Effect of freezing-thawing protocols on the performance of semen from three rabbit lines after artificial insemination

Effect of Honey, Coenzyme Q10, and β-Carotene/α-Tocopherol as Novel Additives in Rabbit-Sperm Cryopreservation Extender

The effectiveness of rabbit-sperm cryopreservation is still below average compared to other domestic species. After the sperm cryopreservation process, post-thawing parameters like motility and membrane integrity are significantly compromised. The use of new extender constituents is an approach that can be used to improve the effectiveness of cryopreservation. Accordingly, we used honey (1.25, 2.5, 5, and 10%), coenzyme Q10 (100 and 200 μM), and β-carotene/α-tocopherol (500 μM/620 μM and 250 μM/310 μM) as candidate components for rabbit-sperm extenders during cryopreservation. Ejaculates from commercial adult rabbit bucks (n = 5) were cryopreserved using conventional freezing. Several post-thawing sperm parameters were assessed, including total motility, membrane integrity, viability, nuclear membrane integrity, acrosome reaction, and mitochondrial membrane potential and activation. Additionally, we performed hormonal analyses of the seminal plasma. Moreover, we analyzed the post-thawing levels of a molecular marker of sperm quality, proAKAP4, which was used in rabbits for the first time. Our findings showed that the 2.5% honey supplementation increased the post-thawing sperm motility (13.75 ± 3.75%) compared to the greater concentrations employed. However, the post-thawing motility was negatively affected by the coenzyme Q10 (0%, in both groups) but was not affected by the β-carotene/α-tocopherol supplementation (22 ± 18.15%, and 11.67 ± 10.17%). In conclusion, the cryopreservation protocols of this study did not help to maintain the sperm parameters after thawing. Further studies are required to identify novel protocols to mitigate the damage caused to rabbit sperm during cryopreservation.

Effect of sulforaphane on long-term storage of rabbit semen

In this study, it was aimed to determine the effect of sulforaphane (SFN) on rabbit semen cryopreservation. Semen collected from animals was divided into 5 equal volumes as Control, SFN 5 µM, SFN 10 µM, SFN 25 µM and SFN 50 µM groups. Afterwards, semen analyzes were performed. According to our results, there was no statistical difference between the groups at 4°C. However after freezing thawing, the highest total motility, progressive motility and rapid spermatozoa rate was seen in the 10 µM SFN group, while the lowest was observed in the 50 µM SFN group (P<0.05). Static sperm ratio was highest in the 50 µM group, while the lowest was observed in the 10 µM SFN group. When flow cytometry results examined the rate of acrosomal damaged and dead sperm was the lowest in the 10 µM SFN group, a statistical difference was observed between the control group (P<0.05). The highest rate of sperm with high mitochondrial membrane potential was seen in the 5 µM SFN and 10 µM SFN groups. Apoptosis and ROS rates were found to be lower in the experimental groups compared to the control groups (P<0.05). As a result, SFN supplementation at a dose of 10 µM increased the quality of sperm in the freezing and thawing processes of rabbit semen. In conclusion, 10 µM SFN improved the quality of cryopreservation of rabbit semen.

Factors affecting rabbit sperm cryopreservation: a mini-review

Rabbits are an important animal species for meeting the nutritional requirements of the world's growing population due to the high conversion rate of feed. In most countries, the rabbit industry currently relies on artificial insemination with fresh or chilled and frozen-thawed spermatozoa. Various factors during the freezing process, including diluents, sperm preparation and freezing techniques, antioxidants, sudden temperature changes, ice formation and osmotic stress, have been proposed as reasons for the poor sperm quality post thaw. Despite the extensive progress reached in the field of rabbit sperm cryopreservation, new methodological approaches that could overcome problems in sperm cryopreservation are necessary. The aim of this review was to describe the factors that affect the cryopreservation of rabbit sperm.

