Comparison of dry matter and neutral detergent fibre degradation of fibrous feedstuffs as determined with in situ and in vitro gravimetric procedures
Introduction
Current feed evaluation systems focus on dynamic aspects of ruminal degradation of dietary constituents (Jarrige, 1989, Sniffen et al., 1992, AFRC, 1993, NRC, 2001). Fibrous feed are the main components of ruminant diets, especially with pasture based systems. In ruminants, variation in fibrous feed digestibility is mainly due to differences in concentration of cell wall carbohydrates (often analyzed as neutral detergent fibre, NDF), and their degradation. The amount of NDF degraded would depend on the relationship between the rate of degradation and the rate of passage of the NDF, and it is influenced by intrinsic characteristics of fibrous feed (Mertens, 1993). It is known that fibre degradation determine physical rumen fill, which is a main factor in ruminant feed intake regulation (Van Soest, 1994).
The nylon or dacron bag technique (IS), is an in situ procedure used to evaluate extent and rate of degradation of nutrients in the rumen, and it is considered a reference technique in current feed evaluation systems (AFRC, 1993, Sniffen et al., 1992, Tamminga and Williams, 1998, NRC, 2001). This procedure is time-consuming and labor intensive, and at least three surgically modified animals are required to obtain valid data.
The in vitro gravimetric procedure using DaisyII (IV DaisyII, ANKOM Corp., Fairtport, NY, USA) appears to provide highly repeatable disappearance data to estimate both the extent, and rate of degradation of fibrous feed (Mould and Nordheim, 1998, Vogel et al., 1999, Julier et al., 1999, Ceballos et al., 2008). In comparison with the nylon bag technique, this procedure provides considerable savings in terms of fistulated animals, feed, and labor input, as well as in time required to conduct an experiment.
The nylon bag technique and the IV DaisyII procedures were compared by Ceballos et al. (2008) to estimate kinetics of degradation of dry matter (DM) of three tropical grasses (Shorgum sp, Pennisetum purpureum, and Pennisetum violaceum). Bags with larger pore size were used in IS (pore size = 50 μm, R1020; ANKOM Co., Fairport, NY) than in IV DaisyII (pore size = 25 μm, F57; ANKOM Co., Fairport, NY). Authors concluded the techniques were not interchangeable to estimate degradation kinetics, but IV DaisyII predicted with accuracy DM disappearance at 96 h.
In this study, the objective was to compare the nylon bag technique with an in vitro gravimetric procedure to estimate DM and NDF degradation kinetics of a wide range of fibrous feedstuffs using bags with similar porosity in both procedures.
Section snippets
Feedstuffs
Three sets of fibrous feeds (cultivated pastures, high dry matter forages, and agro-industrial by-products) selected to represent a wide range of NDF concentration and composition, were evaluated. Cultivated pastures (n = 4) were white clover (Trifolium repens sp.), birdsfoot trefoil (Lotus corniculatus, va. San Gabriel), ryegrass (Lolium sp.), and oat (Avena sativa sp.); high dry matter forages (n = 2) were alfalfa hay, and barley straw, and agro-industrial by products (n = 2) were dried brewers’
Chemical composition
As expected, variability in NDF cell wall content (NDF), and composition (CELL, HEM, and lignin (sa)) was observed among feedstuffs (Table 1). The NDF content ranged from 272 to 824 g/kg DM, and from to 127 to 460, 82 to 427, and 25 to 93 g/kg DM, for CELL, HEM, and lignin (sa), respectively. The NDIN of brewers’ grains was 36 g/kg DM.
Comparison of in situ and in vitro disappearance
The plot of differences between mean values obtained by the IS and IV DaisyII procedures (DIFISIV) for each feedstuff and incubation time (y-axis), against their
Chemical composition
Chemical composition of pastures, dried forages, and agro-industrial by-products evaluated were consistent with data reported by NRC, 2000, NRC, 2001 and Preston (2009). An exception was the aNDF content of brewers’ grains, which was higher than reported in previously cited publications. The high content of NDIN may explain differences (NRC, 2001); removing this fraction (as CP) from aNDF resulted in a value (452 g/kg DM) within the range reported elsewhere (NRC, 2001, Preston, 2009).
Comparison of in situ and in vitro disappearance
Altman and
Conclusions
IV DaisyII underestimated DM and NDF disappearance values compared to IS, and the largest differences between procedures were observed at early incubations times. Both procedures ranked the fibrous feedstuffs similarly for EDDM. This suggests that if one is primarily interested in comparing degradation potential of feedstuffs, the IV DaisyII procedure appears to be a potentially useful tool; especially considering its advantages as a fast and simple technique.
Acknowledgement
This research was partially funded by a postgraduate scholarship of the Comisión Sectorial de Investigaciones Científicas, Universidad de la República, Udelar, Uruguay.
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