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Physiology of spermatozoa at high dilution rates: the influence of seminal plasma.

Cryopreservation and ensuing in vitro fertilization ability of boar spermatozoa from epididymides stored at 4°C

The components of ruminant seminal plasma and their influence on the fertility of spermatozoa are reviewed. Seminal plasma can both inhibit and stimulate sperm function and fertility through the multifunctional actions of organic and inorganic components. These effects are now better understood because the composition of the seminal plasma, including its protein content and that of other structures, specifically membrane vesicles, has been clarified. Spermatozoa gain motility and fertilizing capacity as they transit the epididymis under the influence of factors produced by that organ. At ejaculation, inhibitory (termed "decapacitation") factors, sourced from the accessory sex glands, bind to the sperm surface. The major proteins isolated and characterised in ram seminal plasma, whose specific functions are yet to be determined, originate from the vesicular gland and comprise a spermadhesin together with proteins with fibronectin-II domains. In vitro handling of spermatozoa in preparation for artificial insemination (AI), involving processes such as dilution, cooling, freezing, re-warming and sperm sexing by flow cytometric sorting, can remove seminal plasma and may modify the proteins bound to the sperm surface. This destabilises the membranes and may pre-capacitate the spermatozoa, shortening their fertilizing lifespan. These changes may be reversible by seminal plasma fractions but responses differ depending on the type of sperm pre-treatment. Fertility after AI of ruminant semen may be improved if the role of seminal plasma proteins and their effect, if added individually or in combination to spermatozoa at different stages of preservation, or other manipulations such as flow cytometric sorting, can be determined.

Seminal plasma effects on sperm handling and female fertility.

Optimal sperm cryopreservation is a prerequisite for the sustainable commercial application of frozen-thawed boar semen for AI. Three experiments were performed to identify factors influencing variability of postthaw sperm survival among 464 boar ejaculates. Sperm-rich ejaculate fractions were cryopre-served using a standard freezing-thawing procedure for 0.5-mL plastic straws and computer-controlled freezing equipment. Postthaw sperm motility (assessed with a computer-assisted semen analysis system) and viability (simultaneously probed by flow cytometry analysis after triple-fluorescent stain), evaluated 30 and 150 min postthaw, were used to estimate the success of cryopreservation. In the first experiment, 168 unselected ejaculates (1 ejaculate/boar), from boars of 6 breeds with a wide age range (8 to 48 mo), were cryopreserved over a 12-mo period to evaluate the predictive value of boar (breed and age), semen collection, transport variables (season of ejaculate collection, interval between collections, and ejaculate temperature exposure), initial semen traits, and sperm quality before freezing on sperm survival after freezing-thawing. In Exp. 2, 4 ejaculates from each of 29 boars, preselected according to their initial semen traits and sperm quality before freezing, were collected and frozen over a 6-mo period to evaluate the influence of interboar and intraboar ejaculate variability in the survival of sperm after cryopreservation. In Exp. 3, 12 ejaculates preselected as for Exp. 2, from each of 15 boars with known good sperm cryosurvival, were collected and frozen over a 12-mo period to estimate the sustainability of sperm cryosurvival between ejaculates over time. Boar and semen collection and transport variables were not predictive of sperm cryosurvival among ejaculates. Initial semen traits and sperm quality variables observed before freezing explained 23.2 and 10.9%, respectively, of the variation in postthaw sperm motility and viability. However, more that 70% of total variance observed in postthaw sperm quality variables among ejaculates was explained by boar. This indicates that boar is the most important (P 0.05) sperm cryosurvival over time.

D. Rath

Papers

In vitro fertilization of porcine oocytes with fresh and frozen-thawed ejaculated or frozen-thawed epididymal semen obtained from identical boars.