Osmotic tolerance of rabbit spermatozoa is affected by extender composition and temperature

Sperm osmotic adaptability to anisosmotic conditions is important for sperm epididymal maturation, motility activation at ejaculation, and female tract colonization, or for conducting technological procedures such as cryopreservation. Several factors affect this adaptability, including the fluid composition that contributes to water flow dynamics, and the temperature at which osmotic stress is initiated. This study was designed to investigate the effect of medium composition (electrolyte- or sugar-based extender) and temperature (25 and 5 °C) on rabbit sperm adaptability to anisosmotic conditions. Rabbit spermatozoa, therefore, were diluted at both temperatures (25 and 5 °C) in electrolyte- or sugar-based media at increasing osmotic conditions (100 to 1,000 mOsm/kg), and values for sperm variables (sperm kinetics, membrane integrity, mitochondrial membrane potential) were estimated as endpoints. Sperm kinetics seemed to be more sensitive to osmotic stress than membrane integrity or mitochondrial function. The effect of moderate hypoosmotic stress did not differ when there was use of sugar- and electrolyte-based extenders at 25 °C (P > 0.05). In hyper-tonic conditions at 25 °C, the sugar-based extender was more effective in protecting sperm membrane integrity and mitochondrial function (P < 0.05). The lesser temperature made the differences more relevant because of the detrimental effect of hyperosmotic stress was more evident in the electrolyte-based extender at 5 °C (P < 0.05). The results from this study indicated rabbit spermatozoa have different adaptability to anisosmotic conditions induced by sugar- and electrolyte-based media and that the temperature at which the osmotic stress is initiated affects the cellular response.

Strategies for Highly Efficient Rabbit Sperm Cryopreservation

The rabbit is a valuable animal for both the economy and biomedical sciences. Sperm cryopreservation is one of the most efficient ways to preserve rabbit strains because it is easy to collect ejaculate repeatedly from a single male and inseminate artificially into multiple females. During the cooling, freezing and thawing process of sperms, the plasma membrane, cytoplasm and genome structures could be damaged by osmotic stress, cold shock, intracellular ice crystal formation, and excessive production of reactive oxygen species. In this review, we will discuss the progress made during the past years regarding efforts to minimize the cell damage in rabbit sperms, including freezing extender, cryoprotectants, supplements, and procedures.

Improving the Rabbit Semen Cryopreservation Protocol: Comparison Between Two Extenders and Inseminating Doses

This study has been designed to optimize the semen freezing protocol in rabbits, in this regard we compared a Tris-citrate-glucose (TCG) extender with a commercial one (Cortalap®), that to the best of our knowledge has never been used up to now on the in vitro freezability and fertilizing ability of cryopreserved rabbit semen. Two different inseminating semen doses were considered. Five pooled semen samples were divided into two subsamples and each of them were diluted to a ratio 1:1 (v:v) with a freezing extender composed of TCG or Cortalap® containing 16% of dimethylsulfoxide and 0.1 mol/L of sucrose. The extended semen was filled into 0.25 mL plastic straws and frozen above a liquid nitrogen surface. After thawing (50°C/10 seconds) we determined sperm motility, viability, membrane functionality, acrosome and DNA integrity. Our results showed that the Cortalap® extender significantly improved the in vitro post-thaw sperm quality, in comparison to TCG. When we compared the extenders in vivo, no significant differences in the reproductive performances were observed independently by inseminating doses used. In this study we demonstrated that Cortalap® extender can be used as an alternative to TCG. Thus, the Cortalap® being a ready to use extender, implies a reduction of time, mistakes and microbial contaminations during its preparation. This discovery results as significant because it provides beyond an important contribution to the creation of the first Italian semen cryobank of rabbit breeds and also for livestock rabbit farms based on artificial insemination (AI) program.

Improvement of sperm cryo-survival of cynomolgus macaque (Macaca fascicularis) by commercial egg-yolk-free freezing medium with type III antifreeze protein

When nonhuman primate sperm undergoes cryopreservation in an egg yolk medium there is an increased risk that the egg yolk might adversely affect the sperm due to containing of avian pathogens. Although commercial egg-yolk-free medium for human sperm cryopreservation has been used for macaque sperm, the cryo-survival remains less than optimal. The present study, therefore, was conducted to determine the optimal concentration of antifreeze protein (AFP) III supplemented in a commercial egg-yolk-free medium for cynomolgus macaque (Macaca fascicularis) sperm cryo-survival. The function of frozen-thawed sperm was evaluated by post-thaw sperm motility, acrosome integrity, and mitochondrial function. Results indicate that the sperm motilities were greater when 0.1, 1, and 10 μg/ml of AFP III were supplemented into the sperm freezing medium (P < 0.05). In addition, the mitochondrial membrane potential was greater in the sperm cryopreserved with the medium that was supplemented with 0.1 μg/ml of AFP III (P < 0.05). The addition of AFP III at any of the concentrations, however, did not have any cryoprotection effect on the sperm acrosome, and the greatest concentrations of AFP III at 100 and 200 μg/ml had detrimental effects on acrosomal integrity (P < 0.05). Results of the present study indicated the methods used are effective for the cryopreservation of cynomolgus monkey sperm while reducing associated health risks due to avian pathogens being present in egg yolk-based extenders.

