Bioclimatic Influence on the Pregnancy Rate in Embryo-Recipient Cows in the Amazonian Biome

Abstract

The objective of the research was to evaluate the effect of the climate, through the parameters of rectal temperature (RT), temperature and humidity index (THI), and plasma cortisol concentration, on the physiological responses of embryo-recipient cows in the Amazonian biome. For the conduction of the experiment in which 11 rural properties participated, 235 crossbred cows were used as embryo recipients. The embryos were obtained by means of the in vitro production technique (PIV). The recipients were divided into batches and submitted based on the simplification of the P36 protocol for fixed-time embryo transfer (FTET). To the day of embryo transfer, blood samples were collected by venipuncture of the coccygeal vein in tubes with anticoagulant. Plasma cortisol dosages were done by solid-phase radioimmunoassay (RIA) technique using commercial kits. The rectal temperature of each of the recipients submitted to the protocol was verified using a digital clinical thermometer, and the ambient temperature and the relative humidity of the air were evaluated in this moment, both with the aid of own digital equipment. Statistical analysis of the parameters evaluated was Pearson's correlation and Student's t-test at a significance level of 5%. In the analysis of variance, it was observed that there was a significant difference in plasma cortisol and THI among the groups, where lower mean values were found in the GP group. The Amazonian climate is an inducer of thermal stress, which can cause abnormalities in the estral cycle and changes in the synthesis of sex hormones and embryonic development and, consequently, negatively affect the pregnancy rate in embryo-recipient cows, even in races more adapted to the tropics, as demonstrated by the RT, THI, and plasma cortisol parameters.