Can relative spermatozoal galactosyltransferase activity be predictive of dairy bull fertility?

Selection based on the Breeding Soundness Evaluation is associated with the improvement of the reproductive quality of young Nellore bulls

Breeding soundness evaluation (BSE) is the best methodology to estimate the fertility potential of future bulls and performing indirect selection for their fertility. However, the outcome of the BSE is influenced by several factors, including genetics, environment, and BSE guidelines. Herein, in this retrospective study, our first aim was to characterize the reasons for failure in 46,566 BSE from 2-year-old beef Bos indicus bulls (Nellore) born from 1997 to 2018. Our second aim was to determine whether or not BSE was associated with reproductive potential improvement of the bulls over the years. Due to changes in the BSE criteria, we used the same dataset, but only bulls born from 2002 to 2018 were included resulting in 35,856 BSE. For the second aim, the effect of the year and farm were included in the model of the multivariate logistic regression. We also determined if the main reasons for BSE failure decreased over time. Bulls were classified as approved (satisfactory potential breeders and qualified for natural breeding service) and not approved (deferred and unsatisfactory potential breeders). The reasons for BSE failure in Nellore bulls were poor semen quality (53.1 %) and physical defects (46.9 %), with the main physical defect being testis abnormalities (19.7 %). The overall percentage of bulls approved each year was 87.1 %, with no improvement over the years of study. However, the percentage of approved bulls at the first BSE increased over the years (P < 0.05). This increase was evident by a reduction in the difference between the overall percentage of the bulls approved vs the percentage of bulls approved at the first BSE. Furthermore, there was an increase in the percentage of bulls classified as satisfactory potential breeders in the BSE and an evident decrease in the percentage of bulls qualified only for natural breeding service (P < 0.05). In addition, an increase of the scrotal circumference (SC) of the herd was found (P < 0.05). These results indicate the overall quality of the bulls improved over the years. To associate and identify the main sperm abnormalities, 3461 not approved bulls were clustered. The most frequent defects were strongly coiled tail spermatozoa, proximal droplets, and acrosomal defects. Overall, there was no change in the frequency of bulls not approved by the sperm morphology nor the frequency of the main sperm abnormalities over the years. Nevertheless, the frequency of the defects remained very low, implying they were controlled. Additionally, abnormalities in the testis decreased over the years and was associated with the increase in the SC of the herd and a decrease of culled bulls due to low SC. In conclusion, this study demonstrates that there is an association between implementation and use of BSE with improvements in the reproductive quality of future generation bulls.

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.

Genome-wide association study reveals candidate markers related to field fertility and semen quality traits in Holstein-Friesian bulls

In vitro assessment of bull semen quality is routinely used in bull semen processing centres in order to ensure that semen destined to be used in the field has passed minimum standards. Despite these stringent quality control checks, individual bulls that pass the quality control checks can still vary in field fertility by up to 25%. A genome-wide association study was undertaken to determine genetic markers associated with prefreeze and post-thaw bull sperm quality traits as well as field fertility. Genome-wide association analysis was performed using a single nucleotide polymorphism (SNP) regression mixed linear model in WOMBAT. Genes within a 250 Kb span of a suggestive (P ≤ 1 × 10^-5) SNP were considered as candidate genes. One SNP was associated with adjusted pregnancy rate, and 21 SNPs were associated across the seven semen quality traits (P ≤ 1 × 10^-5). Functional candidate genes include SIPA1L2 which was associated with adjusted pregnancy rate. This encodes a Rap GTPase-activating protein involved in Rap1 signalling pathway and was previously found to play a role in the process of sperm differentiation. Gene ontology (GO) analysis also identified significantly enriched biological processes involved protein tyrosine kinase activity including genes such as DYRK1A, TEC and TXK that were associated with sperm motility prior to freezing. Another candidate gene associated with post-thaw sperm motility was FHDC1 which coordinates actin filament and microtubule dynamics. The induced 11 GO terms in the ejaculates rejected after freezing trait were related to ATPase, phosphatase and hydrolase activity. These results reveal novel specific genomic regions and candidate genes associated with economically important phenotypes such as field fertility and semen quality traits.

