An in vitro rumen-mimetic continuous cultivation system for evaluating the nutritional value of micropulverized roughage based on volatile fatty acid production

Abstract

In order to avoid ruminal acidosis, increasing the amount of energy supplied from roughage (high-cellulose diets) should be considered. The objective is to develop a novel in vitro procedure to evaluate the contribution of micropulverized roughage for which the nutritional value was increased. Ruminal bacteria collected from a Japanese shorthorn cow were continuously cultivated for over 60 days at pH 6.5 using artificial saliva and used to evaluate the nutritional value of 10 or 20 g of dried roughage. The digestion of roughage was monitored using a pH meter to detect the beginning and end of digestion, and the amounts of VFAs (i.e., acetic, propionic, and butyric acids) produced during the digestion were determined by HPLC. The nutritional value (mol-VFAs/kg-substrate; mean ± SE) of microcrystalline cellulose, Italian ryegrass silage, rice straw, alfalfa hay, and micropulverized Japanese cedar were 6.76 ± 0.25, 4.64 ± 0.10, 3.05 ± 0.20, 1.52 ± 0.09, and 0.88 ± 0.10 respectively. By micropulverizing rice straw to an average particle diameter of 20–50 μm, the value of this processed roughage was increased by 135% (4.11 ± 0.27). During cultivation, ruminal bacteria were observed to form biofilms on the surface of feed fragments. The micropulverized roughage became enveloped by these biofilms and was digested by the microbiota growing synergistically within. The digestible nutrients of 20g of roughage were completely digested by feed particleassociated bacteria within approximately 24 h. The microbiota constituted a cellulose metabolic pathway for the conversion of roughage to VFAs. The in vitro procedure measures the accessibility of cellulolytic bacteria to the cellulose of roughage and the amount of digestible cellulose contained in roughage. The procedure is suitable for evaluating the nutritional value of micropulverized roughage and will accelerate the development of it for use in animal feed. *Correspondence to: Hitosi Agematu, Akita National College of Technology, Department of Applied Chemistry, Akita, Japan, Tel: +81-18-847-6063; Fax: +81-18-847-6066; E-mail: agematu@akita-nct.ac.jp