Differences in walking speed and milk yield were compared in dairy heifers and cows of 3 different breeds (Holstein, Montbeliarde, and Tarentaise) during 3 walking trials. Tarentaise cows walked faster than those of both other breeds. For walked distances of 5.6 and 3.2 km (trials 1 and 2, respectively) the mean walking speed of Tarentaises (1.71 and 1.43 m/s) was higher than for Montbeliardes (1.49 and 1.10 m/s) and Holstein (1.50 and 1.23 m/s). In trial 2, the Holstein and the Montbeliarde breeds both required more encouragement to move forward (P < 0.05) than the Tarentaise breed. In trial 3, milk production, milk composition and blood metabolites were evaluated following walked distances of 0, 6.4, 9.6 and 12.8 km. Milk yield and protein decreased (P < 0.01) in proportion to the distance traveled by 1.9 kg/d and -51 g/d, respectively, after 12.8 km. In contrast, milk fat, milk protein and blood-free fatty acids increased (P < 0.01) by 4.6 g/kg, 1.8 g/kg and 0.4 mmol/l, respectively, up to 12.8 km. Decreases in milk yield and protein were greater (P < 0.01) in Holstein cows than in the other 2 breeds. However, all cows regained their former level of milk yield within 3 d following the exercise. Five hours after walking, variation of glycemia was slight (P = 0.06) and the lactate level in the blood did not vary among walked distances. Only walked distances above 6.4 km brought about modifications in milk yield, milk composition and in blood-free fatty acids. These modifications were greater in Holstein cows than in the other 2 breeds.