Identification of differentially expressed mRNAs and miRNAs in spermatozoa of bulls of varying fertility

Bulls used in artificial insemination, with apparently normal semen quality, can vary significantly in their field fertility. This study aimed to characterize the transcriptome of spermatozoa from high (HF) and low (LF) fertility bulls at the mRNA and miRNA level in order to identify potential novel markers of fertility. Holstein-Friesian bulls were assigned to either the HF or LF group (n = 10 per group) based on an adjusted national fertility index from a minimum of 500 inseminations. Total RNA was extracted from a pool of frozen-thawed spermatozoa from three different ejaculates per bull, following which mRNA-seq and miRNA-seq were performed. Six mRNAs and 13 miRNAs were found differentially expressed (P < 0.05, FC > 1.5) between HF and LF bulls. Of particular interest, the gene pathways targeted by the 13 differentially expressed miRNAs were related to embryonic development and gene expression regulation. Previous studies reported that disruptions to protamine 1 mRNA (PRM1) had deleterious consequences for sperm chromatin structure and fertilizing ability. Notably, PRM1 exhibited a higher expression in spermatozoa from LF than HF bulls. In contrast, Western Blot analysis revealed a decrease in PRM1 protein abundance for spermatozoa from LF bulls; this was not associated with increased protamine deficiency (measured by the degree of chromatin compaction) or DNA fragmentation, as assessed by flow cytometry analyses. However, protamine deficiency was positively and moderately correlated with the percentage of spermatozoa with DNA fragmentation, irrespective of fertility group. This study has identified potential biomarkers that could be used for improving semen quality assessments of bull fertility.

Comprehensive functional analysis reveals that acrosome integrity and viability are key variables distinguishing artificial insemination bulls of varying fertility

In vitro methods of assessing bull semen quality in artificial insemination (AI) centers are unable to consistently detect individuals of lower fertility, and attempts to reliably predict bull fertility are still ongoing. This highlights the need to identify robust biomarkers that can be readily measured in a practical setting and used to improve current predictions of bull fertility. In this study, we comprehensively analyzed a range of functional, morphological, and intracellular attributes in cryopreserved spermatozoa from a selected cohort of Holstein Friesian AI bulls classified as having either high or low fertility (n = 10 of each fertility phenotype; difference of 11.4% in adjusted pregnancy rate between groups). Here, spermatozoa were assessed for motility and kinematic parameters, morphology, acrosome integrity, plasma membrane lipid packing, viability (or membrane integrity), superoxide production, and DNA integrity. In addition, spermatozoa were used for in vitro fertilization to evaluate their capacity for fertilization and successful embryo development. The information collected from these assessments was then used to phenotypically profile the 2 groups of bulls of divergent fertility status as well as to develop a model to predict bull fertility. According to the results, acrosome integrity and viability were the only sperm attributes that were significantly different between high- and low-fertility bulls. Interestingly, although spermatozoa from low-fertility bulls, on average, had reduced viability and acrosome integrity, this response varied considerably from bull to bull. Principal component analysis revealed a sperm phenotypic profile that represented a high proportion of ejaculates from low-fertility bulls. This was constructed based on the collective influence of several sperm attributes, including the presence of cytoplasmic droplets and superoxide production. Finally, using the combined results as a basis for modeling, we developed a linear model that was able to explain 47% of the variation in bull field fertility in addition to a logistic predictive model that had a 90% chance of distinguishing between fertility groups. Taken together, we conclude that viability and acrosome integrity could serve as fertility biomarkers in the field and, when used alongside other sperm attributes, may be useful in detecting low-fertility bulls. However, the variable nature of low-fertility bulls suggests that additional, in-depth characterization of spermatozoa at a molecular level is required to further understand the etiology of low fertility in dairy bulls.

