Impact of bull age, sperm processing, and microclimatic conditions on the viability and DNA integrity of cryopreserved bovine sperm

Context Seasonal microclimatic fluctuations can cause changes in sperm quality even in dairy bulls bred under temperate climate. These changes can vary between sires of different age and affect sperm freezability. Aims We aimed to evaluate the modulating effect of bull age and equilibration time before freezing on the seasonal pattern of sperm viability and DNA integrity post-thaw. Methods In the frame of systematic sperm quality control, we assessed the integrity of sperm plasma membrane and acrosome (PMAI) in 15,496 cryopreserved bovine batches, and the percentage of sperm with high DNA fragmentation index (%DFI) after 0h and 3h incubation at 38°C post-thaw (3h) in 3422 batches. Semen was equilibrated for 24h before freezing if collected on Monday or Wednesday and 72h if produced on Friday. We investigated the effect of season, bull age, equilibration, and temperature-humidity index (THI) on the day of semen collection on sperm traits using mixed-effects linear models. Key results PMAI and %DFI (0h and 3h) deteriorated with increasing THI. The effect of THI on %DFI was detected with a 30-day time lag. Seasonal fluctuations of sperm quality were similar between young, mature, and older sires. Prolonged equilibration did not affect PMAI but was linked to elevated %DFI (3h) in summer. Conclusions Extending equilibration from 24 to 72h is compatible with commercial standards of bovine sperm quality post-thaw; however, it could interfere with the seasonal pattern of the latter. Implications Systematic monitoring of bovine sperm quality enables the prompt detection of stress factors related to microclimate and semen processing.

The Effect of Mycotoxins and Their Mixtures on Bovine Spermatozoa Characteristics

There is growing concern about the effects of mycotoxins on mammalian reproduction. Although the effects of single mycotoxins have been well documented, the impact of their mixtures on spermatozoon quality is less known. Here, frozen-thawed semen (n = 6 bulls) was in-vitro-cultured (2 h) without (control) or with (i) a single mycotoxin [zearalenone (ZEN), ochratoxin A (OTA), toxin 2 (T2), and diacetoxyscirpenol (DAS)] in a dose-response manner; (ii) binary mixtures (OTA + T2, OTA + ZEN, OTA + DAS, ZEN + T2, DAS + T2 and ZEN + DAS); or (iii) ternary mixtures (OTA + DAS + T2, OTA + ZEN + T2, and ZEN + DAS + T2). Then, the spermatozoa quality was characterized according to its plasma- and acrosome-membrane integrity, mitochondrial membrane potential, and oxidation status by a flow cytometer. Exposure to single mycotoxins or binary mixtures did not affect the spermatozoa characteristics. However, exposure to the ternary mixtures, OTA + DAS + T2 and OTA + ZEN + T2, reduced (p < 0.05) the mitochondrial membrane potential relative to the control. In addition, OTA + ZEN + T2 increased (p < 0.05) the proportion of spermatozoa with reactive oxygen species relative to the control. The most suggested interaction effect between the mycotoxins was found to be an additive one. A synergistic interaction, mainly regarding the oxidation status of the spermatozoa, was also found between the mycotoxins. The current study sheds light on the potential risk of exposing spermatozoa to a mycotoxin mixture.

Seasonal and climatic factors have a significant influence on fertility associated sperm phenomic attributes in crossbred breeding bulls (Bos taurus × Bos indicus)

Although seasonal variations in semen quality and fertility have been studied to a considerable extent in breeding bulls, the effect of climatic variables on sperm functional competency has not been understood in detail. The present study analyzed sperm functional parameters in breeding bulls, over a period of 1 year, and assessed the effect of climatic variables on fertility associated sperm parameters. Seasons were categorized into summer, rainy, autumn, and winter based on the meteorological data. Semen was collected from crossbred bulls (n = 7) across the seasons and evaluated for functional membrane integrity, acrosome reaction status, protamine deficiency, capacitation, and lipid peroxidation status using specific fluorescent probes. The results of the present study revealed that bulls produced higher (p < 0.05) viable and acrosome intact spermatozoa during the autumn. The proportion of uncapacitated spermatozoa was also higher (p < 0.05) during autumn. Further, correlation of sperm functional attributes with environmental variables revealed that sperm viability was significantly (p < 0.05) and negatively correlated with daylength and temperature; acrosomal integrity was significantly (p < 0.05) and negatively correlated with day length; and protamine deficiency had significant (p < 0.05) positive correlation with day length and average temperature, and negative correlation with relative humidity. It was concluded that semen produced during autumn was superior to the semen produced during other seasons in terms of sperm functional competencies required for fertility.

