Sources of error with in vitro digestibility assay of pasture feeds

Abstract

A series of experiments was undertaken to determine population statistics for in vitro organic matter digestibility (in vitro OMD) data and to examine the effects of basal diet, donor animal and precollection fasting interval on the activity and specificity of rumen fluid inoculum. The experiments utilized wether sheep, a diverse set of pasture grass and legume feeds prominent in the Australian subtropics and the Tilley and Terry in vitro digestibility procedure running under the operating pressure of a practising feeds evaluation laboratory.The standard errors of in vitro OMD estimates for within and between batch runs were ±0-88 X 10"^ and 0-62 x 10"^, respectively. These error terms were used to develop protocols to accept, reject or scale raw in vitro OMD data. Differences between donor animals in the activity of rumen fluid were highly significant. Extending the precollection fasting interval beyond 16 h was associated with a substantial decline in inoculum activity.An in vitro-in vivo calibration relationship based on fifteen test feeds and using lucerne (Medicago sativa) as basal diet was described by the linear model y=l-3 x-0-195±4-9x 10"r =0-79 (y = in vivo OMD, x = />i vitro OMD). Despite large effects of basal diet on both the absolute values and relative ranking of test feeds, neither the RSD nor r values were improved using alternative diets to lucerne chaff.The results highlight the need to formally standardize the analytical and biological components of the in vitro digestibility procedure to safeguard the integrity of data.

Ruminal Degradability and Summative Models Evaluation for Total Digestible Nutrients Prediction of Some Forages and Byproducts in Goats

“…The method of Tilley and Terry [40] as well as that of IVTDMD of Van Soest et al [24] that replaces the 48 hours of pepsin incubation with extraction on neutral-detergent solution has a high correlation with the in vivo DM digestibility under maintenance conditions [27, 41]. …”

Post-weaning growth of cattle in northern New South Wales. 2. Growth pathways of steers

“…Botanical composition, total herbage mass and green herbage mass were estimated using the 'double sampling' method of Morley et al (1964) and the BOTANAL program (Hargreaves and Kerr 1978). In vitro digestibility was estimated by the method of Ayres (1991). Nitrogen content was determined by the Kjeldahl procedure (AOAC 1980).…”

Post-weaning growth of cattle in northern New South Wales. 1. Grazing value of temperate perennial pasture grazed by cattle

“…Forage samples were obtained in conjunction with the pasture observations by taking a pluck sample (using power clippers to ground level) adjacent to each quadrat site and compositing 15 subsamples for each transect. Nutritive value assay was undertaken on whole shoots, green and senesced fractions; in vitro digestibility (% OM basis) was determined by a 2-step procedure comprising 48 h incubation in rumen fluid-artificial saliva followed by 48 h incubation in pepsin solution as described by Ayres (1991); nitrogen content (N, g N/kg DM) was determined using the Kjeldahl procedure (AOAC 1980) using a Kjeltec Auto 1030 (Tecador AB, Sweden); organic matter (OM, %) was determined by ashing at 580°C for 16 h in a muffle furnace.…”