Estimation of the relative fertilizing ability of frozen chicken spermatozoa using a heterospermic competition method

Factors affecting cryopreservation-associated damages in sperm motility of cockerels (Gallus gallus domesticus)

1. Sperm are exposed to severe osmotic stress during cryopreservation, which results in impairment of fertilisation ability, including motility and viability, in poultry. Sperm osmotolerance is regulated by many extracellular factors and varies widely in birds, leading to uncertainty in the nature of the osmotic injury.2. Tail bending is a primary response resulting from cell swelling from excessive osmotic stress. However, the underlying mechanism responsible for tail bending is largely unknown. This study examined the relationship between osmotic stress and post-thaw motility, with a particular focus on the role of Na⁺/K⁺ ATPase (NKA) in the tail bending response.3. Cryopreserved sperm exhibited rapidly reduced motility when maintained at 37°C. The combination of temperature change and osmotic stress was a primary factor responsible for tail bending. This work tested a hypothesis known to be associated with post-thaw tail abnormality in other species and found that cold shock, that is not accompanied by an apoptotic response, may occur. Ouabain inhibition of Na⁺/K⁺ ATPase activity alleviated the tail bending response in fresh and post-thaw sperm.4. These results demonstrated that the combination of temperature change and osmotic stress has a primary impact on the reduction of post-thaw motility, with a particular role in NKA activity, in the tail bending response of chicken sperm. These results provide a foundation for establishing cryopreservation methodology to ensure the optimal fertilisation potential of cryopreserved chicken sperm.

Developmental potential of cryopreserved gonadal germ cells from 7-day-old chick embryos recovered using the PBS(-) method

1. A series of experiments were conducted to examine the developmental potential of cryopreserved gonadal germ cells (GGCs) recovered from both males and females on embryo day 7 (7 d-GGCs) using the PBS(-) method. Germline chimeras were produced by transferring 200 frozen/unfrozen 7 d-GGCs recovered from female/male Rhode Island Red (RIR) embryos into the dorsal aorta of 2-day-old female and male white leghorn (WL) embryos.2. Germ-cell recipient embryos were hatched and raised to sexual maturity and progeny testing was conducted by mating with RIR of the opposite sex. Brown-feathered progeny chicks were hatched in all eight possible progeny testing combinations, except for male GGC recipients produced by transferring female GGCs. Furthermore, brown-feathered progeny chicks were hatched when frozen-thawed sperm from male germline chimeras, produced by transferring unfrozen 7d-GGCs, were inseminated in normal female RIR and female WL germline chimeras.3. The results indicated that cryopreserved female/male GGCs from 7-day-old chick embryos, recovered using the PBS(-) method, were fully capable of developing into normal spermatozoa and ova in the gonad of recipient embryos under appropriate GGC donor/recipient combinations.

Cryopreservation of Avian Semen

Cryopreservation protocols for semen exist for bird species used in animal production, fancy and hobby species, and wild bird species. Freezing of bird oocytes or embryos is not possible. Cryopreservation of avian semen is used for preserving (genetic diversity of) endangered species or breeds. Freezing semen can also be used in the breeding industry for maintaining breeding lines, as a cost-effective alternative to holding live birds. Success and efficiency of cryopreservation of bird semen differs among species and breeds or selection lines. This chapter describes important variables of methods for collecting, diluting, cold storage, and freezing and thawing of bird semen, notably the medium composition, cryoprotectant used and its concentration, cooling rate, freezing method, and warming method. Media and methods are described for freezing semen using either glycerol or DMA as cryoprotectant, which both are known in chicken and a number of other bird species to render adequate post-thaw fertility rates.

