Resumen
This study characterized the environmental?climatic trends occurring in the largest dairy cattle intensive production cluster under arid land conditions in northern Mexico. The study was based on the Temperature Humidity Index (THI); it aimed to identify the number of days with THI values =68 as a bio-marker of heat stress (HS) and evaluate the possible HS effect upon the milk production of dairy cows. Climate data were obtained every 10 min in five farms across years (i.e., 2015?2020). THI was divided into four HS subclasses, 68?71, 72?76, 77?79, and =80, according to the circadian HS occurrence (i.e., 1, 4, 8, 12, 16, 20, 24 h), and analyzed across seasons?years. Thus, a total of 1,475,319 THI across different time-scale subclasses was analyzed. The observed results supported our working hypothesis in that yearling-average periods with more than 300 d, HS was confirmed. A yearly average of 31.2 d with THI = 80 with similar (p > 0.05) trends across dairy farms and a slight annual variation (p < 0.05) were also witnessed. Moreover, the highest days with THI levels =68 occurred in summer and autumn (p < 0.05), while the in the subclasses 68?71, 72?76, and 77?79, THI occurred in any hour-scale subclass (i.e., 1, 4, 8, and 12 h). Furthermore, a trend to observe THI-HS increases either among years or within an hour-scale basis were also observed. On average, HS engendered a reduction of up to 11.8% in milk production. These research outcomes highlight the need to identify and quantify the negative impacts that HS may generate at a productive and reproductive level in order to delineate mitigation strategies that may lessen the environmental impact upon the dairy cattle industry.