Impact of methodological factors on sperm penetration into cervical mucus in cattle

Ram spermatozoa migrating through artificial mucus in vitro have reduced mitochondrial membrane potential but retain their viability

Sperm motility in vitro is one of the most common predictors of fertility in male screening. We propose that a mucus-penetration assay can isolate a cellular subpopulation critical to reproductive success. To this end, a device was designed with three modules (sample, test and collection) and its conditions of use evaluated (length of mucus, incubation time, mucus medium, sperm concentration and position in relation to the horizontal). The number of spermatozoa migrating and the viability and acrosomal status of the spermatozoa not migrating were calculated. The second objective was to evaluate the qualitative parameters of the spermatozoa migrating in 1.6% polyacrylamide for 30 min. The number of spermatozoa migrating and the sperm motility, viability and the acrosomal and mitochondrial status of three sperm populations (fresh, not migrating and migrating) were determined. A higher number of migrating spermatozoa were observed after 60 min of incubation, but this situation adversely affected sperm quality. The methylcellulose-based test showed a significantly lower number of migrating spermatozoa than the polyacrylamide test. The position at an angle of 45° resulted in a higher number of migrating spermatozoa in the polyacrylamide-based test. The sperm counts for three consecutive assays indicated an acceptable repeatability of the method. The viability and acrosomal status of the migrating spermatozoa showed no significant changes with regard to the control when the device was placed at 45°, whereas these parameters showed lower values at 0°. The percentage of high mitochondrial membrane potential spermatozoa was significantly reduced in the population of migrating spermatozoa.

Isolation and characterization of heparin and gelatin binding buffalo seminal plasma proteins and their effect on cauda epididymal spermatozoa

Seventy semen ejaculates were obtained from 14 Murrah buffalo bulls and were subjected to plasma separation immediately after collection by centrifugation at 2000 rpm for 20 min and stored in liquid nitrogen until analysis. In the seminal plasma the total protein concentration were estimated and the heparin and gelatin binding (HB and GB) proteins were isolated using heparin and gelatin affinity column chromatography. The molecular weight of individual isolated HB and GB protein was determined by SDS-PAGE analysis. Buffalo bull spermatozoa was collected from cauda epididymis under aseptic conditions and was used for the in vitro fertility tests (i.e. bovine cervical mucus penetration test (BCMPT) and hypo-osmotic swelling test (HOST)). The heparin and gelatin binding buffalo seminal plasma proteins were used in six concentrations i.e. 10, 20, 30, 40, 50 and 60 microg/ml to test their effect on in vitro fertility assessment of cauda epididymal spermatozoa. The overall mean values of total protein, HB and GB proteins were recorded as 29+/-2.7, 2.61 and 0.2mg/ml, respectively. Eighteen total protein bands were observed in the range of 12-127 kDa. Eight major HB proteins were isolated in the range of 13-71 kDa. Seven major GB proteins were isolated in the range of 13-61 kDa in the buffalo seminal plasma. The mean penetration distance (mm) travelled by the buffalo cauda spermatozoa was maximum in HB proteins (26.9+/-0.6) followed by GB proteins (25.4+/-0.6) and control (21.2+/-1.4). The difference in BCMPT values between protein treated and control group was significant (P<0.05). Almost similar trend in the effect of protein on values of HOST percentage in both HB and GB proteins treated semen samples were recorded (66.4+/-0.65 and 66.1+/-0.6, respectively). The difference in HOST values between proteins treated and control group (50.4+/-2.0) was significant (P<0.05). The present results indicate that among the isolated proteins, 4 proteins were commonly seen in both the heparin and gelatin-sepharose affinity column chromatography, and the addition of buffalo seminal plasma proteins improved the in vitro sperm functions (40 microg/ml gave best results) of buffalo cauda spermatozoa.

Ultrastructural and Rheological Properties of Bovine Vaginal Fluid and its Relation to Sperm Motility and Fertilization: a Review

The tubular genital organs of the mammalian female reproductive tract provide different luminal microenvironments that can act as an aid or a barrier to gamete transport and the first steps of embryonic development. The mechanism of sperm transport through the genital tract has not been fully established but, first of all, sperm cells encounter and need to overcome mucous-like secretions to reach the site where fertilization occurs. One of these secretions, vaginal fluid, is a complex biological product, which is mainly derived from cervical mucus. In this review, we focus on recent studies that describe the relationships between the ultrastructural and rheological properties of bovine vaginal fluid and sperm motion. In the light of this, we propose bovine vaginal fluid as a morphofunctional model for the study of sperm transport in mammals.