Cryopreservation of turkey spermatozoa without permeant cryoprotectants

In avian species, cryopreservation of semen is necessary for developing sperm cryobanks. It is very difficult, however to cryopreserve turkey sperm and have sperm be viable after thawing. Glycerol, the commonly used sperm cryoprotectant in many species, is toxic to sperm of avian species. The aim of this study was to evaluate whether the non-permeating dextran was effective for the cryopreservation and maintenance of turkey spermatozoa viability after thawing, avoiding the use of permeating cryoprotectants. Turkey sperm were diluted with a medium supplemented with 11% glycerol or dextran with a 1,000 molecular weight (MW), dextran with a 10,000 MW, or dextran with a 20,000 MW each at a 2%, 5%, or 10% concentration. Sperm kinetic characteristics, membrane and acrosome integrity (AI), and the capacity of spermatozoa to interact with the autologous perivitelline layer were evaluated after equilibration and cryopreservation. Results indicate that with use of glycerol and the 1,000 MW dextran there was lesser sperm viability after both equilibration and cryopreservation, compared with use of the 10,000 or 20,000 MW dextran compounds. There was a greater cryoprotective effect with the 10,000 and 20,000 MW dextran compounds at the 10% concentration with spermatozoa maintaining a greater functionality and capacity to interact with the autologous perivitelline layer. In conclusion, the results of this study indicate turkey spermatozoa could be effectively cryopreserved in extender without the use of glycerol as a penetrating cryoprotectant but with the use of the 10,000 or 20,000 MW dextran compounds at a 10% extender concentration.

Modification of membrane cholesterol and desmosterol in chicken spermatozoa improves post-thaw survival and prevents impairment of sperm function after cryopreservation

During cryopreservation, spermatozoa are subjected to cryodamage that leads to a decline in fertilisation ability. Due to the complex nature of this process, the initial trigger for cryodamage remains unknown. Recently, we demonstrated that cryopreservation induces early apoptotic changes characterised by phosphatidylserine (PS) translocation via sterol loss from the plasma membrane of chicken spermatozoa. This led us to hypothesise that sterol incorporation into membranes minimises cryodamage, thereby improving the quality of cryopreserved chicken spermatozoa. In the present study, treating spermatozoa with 1.5 mg mL−1 cholesterol- and 3 mg mL−1 desmosterol-loaded cyclodextrin (CLC and DLC respectively) increased post-thaw survival and motility. These effects appeared to be highly dependent the amount of sterol loaded into the spermatozoa. Localisation experiments confirmed the incorporation of exogenous cholesterol into the sperm head region. Detection of PS translocation showed that elevation of these sterols inhibited early apoptotic changes, thereby enhancing post-thaw survival. Furthermore, CLC and DLC treatment suppressed spontaneous acrosome reaction after cryopreservation, preserving the ability of spermatozoa to undergo acrosome reactions in response to physiological stimulation. These results demonstrate that loading sterols into chicken spermatozoa before cryopreservation enhances their quality by inhibiting early apoptotic changes and spontaneous acrosome reactions. The present study provides new mechanistic insight into cryodamage in chicken spermatozoa.

Characterization of the functions and proteomes associated with membrane rafts in chicken sperm

Cellular membranes are heterogeneous, and this has a great impact on cellular function. Despite the central role of membrane functions in multiple cellular processes in sperm, their molecular mechanisms are poorly understood. Membrane rafts are specific membrane domains enriched in cholesterol, ganglioside GM1, and functional proteins, and they are involved in the regulation of a variety of cellular functions. Studies of the functional characterization of membrane rafts in mammalian sperm have demonstrated roles in sperm-egg binding and the acrosomal reaction. Recently, our biochemical and cell biological studies showed that membrane rafts are present and might play functional roles in chicken sperm. In this study, we isolated membrane rafts from chicken sperm as a detergent-resistant membranes (DRM) floating on a density gradient in the presence of 1% Triton X-100, and characterized the function and proteomes associated with these domains. Biochemical comparison of the DRM between fresh and cryopreserved sperm demonstrated that cryopreservation induces cholesterol loss specifically from membrane rafts, indicating the functional connection with reduced post-thaw fertility in chicken sperm. Furthermore, using an avidin-biotin system, we found that sperm DRM is highly enriched in a 60 KDa single protein able to bind to the inner perivitelline layer. To identify possible roles of membrane rafts, quantitative proteomics, combined with a stable isotope dimethyl labeling approach, identified 82 proteins exclusively or relatively more associated with membrane rafts. Our results demonstrate the functional distinctions between membrane domains and provide compelling evidence that membrane rafts are involved in various cellular pathways inherent to chicken sperm.

