The effect of underfeeding and ref eeding on digestion was studied in Bos taurus and Bos indicus cows. Eight nonlactating cows, four B. taurus and four B. indicus (live weight 156 kg and 207 kg respectively) were first given a forage-based diet at a level above energy maintenance requirements for 4 weeks (3·65 and 4·66 kg dry matter (DM) per day respectively for B. taurus and B. indicus). They were then restricted at a low level of intake for 2 months (1·83 and 2·33 kg DM per day respectively for B. taurus and B. indicus) and finally refed at the first level for 2 months. Digestion measurements were made before the underfeeding period, at 3 and 8 weeks of underfeeding and at 3 and 8 weeks ofref eeding. Organic matter apparent digestibility decreased with underfeeding and increased with refeeding (0·637, 0·591, 0·652, 0·692 and 0·669 in B. taurus and 0·674, 0·560, 0·580, 0·698 and 0·692 in B. indicus, respectively 1 week before, 3 and 8 weeks after underfeeding, and 3 and 8 weeks after refeeding). This lower apparent digestibility at low level of intake was not expected either by ruminal particle retention time, which increased when intake decreased, or by measurements ofmicrobial activity: DM degradability measured in situ and ruminal particle size did not vary with level of intake. An effect of the length of underfeeding and refeeding was seen: the apparent digestibility tended to increase after several weeks of undernutrition and was higher after refeeding than before underfeeding. No difference was observed between the two genotypes.