Lipidomic, metabolomic and sperm functional characteristics analysis of bulls with different fertility rates and cryotolerance profiles

Abstract

Reproductive biotechniques applied to cattle livestock are increasingly present in the Brazilian herd, aiming to increase animals' reproductive and consequently productive rates. The use of these techniques, such as Artificial Insemination (AI), with estrus observation or at Fixed-Time (AIFT), and in vitro embryo production, depends fundamentally on sperm cryopreservation, which still presents challenges due to the reduced quality of post-thawing sperm. Moreover, they are strongly influenced by the male effect, and there are bulls with sperm characteristics within the recommended standards that have reduced fertility rates. The relationship between seminal quality and fertility is one of the fundamental points in the cattle production system, and this quality depends on the integrity and function of all structures of the sperm cell. Therefore, the present study applies the association of techniques in order to obtain a more comprehensive evaluation of sperm cell functional attributes and molecular profiles. The project is divided into two chapters, the first related to the fertility rate of bulls used in AIFT programs, while the second involves the analysis of samples with higher and lower susceptibility to the cryopreservation process. In both, seminal samples will be analyzed for functional characteristics (morphology, kinetics, plasma and acrossomal membrane integrity, mitochondrial activity, DNA integrity and oxidative status), and lipid and metabolic profile of the sperm cell. The results of the analysis performed in the first experiment of chapter 1 show that there are important differences in functional characteristics between the evaluated groups (high and low fertility, Angus and Nelore breeds). Among them, it is important to highlight the Angus bulls with low fertility group (Ab), which presented sperm kinetic parameters that may indicate a tendency to a possible early hyperactivation and acrosomal reaction. In this group it was also observed a greater mitochondrial activity associated with medium and low mitochondrial membrane potential, which may result in a higher production of Reactive Oxygen Species (ROS). The Ab group not only presented a higher concentration of ROS, but also an increased susceptibility to lipid peroxidation, as well as a higher percentage of sperm cells with larger and total defects. Differences in the functional profiles, such as those already observed in preliminary results, associated with the molecular analysis of semen samples of bulls with different fertility rates and different semen cryopreservation profiles, may lead to a better understanding of the mechanisms and cell pathways involved, allowing the development of more accurate methods for the identification of breeders with higher fertility rates and lower susceptibility to the semen cryopreservation process. (AU)