Suzane Peres Campanholi, Fabio Morato Monteiro, Erika Aline Ribeiro Dias, Maria Eugênia Zerlotti Mercadante, Claudia Cristina Paro de Paz, José Antoni
Cryopreservation of bull semen is a common biotechnology procedure in cattle breeding. However, when the ejaculate is obtained by electroejaculation, wide variation is observed in the sperm/seminal plasma (SP) ratio that can affect the freezability of semen in this species. The removal of SP may improve the quality of frozen bull semen. The objective of this study was to evaluate the effect of SP removal from the ejaculate on the cryopreservation of semen from 38 Nellore bulls collected by electroejaculation. After collection, the ejaculate was divided into three aliquots: 1) control (N) diluted to a concentration of 60 x 106 spermatozoa/mL and frozen with SP; 2) centrifugation (C) at 600 X g for 10 min and the pellet resuspended and frozen at the same concentration as N; 3) filtration (F) through SpermFilter® and sperm recovered and frozen at the same concentration as N. After thawing, sperm kinetics, plasma and acrosome membrane integrity, mitochondrial membrane potential, oxidative stress and in vitro fertility were evaluated. Statistical analysis was performed using the SAS 9.2 package and differences were considered significant when P < 0.05. Higher average path velocity and straight-line velocity were observed in the groups submitted to SP removal compared to the control group (P < 0.01). In contrast, filtered samples exhibited higher beat cross frequency, straightness and linearity compared to the other groups. Plasma membrane integrity was reduced when SP was removed, but lower oxidative stress was observed in groups C and F (34.91 ± 2.95% and 31.63 ± 2.95%, respectively) compared to group N (57.39 ± 2.95%). However, the percentage of hatched blastocysts was similar in the N and F groups (21.22 ± 1.05% and 24.00 ± 1.05%, respectively) and higher when compared to group C (18.83 ± 1.05%). In conclusion, removal of SP by centrifugation for bull semen freezing reduced the rate of in vitroproduced embryos, while filtration of pre-frozen semen was found to be an efficient alternative in terms of semen freezability and in vitro production of bovine embryos.
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