The Melatonin Treatment Improves the Ovarian Responses After Superstimulation in Thai-Holstein Crossbreeds Under Heat Stress Conditions

The effect of heat stress with melatonin treatment on the superovulatory responses and embryo characteristics in Thai-Holstein crossbreeds under heat stress conditions was examined. Six non-lactating cows (replication = 4; n = 24) were assigned to one of 2 treatments in double cross-over design. All cows were superstimulated with traditional treatment. Melatonin group (n = 12): cows received intramuscularly injection 18 mg/50 kg. simultaneously with GnRH injection, while those in the control group (n = 12) received none. Bloods samples were taken to determine lipid peroxidation (MDA) and the activity of the antioxidant enzymes (superoxide dismutase; SOD). The experiment was conducted from April to September, which determined severe heat stress (the mean temperature-humidity index above 77). The results revealed that numbers of large follicles and corpora lutea were higher in the melatonin group than in the control group (p &lt; 0.01). Numbers of recovered ova/embryos, fertilized ova, and transferable embryos were higher in the melatonin group (p &lt; 0.01); meanwhile, more degenerated embryos were found in the control group (p &lt; 0.01). Increased activity of the antioxidant enzymes SOD after melatonin administration decreased MDA levels (p &lt; 0.05). In summary, melatonin administration benefited the ovarian response and embryo quality in superstimulated Thai-Holstein crossbreed affected by heat stress.

Carryover effects of feeding bulls with an omega-3-enriched-diet-From spermatozoa to developed embryos

The impact of omega-3 nutritional manipulation on semen cryosurvival and quality post thawing is controversial. Our aim was to examine how feeding bulls with omega-3 supplementation from different sources affects the spermatozoa quality parameters. Fifteen Israeli Holstein bulls were fed for 13 weeks with a standard ration top-dressed with encapsulated-fat supplementation: fish or flaxseed oil or saturated fatty acids (control). Ejaculates were collected before, during, and after the feeding trial. Frozen-thawed samples were evaluated by a flow cytometer for spermatozoa viability, mitochondrial membrane potential, the level of reactive oxygen species (ROS), acrosome membrane integrity, DNA fragmentation, phosphatidylserine translocation, and membrane fluidity. Both fish and flaxseed oil treatment resulted in lower ROS levels vs. control groups, during and after the feeding trial. Fewer spermatozoa with damaged acrosomes were observed in the fish oil group after the feeding trial. The spermatozoa membrane fluidity was altered in both the fish and flaxseed oil groups throughout the feeding trial, but only in the flaxseed oil group after the feeding trial. The proportion of spermatozoa with fragmented DNA was lower in the flaxseed oil group after the feeding trial. The spermatozoa fertilization competence did not differ between groups however, blastocyst formation rate was higher in the fish and flaxseed oil groups relative to the control. This was associated with differential gene expression in the blastocysts. Overall, the omega-3-enriched food improved the spermatozoa characteristics; this was further expressed in the developing blastocysts, suggesting a carryover effect from the spermatozoa to the embryos.

Dairy cow reproduction under the influence of heat stress

Dairy farming is vulnerable to global warming and climate change. Improving and maintaining conception rates (CRs) have a paramount importance for the profitability of any dairy enterprise. There is an antagonistic relationship between fertility and milk yield, and intensive selection for milk yield has severely deteriorated reproductive efficiency. Irrespective of geography and husbandry, modern dairy cows experience heat stress (HS) effects leading to fertility declines, but it worsens in tropical climates. The threshold of HS experience among modern dairy cow has lowered, leading to decreased thermal comfort zone. Studies show that this threshold is lower for fertility than for lactation. HS abatement and robustness response to lactation yield lead to negative energy balance, and cow's reproductive requirements remain unfulfilled. The adverse effects of HS commence from developing oocyte throughout later stages and its fertilization competence; the oestrus cycle and oestrus behaviour; the embryo development and implantation; on uterine environment; and even extend towards foetal calf. Even cows can become acyclic under the influence of HS. These harmful effects of HS arise due to hyperthermia, oxidative stress and physiological modifications in the body of dairy cows. Proper assessment of HS and efficient cooling of dairy animals irrespective of their stage of life at farm is the immediate strategy to reduce fertility declines. Other long- and short-term mitigation strategies to reduce fertility declines during HS include feeding care, reducing disease and mastitis rates, using semen from cooled bulls, timed artificial inseminations (AI), allied hormonal interventions and use of embryo transfer technology. Ultimate long-term solution should be well-planned breeding for fertility improvement and HS tolerance.

