measurements taken for sheep and goats respectively were: intake, 21 and 30 g/kg0.9 per d; digestibilities (g/g) of DM, 0.566 and 0.505; OM 0.578 and 0.508; neutral-detergent fibre, 0.584 and 0.532; and acid-detergent fibre, 0.535 and 0.435. None of these measurements was significantly different (P > 0.05) between animal species. There was an apparent net gain in lignin across the rumen and whole intestinal tract for both animal species (19 and 29% for sheep and goats respectively). There were no significant differences between sheep and goats (P > 0.05) detected for any measurements of N excretion and utilization. The overall efficiency of N digestion and utilization was also similar between species. The routes of CT metabolism were compared for both colorimetric estimates (butanol-HCl) of dietary CT (DCT) and the specific radioactivity of [14C]CT in digesta (abomasum) and excreta (urine and faeces) of both sheep and goats. [14C]CT showed total losses of 57 and 56% in sheep and goats respectively whilst losses of DCT of 71 and 70% were detected with butanol-HCl in sheep and goats respectively. The apparent losses of DCT across the rumen of sheep and goats were 12 and 9% whilst higher losses (49 and 42% for sheep and goats respectively) were observed for [14C]CT. Losses of DCT in the lower intestinal tract accounted for 69 and 71% of the total CT leaving the abomasum. By comparison, only 40 and 35% of [14C]CT was lost during intestinal passage in sheep and goats respectively. It was concluded that the infused free [14C]CT interacted with DCT and entered the protein and fibre-bound DCT pools. The loss of DCT during passage through the intestines was considered to be a consequence of either absorption of free CT or the degradation products of CT. It was assumed that free CT arose in the lower gastrointestinal tract from protein-CT and fibre-CT dissociation to be digested and/or absorbed. The higher recoveries of [14C]CT in faeces (32 and 35%) compared with DCT (27 and 26%) for sheep and goats respectively) were associated with the excretion of [14C] degradation products or conjugates which were not reactive to butanol-HCl. It was concluded that both methods (butanol-HCl and labelling CT with 14C) detected a substantial disappearance of CT (free, protein, and fibre-bound) during metabolism in the gastrointestinal tract in sheep and goats.

Effects of the nature of roughage and concentrate and their proportion on ruminal characteristics of non lactating goats, consequences on digestive interactions

The effects on ruminal characteristics of 14 diets differing in nature and level of roughage and concentrate have been studied. The roughages were alfalfa hay (AH) or maize stover silage (MS) distributed alone or in a mixed diet containing 30 or 60% concentrate on a dry matter basis. Three types of concentrate were formulated to be either rich in rapidly degradable starch (RS), slowly degradable starch (SS) or digestible fibre (DF). The post feeding evolutions of pH, volatile fatty acids (VFA) and ammonia (NH 3) concentrations in ruminal fluid were measured. Microbial protein synthesis has been estimated. Ruminal pH was consistently high (pH > 6.3) and VFA concentrations in the rumen were 88.4 mmol L −1. VFA concentrations were higher after AH compared with MS, whereas differences between concentrates were not significant. The proportion of acetate decreased with the concentrate level while that of propionate increased. The NH 3 concentration was always over 50 mg L −1 and varied significantly with the tested diets. The efficiency of microbial nitrogen synthesis (EMS) was 32.7 g per kg of organic matter apparently digested in the rumen without significant differences between roughages or concentrates. No difference ( P < 0.05) was observed between the depressive effect of concentrates on the cellulolysis in the rumen.

Influence of niacin on in vitro ruminal fermentation and microbial synthesis depending on dietary factors

The in vitro degradability of starch by ruminants as influenced by supply of niacin was studied with different dietary factors, and compared to that of fibre (beet pulp) within similar dietary conditions. The batch cultures were supplied rumen contents from cows fed four diets based either on maize silage or on hay, supplemented with soybean meal and urea. Starch, beet pulp or niacin were introduced directly into fermenters. Regardless of niacin supplementation, maize silage and starch intensified fermentations and microbial synthesis when compared respectively to hay and beet pulp. Oil supply did not modify starch fermentation. Niacin enhanced production of total and individual gas and volatile fatty acids, as well as fermented organic matter and ammonia nitrogen uptake, irrespective of dietary conditions. However, responses to niacin were higher with maize silage than with hay, but similar whatever the nitrogen source, oil supply and energy substrate. Treatments did not affect efficiency of microbial synthesis, except for the depression due to added oil. Collectively, these results indicate that sufficient quantities of substrate for maximum growth of microbes would make subsequent positive fermentative and microbial synthesis responses to niacin more probable.

