Desalted and lyophilized bovine seminal plasma delays induction of the acrosome reaction in frozen-thawed bovine spermatozoa in response to calcium ionophore

Seminal plasma removal for medium-term preservation of ram sperm at 5 °C

This study aimed to investigate if washing ram sperm from seminal plasma (SP) could be an effective tool to extend sperm lifespan in medium-term preservation in liquid form to optimize ovine artificial insemination protocols. To this end, in Experiment 1 SP was added to a sperm model without previous contact with this substance (ram epididymal sperm) at the beginning or the end of a 48-hour preservation protocol at 5 °C (n = 13). Sperm motility and kinetic parameters and sperm functionality in terms of sperm viability, apoptosis, mitochondrial activity and reacted acrosomes were assessed after 6 h of storage at 15 °C (standard liquid preservation method) and 24 and 48 h at 5 °C. Extended sperm showed better results after 48 h when stored in the absence than in the presence of SP in most sperm quality parameters. Moreover, the final SP supplementation of this experimental group resulted in the highest sperm motility and kinetic parameters, viability and mitochondrial activity. These results suggested that initial SP deprivation could be beneficial in a medium-term ram sperm preservation protocol in liquid form, as well as a final supplementation. Therefore, we conducted Experiment 2 to evaluate the effect of SP removal from freshly ejaculated ram semen under the same storage conditions as in Experiment 1 (n = 12). Surprisingly, SP withdrawal impaired sperm functionality, leading to increased apoptosis and decreased mitochondrial activity after 24 and 48 h at 5 °C. Conversely, SP supplementation at the end of the preservation protocol of the ejaculate processed as usual had a positive effect on sperm quality and fertility. To summarize, SP absence was beneficial for a medium-term preservation protocol (up to 48 h at 5 °C) of ram epididymal sperm, but the same preservation protocol for ram ejaculated sperm revealed a possible failure of the SP removal method in avoiding the sperm-SP interaction effect. Meanwhile, SP supplementation of ram semen at the end of the preservation protocol increased in vitro sperm quality and fertility after artificial insemination.

Review: Evaluation of bull fertility. Functional and molecular approaches

With the term "assisted reproduction technologies" in modern cattle farming, one could imply the collection of techniques that aim at the optimal use of bovine gametes to produce animals of high genetic value in a time- and cost-efficient manner. The accurate characterisation of sperm quality plays a critical role for the efficiency of several assisted reproduction-related procedures, such as sperm processing, in vitro embryo production and artificial insemination. Bull fertility is ultimately a collective projection of the ability of a series of ejaculates to endure sperm processing stress, and achieve fertilisation of the oocyte and production of a viable and well-developing embryo. In this concept, the assessment of sperm functional and molecular characteristics is key to bull fertility diagnostics and prognostics. Among others, functional features linked to sperm plasma membrane, acrosome and DNA integrity are usually assessed as a measure of the ability of sperm to express the phenotypes that will allow them to maintain their homeostasis and orchestrate-in a strict temporal manner-the course of events that will enable the delivery of their genetic content to the oocyte upon fertilisation. Nevertheless, measures of sperm functionality are not always adequate indicators of bull fertility. Nowadays, advancements in the field of molecular biology have facilitated the profiling of several biomolecules in male gametes. The molecular profiling of bovine sperm offers a deeper insight into the mechanisms underlying sperm physiology and, thus, can reveal novel candidate markers for bull fertility prognosis. In this review, the importance of three organelles (the nucleus, the plasma membrane and the acrosome) for the characterisation of sperm fertilising capacity and bull fertility is discussed at functional and molecular levels. In particular, information about sperm head morphometry, chromatin structure, viability as well as the ability of sperm to capacitate and undergo the acrosome reaction are presented in relation to the cryotolerance of male gametes and bull fertility. Finally, major spermatozoal coding and non-coding RNAs, and proteins that are involved in the above-mentioned aspects of sperm functionality are also summarised.

