Estresse térmico em ovinos: zoneamento bioclimático com estimativa da redução do consumo alimentar no estado do maranhão e avaliação da termografia infravermelha ocular

Abstract

Global warming poses increasing challenges to livestock farming, making heat stress one of the main limiting factors to productivity and animal welfare. The objective of this research was to investigate climate risk and adaptation strategies in sheep production and welfare in Maranhão using two complementary approaches. In Chapter I, a literature review on the topic is presented. In Chapter II, the bioclimatic zoning of Maranhão was carried out via monthly calculation of the Temperature and Humidity Index (THI) and the Black Globe Temperature and Humidity Index (BGHI), using meteorological data from the TerraClimate platform (2014–2024).

Geostatistical modeling via ordinary kriging was used to generate thematic maps of the spatio- temporal distribution of heat stress risk (THI and BGHI) and estimate the associated reduction

in feed intake (RFI). The results showed high susceptibility to annual heat stress throughout the state of Maranhão, with intensification in the second half of the year, especially between August and November. The North and East mesoregions concentrated the highest values of ITU and ITGU, while the South mesoregion presented the highest relative bioclimatic suitability. The RCA estimate exceeded 4 kg animal−1 d−1 in the Central and East mesoregions in October, evidencing severe productive impacts. In Chapter III, the efficiency of ocular infrared thermography as a non-invasive method for detecting thermal stress was evaluated. Six crossbred sheep (Santa Inês × Dorper) were subjected to three controlled temperatures (26, 29, and 34 °C) in a climatic chamber, with measurement of heart rate (HR), rectal temperature (RT), in addition to productive parameters and thermographic temperatures of the regions of interest (ROI): ocular, pupillary, and lacrimal sac. Exposure to 34 °C caused significant increases in RR and RT, as thermoregulatory responses. There were reductions in weight gain (21%) and dry matter intake (38%) and an increase in water intake (39%). The thermographic temperatures of the ROIs responded progressively to the thermal increase. Eye temperature stood out as the most accurate estimate and consistent with the RT, demonstrating that it is a non-invasive, practical method for the monitoring of heat stress in sheep.