Effect of dietary lipids on nitrogen metabolism in the rumen: a review

This paper deals with the influence of supplementary lipids in the diet on protein degradation and microbial synthesis in the rumen, through the effect of lipids on the microbial ecosystem. Global effects of lipids can be summarized by a trend to decrease ammonia ruminal concentration but duodenal non-ammonia nitrogen flow is not modified. The two components of this flow, non-microbial and microbial flows, generally are not modified so that it can be deduced that modifications of degradation and microbial synthesis due to lipid addition are of low extent. The efficiency of microbial synthesis depends on the nature of fatty acids and is increased especially when organic matter ruminal digestibility is depressed; this can be related to the decrease in protozoa number in the rumen. Cette revue traite de l'influence de l'addition de lipides dans la ration sur la dégradation des protéines et la synthèse microbienne dans le rumen, en relation avec les modifications de l'écosystème microbien. Les effets globaux des lipides peuvent être appréhendés par la tendance à la diminution de la concentration en ammoniac dans le rumen; en revanche le flux duodenal total d'azote non ammoniacal ne varie pas. De même, les deux composantes de ce flux (microbienne et non microbienne) ne sont généralement pas modifiées. On peut en conclure que la dégradation des protéines et la synthèse ruminale de protéines microbiennes ne sont que peu affectées par la supplémentation lipidique. L'efficacité de la synthèse de protéines microbienne est accrue en particulier lorsque la digestibilité ruminale de la matière organique est réduite; cela peut être reliéà une réduction de la population de protozoaires dans le rumen. Diese übersicht berichtet über den Einfluβ einer Fettzugabe in die Ration auf den Proteinabbau und die mikrobielle Proteinsynthese im Pansen in Beziehung mit Veränderungen im mikrobiellen Ecosystem. Die Gesamteffekte der Lipide können in der Tendenz zur Verminderung der Ammoniakkonzentration im Pansen erfaβt werden; dagegen bleibt der gesamte Fluβ von Nichtammoniak-Stickstoff ins Duodenum unverändert. Beide Komponenten des Fluβes (mikrobieller und nichtmikrobieller Stickstoff) zeigen in der Regel auch keine Veränderung. Daraus kann man folgern, dass der Proteinabbau und die Synthese von Mikrobenprotein im Pansen durch eine Fettsupplementierung wenig beeinfluβt werden. Die Effizienz der mikrobiellen Proteinsynthese erhöht sich ins besondere, wenn die Verdaulichkeit der organischen Substanz im Pansen beschränkt ist; das könnte mit einer Verminderung der Protozoenpopulation im Pansen zusammenhängen.

In vitro and in vivo comparisons of diaminopimelic acid and purines for estimating protein synthesis in the rumen

Means analyses were used to compare estimates of crude protein (CP) degradation (%), true organic matter (OM) digestion (%), efficiency of microbial synthesis (g N kg −1 OM truly digested) and microbial nitrogen (N) flow (g d −1) using diaminopimelic acid (DAPA) and purines as microbial markers for 12 in vitro and four in vivo experiments. In vitro experiments included 268 determinations and in vivo experiments included 80 determinations of microbial activity by each marker. In vitro estimates of ruminal CP degradation, true OM digestion, efficiency of microbial synthesis and microbial N flow by purines (60.5, 52.4, 33.1 and 1.3) were lower ( P < 0.05) than estimates by DAPA (69.9, 55.0, 36.1 and 1.4). Coefficients of variation of estimates of ruminal CP degradation, true OM digestion, efficiency of microbial synthesis and microbial N flow determined by purines (22.0, 12.4, 17.0 and 22.4) or DAPA (22.2, 12.3, 14.2 and 20.5) were similar for in vitro experiments. In vivo estimates of ruminal CP degradation, true OM digestion and microbial N flow by purines (57.2, 53.1 and 137.2) were lower ( P < 0.05) than estimates by DAPA (65.9, 61.1 and 162.2). Estimates of efficiency of microbial synthesis determined using purines (28.4) and DAPA (27.9) were similar. Coefficients of variation for estimates of ruminal CP degradation, true OM digestion, efficiency of microbia l synthesis and microbial N flow determined by purines (21.4, 23.8, 38.6 and 32.4) and DAPA (16.5, 16.7, 37.3 and 33.9) were similar for in vivo experiments. Estimates of CP degradation exceeded 90% on 26 occasions when DAPA was used as the marker, compared with seven occasions when purines were used. Using purines as the microbial marker resulted in lower microbial activity and similar coefficients of variation compared with DAPA. Unrealistic values of CP degradation were observed more frequently using DAPA as the microbial marker.