Testis-specific isoform of angiotensin-converting enzyme (tACE) as a candidate marker for bull fertility

Although a traditional bull breeding soundness evaluation is designed to identify bulls that are grossly abnormal, bulls classified as satisfactory potential breeders still vary in fertility, implying submicroscopic differences in sperm characteristics. Testis-specific isozyme of angiotensin-converting enzyme (tACE) is involved in the regulation of sperm function. Therefore, the aim of the present study was to determine tACE content, activity and localisation in bull spermatozoa and their associations with fertility. Semen from low-fertility (LF) and high-fertility (HF) Holstein bulls (n=20) with known FERTSOL rates, which represents the 56-day non-return rate, were used. There was greater tACE content (P<0.05) and tACE activity (P<0.01) in HF versus LF spermatozoa. Based on immunolocalisation, tACE was either in the acrosomal or postacrosomal region of the sperm head, with HF bulls having a higher proportion of spermatozoa with tACE in the acrosomal region than LF bulls (P<0.05). tACE content, activity, localisation to the acrosomal region and progressive motility were significantly correlated with fertility and, based on regression analysis, tACE content was predictive of fertility. tACE content and activity in semen were similar between yearling (10-13 months old) and mature (3-4 years old) bulls. Therefore, tACE has potential as a marker of field fertility in bulls at their earliest possible age.

Electrophoretic profile of seminal proteins and their correlation with in vitro sperm characters in Black Bengal buck semen

Aim:

This study aimed to study the electrophoretic properties of seminal plasma and sperm proteins of Black Bengal buck semen and their correlation with in vitro sperm characters and freezability.

Materials and Methods:

Semen ejaculates from nine Black Bengal bucks were collected by artificial vagina (n=20/buck). Ejaculates were evaluated for in vitro sperm characters and electrophoretic profile of seminal protein. In vitro sperm characters were evaluated immediately after collection, after completion of equilibration period, and after freeze-thawing. For seminal protein studies, seminal plasma proteins were precipitated by ice-cold ethanol method, and sperm proteins were extracted by Triton X detergent extraction method. Discontinuous sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) was performed to assess the molecular weight of seminal proteins. Correlation between in vitro sperm characters and protein bands was determined by Pearson’s correlation coefficient, and two-way ANOVA was applied to find the individual buck differences.

Results:

Significant difference (p<0.01) among the bucks was noticed in the in vitro sperm characters evaluated at all the three stages of semen evaluation such as immediately after collection, after completion of equilibration period, and post-freeze thawing. Progressive loss of sperm motility, membrane integrity, and other in vitro sperm characters were noticed during cryopreservation. A total of ten protein bands in the molecular weight ranging from 17 to 180 kDa were found in the SDS-PAGE of seminal plasma proteins, while nine bands of 17-134 kDa were observed in sperm proteins. Seminal plasma proteins of molecular weight 75, 62-49, 20, and 17 kDa and sperm proteins of 75, 20, and 17 kDa were present in all the nine bucks (100%) screened, and variation among the bucks was noticed for the presence of other proteins. Seminal plasma protein of 180-134 kDa showed a negative correlation with individual motility (−0.716) and functional membrane integrity of sperm cells (−0.724) in post-freeze–thaw analysis and 48 kDa protein had a positive correlation with individual motility (0.649) and functional membrane integrity of sperm cells (0.664) in post-thaw analysis. Sperm proteins of 63 kDa had a negative correlation (−0.616) with sperm concentration in neat semen.

Conclusion:

Variation among the bucks was noticed in the in vitro sperm characters and semen freezability. Correlation between seminal proteins and in vitro sperm characters and semen freezability had been found which might be useful as a tool to select breeding bucks.