Heparin-induced and caffeine or ouabain supplemented capacitation of frozen-thawed yak (Bos grunniens) spermatozoa

Our goal was to investigate heparin-induced capacitation of frozen-thawed yak sperm, and to assess the effects of caffeine or ouabain supplementation with heparin on sperm capacitation. Sperm were incubated with varying heparin concentrations, namely, 0, 12.5, 25, 50 and 100 μg/ml, for 0, 15, 30 and 60min. In every treatment, sperm capacitation was assessed using microscopic examination of the sperm acrosomal status and western blot analysis of the levels of tyrosine phosphorylation (Tyr-P). Based on our results, the optimal condition for frozen-thawed yak sperm capacitation was a 30min exposure to 50 μg/ml heparin. Next, we incubated frozen-thawed yak sperm with 50ug/ml heparin, along with varying concentrations of caffeine supplementation, namely, 0, 2.5, 5, and 10mM for 30min. Interestingly, caffeine significantly increased yak sperm acrosome reaction (AR) and Tyr-P (p < 0.05). The optimal caffeine concentration was 5mM, followed by 2.5mM and 10mM, with the lowest AR and Tyr-P found in sperm cells that did not receive any caffeine. To examine the effects of ouabain on sperm capacitation, we next incubated frozen-thawed yak sperm with 50 μg/ml heparin, along with varying concentrations of ouabain, namely, 0, 25, 50, and 100 µM for 30min. We demonstrated that ouabain supplementation did not alter yak sperm AR or Tyr-P in sperm cells, relative to the control (p>0.05). In summary, our findings suggested that caffeine acts synergistically with heparin to increase yak sperm capacitation, but ouabain does not synergize with heparin to promote yak sperm capacitation.

Comparative analysis of various step-dilution techniques on the quality of frozen Limousin bull semen

Background and Aim:

Indonesia has two National Artificial Insemination centers and 17 Regional Artificial Insemination Centers. The frozen semen production techniques differed between the centers, including the type of diluent and semen dilution technique. The aim of the research was to compare the quality of frozen Limousin bull semen diluted using different techniques.

Materials and Methods:

Semen was collected from three sexually mature Limousin bulls using an artificial vagina. Immediately after collection, the semen was evaluated macroscopically and microscopically. Semen that had >70% motile sperm and <20% sperm abnormality was divided into three tubes and diluted with skim milk-egg yolk (SMEY) using three different dilution techniques: One-step dilution (100% SMEY with 8% glycerol) at room temperature ([RT] 20°C until 25°C) two-step dilution (50% SMEY without glycerol at RT, stored at 5°C; and 50% SMEY with 16% glycerol after 1 h stored at 5°C); and three-step dilution (50% SMEY without glycerol at RT, stored at 5°C; and 50% SMEY with 16% glycerol added twice at 1 h and 1.5 h after being stored at 5°C). The diluted semen was loaded into 0.25 mL mini straws, equilibrated, and frozen using a freezing machine. Sperm motility, viability, membranes, DNA integrity, and concentrations of malondialdehyde (MDA) and aspartate aminotransferase (AST) enzymes were evaluated after thawing.

Results:

The results showed that there were no significant differences in sperm motility and DNA integrity between dilutions (p>0.05). However, sperm viability and membrane intactness of one-step dilutions were higher than those of three-step dilutions. The concentrations of MDA and AST enzymes of sperm in one-step dilutions were lower than those of three-step dilutions (p<0.05).

Conclusion:

It was concluded that the one-step-dilution technique was better than three-step dilution for cryopreservation of Limousin bull semen.

