No abstract

M. 2004. Effect of feed carbohydrates with contrasting properties on rumen fermentation and methane release in vitro. Can. J. Anim. Sci. 84: 265-276. The RUSITEC system was used to test eight diets where the supplements differed in their main carbohydrate source. The forage-to-supplement ratio was 1:1. The eight feeds characterizing the supplements by specific carbohydrates were oat hulls (modeling lignified fiber), soybean hulls (non-lignified fiber), apple pulp (pectin), sugar beet pulp (hemicelluloses and pectin), guar gum (galactomannan), Jerusalem artichoke tubers (fructan), molasses (sucrose), and wheat (starch). Supplements were isoenergetic and iso-nitrogenous. The dietary carbohydrate fractions were analyzed in detail with a combination of enzymatic and chemical methods. The methane release (mmol g -1 degraded organic matter) increased in the order of diets characterized by oat hulls (0.92), guar gum (0.99), wheat (1.04), soybean hulls (1.13), apple pulp (1.15), Jerusalem artichoke (1.21), sugar beet pulp (1.24), and molasses (1.37). According to multiple regression analysis, diets with high sugar content enhanced methane release while methane was low with high dietary lignin content. Regressions also showed that different fibrous carbohydrates had only a minor effect on methane release, probably due to lignification of the fiber. The present results suggest that equations for the estimation of methane emission of ruminants should consider dietary carbohydrate composition and lignin content. Les huit aliments modifiant le supplément par leur source de glucides étaient la balle d'avoine (modélisation de la cellulose lignifiée), la pellicule de soja (cellulose non lignifiée), la pulpe de pomme (pectine), la pulpe de betterave sucrière (hémicelluloses et pectine), la gomme de guar (galactomannane), le topinambour (fructane), la mélasse (sucrose) et le blé (amidon). Les suppléments contenaient la même quantité d'azote et d'énergie. Les auteurs ont analysé soigneusement la fraction de glucides alimentaires par des méthodes chimiques et enzymatiques. Le volume de méthane libéré (mmol par gramme de matière organique dégradée) augmente dans l'ordre suivant : balle d'avoine (0,92), gomme de guar (0,99), blé (1,04), pellicule de soja (1,13), pulpe de pomme (1,15), topinambour (1,21), pulpe de betterave sucrière (1,24) et mélasse (1,37). Selon l'analyse par régression multiple, les rations à forte teneur en sucre accroissent les dégagements de méthane, qui sont plus faibles avec les régimes riches en lignine. Les régressions montrent aussi que les divers hydrates de carbone fibreux n'ont qu'une incidence minime sur la libération de méthane, sans doute à cause de la lignification de la cellulose. Les résultats donnent à penser que les équations servant à estimer les dégagements de méthane par les ruminants devraient tenir compte de la composition des hydrates de carbone et de la concentration de lignine dans la ration.

Hemicelluloses, cellulose, and lignin contents of contrasting feeds, with emphasis on concentrate ingredients and complete concentrates, were analyzed using the Van Soest detergent procedure (analyzing neutral detergent fiber, acid detergent fiber, and acid detergent lignin) and the enzymatic-chemical procedure (analyzing cellulose, soluble and insoluble noncellulosic polysaccharides, and Klason lignin). Also, feces from cows fed concentrates differing in carbohydrate composition were analyzed by the 2 procedures. The correlation between acid detergent lignin and Klason lignin was significant, but not as close as the one between individual structural polysaccharides measured with the 2 procedures. The correlation between the results of the 2 procedures was highly significant for apparent cellulose digestibility, as were the correlations between digestibilities of hemicelluloses with total as well as with insoluble noncellulosic polysaccharides. The relationship between dietary lignin content and fiber digestibility was weak. The exclusion of a group of cows fed a concentrate with apple pulp, however, improved the respective correlations. Klason lignin correlated more closely with the measured fiber digestibility than acid detergent lignin. The study showed that results of the detergent method were comparable to those of the enzymatic-chemical method with cellulose, hemicelluloses, and their digestibilities. However, acid detergent lignin was much lower than Klason lignin. When the carbohydrate composition of concentrate varied widely, lignin was not suitable for the prediction of fiber digestibility.

The small intestinal digestibility of microbial amino acids and the apparent re-absorption of endogenous amino acids were estimated in three ruminal, duodenal and ileal fistulated lactating dairy cows. The cows were assigned to a 3 x 3 Latin square and fed diets low in amino acids, composed of straw, starch, molasses and urea. The treatments were three straw to concentrate ratios. The digestibilities and re-absorptions were estimated from duodenal and ileal flows of amino acids from feed, microbial and endogenous sources. The duodenal distribution of amino acids between different origins was determined by the difference method and by the amino acid profile method. The ileal distribution was estimated by a simple method where the feed fraction was estimated by the mobile bag method, the endogenous fraction as the water soluble fraction and the microbial fraction as the rest. In ileal samples, 8.0 +/- 1.1, 52.2 +/- 2.9 and 39.8 +/- 2.6% of total amino acid nitrogen (AAN) were of feed, microbial and endogenous origin, respectively, compared with 5.1 +/- 0.9, 61.6 +/- 6.6 and 32.7 +/- 6.9% in duodenal samples. The small intestinal digestibility of microbial AAN was estimated to be 75.1 +/- 1.8% and the apparent re-absorption of endogenous AAN to be 62.3 +/- 11.1%.

No abstract