Potential of coconut water to enhance fresh semen quality and fertility in rabbits

Coconut water as a natural diluent was evaluated on rabbit semen quality, conception and litter size in artificially inseminated does. A total of 10 bucks and 90 does, all crossbred New Zealand White × chinchilla, were used for the trial. Pooled semen was obtained from bucks using artificial vagina. Semen diluents were prepared at 0%, 20%, 40%, 60% and 80% and control 50% normal saline and designated as T1, T2, T3, T4, T5 and T6 respectively, in a completely randomised design. Semen analysis was conducted on fresh semen and the various diluted semen immediately at 37 °C. Fifteen does each were randomly allotted to the different treatment and were inseminated with their respective treatment diluted semen using the standard procedure, and conception rate, litter size and productivity index at birth were assessed at kindling. Result obtained revealed that spermatozoa motility and structural membrane integrity of the diluted semen were significantly (p < 0.05) affected by the percentage of dilution. The range of values obtained for spermatozoa motility, structural membrane integrity and acrosome integrity is within the accepted values for good-quality semen. Conception rate, litter size and productivity index at birth were highest in does inseminate with T4 (60%), and the least values were obtained in T5 (80%). In conclusion, coconut water is a suitable diluent for rabbit semen for on-farm artificial insemination, the optimal dilution rate of coconut water in rabbit semen is 60%, which guarantees high conception, litter size and productivity index at birth.

Rabbit seminal plasma proteome: The importance of the genetic origin

The present study was conducted to characterise rabbit seminal plasma proteins (SP proteins) focusing on the influence of the genetic origin and seasonality. In addition, β-NGF protein quantity in SP was determined. Semen samples were recovered from January to December 2014 using 6 males belonging to genotype A and six from genotype R. For each genotype, one pooled sample at the beginning, middle and end of each season was selected to develop the experiment. A total of 24 pools (3 for each season and genetic line) were analysed. SP proteins of the two experimental groups were recovered and subjected to in-solution digestion nano LC-MS/MS and bioinformatics analysis. The resulting library included 402 identified proteins validated with ≥95% Confidence (unused Score ≥ 1.3). These data are available via ProteomeXchange with identifier PXD006308. Only 6 proteins were specifically implicated in reproductive processes according to Gene Ontology annotation. Twenty-three proteins were differentially expressed between genotypes, 11 over-expressed in genotype A and 12 in genotype R. Regarding the effect of season on rabbit SP proteome, results showed that there is no clear pattern of protein variation throughout the year. Similar β-NGF relative quantity was observed between seasons and genotypes. In conclusion, this study generates the largest library of SP proteins reported to date in rabbits and provides evidence that genotype is related to a specific abundance of SP proteins.

Freezability genetics in rabbit semen

The aim of this study was to estimate the heritability of semen freezability and to estimate the genetic correlation between frozen-thawed sperm traits and the growth rate in a paternal rabbit line. Estimated heritabilities showed that frozen-thawed semen traits are heritable (ranged between 0.08 and 0.15). In the case of Live-FT (percentage of viable sperm after freezing), the estimated heritability is the highest one, and suggests the possibility of effective selection. After the study of genetic correlations it seems that daily weight gain (DG) was negatively correlated with sperm freezability, but no further conclusions could be drawn due to the high HPD95%. More data should be included in order to obtain better accuracy for the estimates of these genetic correlations. If the results obtained at present study were confirmed, it would imply that selection for DG could alter sperm cell membranes or seminal plasma composition, both components related to sperm cryoresistance.

Factors affecting storage of Slovak native rabbit semen in the gene bank

In this study, fresh and frozen-thawed semen of Nitra and Zobor rabbit breeds were evaluated for potential inter-breed or inter-male differences in sperm quality traits. Individual male semen from four rabbits of each breed were diluted (v:v; 1:1) in a freezing medium composed of a commercial diluent, 16% of dimethyl sulphoxide (DMSO), 4% of Ficoll 70 and 2% of sucrose and frozen in liquid nitrogen vapours before being plunged into liquid nitrogen. Different motility traits, viability and plasma membrane integrity of fresh and frozen-thawed semen were evaluated in vitro using computer-assisted sperm analysis and flow cytometry. To evaluate the sperm fertilization ability, artificial insemination of fresh and frozen-thawed sperm was performed. Our results showed the effect of breed (P ≤ 0.05) on frozen-thawed sperm viability and plasma membrane integrity. Moreover, individual variability in semen quality among the rabbits was revealed (0.31 to 0.71 among quality traits). Our results thereby confirmed that the cryopreservation procedure could not ensure comparable sperm post-thaw survival for different breeds or males. Nevertheless, correlations between numbers of fresh total motile and progressively moving sperm and several quality parameters measured post thawing were revealed. Therefore, we suggest that the objective assessment of fresh rabbit sperm motility may be an effective indicator of frozen-thawed semen quality. Consequently, regular semen assessment is required in order to preserve good-quality insemination doses from native breeds.

