The objective of the present study was to evaluate the productive performance and grazing behavior of 25 primiparous and 44 multiparous Holstein cows in a pasture-based automatic milking system (AMS) while experiencing heat stress (defined as a temperature-humidity index [THI] ≥ 68). Productive traits were analyzed according to the THI from days 0, -1, -2, and -3 in relation to the milking day, and grazing behaviors (expressed as the percentage of daily observation time) were related to the average THI only on the day of observation. Milk yield was not associated with the THI on day 0, but a significant linear relationship was found with the THI on the three previous days, decreasing approximately 0.18 kg (primiparous) and 0.40 kg (multiparous) per THI unit increment. In contrast, for multiparous cows only, the milking frequency was positively associated with the THI on the day of evaluation but not on the previous days, increasing 0.01 milking/THI unit increments. Additionally, for each unit of THI increment, cows spent 0.14% more time standing, whereas they exhibited a decrease in grazing, lying, and ruminating behaviors time by 0.30%, 0.04%, and 0.70%, respectively, for both parities. In conclusion, milk loss was related to heat stress conditions from the previous days, but not milking frequency, which increased with the THI of the same milking day. Lower grazing, lying, and ruminating activities and greater standing behavior were observed due to heat stress.
Keywords: animal welfare; milking visits; pasture; summer.
In higher temperature conditions, dairy cows under pasture-based automatic milking systems may experience heat stress, affecting their health and productive performance. In the present study, the relationships between heat stress, measured by the temperature–humidity index (THI), productive traits, and grazing behaviors were evaluated. Cows exhibited an increase in milking frequency and their time standing, decreasing the time grazing, lying, and ruminating as the THI increased on the same day. Additionally, cows had decreased milk production when the THI increased in the previous days. Understanding how cows adjust their grazing behavior to handle changes in the environment allows for the development of management strategies designed to improve animal welfare.
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