C. Poncet

Feeding ground and pelleted hay rather than chopped hay to ponies: 1. Consequences for in vivo digestibility and rate of passage of digesta

This study was designed to evaluate the effect of the physical form of a hay diet on total tract digestibility in ponies, with particular emphasis in fibre digestion and digesta passage rate. Ten gelded ponies (four of them fitted with cannulae in the cecum and the right-ventral colon) were kept on wood shavings and fed twice daily a maintenance diet of equal parts Lucerne and Cocksfoot hay. The hay was either chopped (CH) or ground (1.5 mm screen) and pelleted (GPH). The apparent total tract digestibility of dry matter (DM), organic matter (OM), and fibre fractions was measured in the six non-fistulated ponies using a crossover design. Two trials were conducted to measure mean retention time (MRT) of digesta in the whole digestive tract in four non-fistulated and four fistulated animals using rare earth labelled hay and Cr-EDTA as markers of the particles and solutes, respectively. In a third trial, MRTs in the hind gut and the colon, as well as in the entire tract, were determined in the fistulated ponies using various markers given by mouth and through the cannulae. OM and fibre digestibility were not significantly different (P > 0.05) between diets. However, particle (P < 0.05) and solute (P < 0.001) MRT were significantly longer on GPH compared to CH as a consequence of an increased retention in the colon. The longer MRTs with GPH did not significantly affect fibre digestibility. This implies a reduction in the rate of fibre degradation in the hindgut in the GPH fed animals.

Effect of linseed oil supplementation on feed degradation and microbial synthesis in the rumen of ciliate-free and refaunated sheep

The consequences of a 6% linseed oil (LSO) supplementation on fibre digestion and microbial protein synthesis in the rumen were investigated in ciliate-free and refaunated sheep, in order to assess the role protozoa depletion plays in the various effects of oil feeding. The incorporation of LSO in the diet decreased protozoal numbers from 565 × 103 ml−1 to 191 × 103 ml−1 (P < 0.01). It did not modify significantly the rumen fluid kinetics. Defaunation and the supply of LSO shifted rumen fermentation to a higher propionateacetate molar ratio. Digesta flows at the duodenum were measured using ytterbium as a flow marker. The addition of LSO significantly reduced the digestion of hemicelluloses in the rumen, mainly by a direct inhibition of bacterial activity. Flow of microbial matter at the duodenum was estimated using 2,4-diaminopimelic acid or purine bases as microbial markers. Both defaunation and LSO supplementation decreased the amount of OM apparently digested in the rumen and increased the flow of microbial nitrogen at the duodenum, leading to an increase in the efficiency of microbial protein synthesis.

Effect of concentrates in a hay diet on the contribution of anaerobic fungi, protozoa and bacteria to nitrogen in rumen and duodenal digesta in sheep

Abstract Two sheep, cannulated at the rumen and the duodenum, were given diets of chopped orchard grass hay (H) and 3 parts grass hay to 2 parts concentrates (M). The the pools and flows of anaerobic fungi, protozoa, liquid-associated bacteria (LAB) and solids-associated bacteria (SAB) were measured. The anaerobic fungi contributed only 11–35 g N/kg of the microbial-N in the rumen and 7–27 g N/kg of the microbial-N flowing to the duodenum. Inclusion of concentrates in the diet increased fungal zoospore counts and biomass and, in sheep 1, resulted in a more than four-fold increase in rumen protozoal counts: the protozoal contribution to its microbial N increased from 41 to 66% in the rumen and from 4 to 15% in duodenal flow. For sheep 2, there was an almost two-fold increase in protozoal counts and their contributions to its rumen and duodenal microbial N increased from, respectively, 35 to 57% and 7 to 9%. These changes were associated with a decrease in the yield of rumen microbial-N from 31 to 25 g/kg OM digested in the stomach for sheep 1 but an increase from 37 to 42 g/kg OM digested in the stomach for sheep 2. In addition, there were decreases in non-ammonia-N (NAN) flow to and digestion in the intestines of sheep 1 but increases in sheep 2. Protozoa obtained 40–58% of their N from bacteria. When diaminopimelic acid was used as the marker, bacterial-N was overestimated in rumen digesta and appeared to be underestimated in duodenal digesta. The ratio of duodenal NA15N to either rumen or duodenal LAB-15N underestimated the contribution of microbial-N to duodenal NAN. The mean retention times (MRT) of protozoa were much longer than those of digesta particles, reflecting protozoal sequestration in the rumen. On the hay diet, the apparent MRTs of LAB were the same as those for SAB and particles whereas, when concentrates were included in the diet, the MRTs of LAB were similar to those of solutes in sheep 2 and between those of solutes and particles in sheep 1; apparent MRTs of SAB were always similar to particle MRT. These results and the calculated generation times of LAB and SAB were consistent with the conclusion that, on the hay diet, LAB were probably SAB “in transit” between particles but, with the inclusion of concentrates, they were predominantly starch-utilizing organisms whose proliferation in the rumen of sheep 1 was limited by predation by its large protozoal population. Ammonia was produced in and absorbed from the omasum and the 15N-incorporation data were consistent with the growth of LAB in the omasum.

