PSVIII-13 Are the heat stress days increasing in central northern Mexico?

Abstract

Abstract The Lagunera region, located in north central Mexico (24° 01′-26° 48 ‘LN and 101° 52′-101° 52′ 104° 40′ LO), produce the 21% of the national Mexican cow’s milk despite its climatic conditions (temperatures that fluctuate between 12.7 °C in January and 28.5 °C in June, with extremes of -5 °C and 41.5 °C, in addition to high solar radiation). The Temperature Humidity Index (THI) is the most useful indicator to define if there are heat stress conditions. To identify whether the days in which THI ≥68 (considering the threshold for signs of heat stress to appear in high-producing lactating cows) are increasingly reached at least one hour a day, the information of this indicator was recorded every 10 min daily, from 5 cow farms for 6 years (2015–2020), using the DiGiTH™ application (DiGiTH Technologies, Mexico), and regressions were run to identify if there is a relationship between the years of study and the THI levels. At any level of THI (≥68), there is a tendency to increase the number of days (10.05 d per year; R2 0.37); Disaggregating the data by THI level, this trend is also observed for levels 68 to 71 and 72 to 76 THI, registering an increase of 11.33 d (R2 0.45) and 9.03 d per year (R2 0.45) respectively. At the 77 - 79 THI level there is no trend, while at the ≥80 THI level, a decrease of 5.66 d per year was registered (R2 0.79). The results suggest that in this region, the days of heat stress are increasing, except for the level ≥80 THI, which indicates that palliative measures for heat stress should be intensified, and it is necessary to identify the reason for the decrease in heat stress days at the most dangerous level for livestock.