Habituation of dairy heifers to milking routine-Effects on human avoidance distance, behavior, and cardiac activity during milking

The onset of lactation marks a significant turning point in a heifer's life, and prior experience with the milking routine could have positive effects on animal welfare and productivity. The objectives of this multifarm (n = 5) study were to investigate (1) whether prelactation training sessions affected behavior during milking, cardiac activity, human avoidance distance, and milk yield, and (2) whether these responses would be modified by the heifer's initial level of fear of humans. Trained heifers (TH, n = 30) experienced the routine in the milking parlor on at least 10 d prepartum, whereas untrained heifers (UH, n = 29) entered the parlor for the first time after calving. Behavior and cardiac activity were recorded on d 1 and 7 after calving, and an avoidance test was carried out on the day of integration into the dairy herd as well as on d 1, 7, and 28 postpartum. Each animal's initial level of fear of humans was classified as high or low based on the first human avoidance distance measured toward an unknown person. Results showed that TH showed less stepping and kicking during the udder preparation phase in the parlor and UH had higher probabilities to put their ears flat on the head, clamp their tail between the hind legs, and have their eyes wide open throughout the different phases in the milking parlor. Heart rate decreased from d 1 to 7, increased from before to during and to after milking and was slightly elevated in TH compared with UH. Milk yield did not differ between TH and UH. Human avoidance distance was not influenced by training, but distance decreased in heifers with a high initial level of fear of humans across repetitions of the test, whereas heifers with a low initial level of fear of humans had generally short avoidance distances. However, initial level of fear of humans neither determined behavior and heart rate during milking nor milk yield of TH and UH. The results indicate that the training regimen applied in the present study habituated heifers, to some extent, to the milking routine.