Digestion and nutrient net fluxes across the rumen, and the mesenteric- and portal-drained viscera in sheep fed with fresh forage twice daily: net balance and dynamic aspects

Digestion and portal net flux of nutrients were studied in sheep fed twice daily with fresh orchard-grass. Digestive flows were measured in six fistulated sheep using the double-marker technique. Three sheep were fitted with catheters and blood-flow probes, allowing nutrient net flux measurements across the portal-drained viscera (PDV), the mesenteric-drained viscera (MDV) and the rumen. Total tract apparent digestion of N was similar to portal net appearance of N, calculated as the sum of free amino acids (FAA), peptide amino acids (PAA), NH3, and urea net fluxes. PAA accounted for 25 % of non-protein amino acid net release across the PDV. With the exception of glycine and glutamate, the small intestine was the main contributor to this PAA net release. The essential amino acid (EAA) apparent disappearance between the duodenum and the ileum was lower than the net appearance of EAA (FAA + PAA) across the MDV. The value of PDV:MDV flux of free EAA was, on average, 78 %. The rumen accounted for 30 % of the net uptake of EAA by the PDV tissues not drained by the mesenteric vein. Rumen net release of acetate, propionate, butyrate, 3-hydroxybutyrate, and lactate accounted for 70, 55, 46, 77 and 52 %, respectively, of their portal net releases. Conversely, the small intestine was a net consumer of arterial acetate and 3-hydroxybutyrate. Dynamic study of nutrient net fluxes across the PDV showed that throughout a feeding cycle, the liver faced a constant flux of amino acids (AA), whereas volatile fatty acid and NH3 net fluxes varied in response to the meal. The present study specified, in forage-fed sheep, the partitioning of nutrient net fluxes across the PDV and the role of peptides in portal net release of AA.

Digestive interactions in the ruminant: relationships between whole tract and stomach evaluation

Two forages, maize stover silage (MS) and alfalfa hay (AH) were combined with 0, 30 and 60% of three types of concentrate either rich in rapidly degradable starch (RS), slowly degradable starch (SS), or rich in digestible fibre (DF). Treatment effects and interactions were compared in terms of organic matter (OM), holocellulose (SC), non-structural carbohydrate (NSC) and starch digestibility in the stomach and the whole tract. Mean intakes of OM, SC, NSC and starch were 925, 472, 270 and 224 g day−1, respectively. Mean digestibilities were 47.8, 59.0, 43.5 and 78.7%, respectively, in the stomach and 68.1, 63.9, 78.5 and 96.1%, respectively, in the whole tract. The precision of the estimates of stomach digestibility was lower than that of the whole tract. Significant treatment interactions were observed at the whole tract level except for the combination AH/DF. The influences of the level of concentrate on stomach and whole tract digestibility were parallel only when diets included RS and DF. In the case of SC digestion, large interactions were observed with MS-mixed rations contrary to AH-mixed ones. For the MS diet, there was good agreement between stomach and whole tract estimations. There was no influence of concentrate level on whole tract NSC digestibility, and no general relationship between stomach and whole tract NSC digestibilities. The use of whole tract digestibility to evaluate or quantify ruminal digestive interactions could be an inaccurate criterion. A specific feed effect must be taken into account when linking stomach and whole tract digestion of OM and SC.

