An experiment using 16 cows (ranging from 11 to 127 days since the cessation of milk production) investigated how varying propionic acid concentration in rumen fluid influenced preference for chaff flavoured with either anise or vanilla. After an initial flavour preference test, cows were allocated among 4 treatments: 0, 5, 10, or 15% of daily maintenance ME requirements supplied by an intraruminal infusion of propionic acid. Cows received an infusion on alternate days in combination with a specific chaff flavour. After 10 days, each cow was offered both flavours simultaneously for 20 min and preference for the flavour associated with the infusion was calculated as the cows’ final preference for the infusion flavour (% of total DM intake) minus the initial preference for that same flavour. Concentration of propionic acid in ruminal fluid ranged between 10 and 50 mmol/L and was significantly correlated with treatment (100r ² = 92.1). Preference for the flavour associated with elevated rumen fluid propionic acid was related to condition score (P = 0.057, 100r ² = 23.4), liveweight (P = 0.042, 100r ² = 26.3), and number of dry days prior to the experiment (P = 0.016, 100r ² = 34.6). Lighter cows generally preferred the infusion flavour, and heavy cows, the alternative flavour, indicating that cows can discriminate between feeds based on rumen fluid propionic acid concentration, but preference is influenced by physiological state.