[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.

, W. 2000. Enhancing pasture productivity with alfalfa: A review. Can. J. Plant Sci. 80: 513-519. Alfalfa has been recognized for its superior yield and quality in seeded pastures. However, when grazing immature alfalfa there is a risk of animal losses due to frothy bloat in some ruminant livestock. Inclusion of at least 50% grass in the pasture mixture is commonly recommended to reduce the risk of bloat. Two decades of plant breeding have resulted in the release of AC Grazeland, an alfalfa cultivar that reduces the incidence of bloat. Other bloat control agents such as pluronic detergents and ionophores can also be of value. Development of grazing-tolerant alfalfa varieties is solving some of the problems associated with lack of persistence of alfalfa in mixed stands; however, they are not bloat-safe. Animal productivity commonly increases when alfalfa is included in pasture mixtures. Improvements in cattle rate of gain are observed when alfalfa contributes as little as 35% to the sward. Grazing management is the principal method for controlling pasture yield and quality as well as animal performance and bloat incidence. When grazing management is used to optimize pasture production and nutrient intake, yearling steers can gain as much as 1.5 kg head -1 d -1 and liveweight production ranging from 107 kg ha -1 (on dryland) to 1946 kg ha -1 (under irrigation) can be expected. Limiting utilization of alfalfa-based pasture to ≤70% may be more important for maximizing gain per head than managing herbage quality. La luzerne est reconnue pour son rendement éléve, tant en quantité qu'en qualité, dans les pâturages de semis. Toutefois quand on fait pâturer de la luzerne trop jeune, on court le risque de pertes d'animaux dues au météorisme chez certaines espèces de ruminants, c'est pourquoi on conseille généralement d'inclure au moins 50 % de graminées dans les mélanges à pâturage. Deux décennies d'amélioration génétique ont abouti à la mise au commerce de AC Grazeland, un cultivar de luzerne moins météorisant. Des substances antimétéorisme comme les détergents pluroniques et les ionophores, peuvent avoir une certaine efficacité. La sélection de variétés de luzerne tolérantes à la pâture règle quelques-uns des problèmes liés au manque de longévité de la luzerne en peuplement mixte, mais elle n'apporte aucune solution au problème du météorisme. La productivité animale augmente généralement lorsque la luzerne est incluse dans les associations à pâturage. Une proportion d'aussi peu que 35 % de luzerne dans la prairie provoque des améliorations du taux de gain des bestiaux. La conduite du pâturage demeure le principal moyen de manipuler le rendement et la qualité de l'herbe, de même que les performances zootechniques et les risques de météorisme. Lorsque la conduite du pâturage est utilisée pour optimiser la production d'herbe et l'absorption d' éléments nutritifs, des bouvillons d'un an peuvent prendre jusqu'à 1,5 kg par jour et par animal avec une production en vif allant de 107 kg ha -1 en culture sèche et à 1 946 kg ha -...

. 1997. Effect of grazing system and stocking rate on the productivity, botanical composition and soil surface characteristics of alfalfa-grass pastures. Can J. Anim. Sci. 77: 669-676. A 4-yr experiment was conducted (1991 to 1994) near Brandon, MB, to determine the effects of grazing system (continuous and rotational) and stocking rate [light (1.1 steers ha -1 ); heavy (2.2 steers ha -1 )] on the productivity, botanical composition and soil surface characteristics of an alfalfa (Medicago sativa L.; approximately 70%), meadow bromegrass (Bromus biebersteinii Roem & Schult.; 25%) and Russian wild ryegrass [Psathyrostachys juncea (Fisch.) Nevski; 5%] pasture. Grazing season length was shorter (P < 0.05) for cattle in continuously compared with rotationally stocked pastures in 1991, while in 1993 and 1994 it was shortest (P < 0.05) in heavily stocked continuously grazed pastures. Carrying capacity (steer days ha -1 ) was greater (P < 0.05) in heavily stocked rotationally grazed pastures compared with other treatments in 1991, 1993 and 1994 . In 1992, it was greater (P < 0.05) in heavy than light stocking rate treatments for both rotationally and continuously grazed pastures. Cattle usually gained more (P < 0.05) per day (kg d -1 ) and during the season (kg hd -1 ) at light than at heavy stocking rates, while total liveweight production (kg ha -1 ) was greater (P < 0.05) at heavy than at light stocking rates. Forage production and disappearance did not differ (P > 0.05) within grazing systems and stocking rates from 1991 to 1993, but in 1994, production and disappearance were greater (P < 0.05) at heavy than at light stocking rates. Mean seasonal herbage mass available and carry-over were greater (P < 0.05) in lightly stocked pastures than heavily stocked pastures from 1991 to 1994. After the first year of grazing, the proportion of alfalfa increased (P < 0.05), while grasses declined (P < 0.05) within all grazing treatments. In subsequent years, a trend was observed, where alfalfa declined and grasses increased in all pastures, except those stocked heavily and grazed continuously, which by 1994 had the greatest (P < 0.05) percentage of alfalfa. As years progressed, increases (P < 0.05) in basal cover concurrent with declines in bare ground were recorded on all grazing treatments, while litter cover often did not differ (P > 0.05) within either grazing system or stocking rate, except in 1992, when basal cover was lowest (P < 0.05), while litter cover was greatest (P < 0.05) on lightly stocked continuously grazed pastures compared with other treatments. Stocking rates were a key factor to optimizing individual animal performance and/or gain per hectare on alfalfa grass pastures, however differences in the effect of continuous and rotational stocking on pasture productivity were minimal. . L'objet était d'établir les effets du système pastoral (pâturage continu ou tournant), du taux de chargement (léger 1,1 ou lourd 2,2 bouvillons par hectare) sur la productivité, sur la composition floristique et sur le recouvrement...