Cluster analysis reveals seasonal variation of sperm subpopulations in extended boar semen

This study aimed to identify motile sperm subpopulations in extended boar semen and to observe the presumptive seasonal variation in their distribution. Data from 4837 boar ejaculates collected over a two-year period were analyzed in terms of kinematic parameters by Computer Assisted Sperm Analysis (CASA). Individual sperm data were used to determine subgroups of motile sperm within the ejaculates using cluster analysis. Four motile sperm subpopulations (SP) were identified, with distinct movement patterns: SP1 sperm with high velocity and high linearity; SP2 sperm with high velocity but low linearity; SP3 sperm with low velocity but high linearity; and SP4 sperm with low velocity and low linearity. SP1 constituted the least overall proportion within the ejaculates (P < 0.05). Season of semen collection significantly influenced the different proportions of sperm subpopulations. Spring was characterized by similar proportions of SP1 and SP4 (NS) and higher proportions of SP3. Summer brought a decrease in both subgroups containing fast sperm (SP1 and SP2) (P < 0.05). During autumn, increases in SP2 and SP4 were recorded. Winter substantially affected the proportions of all sperm subpopulations (P < 0.05) and SP2 became the most represented subgroup, while SP1 (fast and linear) reached its highest proportion compared to other seasons. In conclusion, extended boar semen is structured in distinct motile sperm subpopulations whose proportions vary according to the season of collection. Summer and autumn seem to have a negative impact on the fast and linear subpopulation. Cluster analysis can be useful in revealing differences in semen quality that are not normally detected by classical evaluation based on mean values.

Alginate encapsulation preserves the quality and fertilizing ability of Mediterranean Italian water buffalo (Bubalus bubalis) and Holstein Friesian (Bos taurus) spermatozoa after cryopreservation

The use of artificial insemination (AI) in buffalo (Bubalus bubalis) is limited by poor ovarian activity during the hot season, seasonal qualitative patterns in semen, low resistance of sperm cells in the female tract, difficulties in estrus detection, and variable estrus duration. Although AI procedures are commonly used in bovine, use of AI has been limited in buffalo. In the zootechnical field, different studies have been conducted to develop techniques for improvement of fertilizing ability of buffalo spermatozoa after AI. In this study, for the first time, the use of alginate encapsulation and cryopreservation of buffalo spermatozoa is described, and the same procedure was performed with Holstein Friesian (Bos taurus) semen. Results obtained from in vitro analyses indicate that the encapsulation process does not have detrimental effects (compared to controls) on quality parameters (membrane integrity, progressive motility, path average velocity) in either species. Similarly, there were no detrimental effects after cryopreservation in either species. The fertilizing potential of encapsulated and cryopreserved semen was evaluated after AI in 25 buffalo and 113 bovine females. Pregnancy rates were not affected in either species. The results of this study show proof of concept for the use of frozen semen controlled-release devices in buffalo.

Effect of Heat Stress on Reproduction in Dairy Cows: Insights into the Cellular and Molecular Responses of the Oocyte

Among the components of the female reproductive tract, the ovarian pool of follicles and their enclosed oocytes are highly sensitive to hyperthermia. Heat-induced alterations in small antral follicles can be expressed later as compromised maturation and developmental capacity of the ovulating oocyte. This review summarizes the most up-to-date information on the effects of heat stress on the oocyte with an emphasis on unclear points and open questions, some of which might involve new research directions, for instance, whether preantral follicles are heat resistant. The review focuses on the follicle-enclosed oocytes, provides new insights into the cellular and molecular responses of the oocyte to elevated temperature, points out the role of the follicle microenvironment, and discusses some mechanisms that might underlie oocyte impairment. Mechanisms include nuclear and cytoplasmic maturation, mitochondrial function, apoptotic pathways, and oxidative stress. Understanding the mechanism by which heat stress compromises fertility might enable development of new strategies to mitigate its effects.