Comparison of Membrane Characteristics between Freshly Ejaculated and Cryopreserved Sperm in the Chicken

Cryopreserved sperm undergoes serious damage which affects its fertilizing ability. Despite progress in understanding the nature of functional deterioration in mammalian sperm, little is known about the mechanism involved in the induction of functional damage in avian sperm. Cellular membranes are considered the primary site of cryodamage to sperm. Membrane rafts are specific membrane regions enriched in sterols, ganglioside GM1, and functional proteins and they play important roles in the regulation of diverse functions exerted in mammalian sperm during fertilization. Several reports investigating cryopreservation-induced membrane changes in mammalian sperm have suggested that cryopreservation induces a compositional alteration of membrane rafts via a loss of membrane sterols, leading to impaired fertilizing ability. Recently, we demonstrated that membrane rafts are present in chicken sperm. Therefore, we investigated a possible mechanism for the induction of functional damage in cryopreserved chicken sperm, with particular attention to cryopreservation-induced compositional changes in membrane rafts. Sterol quantification showed that loss of sterols from sperm membranes occurred following cryopreservation. Biochemical analyses of detergent-insoluble membranes showed that the lipid and protein compositions of membrane rafts were altered dramatically by cryopreservation. To determine the physiological role of these changes, we examined external translocation of phosphatidylserine (PS), representing an early apoptotic change, and found that cryopreservation induced apoptotic changes in chicken sperm. Furthermore, methyl-β-cyclodextrin-induced loss of sterols from the plasma membranes stimulated PS translocation that was not accompanied with caspase-3 activation, which plays an important role downstream of the apoptotic cascade. Based on the results obtained in this study, we discuss a new mechanism for reduction of the fertilizing ability in avian sperm after cryopreservation.

Cryopreservation of poultry semen: a review

Although still in the experimental phase, the technique of freezing domestic fowl semen may prove of interest and value to the industry. Various stages of the application of this method of preservation still need to be improved. One of the most critical aspects is the choice of cryoprotectant and its use during the process of freezing and thawing. While glycerol has a better cryopreservative action than other cryoprotectants in domestic fowl semen, it exerts a widely demonstrated contraceptive action, the mechanism of which has not yet been clarified. Thus the use of glycerol as a cryoprotectant must be accompanied by its complete removal before insemination.

The fertilizing capacity of semen preserved by freezing is notably less than that of fresh (non-preserved) material and has been evaluated as 1.6% and 19.7%. Genetic influences appear to affect spermatozoan response and tolerance to thermal treatments resulting in differences in subsequent fertility. Most studies using fowl semen report final freezing temperatures between –79°C and –196°C, a cooling rate of 1–10°C/minute and a thawing rate of 50–70°C/minute.

Straws have been found to be more satisfactory containers than glass vials or ampoules for preserving semen from domestic fowl.

Storage of poultry semen

Methods of semen collection and artificial insemination (AI) in poultry, requirement for diluents, methods of liquid and frozen storage of avian semen and evaluation of spermatozoa after storage for fertilizing ability are reviewed. Frozen storage of semen from non-domestic birds is also briefly discussed.

Cryopreservation of rooster sperm using methyl cellulose

Experiments were designed to determine when, during the cryopreservation process, sperm lose fertilizing capacity and whether the cryoprotectant, methyl cellulose (MC), could be used in combination with glycerol to cryopreserve sperm and remain in the inseminate without reducing fertility. Semen diluted in Minnesota Avian extender (MNA) and inseminated immediately had greater fertility (75%) than semen processed for cryopreservation (12 to 60%). The largest decreases in fertility were due to addition of glycerol to sperm and to cryopreservation. In another experiment, fertility of inseminates containing 0, 1, and 2% glycerol were 82, 29, and 21%, respectively, for eggs collected 2 to 5 d after insemination. When 0.5% MC was added to the same three treatments, fertility rates were 88, 63, and 69%, respectively. Semen cryopreserved in MNA containing 9% glycerol; MC + 3% glycerol; MC + 4% glycerol; MC + 9% glycerol; or 9% glycerol with the cryoprotectant removed post-thaw by dilution and subsequent centrifugation exhibited 59, 30, 35, 60, and 69% viable cells, respectively; and 65, 38, 46, 69, and 65% motile sperm, respectively. Sperm cryopreserved with MC and either 4 or 9% glycerol exhibited similar numbers of sperm binding to chicken perivitelline layers in vitro as did fresh sperm, whereas sperm frozen with MC and 3% glycerol bound oocytes with only 31% efficiency (P < 0.05). The extent to which cryopreserved sperm penetrated the perivitelline layer in vitro was independent of glycerol concentration, but was four times more efficient than that of fresh sperm (P < 0.05). The fertility rates of fresh semen, semen frozen in 9% glycerol with the cryoprotectant removed after thawing, and semen frozen in MC with either 3 or 4% glycerol were 87.4, 27.6, 0.8, and 0.5%, respectively (P < 0.05). The MC reduces the contraceptive effects of glycerol when inseminated with fresh sperm, but does not maintain fertilizing capacity in frozen-thawed sperm when used in combination with 3 or 4% glycerol.

