Monitoring digestibility of forages for herbivores: a new application for an old approach

Abstract

Ruminant populations are often limited by how well individuals are able to acquire nutrients for growth, maintenance, and reproduction. Nutrient supply to the animal is dictated by the concentration of nutrients in feeds and the efficiency of digesting those nutrients (i.e., digestibility). Many different methods have been used to measure digestibility of forages for wild herbivores, all of which rely on collecting rumen fluid from animals or incubation within animals. Animal-based methods can provide useful estimates, but the approach is limited by the expense of fistulated animals, wide variation in digestibility among animals, and contamination from endogenous and microbial sources that impairs the estimation of nutrient digestibility. We tested an in vitro method using a two-stage procedure using purified enzymes. The first stage, a 6 h acid-pepsin treatment, was followed by a combined 72 h amylase-cellulase or amylase-Viscozyme treatment. We then validated our estimates using in sacco and in vivo methods to digest samples of the same forages. In vitro estimates of dry matter (DM) digestibility were correlated with estimates of in sacco and in vivo DM digestibility (both P < 0.01). The in vitro procedure using Viscozyme (r 2 = 0.77) was more precise than the in vitro procedure using cellulase (r 2 = 0.59). Both procedures can be used to predict in sacco digestibility after correcting for the biases of each method. We used the in vitro method to measure digestibility of nitrogen (N; 0.07-0.95 g/g), which declined to zero as total N content declined below 0.03-0.06 g/g of DM. The in vitro method is well suited to monitoring forage quality over multiple years because it is reproducible, can be used with minimal investment by other laboratories without animal facilities, and can measure digestibility of individual nutrients such as N.Résumé : Les populations de ruminants sont souvent limitées par la capacité des individus à acquérir les éléments nutritifs nécessaires à leur croissance, leur maintien et leur reproduction. L'apport en éléments nutritifs d'un animal est dicté par les concentrations d'éléments nutritifs dans les aliments et l'efficacité de la digestion de ces éléments nutritifs (c.-à -d. la digestibilité). De nombreuses méthodes ont été utilisées pour mesurer la digestibilité de fourrages d'herbivores sauvages, qui reposent toutes sur le prélèvement de jus de panse d'animaux ou sur l'incubation dans des animaux. Si les méthodes basées sur des animaux peuvent fournir des estimations utiles, cette approche est limitée par l'utilisation d'animaux fistulés, la grande variabilité de la digestibilité entre animaux et la contamination par des sources endogènes et microbiennes qui entrave l'estimation de la digestibilité des éléments nutritifs. Nous avons testé une méthode in vitro consistant en une procédure en deux étapes faisant appel à des enzymes purifiées. La première étape, un traitement chlorhydropepsique d'une durée de 6 h, a été suivie par un traitement combiné à l'amylase-cellulase ou à l'amylase-...

The nitrogen window for arctic herbivores: plant phenology and protein gain of migratory caribou (Rangifer tarandus)

“…), which has been validated for caribou (Van Someren et al. ). Digestible N (g/100 g DM) was estimated as the difference between total N and the N retained in the residue from in vitro digestion.…”

“…These samples were analyzed for dry matter content (DM) and neutral detergent fiber (total plant cell walls), ADF, and acid lignin (Van Soest et al 1991;Barboza and Parker 2006). We measured digestibility (g digested/g whole) of dry matter by using an in vitro digestibility method with purified enzymes (DeGabriel et al 2008), which has been validated for caribou (Van Someren et al 2015). Digestible N (g/100 g DM) was estimated as the difference between total N and the N retained in the residue from in vitro digestion.…”

“…We used an in vitro method to estimate digestion of dry matter, which was validated for caribou (Van Someren et al. ). The method does not use microbial extracts that colonize the surface of the sample or reagents that contaminate the residues with N (Gustine et al.…”

“…We collected forages over three summers in the migratory range of the Central Arctic Herd in Alaska over three ecoregions from the Brooks Range mountains to the coast of the Arctic Ocean to test the hypothesis that N supply and energy supply vary with ecoregion and with time (i.e., year and day within year). We used an in vitro method to estimate digestion of dry matter, which was validated for caribou (Van Someren et al 2015). The method does not use microbial extracts that colonize the surface of the sample or reagents that contaminate the residues with N ( Gustine et al 2014).…”

Variation in δ15N and δ13C values of forages for Arctic caribou: effects of location, phenology and simulated digestion

“…The early‐season subset ( n = 175) were samples with the highest N content whereas the last sample collected at each location comprised the late‐season subset ( n = 157). Samples from the early‐ and late‐season subsets were analyzed for digestibility of C and N (g digested/g whole) by analyzing the nutrient content of undigested residues after in vitro digestion with purified enzymes by a method that had previously been validated for caribou …”