Assessment of storage effects in liquid preserved boar semen

Fertility of extended boar semen declines within the first 72 h of storage in vitro. Standard semen assessment, such as motility and membrane integrity, allows detection of lethal damage of spermatozoa. However, conventional sperm assessment often lacks standardization and does not allow identification of sub-lethal changes of sperm quality during the initial 72 h of storage. In the present brief review, recent strategies for quality assessment of liquid preserved boar semen are discussed and basic implications for experiments designed to detect storage effects are given.     

Metformin blocks mitochondrial membrane potential and inhibits sperm motility in fresh and refrigerated boar spermatozoa

Metformin is clinically used to treat diabetes. Given its role‐impacting metabolism, metformin has been also added to semen cryopreservation media showing specie‐dependent effects. We aimed to investigate metformin effects in both fresh (38.5°C for 2, 24 hr) and refrigerated (17°C for 10 days) boar spermatozoa. Metformin (2 hr) does not affect fresh sperm viability, membrane lipid organization nor acrosome integrity. However, metformin (24 hr) blocks sperm ΔΨm and significantly reduces % motile spermatozoa (65%), % progressive spermatozoa (50%), % rapid (100%), velocities VCL (69%), VSL (86%), VAP (78%) and motility coefficients. Metformin‐including extender does not modify sperm viability, membrane lipid organization or acrosome integrity. Furthermore, it significantly reduces high ΔΨ‐population spermatozoa at refrigeration day 4. Metformin also significantly reduces sperm motility during refrigeration. Summarizing, metformin inhibits both boar sperm ΔΨ and motility in any sperm condition studied: fresh and refrigerated. These findings dissuade metformin as an additive to improve boar sperm quality.     

Acrosomal and viability status of bovine spermatozoa evaluated by two staining methods

Artificial insemination with frozen-thawed spermatozoa is commonly used in cattle breeding. A simple and fast procedure is needed for routine evaluation of the acrosomal status of frozen-thawed bovine sperm. Therefore, the purpose of this study was to test two staining procedures used to determine the viability and integrity of acrosome of frozen-thawed bovine spermatozoa. Double staining and Hoechst/FITC-Pisum sativum agglutinin (FITC-PSA) labelling were tested for evaluating the viability and acrosome reaction induced by calcium ionophore of bull spermatozoa. In our experiments no significant differences were detected in the frequency of acrosome-reacted sperm either by double staining (37.98%) or by FITC-PSA labelling (39.33%). The viability of sperm stained by the double staining method was 67.17%, and a higher portion of viable sperm (82.67%) was observed by staining with the Hoechst procedure (P < 0.01). On the basis of the results obtained it is concluded that both methods can be used for detecting the acrosome reaction of frozen-thawed bovine spermatozoa.     

Reproductive efficiency of a new modified boar semen extender for liquid storage

In the present study the Authors developed a new modified boar semen extender for short-term liquid storage, based on the use of amikacin sulphate and fructose rather than gentamicin and glucose. The new extender (ME-S) was evaluated and compared in vitro to commercial ones (CRONOS^™, TRIXcell^™) and to a modified extender designated for long term storage (ME-L) for progressive motility. Progressive motility was not different (P>0.05) among extenders until 120 h of storage, as differences among extenders became significant (P<0.05) at 144 and 166 h. Motility data across time were better for ME-S than TRIXcell^™ (P<0.05). No differences were observed about the morphology and membrane integrity (ORT) among the new extender (ME-S) and the commercial ones. Following the results of the in vitro comparison, an artificial insemination field trial was performed for reproductive efficacy. In this trial ME-L was not used because it was not completely reliable yet. A total of 1011 sows were bred: 506 with ME-S and 505 with a commercial one (CRONOS^™). The pregnancy rate for ME-S was 93.68% (474 pregnant sows), as the commercial extender resulted in 452 pregnancies (89.5%). The statistical comparison was significant (P<0.05) and the number of live piglets born showed an increase of 52.     

Effects of glycerol concentration, equilibration time and temperature of glycerol addition on post-thaw viability of boar spermatozoa frozen in straws

Experiments were conducted to study the effect of glycerol concentration, equilibration time and temperature of glycerol addition on post-thaw viability of boar spermatozoa after cryopreservation in straws. Semen (split ejaculate) in maxi-straws (6 mm o.d.) was frozen using a programmable freezing chamber. Three methods for in vitro sperm evaluation were used: motility (MOT), acrosome integrity (NAR) and flow cytometric analysis of sperm treated with carboxyfluorescein diacetate and propidium iodide to assess sperm plasma membrane integrity (PMI). No interactions were found among the three variables evaluated. Length of prefreeze exposure to glycerol, ranging from .5 min to 75 min, had no effect on post-thaw sperm viability. Exposure of sperm to a glycerol-containing extender medium at 5 degrees C gave improved post-thaw viability over that exposed at 0 degree C (P less than .05). Glycerol at a concentration of 3 or 4% resulted in maximum post-thaw MOT. Acrosome integrity values were greatest for 2 and 3% glycerol, whereas PMI was greatest when glycerol concentration was 4 to 6%. The primary cryoprotective effect of glycerol on boar semen may be extracellular. It is concluded that 3 or 4% glycerol gives maximum viability of frozen-thawed spermatozoa when the present methods are employed.     