Cryopreservation of rooster semen in thirteen and sixteen percent glycerol

Semen from Barred Plymouth Rock roosters was cryopreserved with glycerol concentrations of 13 and 16% in a microprocessor-controlled freezer. Thawing and deglycerolation were facilitated by the use of an improved microprocessor-controlled thawing device and high speed dialyzer. Deglycerolated semen (100 mu L; 192 and 154 million sperm, respectively, for the 13 and 16% glycerol concentration) was inseminated into Single Comb white Leghorn hens. Three inseminations were done at 4-d intervals. Eggs were collected for 10 d starting 1 d after the first insemination, and incubated for 4th d. Fertility was determined by candling after the 4th d. Fertility measurements of 62.4 and 65% were obtained from the sperm frozen in 13 and 16% glycerol concentrations, respectively, for the 10-d period.

Effects of genotype and cryopreservation of avian semen on fertility and number of perivitelline spermatozoa

1. The fertility of freshly diluted and cryopreserved samples of semen obtained from a population of chickens selected for duration of fertility of cryopreserved spermatozoa (FS line) and its unselected control (FC line) were compared over a range of spermatozoa concentrations (10, 40, 80, and 160 x 10(6) sperm/50 microliters insemination). 2. The spermatozoa of the FS line had greater fertility than spermatozoa of the FC line, whether freshly diluted or cryopreserved. Cryopreservation resulted in a reduction in fertility, regardless of line. There were no significant line by genotype interactions. 3. There were fewer spermatozoa from the FC line than the FS line found in the perivitelline membrane (perivitelline spermatozoa). The increase in number of perivitelline spermatozoa with increasing sperm concentration was greater in the FS than FC line. However, the slope of the increase in sperm number in the perivitelline membrane with increasing concentrations of cryopreserved spermatozoa was zero. 4. A minimum of 10(3) perivitelline spermatozoa must be found on day 2 post-insemination for duration of fertility to exceed three days. The ability to produce spermatozoa capable of reaching the forming perivitelline membrane appears to be a quantitative, rather than a qualitative, trait and may be subject to genetic manipulation.

Cryopreservation of rooster sperm

Successful cryopreservation of sperm requires: 1) selection of proper diluent; 2) selection of the best cryoprotectant; 3) determination of freezing and thawing rates for optimum retention of fertilization potential; and 4) removal of any materials deleterious to fertility (e.g., glycerol) before insemination. An economically useful process must allow recovery of sperm with sufficient fertilization capacity to enable maximum use of any given superior male. A series of experiments tested a novel semen freezing container (BioPore CryoCell container) having physical characteristics that permit reproducible freezing and thawing plus facile removal of glycerol from the sample after processing. Experiments tested the effect of: a) residual glycerol; b) initial glycerol concentrations on retention of fertility when samples were frozen and thawed at 6 C/min; c) Beltsville Poultry Semen Extender and Minnesota A buffers used during the dialysis procedure; and d) dialysis time. Respectively, the results were: a) .8% (vol/vol) reduced fertility by 5 to 10%; b) 12% glycerol was superior to 10% and 8% glycerol; c) no difference was observed between the two buffers; and d) 90 and 120 min were both superior to 60 min. Numerous pools of rooster sperm cryopreserved in CryoCell containers and dialyzed after thawing in a prototype BioStore environmental control chamber for 90 or 120 min resulted in a mean fertility of 55.6%. This mean fertility of frozen-thawed sperm was based on 3,263 eggs laid by 400 hens on Days +1 through 9 after inseminations on Days -1, 2, and 5. It is likely that broiler stocks might have lower fertility than that obtained from the Barred Plymouth Rock males and the Single Comb White Leghorn females used in these studies. Nevertheless, the procedure described is the first to consistently result in > 50% fertilized eggs as a result of conventional intravaginal insemination (< 200 x 10(6) sperm in 100 microL extender) of sperm processed after thawing by a procedure amenable to the scaleup required for commercial applications.