Effects of zinc-treated soybean meal on ruminal fermentation and intestinal amino acid flows in steers fed corn silage-based diets.

The objectives of this study were to examine the effects of feeding zinc-treated soybean meal (Zn-SBM) on ruminal fermentation patterns and duodenal AA flows in steers fed diets based on corn silage and corn. Six steers (385 kg) fitted with ruminal, duodenal, and ileal cannulas were used in a replicated 3 x 3 Latin square design experiment with 14-d periods. Diets were supplemented with solvent-extracted soybean meal (SBM), Zn-SBM, or a 50:50 combination (CP basis) of SBM:Zn-SBM. Ruminal escape N content of SBM and Zn-SBM were 30.0 and 57.0%, respectively, based on 12-h Dacron bag incubation. Protein sources provided approximately 30% of total CP in diets containing 12.6% CP (DM basis). Dry matter intake was equalized throughout the study at 2.2% of average initial BW. Total N flow at the duodenum was similar (P = .47) among treatments, but a trend (P = .15) for increased nonmicrobial N flow occurred when SBM and Zn-SBM were fed in combination. Micobial N flow and true efficiency of microbial CP synthesis were not affected by treatment (P = .87 and .37, respectively). Ruminal fermentation characteristics generally were unaffected (P > .10) by protein source. A positive quadratic response (P < .06) was observed for total and essential AA flows to the small intestine because flows of total and essential AA from ruminally undegraded dietary protein tended (P = .12) to increase when SBM and Zn-SBM were fed in combination. Absorption of AA from the small intestine also showed a positive quadratic (P < .06) response for SBM:Zn-SBM. Microbial AA flow to the small intestine was similar (P = .87) among treatments.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of rapeseed oil supply on in vitro ruminal digestion in cows: comparison of hay and maize silage diets

The effect of lipid supply on carbohydrate fermentation and nitrogen metabolism in the rumen was investigated using a closed fermenter containing rumen contents from cows receiving different diets. Four diets were compared. They were based either on hay or on maize silage, supplemented or not with 7% rapeseed oil, on a dry matter basis. Energy source in the fermenters came either from starch or from sucrose. No supplemental oil was added in the fermenters. Volatile fatty acid (VFA) production was higher with maize silage diets than with hay diets. Oil supplementation increased VFA production and the molar proportion of propionic acid in these VFA, for starch and sucrose as substrates. Gas production was higher for maize silage diets than for hay diets, but was not modified by lipid supplementation. Forage source and oil supplementation did not affect ammonia nitrogen uptake by bacteria and efficiency of microbial synthesis. These results differ from in vivo results obtained in a previous study utilizing the same diets. These difference could be caused by different fermentation conditions between in vivo and in vitro.

Ryegrass Versus Corn Starch or Beet Pulp Fiber Diet Effects on Digestion and Intestinal Amino Acids in Dairy Cows

Changes in digestion and AA supply in dairy cows were studied when fresh grass was partly replaced by concentrate mixtures based either on corn starch or sugar beet pulp fiber. Treatments were tested in a Latin square utilizing three lactating cows with ruminal and intestinal cannulas. Partial replacement of grass decreased CP digestibility. When high starch concentrate was fed, NDF digestibility was lower than that of the high fiber diet, mainly because of decreased ruminal digestion of NDF. For the high starch concentrate, 39% of the ingested starch escaped ruminal fermentation. Although less OM was fermented in the forestomachs on high starch concentrate, the duodenal AA N flow was higher than for the high fiber concentrate. The proportion of microbial protein was unaffected; thus, efficiency of microbial synthesis was estimated to be higher when high starch concentrate was fed.

