Influence of bovine follicular fluid on thawed bovine spermatozoa - assessment by CASA system and flow cytometry.

AIM: The aim of this study was to analyze the effect of bovine follicular fluid on the survival, morphology and kinetic parameters of bovine thawed spermatozoa under laboratory conditions. MATERIALS AND METHODS: The semen from 5 bulls of proven fertility was incubated in follicular and physiological fluid for 8 hours. During this time assessment using the CASA system was performed. At the beginning and the end of incubation process evaluation by flow cytometry was conducted. RESULTS: The results of the sperm motility assessment showed a significant decrease in the analyzed parameters both in the follicular and physiological fluid. A significant reduction in all parameters characterizing movement properties in the semen incubated in the follicular fluid was found. In the physiological fluid, a similar trend was demonstrated only for the following properties: VAP, VSL, VCL, ALH, BCF. A significant difference was found for both fluids in: VCL (p=0.026), ALH (p=0.038) and LIN (p⟨0.001) at the beginning of incubation. The results of the plasma membrane integrity assessment showed a statistically significant increase in the percentage of dying sperm at the 8th hour of the incubation in the follicular fluid. In the case of semen incubation in physiological fluid, a statistically significant decrease in the percentage of live non-damaged cells was found with a simultaneous increase in the subpopulation of undamaged dead cells. CONCLUSIONS: Follicular fluid rapidly accelerates the capacitation process. The results of flow cytometry support the hypothesis concerning the ability of follicular fluid to prolong sperm survival.

Gene conversion and different population histories may explain the contrast between polymorphism and linkage disequilibrium levels.

To characterize linkage disequilibrium (LD) levels in human populations, we have analyzed 10 independent noncoding segments in three population samples from the major ethnic groups--that is, Africans, Asians, and Europeans. Descriptive statistics show that LD decays much faster in the African samples than in the non-African ones. With the assumption of an equilibrium model, we estimated the population crossing-over parameter (4N(e)r(bp), where N(e) is the effective population size and r(bp) is the crossing-over rate per generation between adjacent base pairs) in the presence of gene conversion. In the African sample, LD and polymorphism levels lead to similar estimates of effective population size, as expected under an equilibrium model. Conversely, in both non-African samples, LD levels suggest a smaller effective population size than that implied by polymorphism levels. This observation is paralleled by significant departures from an equilibrium model in the spectrum of allele frequencies of the non-African samples. Besides ruling out the possibility that non-African populations are at equilibrium, these results suggest different demographic history (temporal and spatial) of these groups. Interestingly, the African sample fits the expectations of an equilibrium model based on polymorphism and divergence levels and on frequency spectrum. For this sample, the estimated ratio of gene conversion to crossing-over rates is 7.3 for a mean tract length of 500 bp, suggesting that gene conversion may be more frequent than previously thought. These findings imply that disease-association studies will require a much denser map of polymorphic sites in African than in non-African populations.