Effect of different freezing velocities on the quality and fertilising ability of cryopreserved rabbit spermatozoa

The freezing step of the cryopreservation protocol negatively influences the quality and fertilising ability of rabbit spermatozoa. This study determines the effect of different rates of freezing on the quality and fertilising ability of rabbit spermatozoa cryopreserved with dimethylsulfoxide (DMSO) (1.75M) and sucrose (0.05M). Ejaculates from meat rabbit line males (n=12) were pooled and each pool (n=7) was split into four aliquots. One group of straws (control, C) was frozen in static liquid nitrogen vapour (5cm above the liquid nitrogen, 10min) and the other groups were frozen at different freezing rates (°Cmin(-1)) from -6°C to -100°C using a programmable freezer: slow (-15°Cmin(-1), S), medium (-40°Cmin(-1), M) or fast (-60°Cmin(-1), F). After thawing (50°C, 12s), the quality was highest (P<0.05) in C and M samples and lowest in S and F samples. F samples presented the lowest litter sizes (P≤0.05) and fertility whilst M samples exhibited the highest values. In conclusion, the freezing rate affects both the quality and the fertilising ability of frozen-thawed rabbit spermatozoa, with both slow (-15°Cmin(-1)) and fast (-60°Cmin(-1)) freezing rates being detrimental for the quality and fertilising ability.

The cryoprotective effect of Ficoll on the rabbit spermatozoa quality

The aim of this study was to evaluate the effect of the addition of Ficoll 70 into the cryopreservation medium containing sucrose and dimethyl sulfoxide (DMSO) on rabbit spermatozoa characteristics following freezing/thawing. This large molecular weight polymer elevates the viscosity of medium and, therefore, could better protect spermatozoa during the freezing process. Only ejaculates of good initial motility (>80%) were used in the experiments. Heterospermic pools were diluted in a freezing medium composed of commercial diluent, 16% dimethyl sulphoxide (DMSO) and 2% sucrose (control) or in the same medium enriched with 4% Ficoll 70 (Ficoll) and frozen in liquid nitrogen vapours for 10 min before being plunged in liquid nitrogen. The quality of fresh and frozen/thawed spermatozoa samples was evaluated in vitro using the Computer Assisted Semen Analysis (CASA) system, fluorescent probes (peanut agglutinin (PNA)-Alexa Fluor®; annexin V-FLOUS) and by electron microscopy. Better cryoprotective effect was observed when Ficoll 70 was added, compared with the semen cryopreserved with sucrose and DMSO only. The higher values (P < 0.05) of motile and progressively moving spermatozoa immediately after thawing and at 30 min following incubation at 37°C were obtained in the Ficoll group. Moreover, the higher number (P < 0.05) of acrosome intact sperm was found in the Ficoll compared with the control group. Furthermore, no significant differences in kindling rates and number of pups born between frozen/thawed and fresh semen group were found. In conclusion, our study showed that the addition of Ficoll 70 might improve several characteristics of rabbit spermatozoa measured in vitro following freezing/thawing.

Reducing the time rabbit sperm are held at 5 °C negatively affects their fertilizing ability after cryopreservation

