Effect of maturity on digestion kinetics of water-soluble and water-insoluble fractions of alfalfa and brome hay.

Abstract

Alfalfa and bromegrass, each harvested at five different stages of maturity, were separated into water-insoluble and -soluble fractions. The NDF concentrations ranged from 19 to 43% for alfalfa and from 42 to 58% for brome. The rates of digestion, by mixed ruminal microflora, of the unfractionated forage and of the water-insoluble and -soluble fractions were measured in vitro using pressure sensors to monitor gas production. Both forages showed the expected decline in fiber digestibility with increasing maturity. A dual-pool logistic model gave pool sizes, specific rates, and a single lag time for both the faster- and slower-digesting fractions. The main difference between alfalfa and brome was in the soluble pool. This pool produced approximately 40% of the total gas in alfalfa, 25% in brome. The specific digestion rates of the brome soluble pool were approximately 50% higher than those for alfalfa. Net VFA production showed a somewhat higher acetate: propionate ratio for brome (3.2) compared with alfalfa (2.2), but there was little change with increasing maturity within a given forage. Gas production curves for the unfractionated forage showed a 0 to 10% positive deviation from curves created by adding data from separate digestion of the insoluble and soluble forage fractions. Gas measurements offer a promising approach to the study of the water-soluble extracts of forages and the interaction of the soluble- and insoluble-fractions during fermentation.

<i>In vitro</i> gas production kinetics of whole citrus fruits

“…The fermentation rate of the fraction related to pectins (C 2 ) was correlated with the sugar content and the pH, while the fermentation rate of the fraction related to fibres (C 3 ) was also correlated to the NDF and ADF content. Moreover, the value for C 2 specific rate obtained by Stefanon et al (1996) for the insoluble fraction of lucerne (0.038 h -1 ) was comparable to the C 3 TLOG L (0.033 h -1 ) values obtained for the WCF. These results could indicate that it is likely possible to distinguish three fermentable fractions for the WCF in vitro incubated with rumen fluid, which were fermented at three different specific rates.…”

“…One way to test the validity of theses assignments is to examine mixtures of simple homogeneous substrates as reported by Schofield et al (1994), and to determine the biological meaning of the different fractions by analysing the correlation between the kinetic parameters and the chemical composition of the substrate. For this reason, as we will see below, the results obtained in the present work have been compared with those given by authors who tested individual components of the foods (Schofiel et al, 1994;Stefanon et al, 1996). The values for B 1 and C 1 EXP L parameters (184 ml and 0.19 h -1 , respectively) were consistent with those obtained by Getachew et al (2004) for beet pulp (B 1 =163.1 ml and C 1 =0.10 h -1 ), whose fibre characteristics are close to citrus fibre.…”

Composición química, contenido mineral y digestibilidad in vitro de raigrás (Lolium perenne) según intervalo de corte y época de crecimiento

“…Los componentes solubles en detergentes neutros (SDN) comprenden azúcares simples, y sus polímeros de cadena corta, sustancias pécticas y alimidones, una fracción no carbohidratada, que incluye proteínas, polifenoles solubles, cenizas solubles, ácidos orgánicos y lípidos. Los SDN son importantes en la etapa temprana de la fermentación del sustrato (forraje), pero menos significativos en etapas posteriores (41) . Los sustratos con alta degradabilidad verdadera pero, proporcionalmente a la cantidad de sustrato, con baja producción de gas, presentan mayor consumo de MS, mayor producción de masa microbiana, mayor eficiencia en la síntesis de proteína microbiana, menor producción de metano y menor producción de AGV (36,42) .…”

Fermentation kinetics of carbohydrate fractions of maize grains as determined by <i>in vitro</i> gas production curve subtraction technique

“…The criteria used to judge the fitness of a given model were the fit statistic (F-values, mean square of regression/mean square error) (Schofied et al, 1994;Stefanon et al, 1996). A larger F-value indicates a better fit of the gas data to the mathematical model (Chen et al, 1999).…”