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The effects of diet composition and chemical form of Se on intestinal flow, absorption, and retention of Se were determined in sheep by the balance technique and by disappearance of Se from sites along the gastrointestinal tract with reference to dual-phase digesta markers. Six sheep with ruminal and duodenal cannulas were used in a crossover design with a split-plot arrangement of the Se isotope treatments. Sheep were fed a forage (alfalfa hay)-based (.37 mg Se/kg) or concentrate (barley)-based (.27 mg Se/kg) diet at 90% of ad libitum intake. Selenium stable isotopes (enriched [77Se]yeast, enriched [82Se]selenite) and fluid (Co-EDTA) and particulate (Cr-mordanted fiber) markers were administered simultaneously into the rumen four times daily for 7 d, and total collections of feces and urine were made every 24 h for these and the following 7 d. A larger proportion (51 to 61%) of the Se tracers flowing to the duodenum was associated with the particulate fraction, mainly as bacteria-associated Se, than with the fluid fraction. The [82Se]selenite was more available (P < .05) for absorption and retention than [77Se]yeast, indicating that inorganic chemical forms of Se are as available to the ruminant as organic forms of Se commonly found in feedstuffs. Selenium absorption and retention were greater (P < .05) in sheep receiving the concentrate-based diet than in sheep receiving the forage-based diet. Thus, the availability of Se from inorganic and organic sources in sheep seems to be influenced by diet composition.

, 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 -...

The influence of temperature (125 or 145 °C) and duration (10, 20 or 30 min) of heating, or chemical treatment (acetic (AA) or formic (FA) acid) on in vitro insoluble DM (IDM) and insoluble CP (ICP) and 12 h in situ ruminal disappearance of canola meal was examined. Ruminal disappearances of dry matter (DDM) and crude protein (CPD) were expressed as apparent (ADMD and ACPD), insoluble (IDMD and ICPD) and degradable (DDMD and DCPD). Insoluble DM content was reduced by AA and FA (P < 0.01), while ICP was reduced by FA (P < 0.01). Acid treatment had no effect on in situ DMD or CPD. Heating increased IDM and ICP (P < 0.01). Duration of heating increased ICP at 145 °C (P < 0.01). Apparent DMD was influenced by temperature (P < 0.01) but not duration of heating. Mean ADMD and ACPD for control, 125 and 145 °C were 57.8, 59.6; 36.8, 24.1; and 27.4%, 13.7%, respectively, (P < 0.01). Insoluble and degradable DMD and CPD were reduced by heating (P < 0.01) but the influence of temperature or duration of heating was not consistent. The results indicate that heating at 125 or 145 °C for 10 min or more will reduce in situ DM and CP disappearance of canola meal, and increase the post-ruminal supply of DM and CP. Key words: Canola meal, in vitro solubility, in situ digestibility, heat and acid treatment

. 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...