Integrity of the plasma membrane, the acrosomal membrane, and the mitochondrial membrane potential of sperm in Nelore bulls from puberty to sexual maturity

ABSTRACT This study evaluated the plasma membrane integrity, acrosomal membrane integrity, and mitochondrial membrane potential of Nelore bull sperm from early puberty to early sexual maturity and their associations with sperm motility and vigor, the mass motility of the spermatozoa (wave motion), scrotal circumference, and testosterone. Sixty Nelore bulls aged 18 to 19 months were divided into four lots (n=15 bulls/lot) and evaluated over 280 days. Semen samples, collected every 56 days by electroejaculation, were evaluated soon after collection for motility, vigor and wave motion under an optical microscope. Sperm membrane integrity, acrosomal integrity, and mitochondrial activity were evaluated under a fluorescent microscope using probe association (FITC-PSA, PI, JC-1, H342). The sperm were classified into eight integrity categories depending on whether they exhibited intact or damaged membranes, an intact or damaged acrosomal membrane, and high or low mitochondrial potential. The results show that bulls have a low amount of sperm with intact membranes at puberty, and the sperm show low motility, vigor, and wave motion; however, in bulls at early sexual maturity, the integrity of the sperm membrane increased significantly. The rate of sperm membrane damage was negatively correlated with motility, vigor, wave motion, and testosterone in the bulls, and a positive correlation existed between sperm plasma membrane integrity and scrotal circumference. The integrity of the acrosomal membrane was not influenced by puberty. During puberty and into early sexual maturity, bulls show low sperm mitochondrial potential, but when bulls reached sexual maturity, high membrane integrity with high mitochondrial potential was evident.

Progressive motility – a potential predictive parameter for semen fertilization capacity in bovines

We examined the association between progressive motility of spermatozoa andin vitrofertilization (IVF) competence of bovine ejaculates. Fresh semen was evaluated using a computerized sperm quality analyzer for bulls using progressive motility as the primary parameter. Ejaculates with high progressive motility (HPM; >81%) were compared with those with low progressive motility (LPM; <62%). Semen concentration and sperm velocity were lower (P< 0.05) in HPM versus LPM ejaculates. Volume and motile sperm concentration did not differ between groups (P> 0.05). Examination of sperm morphology revealed a higher proportion of spermatozoa with abnormal morphology (P< 0.01) in LPM versus HPM ejaculates, the predominant abnormal feature being a bent tail (P< 0.05). Sperm viability, acrosome integrity and DNA fragmentation did not differ between HPM and LPM samples. Mitochondrial membrane potential was higher (P< 0.01) in HPM versus LPM semen. Zinc concentrations in the seminal plasma correlated with progressive motility (R2= 0.463,P= 0.03). In addition, representative ejaculates from HPM and LPM groups were cryopreserved in straws and used for IVF. The proportions of embryos cleaved to 2- and 4-cell stages (88.1 ± 1.1 versus 80.5 ± 1.7,P= 0.001) and developed to blastocysts (33.5 ± 1.6 versus 23.5 ± 2.2,P= 0.026) were higher for HPM than LPM semen. The total cell number of embryos and blastocyst apoptotic index did not differ between groups. Although sperm progressive motility is associated with IVF competence, further examination is required to determine whether progressive motility can serve as a predictor of semen fertilization capacityin vivo.

