Fertility traits of recipient cows raised in the Amazon biome

Abstract

This study aimed to evaluate a correlation between environmental temperature-humidity index (THI), rectal temperature (RT) and plasmatic concentration of cortisol in pregnancy rates of recipient cows in the Amazon biome. Recipient cows (n = 235) were submitted to an estrus synchronization simplified P36 protocol for a Fixed-Time Embryo Transference (FTEF). Rectal temperature of recipient cows and ambient temperature, relative humidity (RH) and dry-bulb temperature ( °C) were recorded on day zero (D0), eight (D8) and 16 (D16) of the protocol. On D16, each recipient received an embryo after the confirmation of a corpus luteum. At this moment, a blood sample was collected and cortisol concentration was evaluated in the sample with radioimmunoassay. On D41 (D33 embryo), pregnancy diagnosis was assessed (PD). The yield rates of recipient cows and pregnancy after the protocol were 66.81% (151/226) and 35.76% (54/151), respectively. Cows that became pregnant presented lower means in RT, plasmatic cortisol and THI parameters (P < 0.05) in comparison to non-pregnant group. The percentage of pregnant cows at Day 41 was higher (P < 0.0001) for cows that had RT ≤ 39.1 °C in all the days analyzed (D0, D8 and D16). Likewise, cows that entered the chute area under a low THI (< 74) had better (P < 0.005) pregnancy rates when compared with cows that were at the chute under a higher THI. This was observed on the three days evaluated throughout the protocol. The correlation coefficient between cortisol, RT and THI was above 59%. In addition, cortisol was lower in the PG cows. In conclusion, THI, RT and cortisol level are directly related to pregnancy success. Furthermore, this study could validate the use of THI as an auxiliary tool to assess thermal comfort and stress, which may reflect in the pregnancy outcome of recipient cows in the Amazon biome.