Three ethanol extracts, chamomile (CHA), clove (CLO) and tarragon (TAR), were tested at five doses (0, 250, 500, 750 and 1000 μL/L) to determine their effects on in vitro organic matter digestibility (IVOMD), metabolizable energy (ME), net energy of lactation (NEL), short-chain fatty acids (SCFA), microbial mass (MM) and rumen fermentation kinetics of a 40:60 forage: concentrate diet using in vitro gas production. These three extracts had significant effects on gas production kinetics. CHA (at 500 μL/L dose) and CLO (at 1000 μL/L dose) decreased (P<0.05) potential gas production. The initial gas production rate constants (c) was increased (P<0.05). However, CHA, CLO and TAR ethanol decreased (P<0.05) later gas production rate constants (d). Lag time (h) was decreased (P<0.05) due to addition of CHA and TAR ethanol (at 750 μL/L dose), and CLO (at 500 and 1000 μL/L doses). TAR and CLO ethanol did not affect fermentation rate (h-1), but CHA at 1000 μL/L increased it. The TAR and CLO ethanol did not affect IVOMD, ME, NEL, SCFA and microbial mass. However, organic matter digestibility, ME, NEL, SCFA and microbial mass were increased by addition of CHA ethanol at 750 and 1000 μL/L doses. Results suggest that CHA, CLO and TAR ethanol extracts at appropriate doses may have potential to improve the rumen fermentation kinet-ics and nutritive value of ruminant diets due to secondary metabolites contents.