Genome-wide association study for poor sperm motility in Holstein-Friesian bulls

The aim of the study was to screen the whole bull genome to identify markers and candidate genes underlying poor sperm motility. The analyzed data set originates from the Polish Holstein-Friesian bull population and consists of 41 Case and 279 Control bulls (selected from 1581 bulls). The most distinguishing trait of case group was very poor sperm motility (average 25.61%) when compared to control samples (average 72.95%). Each bull was genotyped using the Illumina BovineSNP50 BeadChip. Genome-wide association analysis was performed with the use of GoldenHelix SVS7 software. An additive model with a Cohran-Armitage test, Correlation/Trend adjusted by Bonferroni test were used to estimate the effect of Single Nucleotide Polymorphism (SNP) marker for poor sperm motility. Markers (n=34) reached genome-wide significance. The most significant SNP were located on chromosome 24 (rs110876480), 5 (rs110827324 and rs29011704), and 1 (rs110596818), in the close vicinity of melanocortin 4 receptor (MC4R), PDZ domain containing ring finger 4 (PDZRN4) and ethanolamine kinase 1 (ETNK1), olfactory receptor 5K3-like (LOC785875) genes, respectively. For five other candidate genes located close to significant markers (in distance of ca. 1 Mb), namely alkaline phosphatase, liver/bone/kidney (ALPL), tripartite motif containing 36 (TRIM36), 3-hydroxyisobutyrate dehygrogenase (HIBADH), kelch-like 1 (KLHL1), protein kinase C, beta (PRKCB), their potential role in sperm motility was confirmed in the earlier studies. Five additional candidate genes, cystic fibrosis transmembrane conductance regulator (CFTR), insulin-like growth factor 1 receptor (IGF1R), steroid-5-alpha-reductase, alpha polypeptide 2 (SRD5A2), cation channel, sperm associated 1 (CATSPER1) calpain 1 (mu/I) large subunit (CAPN1) were suggested to be significantly associated with sperm motility or semen biochemistry. Results of the present study indicate there is a genetic complexity of poor sperm motility but also indicate there might be a causal polymorphism useful in marker-assisted selection. Identifying genomic regions associated with poor sperm motility may be very important for early recognition of a young sire as unsuitable for effective semen production in artificial insemination centers.

Season-induced variation in lipid composition is associated with semen quality in Holstein bulls

Season-induced variation in fatty acid and cholesterol composition in bovine semen has been associated with semen quality. Given the specific roles of the various semen compartments (seminal fluids, sperm head, and sperm tail) in fertilization, we hypothesized that environmental-stress-induced alterations in the lipid composition of a specific compartment might impair semen quality and sperm function. Semen samples were collected from five mature Holstein–Friesian bulls during the summer (August to September) and winter (December to January). Semen was evaluated by computerized sperm-quality analyzer, calibrated for bulls' semen, and centrifuged to separate the spermatozoa from the seminal fluids. The spermatozoal fraction was sonicated to separate the sperm head and tail compartments. Cold lipid extraction was performed with chloroform:methanol (2:1, vol/vol). Lipids were identified and quantified by gas chromatography. Seasonal variation was found in both physiological and structural parameters. The proportion of spermatozoa defined as morphologically normal was higher in the winter, with higher motility, progressive motility, and velocity relative to summer samples. Lipid composition within fractions varied between seasons with prominent impairment in the tail compartment, characterized by high saturated fatty acid, low polyunsaturated fatty acid, and low cholesterol concentrations during the summer. Given the association between alterations in lipid composition and reduced sperm motility and velocity during the summer, it is suggested that lipid composition might serve to predict sperm quality.

Effect of di-(2-ethylhexyl) phthalate and mono-(2-ethylhexyl) phthalate on in vitro developmental competence of bovine oocytes

In the last decade, potential exposure of humans and animals to industrial chemicals and pesticides has been a growing concern. In the present study, di-(2-ethylhexyl) phthalate (DEHP) and mono-(2-ethylhexyl) phthalate (MEHP) were used to model the effects of endocrine-disrupting compounds and their risk in relation to early embryonic losses. Exposure of cumulus oocyte complexes during maturation to 50 μM MEHP reduced the proportion of oocytes that underwent nuclear maturation (p < 0.05) and increased the proportion of apoptotic oocytes (p < 0.05). Furthermore, phthalates reduced cleavage rate in the MEHP-treated group (p < 0.05) and the proportion of embryos developing to the blastocyst stage in both DEHP- and MEHP-treated groups (p < 0.05). The total cell count for blastocysts developing from MEHP-treated oocytes was lower than in controls (p < 0.05). Exposure of oocytes to MEHP during maturation reduced (p < 0.05) the expression of ASAH1 (an anti-apoptotic factor), CCNA2 (involved in cell cycle control), and POU5F1 (responsible for pluripotency) in matured oocytes. Furthermore, the reduced mRNA expression of POU5F1 and ASAH1 lasted into two-cell stage embryos (p < 0.05). Phthalate-induced alterations in POU5F1, ASAH1, and CCNA2 expression might explain in part the reduced developmental competence of MEHP-treated oocytes.