Mastitis is a frequent and painful disease in dairy cows. However, pain detection and alleviation in mastitic cows has been overlooked. The objectives of this study were to measure behavioral changes in dairy cows with clinical mastitis and to investigate the effect of intramammary infusion of an antibiotic on lying behavior and behavior during milking. In experiment 1, 42 lactating cows were used: 14 mastitic cows and 28 control cows. Mastitic and control cows were subjected to an evaluation of pain responses on d 1 (mastitis detection day), and 2, 3, and 7 d after the last antibiotic treatment (d 10+). The antibiotic treatment was administered to mastitic cows twice a day, starting on d 1, for at least 3 consecutive days. Behavioral changes were evaluated by measuring lying behavior, reactivity during milking (stepping, lifting, and kicking), weight distribution, and hock-to-hock distance. Overall, mastitic cows spent less time lying down on d 2 compared with control cows. The percentage of time lying on the mastitic quarter side did not differ significantly between mastitic and control cows. No differences were observed between control and mastitic cows on the number of steps per 24 h on each day. Restless behavior during milking did not differ between treatments. Restless behaviors differed significantly within mastitic cows between days. Frequency of kicks per minute was higher on d 1 compared with d 2, frequency of lifts was higher on d 1 and 2 compared with d 10+, and frequency of steps was higher on d 2 compared with d 10+. The variability of weight that mastitic cows applied to the leg on the mastitic quarter side was higher on d 1 than on d 10+. For control cows, the variability in weight applied to the homologous leg of the mastitic quarter side leg was higher on d 1 compared with d 2 and 3. The hock-to-hock distance did not differ between treatments. Mild clinical mastitis might not cause sufficient pain to observe marked changes in behaviors. However, cows showed differences in lying time and reactivity during milking and slight differences in the laterality of lying. To further develop methodologies for assessing pain in mastitic cows, it is worth applying the methodologies used in this study to cows with moderate to severe mastitis, followed by their validation using analgesic treatment, to ensure that any change is a pain-specific behavior rather than a simple reflex. In experiment 2, no effect of intramammary infusion of the antibiotic was observed on lying behavior or behavior during milking. Cows with mild clinical mastitis present behavioral changes in lying behavior and at milking time, which could be associated with discomfort.
