[469][470][471][472][473][474][475][476][477][478][479][480][481][482][483][484][485]. Condensed tannins (CT) are polyphenolic secondary plant products that are widespread in the plant kingdom. By definition, CT bind to protein and are regarded as "antinutritional" compounds which reduce protein digestibility. Variations in CT chemistry alter protein binding capacities among polymers from different plant species and developmental stages. Condensed tannins interact with proteins in feed, saliva and microbial cells, with microbial exoenzymes, and with endogenous proteins or other feed components, which alters digestive processes as compared with diets free of CT. Tannin levels exceeding 40 to 50 g kg -1 DM in forages may reduce protein and DM digestibility of the forages by ruminants. At low to moderate levels, CT increase the quantity of dietary protein, especially essential amino acids, flowing to the small intestine. Unlike alfalfa, legumes that contain CT do not cause bloat. Dietary CT may provide a means to beneficially manipulate protein digestion and/or prevent pasture bloat in ruminants. Research efforts are also currently being directed to genetically modify alfalfa to de-repress its CT biosynthetic pathway, or to move genes encoding steps of this pathway into alfalfa from other legumes. The effects of CT in forage legumes on digestion in ruminants and the potential use of tannin-rich forages for preventing bloat in grazing systems are discussed. Les tanins condensés (TC) sont des substances secondaires polyphénoliques répandues dans le règne végétal. Par essence fixés aux protéines, ils sont considérés comme substances antinutritionnelles qui réduisent la digestibilité des protéines. Leur constitution chimique, et par conséquent leur aptitude à se fixer aux protéines, fluctue selon la nature et le stade de croissance des espèces végétales. Les tanins condensés interagissent avec les protéines dans les aliments du bétail, dans la salive et dans les cellules microbiennes; avec les exoenzymes microbiens et avec les protéines endogènes ou avec d'autres composants des aliments du bétail, modifiant ainsi le processus de la digestion par rapport aux aliments sans TC. Des teneurs en tanins de plus de 40 à 50 g kg -1 m.s. dans les fourrages peuvent abaisser la digestibilité des protéines et de la matière sèche chez les ruminants. À des niveaux faibles à moyens, les TC accroissent le flux de protéines alimentaires, en particulier celui des acides aminés essentiels, vers l'intestin grêle. À la différence de la luzerne, les légumineuses qui contiennent des TC ne provoquent pas le météorisme. L'apport de TC dans l'alimentation des animaux peut être un moyen de manipuler positivement la digestion des protéines ou de prévenir le météorisme chez les ruminants au pâturage. Les recherches s'orientent également ves la modification génétique de la luzerne pour contrer l'inhibition de la biosynthèse des TC ou pour introduire dans l'espèce, à partir d'autres légumineuses, des gènes codant pour certaines étapes de cette voie....

A study using 144 one-day-old Arbor Acres broilers was conducted to assess the effects of dried ginger root (Zingiber officinale) that was processed to particle sizes of 300, 149, 74, 37, and 8.4 microm on growth performance, antioxidant status, and serum metabolites of broiler chickens. The birds were housed in 24 wire cages in an environmentally controlled room. Dietary treatments were no supplementation (control) and supplementation with ginger root processed to 5 particle sizes at the level of 5 g/kg of diet. Average daily gain, ADFI, and feed conversion rate of chicks of each cage were measured weekly. Blood samples from 8 broilers per treatment were obtained at d 21 and 42 of the experiment to determine antioxidant enzymatic activities and metabolites in the serum, and the birds were subsequently killed to determine carcass yield and abdominal fat content. All broilers had similar ADFI or feed conversion rate over the entire experimental period. However, broilers supplemented with ginger powder tended to have higher ADG and had greater (P=0.014) carcass yield compared with that of the control. Supplementation of ginger increased (P<0.001) activities of total superoxide dismutase and glutathione peroxidase but reduced (P<0.01) concentrations of malondialdehyde and cholesterol in serum of broilers at 21 and 42 d of age. Concentration of total protein in serum of ginger-supplemented broilers tended (P=0.092) to be higher at 21 d and was higher (P=0.002) at 42 d of age compared with that of control broilers. Reducing particle size of ginger powder linearly reduced (P<0.05) cholesterol (d 21) and linearly increased (P<0.05) glutathione peroxidase (d 21), total superoxide dismutase (d 42), and total protein (d 21 and 42). Supplementation of ginger at the level of 5 g/kg improved antioxidant status of broilers and the efficacy was enhanced as the particle size was reduced from 300 to 37 microm.

The effects of an exogenous enzyme preparation, the application method and feed type on ruminal fermentation and microbial protein synthesis were investigated using the rumen simulation technique (Rusitec). Steam-rolled barley grain and chopped alfalfa hay were sprayed with water (control, C), an enzyme preparation with a predominant xylanase activity (EF), or autoclaved enzyme (AEF) 24 h prior to feeding, or the enzyme was supplied in the buffer infused into the Rusitec (EI). Microbial N incorporation was measured using ( 15 NH 4 ) 2 SO 4 in the buffer. Spent feed bags were pummelled mechanically in buffer to segregate the feed particleassociated (FPA) and feed particle-bound (FPB) bacterial fractions. Enzymes applied to feed reduced neutral-detergent fibre content, and increased the concentration of reducing sugars in barley grain, but not alfalfa hay. Ruminal cellulolytic bacteria were more numerous with EF than with C. Disappearance of DM from barley grain was higher with EF than with C, but alfalfa was unaffected by EF. Treatment EF increased incorporation of 15 N into FPA and FPB fractions at 24 and 48 h. In contrast, AEF reduced the 24 h values, relative to C; AEF and C were similar at 48 h. Infused enzyme (EI) did not affect 15 N incorporation. Xylanase activity in effluent was increased by EF and EI, compared to C, but not by AEF. Xylanase activity in FPA was higher at 48 h than at 24 h with all treatments; it was higher with EF than C at 24 and 48 h, but was not altered by AEF or EI. Applying enzymes onto feeds before feeding was more effective than dosing directly into the artificial rumen for increasing ruminal fibrolytic activity.

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The mechanism by which enzyme additives improve feed digestion in ruminants is not fully understood. Direct hydrolysis of feed in the rumen is a potential mode of action, but the importance of this mode needs to be quantified because of the relatively low exogenous hydrolase activity added compared with the total activity present in the rumen. We examined the interactions between ruminal and exogenous enzymes on fiber degradation using a completely randomized experimental design, with an 11 (enzyme preparations and their combinations) x 5 (assay pH) arrangement of treatments. Ruminal enzymes were extracted from cattle receiving high fiber or high concentrate diets and exogenous enzymes were Trichoderma longibrachiatum preparations containing different proportions of xylanase and cellulase activities. Ruminal and exogenous enzyme preparations and their combinations were tested for the ability to degrade soluble cellulose, xylan, and corn silage over a range of pH from 4.5 to 6.5 at 39 degrees C. T. longibrachiatum enzymes acted synergistically with enzymes from mixed rumen microorganisms in degrading soluble cellulose, xylan, and corn silage. Hydrolysis increased by up to 35, 100, and 40% for soluble cellulose, xylan, and corn silage, respectively, and was most evident at a pH range between 5.0 and 6.0. The synergistic effect between ruminal and exogenous enzymes increases the hydrolytic potential within the rumen environment and is likely a significant mechanism by which enzyme additives improve feed digestion.