[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....
. 1999. Effect of sainfoin on in vitro digestion of fresh alfalfa and bloat in steers. Can. J. Anim. Sci. 79: 203-212. The effects of sainfoin (Onobrychis viciifolia) on digestion of alfalfa (Medicago sativa) were investigated in vitro and in vivo. Fresh alfalfa and sainfoin were incubated in an artificial rumen (Rusitec) in ratios of 100:0, 75:25, 50:50, 25:75 and 0:100 (as-fed). Disappearances of dry matter and N from sainfoin were 77 and 65% of those from alfalfa, respectively. Protease and endoglucanase activities, NH 3 -N and methane production declined (P < 0.05) as sainfoin increased. Bacterial numbers and microbial outputs were unchanged (P > 0.05), but cells incorporated more 15 NH 3 N as sainfoin in the diet increased. Chopped leaves (100:0, 95:5 and 90:10 alfalfa:sainfoin) were incubated for 48 h with diluted ruminal fluid containing 0 or 50 mg polyethylene glycol, which binds tannins. Gas and volatile fatty acid productions were similar (P > 0.05) across treatments, but including 10% sainfoin (without polyethylene glycol) reduced (P < 0.05) NH 3 concentrations between 8 and 24 h. Sainfoin tannins reduced degradation of forage protein without affecting the digestibility of the nonprotein fraction. Alfalfa herbage was fed alone or with early-to full-bloom sainfoin herbage (at 10 or 20% of ad libitum alfalfa dry matter intake) or with sainfoin hay or pellets, to eight Jersey steers in crossover trials conducted over 4 yr. Including sainfoin in the diet reduced (P < 0.001) the incidence of bloat by 45 to 93% in 3 of 4 yr, irrespective of the form in which it was supplied. Co-feeding sainfoin can markedly reduce the incidence of bloat in ruminants consuming fresh alfalfa. De l'herbage de sainfoin et de luzerne étaient mis à incuber dans un rumen artificiel (Rusitec) dans les proportions, en l'état, de 100:0, 75:25, 50:50, 25:75 et 0:100. La digestibilité apparente de la m.s. et du N du sainfoin correspondait, respectivement, à 77 % et 65 % des valeurs obtenues pour la luzerne. Les activités de la protéase et de l'endoglucanase de même que la production de N ammoniacal et de méthane diminuaient (P < 0,05) à mesure qu'augmentait la proportion de sainfoin. Par ailleurs, les numérations bactériennes et les apports microbiens restaient inchangés (P > 0,05), mais les cellules microbiennes incorporaient plus de 15 NH 3 -N. Des feuilles hachées (100:0, 95:0 et 90:10 luzerne:sainfoin) étaient mises à incuber pendant 48 h en présence de liquide ruminal dilué contenant 0 ou 50 mg de polyéthylène glycol (PEG), substance qui a pour effet de lier les tanins. Les productions de gaz et d'AGL étaient du même ordre (P > 0,05) d'un traitement à l'autre, mais l'inclusion de 10 % de sainfoin, sans PEG avait pour effet de réduire (P < 0,05) les concentrations de NH 3 entre 8 et 24 h. Les tanins du sainfoin diminuaient la dégradation des protéines du fourrage, sans toutefois altérer la digestibilité de la fraction non protéique. Nous avons aussi servi pendant 4 ans à 8 bouvillons de la luzerne, seule ou combinée, soit à du sain...
Improvements in feedlot management practices and the use of various feed additives have reduced, but not eliminated, the occurrence of bloat in feedlot cattle. Feedlot bloat reduces the profitability of production by compromising animal performance and more directly by causing fatalities. In feedlots, bloat is associated with the ingestion of large amounts of rapidly fermented cereal grain and destabilization of the microbial populations of the rumen. An abundance of rapidly fermented carbohydrate allows acid-tolerant bacteria (e.g., Streptococcus bovis and Lactobacillus spp.) to proliferate and produce excessive quantities of fermentation acids. As a result, ruminal pH becomes exceedingly low, and this impairs rumen motility. Further, the excessive production of mucopolysaccharide or "slime" increases the viscosity of ruminal fluid and stabilizes the foam implicated in frothy feedlot bloat. Although protocols have been developed to treat feedlot bloat, the most profitable approach is to use management strategies to reduce its likelihood. Amount of roughage, grain processing techniques, selection of cereal grain (e.g., corn, barley, and wheat), dietary adaptation periods, and various additives (e.g., ionophores) can influence the occurrence of bloat in feedlot cattle. Successful management of these factors depends on a thorough understanding of the behavioral, dietary, and microbial events that precipitate bloat in feedlot cattle.