Effect of site of starch digestion on portal nutrient net fluxes in steers

Processing of maize grain is known to modulate the site of starch digestion, thus the nature and amount of nutrients delivered for absorption. We assessed the effect of site of starch digestion on nutrient net fluxes across portal-drained viscera (PDV). Three steers, fitted with permanent digestive cannulas and blood catheters, successively received two diets containing 35 % starch as dent maize grain. Diets differed according to maize presentation: dry and cracked (by-pass, BP) v. wet and ground (control, C). Ruminal physicochemical parameters were not significantly affected. Between C and BP, the decrease in ruminal starch digestion was compensated by an increase in starch digestion in the small intestine. The amount of glucose and soluble alpha-glucoside reaching the ileum was not affected. The amount of glucose disappearing in the small intestine increased from 238 to 531 g/d between C and BP, but portal net flux of glucose remained unchanged (-97 g/d). The portal O2 consumption and net energy release were not significantly affected, averaging 16 % and 57 % of metabolizable energy intake, respectively. The whole-body glucose appearance rate, measured by jugular infusion of [6,6-2H2]glucose, averaged 916 g/d. The present study shows that the increase in the amount of glucose disappearing in the small intestine of conventionally fed cattle at a moderate intake level induces no change in portal net flux of glucose, reflecting an increase in glucose utilization by PDV. That could contribute to the low response of whole-body glucose appearance rate observed at this moderate level of intestinal glucose supply.

Influence of the nature of forage and concentrate on the digestive interactions measured in sacco and in vivo

Abstract Reticulo-ruminal digestive interactions in complete mixed diets were studied in goats using various approaches. The nylon bag technique was used and the results were compared with stomach digestion estimated by duodenal flow from the same goats. Basal diets were composed of maize stover silage (MS) or alfalfa hay (AH) combined with 0, 30, or 60% of three types of concentrate, rich in rapidly (RS) or slowly (SS) degradable starch, or in digestible fibre (DF). Effective degradation (ED) of dry matter, structural carbohydrate (SC), neutral detergent soluble (NDS) and starch of roughage and concentrate were estimated. Significant decreases in ED of SC from roughage and concentrate were seen when the level of concentrate was increased in the basal diet. Compared with the duodenal flow technique, the in sacco measure overestimated the decrease in the SC degradation rate. Degradation of SC after 48 h of incubation in nylon bags was a better predictor than ED for SC duodenal digestibility. The in sacco method underestimated starch degradation of SS. Effective degradation of starch in SS has confirmed higher amilolytic activity after the (AH + SS) vs. (MS + SS) diets which had already been observed from in vivo duodenal digestion data.

A comparison of in situ and in vitro methods to estimate in vivo fermentable organic matter of forages in ruminants

Several known in situ and in vitro methods were compared for their reliability for determining directly or indirectly in vivo fermentable organic matter (in vivo FOM) of forages in ruminants. Twelve forage types were used: fresh and conserved forms of lucerne, red clover, orchard grass and perennial ryegrass. Organic matter truly digested in the rumen which in our study was regarded as equivalent to in vivo FOM was determined in six cannulated sheep, using the flow markers %sup51;Cr-EDTA and sRu-Phenanthrolin. In vivo FOM was estimated directly from results of the in situ nylon bag technique using three cows, and from the results of three in vitro methods, and indirectly by calculating in vivo FOM using equations from the Dutch and French protein evaluation systems. The in vitro methods were an enzymatic technique using pepsin and cellulase, the method of Tilley & Terry and the gas production technique. In vivo FOM was best correlated (R² = 0.74; n = 12) with gas production after 20 hours of incubation. The correlation improved when fresh and conserved forages were considered separately (R² = 0.90; n = 12). Indirectly, in vivo FOM was well estimated from the results of the in situ , the gas production and the Tilley & Terry methods (R² = 0.760.80; n = 12). The accuracy of the direct and indirect in vivo FOM estimates was similar. However, the direct in vivo FOM estimate was a regression and the indirect estimate was a validation. In conclusion, in vivo FOM was best estimated indirectly using the equation from the Dutch protein evaluation system, whereas the estimate was more accurate with the in situ and the gas production techniques than when the other in vitro methods were used.

Etude in sacco et in vitro de la diminution de charge bactérienne de fourrages et d'aliments concentrés lors du passage dans la caillette

avant et après séjour dans la caillette, traduisent les modifications de la charge bactérienne sur les particules. Dans l’essai in vitro, un échantillon de contenu de rumen d’un mouton, marqué au 15N comme précédemment, a été fractionné en grosses particules par filtration (tamis à 250 pm) et lavage, petites particules (centrifugation du filtrat à 1 000 g pendant 30 min) et bactéries libres de la phase liquide (centrifugation du surnageant à 27 000 g pendant 30 min). Ces trois fractions ont aussitôt séjourné pendant 1,5 h en incubateur dans du liquide de caillette centrifugé à 27 000 g pendant 30 min pour en éliminer les particules et les bactéries. Le dosage des teneurs en N et 15 N, ainsi que des observations en microscopie électronique à balayage, ont été réalisés pour chaque fraction avant et après séjour en fermenteur. La charge bactérienne des particules exprimée en terme de matière