Cooling sperm to and equilibrating the sperm at 5 °C require the most time in any sperm cryopreservation protocol. Reducing the time required for these phases would simplify sperm freezing protocols and allow greater number of ejaculates to be processed and frozen in a given time. This study determined how holding rabbit sperm at 5 °C for different lengths of time (0, 10, 15, 20, 30, or 45 minutes) affected the quality of rabbit sperm, measured by in vitro assays, and if reducing the cooling time to only 10 minutes affected the fertilizing ability of the sperm. Reducing the time sperm were held at 5 °C to 10 minutes did not affect the in vitro quality of the sperm (percent motile and with intact plasma membranes), although eliminating the cooling phase completely (directly freezing the sperm from room temperature) decreased in vitro assessed sperm quality (P<0.01). However, reducing the time sperm were held at 5 °C, from 45 to 10 minutes, negatively affected the fertilizing ability of sperm in vivo (P<0.05). In conclusion, completely eliminating cooling rabbit sperm to 5 °C before freezing is detrimental for rabbit sperm cryosurvival, and although shortening the time sperm are held at 5 °C to 10 minutes does not reduce in vitro sperm quality, it does reduce the fertility of rabbit sperm. Therefore, the length of time rabbit sperm equilibrate at 5 °C is crucial to the fertilizing ability of rabbit sperm and must be longer than 10 minutes. Currently, it is not known if holding rabbit sperm at 5 °C for less than 45 minutes will affect sperm fertilizing ability.

The effect of bovine serum albumin and fetal calf serum on sperm quality, DNA fragmentation and lipid peroxidation of the liquid stored rabbit semen

The aim of the present study was to determine the effects of the bovine serum albumin (BSA) and fetal calf serum (FCS) on sperm quality, DNA fragmentation and lipid peroxidation of liquid stored rabbit semen stored up to 72 h at 5 °C. Ejaculates were collected from five New Zealand male rabbits by artificial vagina and pooled at 37 °C following evaluation. Each pooled ejaculate was split into three equal experimental groups and diluted to a final concentration of approximately 40 × 10(6)sperm/ml (single step dilution), in an Eppendorf tube, with the Tris based extender containing BSA (5mg/ml), FCS (10%) or no additive (control) at 37 °C, cooled to 5 °C and stored for up to 72 h. The extender supplemented with BSA and FCS did not improve the percentages of motility and acrosomal abnormality during 48 h compared to the control. The additives BSA and FCS had a significant effect in the maintaining of plasma membrane integrity between 48 and 72 h storage period, compared to the control (P<0.01). The supplementation of BSA and FCS had a protective effect on motility (P<0.05), plasma membrane integrity (P<0.01) and acrosomal integrity (P<0.01) at 72 h compared to the control. The supplementations with BSA and FCS led to a reduction in DNA damage of rabbit sperm at 48 and 72 h during storage period, compared to the control (P<0.001). Although supplementation of BSA and FCS caused significant (P<0.01) decreases in malondialdehyde (MDA) level at 48 h and 72 h, they significantly (P<0.01) increased the glutathione peroxidase (GPx) antioxidant activity up to 72 h when compared to the control group. In conclusion, BSA and FCS supplementation to liquid stored rabbit semen provide a protection for spermatozoa against cool storage-induced DNA damage and plasma membrane integrity by their antioxidative properties.

[Effects of some extenders and monoamines on sperm cryopreservation in tree shrews (Tupaia belangeri)]

The tree shrew may be an important experimental animal for disease models in humans. The effects of some extenders and momamines on sperm cryopreservation will provide helpful data for experimentation of strains and conservation of genetic resources in tree shrews. Epididymal sperm were surgically harvested from male tree shrews captured around Kunming, China and sperm motility, acrosome integrity and fertility were assessed during cryopreservation. In Experiment 1 eight extenders (TTE, TCG, TCF, TTG, BWW, BTS, DM, and SR) supplemented with 0.4 mol/L DMSO were used to dilute the sperm: only TTE, DM and SR showed no differences in motility and acrosome integrity compared to fresh controls after equilibration. After freezing and thawing, sperm in any extender showed lower motility than fresh control and sperm in DM showed higher motility than other groups. However, BWW produced the lowest motility. For acrosome integrity, TTE and DM showed higher than BWW, BTS and SR after equilibration. The parameter in DM was higher than other groups (except TTE) after thawing. In Experiment 2 four penetrating cryoprotectant agents (CPA) [dimethyl-formamide (DF), formamide (F), dimethylacetamide (DA), and acetamide (A)] at 0.2 mol/L, 0.4 mol/L, 0.8 mol/L, and 1.2 mol/L, respectively were added to the DM extender. Motility showed no difference among CPA groups and non-CPA group (control) after equilibration, but all thawed sperm showed lower values in motility and acrosome integrity than pre-freezing groups. However, sperm in 0.8 mol/L DF and 0.4 mol/L DMSO showed higher values in both parameters than that in other CPA groups (P>0.05). In Experiment 3 the fertilization rate of oocytes inseminated with 0.4mol/L DMSO (50%) were higher than that with 0.8mol/L DF (16%). In conclusion, non-ion extenders supplemented with egg yolk may be better for sperm cryopreservation in tree shrews and cryoprotectant effects of monoamines agents should be further studied in this species.