. 1999. Effect of exogenous enzymes on digestibility of barley silage and growth performance of feedlot cattle. Can. J. Anim. Sci. 79: 353-360. Barley silage was sprayed with water or with a 2:1 combination of commercial cellulase and xylanase preparations, or the enzymes were introduced directly into the rumen, in a digestibility study (replicated incomplete 3 × 3 Latin square) using 10 sheep. Apparent digestibilities of dry matter (DM) and neutral detergent fibre (NDF) were lower (P < 0.05) when enzymes were dosed intraruminally than when applied to silage, but enzymes by either route did not affect (P > 0.05) intake of DM, organic matter or digestible organic matter, or digestibilities of DM or NDF, ruminal pH, xylanase activity, endoglucanase activity or ruminal cellulolytic bacterial populations. Treating the silage portion of an 82.5% barley silage backgrounding diet with the enzyme mix at 0, 1.25, 3.5 or 5.0 L t -1 DM tended to linearly increase (P = 0.08) final weights of steers (n = 24). Average daily gain tended to be (P = 0.06) and feed intake and feed efficiency were (P = 0.04 and P = 0.03, respectively) quadratically related to these enzyme concentrations from days 0 to 56, but not overall (days 0 to 120). In contrast, treatment of both portions (forage and concentrate) of a 70% barley-ryegrass silage finishing diet at 3.5 L t -1 DM increased (P < 0.01) the average daily gain of finishing feedlot cattle by 10%. Carcass weights and traits were not affected (P > 0.1) by enzyme supplementation. In this study, treating the total mixed ration improved feedlot cattle performance more than treating the silage component alone. Les coefficients de digestibilité apparente de m.s. et de FDN étaient plus bas (P < 0,05) lorsque les enzymes étaient administrées directement dans le rumen que par vaporisation sur l'ensilage, mais quelle que soit la voie d'administration utilisée, les enzymes n'avaient pas d'effet (P > 0,05) sur l'ingestion de matière sèche (m.s.) et de matière organique totale ou digestible, ni sur la digestibilité de m.s. ou de FDN, sur le pH ruminal, sur l'activité de la xylanase ou de l'endoglucanase, ni enfin sur les populations de bactéries cellulolytiques. Le traitement de la portion ensilage (82,5 %) d'un aliment de semi-finition avec la combinaison enzymatique, à raison de 0, 1,25, 3,5 ou 5,0 L t -1 m.s., produisait un accroissement plus ou moins linéaire (P = 0,08) du poids des bouvillons (n = 24) en fin d'engraissement. L'ingéré alimentaire et l'indice de conversion (respectivement P = 0,04 et P = 0,03) et, à un degré moins net, le GMQ, présentaient une relation quadratique avec les concentrations enzymatiques de 0 à 56 j, mais pas pour la durée totale de l'expérience (0 à 120 j). En revanche, le traitement des deux portions, ensilage et concentré, d'un aliment de finition contenant 70 % d'ensilage orge-raygrass, à raison de 3,5 L t -1 m.s. produisait une augmentation de 10 % (P < 0,01) du GMQ des bovins en phase de finition. Le supplément enzymatique n'avait par ailleurs pas d'effet (P >...
The objective was to determine the effects of a recombinant fusion protein anti-GnRH vaccine on testicular development, feedlot performance, and carcass quality of beef bulls. Crossbred beef bulls (n = 58, average weight 306 kg, 9 mo of age), were randomly allocated to two groups and received either an anti-GnRH vaccine (GnRH) or placebo (Control) by intramuscular injection on d 0, 56, and 112. There were group effects (P < 0.01; as a percentage of Control) on testicular weight (53%), daily sperm production (40%), and epididymal sperm reserves (16%). There were group x time interactions (P < 0.0001) for scrotal circumference and serum testosterone concentrations; at slaughter, bulls in the GnRH group had a smaller (P < 0.05) scrotal circumference (28.3 vs 33.9 cm) and lower (P < 0.05) serum testosterone concentrations (2.2 vs 8.6 ng/mL) than those in the Control group. Average daily gain, feed intake, and feed efficiency were not different between treatments during the backgrounding phase (d 0 to 84). During the finishing phase (d 98 to 182), ADG was greater (P < 0.05) for bulls in the Control group (1.69 vs 1.42 kg/d), as was carcass weight (6.9%; P < 0.01). However, GnRH bulls had numerically better feed efficiency (6.12 vs 7.08 kg DMI/kg gain; P < 0.23) and shear force values for ribeye that were 16% lower (P < 0.14) than Control bulls, warranting further investigation. Vaccinating bulls against GnRH suppressed testicular function, with growth and carcass characteristics similar to that expected with steers.
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