The relationship between sperm quality parameters and stallion fertility

Abstract

There are stallions with apparently good sperm quality that achieve low pregnancy rates when their semen is used for artificial insemination (AI). Thus, additional methods of evaluating sperm quality that result in better methods of predicting stallion fertility, are essential. Semen samples were obtained in April-June from 8 stallions, 4 trotters and 4 warmblood sport horses, which were sampled Monday, Wednesday and Friday each week. From each stallion, 1-4 samples were obtained, and evaluated after cold storage for 24 hours. The samples were evaluated for kinematic variables using CASA, and for membrane integrity, mitochondrial membrane potential (MMP), production of reactive oxygen species, acrosome integrity and chromatin integrity using flow cytometry. Relationships with fertility, calculated as number of pregnant mares/number of inseminated mares for samples used for artificial insemination after transport in cold storage, were evaluated by linear regression, following log-transformation of variables found not to be normally distributed. The following sperm variables were found to have a positive relationship with fertility: Straightness (r2=0.86, p= 0.0009), Viable with High mitosoxred/Low MMP (r2=0.70, p= 0.01), Viable non acrosome reacted (r2=0.68, p= 0.01), Viable by calceinviolet (r2=0.67, p= 0.01), Viable non H2O2-producing (r2=0.66, p= 0.01), Viable with High mitosoxred/High MMP (r2=0.65, p= 0.02), Viable non superoxide-producing (r2=0.60, p= 0.02), Linearity (r2=0.56, p= 0.03). The only variable found to have a negative relationship with fertility was Amplitude of lateral head displacement (r2=0.63, p= 0.02). The other 26 measured variables did not show a significant relationship with fertility. The results of the study shows that both kinematic variables as well as flow cytometric analysis can be valuable for relating fertility with sperm quality in vitro. The flow cytometry results indicate that analysis of the production of different reactive oxygen species can be valuable when predicting stallion fertility. Acknowledgments: Special thanks to Menhammar, Västerbo, Markebäck and Stockholm Seminstation for providing stallion semen. This work was supported by funding from FORMAS (2018-01083; awarded to AJ). The work was also supported by the Swedish University of Agricultural Sciences via the Cells for Life Platform.