Avaliação dos efeitos in vitro dos antígenos solúveis de Neospora caninum e Toxoplasma gondii na qualidade do sêmen bovino

Abstract

Toxoplasma gondii is an obligate intracellular parasite that affects humans and several vertebrate hosts; this protozoan has a complex life cycle in which cats and other members of the Felidae family participate as definitive hosts. Infections by this parasite are prevalent in humans and animals worldwide; both humans and other species are infected transplacentally during pregnancy, or after birth, by ingesting tissue cysts from undercooked meat, food, and beverages contaminated with oocysts, or oocysts from the environment accidentally. This disease is currently considered an important cause of reproductive losses in sheep, goats, cows, and pigs raised on farms. Neospora caninum is a parasite distributed worldwide; this protozoan has a cycle like that of T. gondii in which dogs participate as definitive hosts. This protozoan can be transmitted through the ingestion of contaminated food or transplacentally during pregnancy. Infection by this parasite is an important factor that challenges the healthy development of livestock, causing great economic losses worldwide due to abortion, fetal death, and diseases of the nervous system in cattle. It is known that infected animals eliminate DNA, protein and even infective forms of N. caninum and T. gondii in semen, however, it is not known exactly what the effect of contact with cellular debris of this parasite on semen quality is. This study aimed to evaluate the in vitro effects of soluble antigens of N. caninum and T. gondii on the quality of bovine semen. Sperm were treated with N. caninum antigens in double serial dilution classified as high, medium and low doses (8, 4, 2 µg/ml) in "TALP-SPERM and TALP-FERT" medium. After treatments, sperm were evaluated for motility, chromatin alterations, integrity of the cytoplasmic membrane and acrosome and mitochondrial activity. The results showed that soluble antigens of T. gondii and N. caninum affect the speed and mean angle of sperm trajectory in the absence and presence of flow in a simulated environment of the bovine fallopian tube. It was demonstrated that treatment with antigens of both parasites causes changes in sperm chromatin integrity, severe damage to the sperm membrane and acrosome, as well as decreased mitochondrial activity. Finally, the fertilization rate was evaluated using the mean dose of antigens as treatment in sperm to be used in in vitro embryo production (IVEP). In the case of treatment with soluble antigens of N. caninum, the results showed that the cleavage and blastocyst rates were affected, and with treatment with soluble antigens of T. gondii, only the blastocyst rate was affected. Considering all the results, it is concluded that bulls after being infected by these parasites may present changes in their sperm, which may compromise fertilization and embryonic development, affecting their fertility.