Effect of cooling rate to 5 °C, straw size and farm on fertilizing ability of cryopreserved rabbit sperm

High fertility and prolificacy in rabbits are currently only achieved using fresh sperm. This study was conducted to determine if the cooling rate to 5 °C, the straw size and the farm where artificial inseminations are performed have an impact on the fertilizing ability of rabbit sperm cryopreserved with an extender containing dimethyl sulphoxide (DMSO; 1.75 m) and sucrose (0.05 m). Slow cooling to 5 °C improved neither fertility rate (58 vs 56% kindling rate for fast and slow cooling, respectively) nor prolificacy (6.5 vs 8.7 total born for slow and fast cooling, respectively; p < 0.05) compared to fast cooling rate to 5 °C. The straw size did not have an effect on either fertility or prolificacy (47 vs 57% kindling rate and 6.3 vs 6.8 total born for sperm loaded into 0.25 and 0.5 ml straws, respectively). In addition, similar results were obtained between farms (46-57% kindling rate and 4.9-6.7 total born), although this effect should be studied further. In conclusion, with this extender, slow cooling does not present a beneficial effect on sperm fertilizing ability and either 0.25 or 0.5 ml straws can be used to freeze the sperm, obtaining similar results after artificial insemination. In addition, similar results were obtained between farms when using cryopreserved sperm, and these results were lower than those obtained after artificial insemination with fresh semen. Therefore, new approaches are needed to improve the results obtained when cryopreserved sperms are used before this type of sperm can be used for commercial purposes.

Artificial fertilization in rabbits by intracytoplasmic sperm injection (ICSI)

Intracytoplasmic sperm injection (ICSI) consists of the injection, under microscopic observation, of a single spermatozoon directly into the cytoplasm of an oocyte using an injection capillary. This technique is used commonly in human medicine in cases of infertility. The advantage of ICSI is that the technique requires only one spermatozoon per oocyte for fertilization. Spermatozoa used for ICSI do not require high motility; ICSI works as long as the sperm nucleus is genetically intact. This protocol describes methods for performing ICSI in rabbits using either fresh or frozen/thawed sperm.

Artificial insemination in rabbits

Artificial insemination (AI) is used in rabbit husbandry to improve breeding management. Conception rates after AI with fresh semen are equivalent to or even better than those obtained by natural mating. Also, AI has the advantage of avoiding contact between animals. Furthermore, AI with frozen sperm is particularly useful for assisted reproduction and conservation of rabbit genetic resources, and in some cases, frozen semen produce results similar to those obtained in AI using fresh sperm. This protocol describes the most commonly used protocol for AI using fresh sperm.

Effect of different number of frozen spermatozoa inseminated on the reproductive performance of rabbit does

The relationship between the number of frozen spermatozoa inseminated and fertility rate and litter size at birth in rabbit does was investigated. Six hundred artificial inseminations (AI) were performed on multiparous lactating does with three spermatozoa concentrations: 10, 25, 50x10(6)spermatozoa/AI. All the does were synchronized with 20 UI of eCG 2 days before AI. The estimated sexual receptivity was 87%. The freezing-thawing procedure strongly reduced kinetic and functional traits (acrosome integrity, capacitation) of the spermatozoa. The number of spermatozoa inseminated did not affect the reproductive performance: the mean fertility rate and litter size values were 51.5% and 7.6%, respectively. Sexually receptive does (n=522) inseminated with frozen spermatozoa showed a 58.0% fertility rate whereas, non-receptive does (n=78), had a very poor fertility rate (7.8%).

Effect of antibiotics on thermodynamic properties of freezing media in rabbit species: A first calorimetric approach

Semen freezing is an effective and safe solution for the cryopreservation of animal genetic resources and for the diffusion of the genetic progress. Actually, these techniques are not yet under control for the rabbit species partly because methods are not clearly defined. Thus, the aim of this work is to study the effect of antibiotics (Penicillin G, Streptomycin) routinely used in freezing semen on the thermodynamic properties of freezing media mainly used in rabbit species. Measurements realized by differential scanning calorimetry show that these antibiotics may change the temperature of crystallization and the quantity of ice formed in the freezing media considered. Our calorimetric approach underlined that the composition and the properties of the cryoprotective solutions should be studied more precisely.

