A Standard Procedure for In Vitro Digestion Using Rumen Fermenters: A Collaborative Study

SIMPLE SUMMARY: Knowledge of the nutritive value of feeds is essential to feed animals with adequate diets and to optimize production with minimal environmental impact. In vitro digestibility might be an important source of information for nutritionists, because it is a cheap and fast way to assess information on feed digestion for ruminants, notably when the main objective is to compare feeds or diets. A rumen fermenter is a relatively new type of equipment which improves the operational capacity of in vitro procedures. However, the lack of standardized procedures for in vitro trials using rumen fermenters may compromise the reliability of information obtained, mainly due to the high variability among laboratories. Hence, we proposed and evaluated a standard method for in vitro digestion using rumen fermenters, through a collaborative study involving seven feed analysis laboratories. On average, the method showed adequate performance, where the random variation among laboratories was lower than the random variation within laboratories (i.e., error variation). Considering that in vitro digestibility is an analytical entity that is defined by the method itself, the proposed method was considered reproducible. Our results highlighted that, if the method is followed exactly, its results present adequate levels of repeatability and reproducibility. ABSTRACT: Our objective was to propose and evaluate a standard procedure for the evaluation of in vitro dry matter digestibility for ruminant feeds, using artificial fermenters. A collaborative study was performed with seven feed analysis laboratories and four feeds (Tifton 85 hay, corn silage, soybean hulls, and soybean meal). Two types of artificial fermenters were evaluated (DaisyII Ankom and TE-150 Tecnal). Each laboratory received 80 sealed filter bags with samples (20 per feed), eight blank filter bags, a plastic bag with buffer solution reagents, and instructions describing how to conduct a 48 h in vitro assay using an artificial fermenter and how to collect bovine ruminal inoculum. On average, the contribution of laboratory effect to the total random variance was 24%, being less than the contribution of equipment (42%) and error (34%). The repeatability ranged from 3.34 to 5.79%, across feeds. The reproducibility ranged from 5.93 to 8.94% across feeds, which implied Horwitz ratios ranging from 2.94 to 4.10. Due to the specific characteristics of the analytical entity evaluated here, which is defined by the method itself, the proposed method was considered reproducible. The results highlighted that, if the method is followed exactly, its results are precise and present adequate levels of repeatability and reproducibility.