Mitochondrial injury to ram sperm during procedures associated with artificial insemination or frozen storage

Influence of different extenders on morphological and functional parameters of frozen-thawed spermatozoa of jaguar (Panthera onca)

Due to the global decrease in jaguar population, conservation strategies are essential and the development of effective semen cryopreservation protocols would contribute to the formation of germplasm banks. Therefore, the objectives were to (1) evaluate the use of TRIS and ACP-117c extenders for jaguar semen freezing, (2) describe the ultrastructural changes in sperm after cryopreservation, and (3) evaluate the binding capacity of the thawed sperm. Eight ejaculates from five mature individuals were collected by electroejaculation, extended in TRIS or a coconut based-extender (ACP-117c), and frozen in liquid nitrogen. Samples were evaluated for sperm motility, vigor, membrane functionality, mitochondrial activity, morphology (using light microscopy, scanning electron microscopy - SEM and transmission electron microscopy - TEM), sperm kinetic parameters (by computerized analysis - CASA), and sperm binding capability using an egg yolk perivitelline membrane assay. Samples preserved in TRIS presented better post-thaw motility (46.0 ± 7.7%) and membrane functionality (60.5 ± 4.2%) and higher mitochondrial activity (21.5 ± 3.7%) than those preserved in ACP-117c (20.9 ± 5.4% motile sperm; 47.1 ± 2.5% functional membrane; 11.8 ± 1.7% mitochondrial activity). Regarding ultrastructural evaluations, SEM showed that both extenders were able to preserve the superficial membrane of the sperm, but TEM revealed the occurrence of nuclear electron lucent points, especially in samples extended in ACP-117c. Additionally, TRIS also provided a higher number of sperm bound to the perivitelline membrane (29.5 ± 3.3%) in comparison to samples diluted in ACP-117c (18.6 ± 1.5%). Overall, we suggest the use of a TRIS-based extender for cryopreservation of jaguar semen.

Traversing the ovine cervix - a challenge for cryopreserved semen and creative science

This review brings together research findings on cervical relaxation in the ewe and its pharmacological stimulation for enhancement of the penetration needed for transcervical insemination and embryo transfer. On the basis that the success of artificial insemination is the percentage of ewes lambing, a review is made of recent research aimed at understanding and minimising the sub-lethal effects of freezing and thawing on the viability of spermatozoa, their membrane integrity and their ability to migrate through cervical mucus, as these characteristics have a major influence on fertility, particularly when semen is deposited, artificially, in the os cervix. Milestones of achievement are given for transcervical intrauterine insemination, embryo recovery and transfer and the birth of lambs of pre-determined sex, firstly following intracytoplasmic sperm injection, then laparoscopic intrauterine insemination using highly diluted flow-cytometrically sorted fresh semen and subsequently by os cervix insemination using sexed semen that had been frozen and thawed. Diversity of research endeavour (applied, cellular, molecular), research discipline (anatomy, histology, immunology, endocrinology) and research focus (cell, tissue, organ, whole animal) is embraced within the review as each has significant contributions to make in advancing recent scientific findings from the laboratory into robust on-farm transcervical insemination and embryo transfer techniques.

Morphometric changes in boar spermatozoa induced by cryopreservation

Computer-assisted sperm morphometry analysis was used to determine the effects of cryopreservation on boar sperm head and midpiece morphometry. Sperm-rich fractions were collected from five mature boars. Three microscope slides were prepared from single extended sperm samples prior freezing and post-thawing. All slides were stained with Hemacolor, and 250 sperm images were obtained from each slide. The sperm head dimensions for length, width, area, perimeter and four shape factors and sperm-midpiece dimensions for area, width, angle and distance were determined in each spermatozoa. The effects of sperm freezing on sperm dimensions within and among boars were determined. A previous discriminant analysis of the results was able to correctly classify a 78.3 and 82% of fresh and frozen-thawed spermatozoa respectively. Sperm heads were significantly smaller in cryopreserved spermatozoa than in the companion extended samples for length, width, area and perimeter. Sperm midpieces were also significantly smaller in cryopreserved spermatozoa for width and area. The highest changes in morphometric dimensions after the freeze-thawing process were found in the midpiece of spermatozoa. The variability of morphometric measurements only was significantly different between fresh and thawed samples for head rugosity and midpiece area. The effects of cryopreservation on morphometric parameters were similar in the boars, which allow us to conclude that cryopreservation process does not have a different effect in each individual boar. In summary, morphometric changes associated with the cryopreservation process on boar spermatozoa do not apparently depends on an effect at individual level.

