Bioclimatic interference in fertility in cows in the Amazon biome

The objective was to evaluate the correlation between environmental temperature-humidity index (THI), rectal temperature (RT), plasma cortisol concentration and pregnancy rate in embryo recipient cows in the Amazon biome. Embryo recipients (n=235) underwent estrus synchronization via simplification of the P36 protocol for Fixed-Time Embryo Transfer (TETF). On days zero (D0), eight (D8) and day 16 (D16), the rectal temperature of the recipient cows was measured, as well as the ambient temperature and relative humidity. On the 16th day after the start of the synchronization protocol (D16), each recipient received an embryo transferred after being diagnosed with a corpus luteum (CL) in one of the ovaries by ultrasonography (US) and, from each of them, a blood sample was collected by venipuncture of the coccygeal vein, in tubes with ethylenediaminetetraacetic acid (EDTA) as an anticoagulant to obtain blood plasma, where cortisol was measured by radioimmunoassay (RIA) in solid phase, using commercial kits. It was found that in the group of pregnant cows, the mean values of the parameters RT, plasma cortisol and THI (P < 0.05) were lower than those presented in the group of non-pregnant cows. Moreover, between the two groups there were positive and significant correlations between RT and THI (P < 0.05), as well as in relation to plasma cortisol parameters and THI (P < 0.05). It is concluded that it is possible to validate the use of RT and THI as an auxiliary tool for estimating plasma cortisol concentrations.