Influence of sperm post-thaw subpopulations of angus and nelore bulls on pregnancy rates by fixed-time artificial insemination.

BACKGROUND: The heterogeneity of ejaculate indicates that fertility is still variable among bulls and that more stringent evaluation methods are needed to identify the ejaculates suitable for AI. OBJECTIVE: To identify and characterize the sperm subpopulations (SP) in thawed semen doses of Nelore and Angus bulls and to evaluate the influence of these sperm subpopulations on pregnancy rate in cows submitted to fixed-time AI (FTAI). MATERIALS AND METHODS: A dose of post-thawed semen from each bull (n=18; consisting of Angus n = 9 and Nelore n = 9) was analyzed for: sperm kinetics; morphology and plasma membrane integrity; and the determination of the sperm subpopulations. Differences between the groups were estimated with the t-test considering a significance level of <5%. RESULTS: There was no influence between breeding bulls for sperm morphology, plasma membrane integrity, and pregnancy rate (P > 0.05). Regarding the kinetic parameters evaluated by the CASA system, Nelore had greater values, for cells with slow velocity (Angus: 16.4 %; Nelore: 21.7%; P = 0.028). In contrast, ANGUS bulls had more static cells (Angus: 27.2%; Nelore: 9.3%; P = 0.048). Based on CASA system data and clustering procedures, four sperm subpopulations were statistically established. In Angus bulls, a higher level of fast and nonlinear spermatozoa were found in SP3 (33.3%), followed by SP1 (32.7%%) with fast and progressive spermatozoa. Whereas, SP1 of Nelore bulls had 33.8% fast and progressive spermatozoa, followed by 32.2% of SP3 with fast and nonlinear spermatozoa. CONCLUSION: Both breeds of bulls presented similar proportions of sperm SP. Consequently, no influence on the pregnancy rates was shown in cows submitted to the IATF programs on a large scale. doi.org/10.54680/fr22310110312.

Evaluation of the Freezability of the Bovine Epididymis Tail Sperm with the Addition of Antioxidants.

BACKGROUND: The cryopreservation and recovery of epididymis tail sperm is an important biotechnology dependent on the composition of the freezing medium. OBJETIVE: To evaluate the effect of melatonin, added to commercial freezing medium extender, on the kinetics and viability of bovine epididymis tail sperm. MATERIAL AND METHODS: Five routines were performed, each consisting of eight epididymis and the structures were sliced onto a glass plate containing a commercial diluting medium for Botubov. The samples were divided into four groups, with 80 x 106 spermatozoa per mL. Group 1: samples diluted in Botubov. Group 2: samples centrifuged (600 g, 10 min), and the pellet re-suspended in Botubov. Group 3, samples diluted in Botubov containing 100 pM melatonin. Group 4: samples centrifuged (600 g, 10 min) and the pellet resuspended in Botubov with 100 pM melatonin. The samples were transferred to 0.5 mL straws at 40 x 106 viable spermatozoa, stabilized at 5º C for 4 h, transferred to liquid nitrogen vapour for 20 min, dipped in liquid nitrogen and stored in a cryogenic cylinder. After thawing (46ºC, 15s), sperm kinetics and viability parameters were evaluated. RESULTS: There was no difference in the parameters of total motility (MT, %), progressive motility (MP, %), progressive linear velocity (VSL, µm/s), curvilinear velocity (VCL, µm/s), linearity (LIN, %), spermatozoa with rapid movement (RAP, %) and level of intact plasma membranes and acrosome (IPMA, %) among the groups studied. However, a difference was observed between the routines performed. CONCLUSION: The protocol for freezing bovine epididymis tail sperm is applicable; however, there is an influence of the epididymis used, for the best efficacy of this biotechnology.