Effects of Incubation Time and Sodium Sulfite upon in-vitro Digestibility Estimates and Sample Filtering Time

Abstract

We conducted 2 experiments to quantify the effects of incubation time, filtering method, forage type, and associated interactions on the precision and accuracy of in-vitro digestibility as estimates of in-vivo digestibility. Experiment I used 10 incubation times and alfalfa (Medicago sativa L.), kleingrass (Panicum coloratum L.), prairie grass, and wheat straw (Triticum aestivum L.) hays to determine whether a single incubation time should be employed to estimate digestibility of a variety of forages. Additionally, 2 second stage neutral detergent extraction methods were evaluated to determine sodium sulfite effect on fiber recovery and filter time. An interaction existed between incubation time and in-vitro estimates of digestibility. The use of sodium sulfite increased (P<0.05) digestibility estimates (1.3 units) across all hays and decreased filtering times by as much as 9.5 min/sample. Experiment II utilized 3 hays (alfalfa, kleingrass, and wheat straw), 4 incubation times and 4 neutral detergent extraction methods in an effort to isolate where the changes in neutral detergent fiber (NDF) estimates due to sodium sulfite occurred and if a method could be developed to maximize filtering speed without compromising the accuracy of digestibility estimates. Use of sodium sulfite in the rinse water did not affect apparent NDF recovery and decreased filtering time by approximately 10 min. when compared to no sulfite additions. Results of this study confirm previous observations that a single incubation period should not be used to estimate in-vivo digestibility. Addition of sodium sulfite to the rinse water provides a viable means to decrease sample analysis time without jeopardizing the accuracy of digestible NDF estimates.