PSXIII-22 - Heat stress in north central Mexico and time of exposure to it, measured by the Environmental Temperature Index.

The Temperature Humidity Index (THI) is the most used to identify the risk of heat stress for dairy cattle, which is based on the environmental temperature (ºC) and humidity (%), and of which they are currently considered 68 points as the threshold for high producing dairy cows. In the Comarca Lagunera, located in north central Mexico, 21% of the Mexican dairy production is generated annually, despite its environmental conditions characterized by temperatures up to 41.5 ° C in the summer, low relative humidity and high solar radiation. The objective was to identify the average number of days in which a THI ≥68 is reached per month in each season of the year with 1, 8 and 16 h of exposure in dairy farms of the region, for which, the information recorded every 10 min was analyzed daily in five farms for 6 years (2015-2020), using the DiGiTH ™ application (DiGiTH Technologies, Mexico) and through ANOVA (proc GLM; SAS Inst. Inc., Cary, NC, USA), to identify differences seasonal for this variable. The attached table shows that spring and summer were the seasons in which the highest number of average days per month were recorded, and winter in which the fewest days were recorded. Regarding the hours of exposure, it is observed that spring and summer are very similar in 1 and 8 hours of exposure, while for autumn and winter a clearer decrease is observed according to the hours of exposure for these seasons. These results indicate a very marked seasonal variability and in terms of the hours of exposure, which should be considered in order to adopt the measures to reduce the negative effects for the dairy cattle of the region.