Physiological, endocrine and molecular responses to protocols for artificial insemination stimulated with chorionic gonadotropins

Abstract

In recent years, several changes have been observed in reproductive physiology of dairy cows, affecting conception rates. These changes are apparently related to high milk production, the result of intense feed intake, genetic selection and management techniques for milk production. Given the direct relationship between the increase in milk production and decreased fertility, management alternatives are needed to increase fertility indexes. One alternative is the development of fixed-time artificial insemination (FTAI) protocols using exogenous hormones, since endogenous steroid hormones in high producing dairy cows are metabolized in a high proportion because of the high liver blood flow. This study will involve several experiments that, at the end, may develop a FTAI protocol that ensures high rates of synchronization of ovulation, as well as appropriate oocyte and embryo quality in high-producing dairy cows. In Experiments 1, 2 and 3 we will evaluate whether supplementation with hCG or hCG in FTAI protocols can increase circulating proestrus estradiol, the size of the dominant follicle and thereby increase the volume of the CL and progesterone at diestrus. In Experiment 4, we will evaluate whether stimulation with gonadotropins is able to change the amount and size of CL cells and mitochondria. Moreover, it will be assessed whether these hormones can alter the expression of genes related to steroidogenesis, angiogenesis, and luteolysis. The perspective of this study is to promote substantial increase in knowledge of the factors involved in the success or failure of FTAI protocols, and increase the knowledge about the reproductive physiology of dairy cows managed under intensive and semi-intensive systems. (AU)