Evaluation of plasma membrane stability by detergent-induced rupture of osmotically swollen sperm

A general assay for plasma membrane stability was developed and tested. Osmotically swollen spermatozoa were ruptured with detergents and their volume distribution was monitored with resistance pulse spectroscopy. The extent of cell breakage was determined and expressed as [D]50, the concentration of detergent necessary to lyse 50% of the initially intact cells. Preliminary experiments established the degree to which spermatozoa could be swollen without lysis (no detergent) and the ability of the method to detect known mixtures of intact and membrane disrupted spermatozoa. [D]50 values were determined for caput (immature) and cauda (mature) ram epididymal spermatozoa with four detergents (cetyltrimethylammonium bromide, sodium dodecylsulfate, Zwittergent 3-14, and sodium deoxycholate). [D]50 values for caput spermatozoa were higher than those for cauda spermatozoa (P less than 0.05) for all detergents but cetyltrimethylammonium bromide. These changes are consistent with a qualitative model of membrane structure and stability based on lipid shape and composition and with the compositional changes known to occur during epididymal maturation. Additional studies using rooster spermatozoa established that a typical cryopreservation protocol leaves the surviving spermatozoa with membranes with greater sensitivity to detergent-induced stress. Since osmotic swelling has been microscopically localized to the tail plasma membrane, the changes in membrane stability can be assigned specifically to that region.

Cryopreservation of poultry sperm: the enigma of glycerol

This review summarizes recent data for cryopreservation of poultry sperm and data establishing the contraceptive effect of glycerol. Successful cryopreservation protocols for bovine sperm are compared to the requirements for rooster sperm, with emphasis on glycerol-induced alterations in avian reproductive systems. It has been shown that molar concentrations of glycerol can affect (a) physical features of the cytoplasm (cytoplasmic organization and viscosity), (b) permeability and stability of the membrane bilayer(s), and (c) noncovalent attachment of proteins to the sperm surface. Perturbing effects of glycerol on sperm metabolism and the essentiality of maintaining bioenergetic balance during the temperature changes associated with any cryopreservation protocol are discussed. Emphasis is placed on the processes in avian reproduction that may be altered by interactions with glycerol. Finally, we discuss the potential value of using available genetic models (lines of roosters differing in the capacity of their sperm to survive a freeze-thaw cycle) to clarify and overcome damage to poultry sperm induced by cryopreservation.

Analysis of poultry fertility data

Single Comb White Leghorn (SCWL) hens were inseminated intravaginally with spermatozoa from either SCWL or subfertile Delaware roosters in three replicate fertility trials. Overall fertility was analyzed with a log odds model following logit transformation. Duration of fertility was analyzed by iterative least squares. Hens inseminated with spermatozoa from SCWL males laid a higher proportion of fertilized eggs over a longer interval than those inseminated with spermatozoa from affected Delawares. Log-odds and logistic models may have advantages over the more traditional methods of evaluation. This is particularly true in regard to the distribution and normalization of error variances via the logit transformation and removal of nonadditivity via logistic regression.

Cryopreservation of semen from unique lines of chicken germ plasm

Frozen semen is a practical means of preserving valuable germ plasm. Monitored samples of semen cryopreserved with glycerol for heterozygous, dominant marker stocks and for nine chromosomal rearrangement lines had sufficiently high fertility for germ-line retrieval. The results also indicated a potential for the genetic selection of certain lines for the freezability of spermatozoa, since stock and line differences in fertility occurred when previously frozen semen was used for insemination. Freezing the semen of stocks routinely reproduced provides insurance against possible disasters.