丁羟基甲苯抗猪精子氧化损伤作用

分别在稀释、离心猪精液中添加0.2、0.4、0.8、1.6 mmol/L丁羟基甲苯(Butylated hydroxytoluene,BHT),15℃保存,检验保存35、d后精子TMS、PMI和NAR(%)、测定MDA浓度;确定并选择最佳BHT浓度用于猪精液冷冻保存,检验解冻后TMS、PMI、NAR和Mt-MP(%)、测定MDA浓度。结果显示:BHT显著提高稀释精液、离心精液各项指标百分率(P0.05),且MDA浓度显著降低(P0.05),BHT最佳浓度分别为0.8、1.6 mmol/L;0.8 mmol/L BHT显著提高冷冻-解冻精液各项指标百分率(P0.05),且MDA浓度显著降低(P0.05)。结果表明,BHT能通过抑制精子质膜氧化损伤,提高猪精液保存效果。     

Morphological defects of the acrosome in boar spermatozoa

Morphological examination of semen from 17 boars of five breeds showed the presence of acrosome defects in 11 boars from four breeds. Two distinct types were seen; 'knobbed' sperm (type 1), of which two forms were found to be present by electron microscopy, and an uneven swellling of part of the acrosome (type 2) whose contents consisted of cytoplasmic and membrane-like material. The incidence of 'knobbed' sperm ranged from 0.2 to 6.3 per cent. Type 2 abnormalities were seen in only two boars, at 0.66 and 1.33 per cent.     

Size of pellets and individual properties of boar semen in relation to the number of motile spermatozoa following defrosting]

The second fraction of the ejaculate of five boars of the Landrace breed was used for the experiments. Non-diluted semen was kept in hydrogen atmosphere for three hours at + 5 degrees C; then it was frozen in solid carbon dioxide into 0.1 ml, 2.0 ml, and 5.0 ml pellets and in liquid nitrogen vapours into the shape of disk or cylinder 5 ml in volume. The pellets were de-frozen on a teflon pan at 42 degrees C without addition of any other diluent. Ejaculate in which at least 25% of the spermatozoa were motile was considered to be usable. No statistically significant difference was found between the motility of spermatozoa frozen in the 0.1 ml and 2.0 ml pellets, but it can be said that on an average the motility of the spermatozoa was lower in larger pellets; this could be observed mainly in the pellets with the volume of 5.0 ml. Large differences were revealed in the freezability of the semen of different boars, irrespective of the size of the frozen pellet. Insemination of 38 gilts with semen from 2.0 ml pellets gave a 57,8 % concentration rate (22 gilts) and the average litter size was 8.25 piglets.     

Long-term liquid storage of porcine spermatozoa separated using a discontinuous bovine serum albumin gradient

Two experiments were conducted to determine efficacy of a discontinuous bovine serum albumin (BSA) gradient for isolating viable porcine spermatozoa more tolerant to 5-d liquid storage in Beltsville Thawing Solution (BTS) at 15 degrees C. The gradient, contained in a 500-ml separatory funnel, consisted of 4% BSA (60 ml) over 10% BSA (60 ml). Spermatozoa were extended in 26 ml of BTS, layered on top of the gradient, and allowed to migrate through the BSA. The quality of spermatozoa separated by the gradient varied among boars. However, populations of spermatozoa isolated from the bottom 30 ml of the gradient (Fraction 4) consistently contained a high percentage of spermatozoa with acrosomes possessing normal apical ridges (NAR; 89.6%) and progressively motile spermatozoa (MOT; 84.0%), as well as spermatozoa with high velocity (VEL; 336.5 mu/s). Increasing sperm migration time, but not gradient temperature, increased the number of spermatozoa recovered in Fraction 4, but it did not reduce quality of the separated spermatozoa. Spermatozoa isolated in Fraction 4 had greater NAR, MOT and VEL after 5-d storage in BTS than did unseparated spermatozoa. Boar spermatozoa isolated on a discontinuous BSA gradient were more tolerant to storage at 15 degrees C than were unseparated spermatozoa. Such a population may be desirable for use in artificial insemination programs.