Abstract: The effect of the treatment with acetic acid in 4 different concentrations: 0, 1.25 and 2.5% (Dry Matter) in Agave blue tequilana Weber leafes 24 h after harvesting, were tested in situ rummen digestion of dry matter, Neutral Detergent Fibre (NDF) and Acid Detergent Fibre (ADF) in a rummen cannulated Holstain Frisian. Incubation times for in situ procedures were 72, 96 and 120 h. In situ rates of dry matter desapearence were similar (p>0.05) and NDF. Nevertheless, there were found significative diferences (p<0.05) for ADF between treatments at 96 and 120 h, where concentrations of 0 and 1.25% acetic acid showed better rates of digestibility (NDF and ADF) in comparision with 2.5% acetic acid treatment. At 120 h of incubation, treatment with 1.25% treatment had the best results followed by the control.