PSI-35 Comparison of in situ techniques to evaluate the recovery of indigestible components and the accuracy of digestibility estimates

Abstract

Abstract Our objective was to evaluate the effects of bag type (BT) and incubation length (IL) when using in situ incubations for determination of indigestible components. Indigestible components play an integral role as an internal marker for rumen kinetics and digestibility estimations, as well as providing parameter estimates for nutritional models. However, the accuracy of internal markers is dependent upon the incubation technique utilized, with BT and IL acting as sources of error. A 3 × 2 factorial design was used to investigate the effect of BT (F57, F58, and Dracon) and IL (288 and 576 h) on indigestible dry matter (iDM) and neutral detergent fiber (iNDF) residues, as well as estimated DM and NDF digestibilities. Feed and fecal samples were obtained from two animals from an independent trial that collected total fecal production over 4 days. All bags contained a sample size-to-surface area ratio of 20 mg/cm2 and were ruminally incubated within three rumen-cannulated steers (229.5 ± 10 kg). For iDM and iNDF, feed residues demonstrated a BT × IL interaction (P < 0.01). Fecal residues for iDM and iNDF had BT and IL effects (P < 0.01) with the Dracon BT and 576 h IL having the least residues. Digestibility estimates for DM and NDF were influenced by BT × IL (P < 0.01) with the accuracy of estimates demonstrating a BT × IL interaction (P < 0.01) in which F57 at 576 h had the greatest accuracy. Resultant fecal recovery estimates for DM and NDF excreted exhibited a BT × IL interaction (P < 0.01), with F57 at 576 h better representing the excretion profiles. Based upon our analysis, utilizing the F57 BT at 576 h IL combination provides more accurate estimates relative to all other combinations used within the current study.