Animal Feed Science and Technology 138 (2007) 318–330 Available online at www.sciencedirect.com In vitro fermentation and microbial protein synthesis of some browse tree leaves with or without addition of polyethylene glycol A.Z.M. Salem a,∗ , P.H. Robinson b , M.M. El-Adawy a , A.A. Hassan c a Department of Animal Production, Faculty of Agriculture (El-Shatby), Alexandria University, Alexandria, Egypt b Department of Animal Science, University of California, Davis, CA 95616-8521, USA c Animal Production Research Institute, Ministry of Agriculture, Dokki, Gizza, Egypt Received 10 January 2006; received in revised form 15 November 2006; accepted 30 November 2006 Abstract To assess the nutritional value of the leaf of four browse trees (Chorisia speciosa, Cassia fistula, Schinus molle, Eucalyptus camaldulensis), that are grown in semi-arid regions of northern Egypt, this study evaluated effects of incorporation of polyethylene glycol (PEG) on their nutritional value. In vitro gas production after 24 h of fermentation (IVGP 24 ), volatile fatty acids (VFA), ammonia concentrations and microbial protein synthesis were determined, and in vitro organic matter digestibility (IVOMD) and metabolizable energy (ME) were estimated. The IVGP 24 , VFA and ammonia N concentrations varied (P<0.001) among browse species, with the IVGP 24 and VFA highest (P<0.001) for C. speciosa, lowest (P<0.001) for E. camaldulensis, and intermediate for C. fistula and S. molle. C. speciosa had the highest (P<0.05) IVOMD, microbial protein synthesis, IVOMD and ME, while these measurements were lowest in E. camaldulensis and intermediate in the other browse leaves. In general, C. speciosa has Abbreviations: ADFom, acid detergent fiber; AF, aqueous fraction; ALKA, alkaloids; CP, crude protein; CT, condensed tannins; DM, dry matter; EO, essential oils; IVGP, in vitro gas production; IVOMD, in vitro OM digestibility; lignin(sa), acid detergent lignin; ME, metabolizable energy; NDFom, neutral detergent fiber; OM, organic matter; PEG, polyethylene glycol; SAP, saponins; TEP, total extractable phenolics; VFA, volatile fatty acids ∗ Corresponding author. Tel.: +20 3 5292727; fax: +20 3 5922780. E-mail address: asalem70@yahoo.com (A.Z.M. Salem). 0377-8401/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.anifeedsci.2006.11.026