Comparative proteomic analysis of high- and low-fertile buffalo bull spermatozoa for identification of fertility-associated proteins

The present study identified few potential proteins in the spermatozoa of buffalo bulls that can be used as an aid in fertility determination through comparative proteomics. The sperm proteome of high-fertile buffalo bulls was compared with that of low-fertile buffalo bulls using two-dimensional difference gel electrophoresis (2D-DIGE), and the differentially expressed proteins were identified through mass spectrometric method. The protein interaction network and the functional bioinformatics analysis of differentially expressed proteins were also carried out. In the spermatozoa of high-fertile bulls, 10 proteins were found overexpressed and 15 proteins were underexpressed at the level of twofold or more (p ≤ 0.05). The proteins overexpressed in high-fertile spermatozoa were PDZD8, GTF2F2, ZNF397, KIZ, LOH12CR1, ACRBP, PRSS37, CYP11B2, F13A1 and SPO11, whereas those overexpressed in low-fertile spermatozoa were MT1A, ATP5F1, CS, TCRB, PRODH2, HARS, IDH3A, SRPK3, Uncharacterized protein C9orf9 homolog isoform X4, TUBB2B, GPR4, PMP2, CTSL1, TPPP2 and EGFL6. The differential expression ranged from 2.0- to 6.1-fold between the two groups, where CYP11B2 was high abundant in high-fertile spermatozoa and MT1A was highly abundant in low-fertile spermatozoa. Most of the proteins overexpressed in low-fertile spermatozoa were related to energy metabolism and capacitation factors, pointing out the possible role of pre-mature capacitation and cryo-damages in reducing the fertility of cryopreserved buffalo spermatozoa.

Sperm function during incubation with oestrus oviductal fluid differs in bulls with different fertility

Spermatozoa undergo several modifications in the oviduct before acquiring fertilising capacity. Although spermatozoa are exposed to similar conditions in the oviduct, the speed of the response varies with the male and the state of the spermatozoa. We hypothesised that spermatozoa from bulls with different fertility may differ in their ability to respond to oviductal fluid (ODF). Frozen-thawed spermatozoa from four bulls were incubated with oestrus oviductal fluid (OODF) for 6h. Sperm kinematics, tyrosine phosphorylation, phosphorylation patterns, capacitation and acrosome reaction were analysed at hourly intervals. The amplitude of lateral head displacement (ALH) and straightness coefficient (STR) were higher (P<0.05) in bulls with higher fertility compared with those with lower fertility, at 1-4h of incubation. At 4h of incubation and onwards, spermatozoa from bulls with higher fertility showed a lower degree (P<0.05) of tyrosine phosphorylation and higher degree of capacitation and acrosome reaction. At least five tyrosine-phosphorylated sperm proteins were detected in all bulls. However, the expression of two phosphorylated sperm proteins (183 and 109 kDa) was upregulated in bulls with lower fertility. It may be concluded that cryopreserved spermatozoa from high- and low- fertile bulls differ in their ability to respond to OODF. This may help in developing tools for assessing fertility of bulls, once validated in more animals.

Identification of suitable combinations of in vitro sperm-function test for the prediction of fertility in buffalo bull

The present study assessed sperm functional characteristics in the frozen-thawed semen of buffalo bulls and estimated their relationship with field fertility. Frozen semen samples from three different freezing operations each from nine Murrah buffalo bulls were used for the assessment of different sperm functions related to fertilizing potential. Bulls were classified into high (n = 2), medium (n = 5), and low (n = 2) fertile based on adjusted field fertility. The sperm functions estimated included membrane integrity using carboxyfluorescein diacetate-propidium iodide, acrosome reaction status using fluorescein isothiocyanate peanut agglutinine, status of apoptosis using Annexin-V, protamine deficiency using Chromomycin A₃, membrane stability using Merocyanine 540 and lipid peroxidation status using 4, 4-difluoro-4-bora-3a, 4a-diaza-s-indacene. The relationship between the proportion of live acrosome-intact spermatozoa and fertility was positive and significant (r = 0.59; P = 0.001). The proportion of moribund spermatozoa showed a significantly negative correlation with fertility (r = -0.50; P = 0.008). Similarly, the relationship of spermatozoa with unstable membrane (r = -0.51; P = 0.007), necrotic (r = - 0.42; P = 0.028), early necrotic (r = -0.42; P = 0.031), and apoptotic spermatozoa (r = -0.39; P = 0.046) with bull fertility was negative and significant. The correlation between the protamine-deficient spermatozoa and fertility was negative, but not significant. Among different combinations of tests, live acrosome-intact spermatozoa and lipid peroxidation status of spermatozoa revealed high positive correlation with buffalo bull fertility (adjusted R² = 0.73, C[p] = 0.80). These preliminary findings may help in developing tools for assessing fertility of buffalo bulls, once validated in more animals.