The influence of antioxidant, cholesterol and seminal plasma on the in vitro quality of sorted and non-sorted ram spermatozoa

In an effort to improve the number of functional spermatozoa following sex-sorting and cryopreservation, the effects on in vitro sperm characteristics of the additives: (i) catalase (pre-sorting); (ii) cholesterol-loaded cyclodextrins (CLCs; pre-sorting); and (iii) seminal plasma (post-thawing) were investigated. For all experiments, spermatozoa (three males, n=3 ejaculates/male) were processed using a high speed flow cytometer before cryopreservation, thawing and incubation for 6h. Catalase had no effect (P>0.05) on post-thaw motility characteristics (as measured by CASA) of sex-sorted ram spermatozoa, but pre-sort addition of CLCs reduced (P<0.05) sperm quality after post-thaw incubation for 0 h (motility), 3h (motility, average path velocity, viability and acrosome integrity) and 6h (motility, average path and curvilinear velocity, straightness, linearity, viability and acrosome integrity). Seminal plasma had a differential effect (P<0.001) on sex-sorted and non-sorted spermatozoa. Post-thaw supplementation of increasing levels of seminal plasma caused all motility characteristics of sex-sorted, frozen-thawed spermatozoa to decline (P<0.05); conversely, non-sorted, frozen-thawed spermatozoa exhibited improvements (P<0.05) in motility, viability, acrosome integrity and mitochondrial respiration. In summary, incorporation of catalase, CLCs and seminal plasma into the sorting protocol failed to improve post-thaw sperm quality and, consequently efficiency of sex-sorting of ram spermatozoa. The paradoxical effect of seminal plasma supplementation on the in vitro characteristics of ram spermatozoa provides further evidence that sex-sorting by flow cytometry produces a selected population of cells with different functions compared with non-sorted spermatozoa.

Preservation and evaluation of semen for artificial insemination

Many years of research have been devoted to improving the fertility of preserved semen of small ruminants. There have been few significant advances in preservation in recent times, but considerable knowledge has been gained on the effect of preservation on the structure and function of spermatozoa. It has become evident that preservation greatly affects many sperm attributes, such as motility, respiratory activity, membrane status and DNA quality. Consequently, viability is reduced, transport in the female reproductive tract is inhibited, the timing of fertilisation is altered and embryo development is affected following insemination of preserved, compared to fresh spermatozoa. A greater understanding of their functional condition may lead to the development of methods of preventing these alterations or to improved methods of using the preserved spermatozoa for artificial insemination in their altered state.

Membrane changes during different stages of a freeze-thaw protocol for equine semen cryopreservation

Many theories have been postulated concerning the possible effects of cryopreservation on spermatozoa, including suggestions the freeze-thawing process produces membranes that have greater fluidity and are more fusogenic, thus inducing changes similar to those of capacitation. The main objectives of this study were to determine at what stage of the freeze-thaw process membrane changes occur and whether evaluation with chlortetracycline (CTC) stain could predict the freezability of stallion sperm. Sperm viability and state of capacitation were simultaneously evaluated using CTC and Hoechst 33258 (H258) techniques. Membrane function was evaluated using the hypo-osmotic swelling test (HOS) and progressive motility (PM) was evaluated under light microscopy at each stage of a freeze-thaw protocol. Evaluated were raw semen; after dilution and centrifugation; after redilution and equilibration at room temperature; after cooling to 5 degrees C; after super cooling to -15 degrees C; and after thawing. The most pronounced functional damage to membranes and the greatest decrease in PM occurred in samples of all stallions after thawing (P<0.05). Cryopreservation, as evaluated by CTC/H258 staining, significantly (P<0.05) affected sperm membrane integrity after centrifugation, after redilution and equilibration at room temperature and after cooling to 5 degrees C. The HOS and H258 tests gave similar results (R values of approximately 0.75) and correlated inversely with the number of live noncapacitated sperm cells (R values of approximately -0.75). Remarkably, the subpopulation of capacitated live cells was unaffected in all freeze-thawing steps and the number of live acrosome reacted cells increased by a factor of 4. However, it was not possible to determine whether the changing CTC patterns reflect a true capacitation phenomenon or an intermediate destabilized state of the sperm cell membrane. This increase may indicate that the subpopulation of functional sperm cells capable of binding to the zona pellucida increases after freeze-thawing despite the deteriorative effect of this procedure for the entire live sperm population.