The soluble antigens of Neospora caninum affect the integrity and vital characteristics of bovine sperm, compromising in vitro fertilization and embryonic development.

N. caninum is a parasite found worldwide that can be transmitted through contaminated food or from an infected mother to her offspring during pregnancy. This protozoan is a major threat to the healthy development of livestock, causing significant economic losses due to abortion, fetal death, and nervous system diseases in cattle. The effect of contact with cell debris from N. caninum on semen quality is not known, although infected animals shed DNA, protein, and even infective forms of the parasite. This study aimed to evaluate the effects of soluble N. caninum antigens on bovine semen quality in vitro. The spermatozoa were subjected to serial double dilutions of N. caninum antigens at high, medium, and low doses (8, 4, 2 µg/ml) using TALP-Sperm and TALP-Fert medium. Results indicated that soluble N. caninum antigens can affect the velocity and angle of sperm trajectory, both in the presence and absence of flow, within a simulated fallopian tube environment. In addition, several techniques, including Toulidine Blue, Propidium Iodide, transmission electron microscopy, Pisum sativum Lectins, and mitochondrial labeling with MitoTracker, have been used to demonstrate that treatment with soluble N. caninum antigens can affect the integrity of sperm chromatin and cause severe damage to the sperm membrane and acrosome. Finally, the spermatozoa were treated with antigens before in vitro embryo production, which impacted the cleavage and blastocyst rates. After being infected with N. caninum, bulls may experience changes in their sperm, which can compromise fertilization process and embryonic development, affecting their fertility.