The aim of this experiment was to determine the effect of polyethylene glycol (PEG) on in vitro gas production (GP) kinetics of Prosopis cineraria leaves at different growth stages. The contents of total phenol (TPH), total tannin (TT) and condensed tannin (CT) were determined. Effects on in vitro organic matter digestibility (OMD), metabolisable energy (ME) and effective dry matter digestibility were assessed by PEG tannin bioassay. No significant differences (P>0.05) were observed for TPH content; however, the stage of flowering had the highest (P0.05) were observed between the growth stage and PEG addition for in vitro GP and its parameters. Addition of PEG increased (P<0.05) GP, OMD and ME in all stages. In conclusion, adding PEG to P. cineraria leaves can improve their nutritive value and could be considered as a potential feed for ruminants