Multicolor flow cytometric analysis of cryopreserved bovine sperm: A tool for the evaluation of bull fertility

The study aimed at the analysis of the functional status of cryopreserved bovine sperm using multicolor flow cytometry. The value of sperm functional traits as predictors of bull fertility was further evaluated through a retrospective fertility study. For this purpose, 20 Holstein-Friesian bulls serving as mature sperm donors in an artificial insemination (AI) center were selected based on their annual 56-d non-return rate (%) after at least 1,000 AI, and were accordingly classified as high (HF; n_HF = 10 bulls) or low fertility bulls (LF; n_LF = 10 bulls). Four to 5 cryopreserved ejaculates per bull (91 ejaculates in total) were examined immediately after thawing (0 h) and after a 3-h incubation at 38°C (3 h). A panel of 5 fluorochromes including calcein violet, propidium iodide, pycoerythrin-conjugated lectin of Arachis hypogea, Fluo-4, and cyanine dye DiIC₁(5) was configured by means of a 3-laser flow cytometer, to simultaneously assess sperm esterase activity, plasma membrane integrity, acrosomal status, intracellular Ca²⁺ levels, and mitochondrial membrane potential, respectively. The % relative size of 18 sperm sub-populations showing 2 or more of a combination of the following features was determined: high esterase activity (C_pos), intact plasma membrane (PI_neg), unstained acrosome (PNA_neg), low intracellular Ca²⁺ levels (F_neg), and high mitochondrial membrane potential (M_pos). In both fertility groups, M_pos cells comprised more than 90 and 84% of PI_negPNA_neg sperm at 0 and 3 h, respectively. The percentage of C_posPI_negPNA_negF_negM_pos sperm did not differ between HF and LF ejaculates; however, the percentage of F_neg cells within the PI_negPNA_neg and PI_negM_pos sperm populations at 0 h was higher in the HF than in the LF bulls. Applying the random forest ensemble learning method, approximately two-thirds of ejaculates could be correctly assigned to their fertility group. The fraction of F_neg sperm within the PI_negM_pos population at 0 h was the most important fertility predictor among the 18 defined sperm populations. In conclusion, multicolor flow cytometry offered an insight into the functional heterogeneity of cryopreserved bovine sperm. Indeed, the ability of viable sperm to retain low Ca²⁺ levels differed between bulls of diverse fertility. A classifier based on selected sperm populations assessed through multicolor flow cytometry could contribute to the prognosis of bull fertility after AI.

Protein and lipid species in seminal plasma of fertile Holstein-Friesian bulls

Protein and lipid molecules in seminal plasma (SP) collected from fertile bulls were investigated. Semen was collected from 10 bulls (2 ejaculates each) and examined for standard semen analysis. Raw SP was recovered by centrifugation and total protein (TP) concentration was determined using a refractometer. Raw SP was desalted using a Sephadex G-25 desalting column then both raw and desalted SP was subjected to SDS-PAGE. Neutral lipids and phospholipids of raw and desalted SP were separated by thin-layer chromatography (TLC). The results revealed that, all bulls had normal semen characteristics and TP concentration in SP ranged from 7.0 to 10.4 g/dL except bull No. 6 had a relatively low concentration of 4.9 to 6.8 g/dL. Neither proteins nor lipids species were different between raw and desalted SP. Seventeen proteins were detected ranging from 8.5 to 185.8 kDa, and those of 12, 13.5, 15, 21, 23 and 38 kDa were predominant. Notably, proteins of 10, 17.5, 19, 21, 80 and 185.8 kDa might be new candidates of SP proteins (SPPs). The detected neutral lipid spots corresponded to cholesterol, 1,2-dimyristoyl glycerol, 1,2-dioleoyloglycerol, 1,3-dimyristoyl glycerol and 1,3-dioleoyloglycerol. The detected phospholipids spots corresponded to non-migrating phospholipids, sphingomyelin (SM), phosphatidylcholine (PC), phosphatidylserine (PS), phosphatidylinositol (PI), phosphatidylethanolamine (PE), cerebroside and polyglycerol phosphatide. Cholesterol represents the major molecule of neutral lipids, whereas SM, PC, PI and PE represent the major phospholipids. Noteworthy, there were 2 species of diacylglycerol (DAG) and 3 species of PI in bovine SP. In conclusion, this study gave a general picture of SP protein and lipid species in fertile bull semen, which might serve as fundamental knowledge for either semen analysis or prediction of male fertility.