. 1997. Effect of grazing system, stocking rate and season of use on diet quality and herbage availability of alfalfa-grass pastures. Can. J. Anim. Sci. 77: 111-118. A 3-yr field experiment was conducted (1991)(1992)(1993) near Brandon, MB to determine the effects of continuous and rotational stocking, both at heavy (2.2 steers ha -1 ) and light (1.1 steers ha -1 ) stocking rates, and of season of use on nutritive value and sward characteristics of an alfalfa-grass pasture [approximately 70% alfalfa (Medicago sativa L.), 25% meadow bromegrass (Bromus biebersteinii Roem & Schult.) and 5% Russian wildrye (Psathyrostachys juncea (Fisch.) Nevski)]. Grazed herbage quality and herbage mass were determined concurrently on continuous and rotational stocking treatments several times each year, as animals entered and exited the 5th of 10 rotationally stocked paddocks. Grazing system and stocking rate did not affect (P > 0.05) dietary CP and IVDOM, except once (P < 0.05) for IVDOM in 1993. Both ADF and NDF were sometimes greater (P < 0.05) on heavy compared to light stocking rate treatments, but did not differ (P > 0.05) between grazing systems. As the 1991 season advanced, there was a decline (P < 0.05) in CP, but IVDOM, ADF and NDF remained unchanged (P > 0.05). In 1992, seasonal declines (P < 0.05) in CP and IVDOM and increases (P < 0.05) in ADF and NDF were observed for all treatments. In 1993, in vitro digestible organic matter and CP decreased (P < 0.05) on most treatments, while ADF and NDF increased (P < 0.05). Herbage mass tended (P < 0.10) to be lower when heavy stocking rates were used in all years, but was not affected (P > 0.05) by grazing system. Significant relationships (P < 0.001) among IVDOM, ADF and NDF were found. Neither grazing system nor stocking rate appeared to affect the quality of herbage ingested by cattle grazing alfalfa-grass pastures. La qualité de l'herbe et la quantité produite étaient déterminées simultanément dans les deux types de pâturage, plusieurs fois par année, à l'entrée des bêtes dans le cinquième de dix parquets conduits en pâturage tournant ainsi qu'à leur sortie. Le système pastoral et le taux de chargement n'avaient pas d'effet (P > 0,05) sur la teneur en PB de l'herbage ni sur la teneur en matière organiques digestible de la matière organique (MODIV), sauf une fois (P < 0,05) pour la MODIV en 1993. Les teneurs en ADF et en NDF étaient parfois plus élevées (P < 0,05) en régime de chargement lourd que sous chargement léger mais on n'observait pas de différence (P > 0,05) entre les deux systèmes de pâturage. A mesure que la saison de paissance 1991 avançait, il y avait une chute (P < 0,05) de la teneur en PB mais on ne notait pas de changement (P > 0,05) en ce qui touche MODIV, ADF et NDF. En 1992, on observait de même une chute (P < 0,05) des teneurs en PB au fil de la saison, mais également des accroissements (P < 0,05) des teneurs en ADF et en NDF dans tous les traitements. En 1993, les teneurs en MODIV et en PB diminuaient (P < 0,05) dans la plupart des traitements, tandis q...