Preliminary studies on cryopreservation of hare (Lepus europaeus Pallas, 1778) semen

In the last decades, a significant decrease in hare population has been observed; for this reason, the aim of the study was to check if hare semen could be preserved in liquid nitrogen, with an extender used for rabbit semen. The results should provide a basis for creating a gene bank of the species. Ten ejaculates (volume above 0.4 ml, percentage of motile spermatozoa above 75%, spermatozoa concentration above 250 x 10(6) ml), obtained with electroejaculation method from four males, were frozen in an extender of the following composition: Tris (3.028 g), citric acid (1.675 g), glucose (1.25 g), dimethylsulphoxide (DMSO) (4.5%, v/v), egg yolk (17%, v/v) and distilled water to 100.00 ml. The motility of post-thawing spermatozoa was 40.50+/-7.97%, percentage of spermatozoa with normal acrosomes 76.10+/-3.69% and percentage of live spermatozoa 35.05+/-4.21%. Based on the properties of freezing-thawing semen, the hare semen can be successfully preserved in extender used for rabbit semen.

The successful double cryopreservation of rabbit (Oryctolagus cuniculus) semen in large volume using the directional freezing technique with reduced concentration of cryoprotectant

Using directional freezing, our objective was to cryopreserve rabbit semen and achieve fertility that was equal or higher than that achieved with conventional freezing. The working hypothesis was that controlling the ice-front propagation would allow reduction of DMSO concentration to <1M, in addition to the capability to freeze large volumes (2-10 mL). Moreover, single and double freezing of semen were used to demonstrate the abbreviated mechanical stress imparted by directional freezing. Single-cryopreserved semen from 15 males extended with 0% egg yolk/1.75 M DMSO, 15.3% egg yolk/0.88 M DMSO and 20% egg yolk/0M DMSO resulted in lower (P<0.05) mean+/-S.E.M. post-thaw motility (3.6+/-1.1, 28.5+/-2.8 and 36.3+/-1.8%, respectively) compared to fresh semen (73.3+/-1.2%). Semen from seven of these males, subject to double freezing using only egg yolk based extenders, resulted in post-thaw motilities of 18.1+/-2.2 and 16.4+/-3.3%. Despite the reduced functional parameters of cryopreserved semen, fertility and kindling rates of 73.9 and 56.5% for single frozen-thawed, and 28.6 and 35.7% for double frozen-thawed semen were achieved (with insemination of 98 females). There was no significant difference in fertility rate between fresh semen (87.5%) and semen that was single frozen-thawed with the 15.3% egg yolk/0.88 M DMSO extender (73.9%). In conclusion, cryopreservation of rabbit semen in large volumes using directional freezing achieved fertility rates similar to those achieved with fresh semen. Furthermore, acceptable fertility rates with double frozen-thawed semen could facilitate the future use of sex-sorted semen in rabbits.

Comparison of Glycerol, Lactamide, Acetamide and Dimethylsulfoxide as Cryoprotectants of Japanese White Rabbit Spermatozoa

The rabbit is considered to be a valuable laboratory animal. We compared glycerol, lactamide, acetamide, and dimethylsulfoxide (DMSO) as cryoprotectants in egg-yolk diluent of ejaculated Japanese white rabbit spermatozoa for improvement of sperm cryopreservation methods. Rabbit semen was frozen with 1.0 M glycerol, lactamide, acetamide, or DMSO in plastic straws. Forward progressive motility and plasma membrane integrity of the post-thaw spermatozoa were examined. The rate of forward progressive motile spermatozoa in lactamide (37.8 +/- 3.0%) was significantly (P<0.05) higher than in glycerol (17.0 +/- 3.3%). In addition, the rates of sperm plasma membrane integrity in lactamide and acetamide (35.9 +/- 3.3% and 30.2 +/- 3.0%, respectively) were significantly (P<0.05) higher than in glycerol (17.0 +/- 2.6%). The results indicate that 1.0 M lactamide and acetamide have higher cryoprotective effects than 1.0 M glycerol for cryopreservation of Japanese white rabbit spermatozoa.

Influence of the Donor Male on the Fertility of Frozen-Thawed Rabbit Sperm after Artificial Insemination of Females of Different Genotypes

In this work, the influence of the donor male on the fertility of cryopreserved rabbit sperm after artificial insemination into females from different genotypes was evaluated. Females belonged to three lines selected for maternal characteristics (A, V and H) and all the possible crosses between them. Sperm from five males from the line selected for one of the maternal characteristics (line V) was frozen individually in a Tris-citric acid-glucose diluent with 1.75 m of DMSO and 0.05 m of sucrose (final concentrations). After artificial insemination of the cryopreserved sperm, fertility rates and prolificacy were similar for all groups of females (56% of fertility rate and 7.2 total born). Significant differences between males were observed for both fertility (p < 0.05) and kindling (p < 0.01) rate. These differences could be because of differences in the freezing resistance of sperm from the different males.