The effect of starch sources barley, maize and potatoes and their ration portions on the nutrient digestibility and energy utilization in ruminants. 4. Nitrogen metabolism in the rumen

In 9 experimental periods on four adult bulls (LW 550 kg) fitted with re-entrant cannulae in the proximal duodenum isoenergetic rations were used on feeding level 1.7 with ground barley, ground maize or fresh potatoes as starch sources. The net energy parts of these concentrates in the ration amounted to 50, 25 and 10%. 50 to 80% of the ration DM consisted of dried grass and about 10% of sugar beet pulp. The dried grass supplied on an average 87, 79 and 62% of the feed crude protein. The intake of DM was 7.74 +/- 0.42 (mean +/- SD) kg/d. The energetic efficiency of microbial N synthesis in the rumen (g N/kg organic matter true fermented in the rumen, TFOM) was averaged 16.4 with a range of 10.6 to 21.4. The microbial efficiency achieved a maximum when the ratio of nitrogen-free extract to crude fibre in the diet was 1.7 and 2.1 with barley, 1.8 with potatoes and 2.1 and 3.3 with corn as starch source. Changes in the microbial efficiency were positively correlated with the rate of passage of non-microbial organic matter from the rumen (g/d) and with the duodenal flow rate (kg digesta/kg DM intake). The relation to the rate of carbohydrate fermentation in the rumen (in %) and to the amount of TFOM (g/d) was negative. The duodenal flow of microbial N and non-ammonia N (g/d) correlated negatively with the organic matter apparently fermented in the rumen (AFOM) and positively with the non AFOM. The amino acid (AA) profile of the duodenal protein was affected by the starch source. It was concluded that the metabolism of nitrogen in the forestomachs of cattle is affected by the source of starch and the ratio of forage to concentrate. There exists a relationship between both factors. The net synthesis of microbial protein in the rumen is not only the result of substrate fermentation. The passage of non-AFOM from the rumen significantly affects the energetic efficiency of microbial nitrogen synthesis and the duodenal supply of AA.

Effects of diet, level of intake, sodium bicarbonate and monensin on urinary allantoin excretion in sheep.

The present experiment was designed to study the effects of factors likely to alter microbial purine yield from the rumen on urinary excretion of allantoin-nitrogen (UAN). Sixteen mature Clun Forest-Welsh crossbred wethers were used in a 2 x 2 x 2 x 2 factorial design to investigate the effects of (1) level of intake, (2) wheat:nutritionally improved straw (NIS) ratio, (3) sodium bicarbonate inclusion and (4) monensin inclusion on diet digestibilities, fractional outflow rates of solids and liquids from the rumen and urinary allantoin excretion. Each treatment occurred in each of two experimental periods. The treatments were designed to influence microbial purine yield via changes in rumen outflow rate and microbial maintenance coefficient. Increasing the proportion of NIS and increasing feeding level decreased digestibility and increased the fractional outflow rate of solids. Increasing the level of intake increased the fractional outflow rate of liquids. Urinary allantoin excretion (/kg live weight0.75 per d) was significantly increased by an increased proportion of wheat in the diet and increased level of intake, and significantly reduced by NaHCO3. There was a significant interaction effect such that increasing level of intake did not increase UAN with the high-NIS diet, despite an increased fractional outflow of solids from the rumen, in contrast to the increase observed with the high-wheat diet. Taken together with other observations it is suggested that high sodium concentrations in the diet reduce the efficiency of microbial synthesis, probably by increasing the energy cost of maintaining osmolarity.(ABSTRACT TRUNCATED AT 250 WORDS)

The influence of lasalocid and cationomycin on nitrogen digestion in sheep: Comparison of methods for estimating microbial nitrogen

An in vivo study was carried out to evaluate the effect of a new ionophore (cationomycin) on nitrogen digestion compared with lasalocid. Three diets based on forage were given (a control diet, a "cationomycin" diet, a "lasalocid" diet) to six sheep fitted with rumen duodenal and ileal cannulae over three different periods in a Latin square design experiment. The supply of lasalocid or cationomycin (33 mg kg−1) decreased (P &lt; 0.05) the breakdown of dietary proteins in the rumen and lowered the microbial protein synthesis whatever the microbial marker used (diaminopimelic acid or purine bases). The duodenal and ileal flows of organic matter (OM), ammonia nitrogen (NH3-N), nonammonia nitrogen, and amino acids (AA) were not affected by the ionophore addition. We could not use the AA profile method to estimate the microbial contribution to the duodenal flow of nonammonia nitrogen because of the strong similarities in AA composition of the feed and the rumen microbial sample. The efficiency of microbial synthesis was significantly (P &lt; 0.05) decreased by cationomycin, and tended to decrease with lasalocid. Only lasalocid increased the digestibility of dietary nitrogen in all the digestive tract. Key words: Ionophore, lasalocid, cationomycin, digestion, nitrogen, sheep, rumen