Animal Feed Science and Technology 123–124 (2005) 107–118 Effect of preservation on fermentative activity of rumen fluid inoculum for in vitro gas production techniques Gonzalo Herv´ as ∗ , Pilar Frutos, F. Javier Gir´ aldez, Manuel J. Mora, Bego˜ na Fern´ andez, ´ Angel R. Mantec ´ on Estaci´ on Agr´ ıcola Experimental, CSIC, Apartado 788, 24080-Le ´ on, Spain Abstract Use of preserved rumen fluid (RF) as microbial inoculum for in vitro gas production techniques (IVGPT) would be of practical importance when access to ruminally cannulated animals is limited. This experiment was designed to study effects of RF preservation on its subsequent fermentative activity. Four substrates being: alfalfa hay (AH), barley straw NDF (BS-NDF), cellulose and starch were incubated with rumen inoculum obtained from 12 rumen cannulated grazing sheep, of which six (G) received no supplement and the other 6 (G+S) received 500 g/day of a concentrate. Sub-samples of RF were processed without delay (i.e., control) or stored at approximately 0 ◦ C in a chest with crushed ice for 3, 6 and 24 h (treatments 3, 6 and 24 h, respectively) or at -18 ◦ C for 24 h in a freezer (treatment 24 F). An IVGPT was used to determine the rate and extent of gas production and DM disappearance. Average fermentation rate (AFR) and extent of degradation in the rumen (ED) were estimated. Incubations with inoculum derived from supplemented sheep (G+S) resulted in faster rates of gas production (with differences, as proportionate increases, of 0.77 for the barley straw NDF; P<0.01), lower lag times (e.g., 13.2 versus 4.0 h for the starch; P<0.05), and higher ED values (e.g., 229 versus 331 g/kg for the barley straw NDF or 173 versus 409 g/kg for the cellulose; P<0.05). Storing RF in ice for 3 or 6 h had no effect on any fermentation parameter. Treatment 24 h did not affect IVGPT parameters when starch and cellulose were fermented, but estimates of rates and ED were lower (P<0.05) with BS-NDF and AH. Fermentative activity of rumen inoculum was, in general, Abbreviations: ADF, acid detergent fibre; AFR, average fermentation rate; AH, alfalfa hay; BS-NDF, barley straw NDF; C, cellulose; CP, crude protein; DM, dry matter; DMD, dry matter disappearance; ED, extent of degradation in the rumen; IVGPT, in vitro gas production technique; NDF, neutral-detergent fibre; OM, organic matter; RF, rumen fluid; S, starch ∗ Corresponding author. Tel.: +34 987 317 156; fax: +34 987 317 161. E-mail address: hervas@eae.csic.es (G. Herv´ as). 0377-8401/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.anifeedsci.2005.05.004