A structural study of the bovine vaginal fluid at estrus

The present study describes the structural components of the bovine vaginal fluid at estrus by scanning electron microscopy (SEM) following critical point- and freeze-drying preparation procedures. Confocal scanning laser microscopy (CLSM) was also used to evaluate the structural integrity of samples, and a control sample was assessed by adding sperm to the vaginal fluid. Samples were collected from 10 cows at the time of artificial insemination, prepared for SEM by using critical point- and freeze-drying procedures, gold coated, and observed by SEM. Mesh size and filament thickness were measured with an image analyzer. Of the 10 samples processed, 4 were considered altered following critical point drying. Compaction and lack of filaments were observed in these samples. A small area of one sample showed a honey comb-like structure when freeze drying was used. Nonoriented filaments with different thicknesses and with a network-like structure were observed throughout the remainder of the samples. Filaments throughout all samples were also observed by CSLM. After critical point drying, the mesh area ranged from 0.8 to 101.4 microns 2; the minor axis from 0.7 to 10.8 microns; and filament thickness from 40 to 442 nm. Using freeze drying, the mesh area ranged from 0.9 to 493.8 microns 2; the minor axis from 0.7 to 27.5 microns; and filament thickness from 40 to 800 nm. When samples were freeze dried, mesh values were similar to the interstrand channels observed by CSLM. In sperm-vaginal fluid samples, following critical point- or freeze-drying procedures, spermatozoa were oriented randomly in the vaginal fluid and did not seem to alter filamentous structure. Our data suggest that the freeze-drying procedure better preserves the true structural dimensions of the vaginal fluid. Furthermore, the filamentous structure of the vaginal fluid does not appear to impede sperm transport.

Sperm motion and rheological behavior of the vaginal fluid of superovulated dairy heifers

The present study was conducted to determine whether there is any correlation between sperm motion and rheological behavior of the anterior vaginal fluid of superovulated dairy heifers. Vaginal fluid samples were collected from 16 superovulated dairy heifers from 12 to 20 h after estrus detection. Flow behavior was evaluated. The mean consistency index was 56.6 +/- 23.9 miliPascals per second(n) (mPa.s(n)) and ranged from 2.2 to 278 mPa.s(n). Of 16 samples of anterior vaginal fluid, 11 (69%) behaved as Newtonian fluids, while 5 (31%) behaved as non-Newtonian fluids. Concentrations and motility parameters of bull spermatozoa were evaluated into vaginal fluid samples after 30 min of incubation. The sperm concentrations were lower (P=0.01) in non-Newtonian than in Newtonian samples and were negatively correlated (P=0.009; r = - 0.62) with the index of consistency. The motility parameters such as average path velocity (VAP), curvilinear velocity (VCL) and linear velocity (VSL) were significantly higher in non-Newtonian than in Newtonian samples and were positively correlated with the index of consistency. Our data show that as mechanical resistance of vaginal fluid to sperm increases, the motility parameters increase while the migration efficiency appears to decrease.

Relationship of sperm migration in anterior vaginal fluid and embryo quality in superovulated dairy heifers

Anterior vaginal fluid samples from 26 superovulated dairy heifers at insemination were classified into 2 grades: 1) with abnormal sperm penetration ability when vanguard sperm migration was randomly oriented; and 2) with normal sperm penetration ability when vanguard sperm migration was parallel and unidirectional. Vanguard sperm behavior and vanguard sperm migration distances were evaluated for their effects on fertilized ova recovery rates and transferable embryo recovery rates. Twelve vaginal fluid samples (46%) showed abnormal sperm penetration ability (Grade 1) and the mean +/- sem distance traveled by the vanguard spermatozoa into these samples (7.3 +/- 0.9 mm) was different (P<0.0001) from the remainder of the samples (48 +/- 3.4 mm) in which sperm penetration was registered as normal (Grade 2). In heifers in which anterior vaginal fluid samples were Grades 1 and 2, the fertilized ova recovery rates were 78.3% and 80.2%, respectively (P=0.91). Transferable embryo recovery rates were 54.2% and 32% for Grades 1 and 2, respectively (P<0.001). Using correlation and linear regression analysis, the sperm migration distance in Grade-2 samples was not related to fertilized ova (P=0.77) or to transferable embryo recovery rates (P=0.97). These results indicate that vanguard sperm movement into capillary tubes varied qualitatively and was related to subsequent embryo quality.