Effect of solid storage at 15°C on the subsequent motility and fertility of rabbit semen

We conducted two studies to improve preservation of rabbit semen. The objective of the first study was determine whether a glucose- and fructose-based extender with two different amounts of gelatin would solidify at 15 degrees C, and to evaluate the influence of gelatin supplementation on sperm motility parameters after storing semen up to 10 days at 15 degrees C. The fertility of rabbit semen diluted in the best gelatin-supplemented extender established in Study 1 and stored for up to 5 days was evaluated in the second study. In Study 1, semen was collected with an artificial vagina from 40 bucks. Each ejaculate was diluted to (80-100) x 10(6) spermatozoa/mL (1:3, semen/extender) at 37 degrees C in one of the three following glucose- and fructose-based extenders: control (standard liquid extender), semi-gel or gel (0.7 or 1.4 g gelatin in 100 mL extender, respectively). Pools of semen were allocated among 0.6 mL plastic artificial insemination (AI) guns. Thirty (10 per extender group) AI doses were immediately analyzed (0 h) and the remainder stored in a refrigerator (15 degrees C) for 12, 24, 36, 48, 72, 96, or 240 h. All doses with gelatin extenders solidified at 15 degrees C. Semen samples, prewarmed to 37 degrees C, were evaluated with a computer-assisted sperm analysis (CASA) system. The percentage of motile cells was significantly lower using the liquid compared to the gel extenders during semen storage from 0 to 96 h. Although significance was lost, these differences persisted after 240 h of storage. Motility of spermatozoa in the semi-gel extender was intermediate between that of liquid and gel extender throughout the study. Study 2 was performed on 1250 multiparous lactating does. Five homogeneous groups of 250 does previously synchronized were inseminated using semen previously stored for 120, 96, 72, 48 or 24 h, respectively. Rabbit does receiving 24 h-stored semen (diluted with the control extender used in Study 1) served as controls. The remaining females received seminal doses supplemented with 1.4 g/100mL gelatin (gel extender used in Study 1). Kindling rates for rabbit does inseminated with gelatin-supplemented (solid) semen doses stored for 48 h (88%) or 72 h (83%) were similar to those recorded for liquid controls stored for 24 h (81%), whereas rates significantly decreased when the semen was solid and stored for 96 h (64%) or 120 h (60%) before AI. In conclusion, rabbit spermatozoa were effectively stored in the solid state at 15 degrees C, with fertility preserved for up to 5 days. Solid storage of rabbit semen would facilitate commercial distribution.

In vitro Evaluation of in vivo Fertilizing Ability of Frozen Rabbit Semen

The present work studied different spermatozoa parameters and the ability of frozen rabbit spermatozoa to fertilize, in vitro, in vivo-matured oocytes, as a test to predict their in vivo fertility and prolificacy. Semen from rabbit bucks was frozen using two freezing protocols [in a freezer at -30 degrees C or in liquid nitrogen vapour (LNV)]. For the in vivo trial, females were inseminated with frozen-thawed spermatozoa. Oocytes used for in vitro testing were recovered 14 h after ovulation induction from donors and co-incubated with 2 x 10(6) frozen-thawed spermatozoa during 4 h at 37 degrees C in Tyrode's medium under an atmosphere of 5% CO(2) in air with maximal humidity. After co-incubation period, presumptive zygotes were cultured in TCM199 supplemented with 20% foetal bovine serum (FBS), under the same conditions described above. Although no statistical differences were observed between freezing protocols in seminal parameters [motility rate: 40 and 35%, VCL: 35 and 46 microm/s, amplitude of lateral head displacement (ALH): 1.7 and 2.4 mum, for semen frozen at -30 degrees C and in LNV, respectively], significant differences were noted in the fertilizing ability in vivo and in vitro. Semen frozen at -30 degrees C showed the highest fertilizing ability in vitro (26.7% vs 6.2 and 8.7% for semen frozen at -30 degrees C, in LNV and fresh semen, respectively) and the lowest fertility rate in vivo (21.7% vs 64.2% and 70.6% for semen frozen at -30 degrees C, in LNV and fresh semen, respectively). Sperm frozen at -30 degrees C seemed to be more capacitated.