Relationship between sperm apoptosis and bull fertility: In vivo and in vitro studies

The objectives of this study were to confirm the relationship of apoptosis-associated membrane and nuclear changes in bull spermatozoa with field fertility, to predict the fertility of beef bulls used for natural breeding and to study the role of DNA-nicked spermatozoa in early embryonic development. In Experiment 1, the relationship between fertility and different sperm populations identified by the Annexin V/propidium iodide (PI) and terminal deoxynucleotidyl transferase mediated dUTP nick end labeling (TUNEL) assays was determined. Bull fertility was related to live (P<0.05) and necrotic (P<0.01) and DNA-nicked (P<0.001) spermatozoa. In Experiment 2, the percentage of DNA-nicked spermatozoa was determined in 15 beef bulls used for natural breeding and their fertility potential was determined using a regression model developed in Experiment 1.The predicted fertility deviation of beef bulls ranged from -7.3 to 2.4. In Experiment 3, the effect of DNA-nicked spermatozoa on in vitro cleavage and blastocyst rates was evaluated, using 30000 or 300000 spermatozoa per droplet. Cleavage rate was adversely affected (P<0.05) by DNA-nicked spermatozoa, regardless of sperm concentration. Blastocyst rate was lower (P<0.05) in high DNA-nicked spermatozoa at the lower sperm concentration. In conclusion, the incidence of DNA-nicked spermatozoa is a useful marker to predict a bull's fertility potential. DNA-nicked spermatozoa showed adverse effects on early embryonic development.