Biometry of frozen–thawed sperm from eight breeds of Indian buffaloes (Bubalus bubalis)

Sperm morphometry, in combination with other objective traits, can be useful for developing a fertility index. The objective of the present study was to measure various biometric end points of frozen-thawed sperm from eight breeds of Indian buffaloes (Murrah, Surti, Tarai, Mehsana, Jaffrabadi, Bhadawari, Pandharpuri and Nili-Ravi). The sperm head of Pandharpuri buffaloes had the greatest length (10.21 microm), width (6.05 microm), area (52.31 microm(2)) and perimeter (31.86 microm). The ratio of sperm width to length was also greatest (0.61) in Pandharpuri as well as in two other breeds, viz. Nili-Ravi and Jaffrabadi. Murrah had the smallest sperm head width (4.75 microm), area (41.65 microm(2)) and perimeter (29.17 microm), but its sperm tail was longest (57.02 microm), along with that of Jaffrabadi buffaloes (56.96 microm). Based on mean values of sperm tail length, mid piece length and its width the eight buffalo breeds were categorized into three, four and five groups, respectively. Multivariate analysis and clustering put six breeds (Surti, Tarai, Mehsana, Jaffrabadi, Bhadawari and Nili-Ravi) in one cluster, whereas Murrah and Pandharpuri appeared as separate entities.

Proacrosin/acrosin quantification as an indicator of acrosomal integrity in fresh and frozen dog spermatozoa

The scope of the present study was to evaluate the presence and activation of proacrosin/acrosin as a tool to determine the acrosomal status of fresh and frozen/thawed dog spermatozoa. Monoclonal antibody C5F11, directed against human acrosin, cross-reacted with dog spermatozoa and labeled the acrosome of both fresh and frozen/thawed dog spermatozoa. Frozen/thawed spermatozoa had a lesser proportion of labeled spermatozoa than fresh spermatozoa (P<0.05). When live spermatozoa were labeled with soybean trypsin inhibitor conjugated with Alexa 488 (SBTI-Alexa 488), the proportion of acrosome-labeled fresh spermatozoa was less than frozen/thawed spermatozoa (P<0.05). By using Western blots and enzymatic activity, frozen/thawed spermatozoa had a greater proportion of active acrosin than fresh spermatozoa. In addition, beta 1,4-galactosyl-transferase (GalT), a plasma membrane bound protein, remained attached to frozen/thawed spermatozoa. Proacrosin is activated during freezing/thawing of dog spermatozoa, and that proacrosin/acrosin may be a good indicator of acrosomal integrity of frozen/thawed spermatozoa.

Evaluation of fertility and infertility in natural service bulls

The potential fertility of bulls can be evaluated in the field by assessment of mating ability and physical examination. Both methods are useful for screening out low fertility bulls, although neither allows precise determination of the pregnancy rates that bulls actually achieve. Observations of coitus, libido testing and service capacity testing are the main methods of assessing mating ability in the field and, although not reliable for virgin bulls, are widely used for older bulls. Of the traits that are assessed during physical examination, those most closely correlated with fertility are scrotal circumference and the semen quality parameters of motility and morphology. Whilst these methods allow reasonable accuracy in determining the fertility potential of an individual bull, they do not take into account other managemental constraint to bulls' fertility. Although these are reasonable well understood for beef herds, the managemental factors that affect the performance of natural service sires in dairy herds are poorly understood.