Can spermatozoa with abnormal heads gain access to the ovum in artificially inseminated super- and single-ovulating cattle?

Sperm head morphometry and chromatin alterations in bulls with different conception rates

The objective of this investigation was to analyze timed-AI conception rates (CRs) of different sires in light of their conventional semen quality parameters, sperm head morphometry, and chromatin alterations. Semen was collected in the field from six Angus bulls and used for the timed-AI of 890 suckled multiparous Nellore cows at a single farm. Semen batches were evaluated on the following in vitro parameters: sperm motility, concentration, and morphology, sperm head morphometry, and chromatin alteration types. The overall CR was 49% and Bulls 1 (43%) and 2 (40%) presented reduced (P < 0.05) pregnancies per AI compared to Bull 6 (61%), even though no differences were observed between their conventional semen quality parameters. Bull 1, however, presented higher (P = 0.0001) shape factor, smaller (P = 0.0025) antero-posterior symmetry, and elevated (P = 0.0141) Fourier 1 parameter, whereas Bull 2 exhibited a higher (P = 0.0023) percentage of chromatin alteration along the central axis of the sperm head. In conclusion, bulls with varying CRs may present sperm head morphometric differences and/or chromatin alterations while not presenting differences in conventional in vitro semen quality parameters. Although further studies are needed to elucidate the concrete implications of chromatin alterations on field fertility, sperm morphometric differences and chromatin alterations may be at least partially causative of the lower pregnancies per timed-AI of certain sires.

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.

Seasonal variation in bull semen quality demonstrates there are heat-sensitive and heat-tolerant bulls

Using semen data from 1271 ejaculates (79 different bulls, 11 different breeds) we have investigated the variability of semen quality in cattle living in sub-tropical conditions. Modelling shows definitive evidence of seasonal variation. Semen quality from the same bulls had a 90% "pass rate" for cryopreservation purposes in winter, dropping to less than 50% in summer. Notably, individual bulls could be classified as either "heat-tolerant" (produce good quality spermatozoa all year regardless of temperature) or "heat-sensitive" (only produce good quality sperm in summer). Nominal logistic regression demonstrated when temperatures reach 30.5 °C, 40% of heat-sensitive bulls fail a semen analysis 17 days later. At 34 °C, the proportion of bulls failing reached 63%. Ratifying this, the purposeful heating of bulls to 40 °C for 12 h showed that individual animals had different degrees of heat-sensitivity. Using historical temperature data, we then modelled how many days/decade bulls would be subject to heat-events. Beginning from 1939 to 1949, on average, the area in which bulls were kept recorded 19, 7 and 1 day over 38 °C, 39 °C and 40 °C respectively. This number steadily increases and of last decade (2010-2010), the numbers of days per decade over 38 °C, 39 °C and 40 °C jumped to a staggering 75, 39 and 15 respectively. These data show the urgent need to identify heat-tolerant bulls as future sires. Such variation likely explains why the veterinary bull breeding test often fails to accurately predict bull breeding potential.

The Role of Sperm Morphology Standards in the Laboratory Assessment of Bull Fertility in Australia

The lack of standardization in the laboratory assessment of semen questions the reliability of semen analysis, and makes meaningful interpretation of these evaluations impossible. We herein describe a standardization program for morphology assessment currently in place in Australia and outline the methods used, both for the categorization of the abnormalities, including newly described abnormalities, and those that permit standardized microscopic assessment between laboratories.

Impact of in vitro fertilization by refrigerated versus frozen buffalo semen on developmental competence of buffalo embryos

The objective of this study was to evaluate the fertility of buffalo semen for in vitro embryo production (IVEP) by comparing the effectiveness of refrigerated versus frozen semen. Three OPU sessions were held at 30-day intervals. For oocyte fertilization three buffalo bulls were used, one per session. At each OPU-IVEP session, one ejaculate was collected and divided into two equal aliquots. Each aliquot was either refrigerated at 5ºC/24 hours or frozen. A TRIS extender containing 10% low density lipoproteins, 0.5% lecithin and 10 mM acetylcysteine was used adding 7% glycerol for freezing. Sperm motility/kinetic was evaluated by CASA and sperm membrane integrity by the hypoosmotic swelling test. The evaluations were performed at 0 h (post final dilution at 37ºC), at 4 and 24 hs post-incubation at 5ºC and post-thaw. At 24 hs incubation and immediately post thaw sperm cells were used for in vitro fertilization of buffalo oocytes equally distributed between both groups. Cleavage rates and embryo development were followed. The embryo/matured and embryo/cultured rates were 25.4 x 14.0% and 29.4 x 18.5% (P<0.05), for chilled and frozen semen, respectively. It is concluded that cooled semen can be used for in vitro embryo production in buffalo and that a better efficiency may be expected for cooled compared to frozen semen.

Factors affecting embryo production in superovulated Bos taurus cattle

Despite a long history of bovine superovulation research, significant commercial applications did not start until the early 1970s. For some 20 years thereafter, superovulation represented the primary tool for the production of cattle embryos. In the early 1990s, commercial invitro production (IVP) was initiated in cattle. Although ovum pick-up and IVP are now commercially practiced on a wide scale, superovulation and embryo recovery by flushing remain a widespread and very effective approach to the production of cattle embryos. This review covers both the history and the effects of multiple factors on superovulation in Bos taurus cattle. There are three general protocols for suitable pre-FSH programming of donors so that gonadotrophin-responsive follicles are available. Superovulation protocols vary widely based on the FSH source, the diluent used, the number and timing of FSH injections and the timing and utilisation of various prostaglandins, controlled internal progesterone releasing devices, gonadotrophin-releasing hormone, and other means of controlling follicular development and ovulation. The number of oocytes that can be stimulated to grow and ovulate within any given donor can be estimated by either ultrasound-guided sonography or by measuring concentrations of anti-Müllerian hormone in the blood. Animal-related factors that can influence the efficacy of superovulation include cattle breed, age, parity, genetics, lactational status and reproductive history. In addition, nutrition, stress, season, climate, weather and several semen factors are discussed.

Angus sire field fertility and in vitro sperm characteristics following use of different sperm insemination doses in Brazilian beef cattle

The primary objective was to determine if Angus bull fertility varied by number of sperm inseminated. A secondary objective was to characterize the potential impact of random variation on fertility using two identical sperm per dose treatments, which differed only in straw color. Computer-assisted sperm analysis (CASA) and flow cytometry (FC) were used to identify post-thaw sperm characteristics associated with field fertility differences between bulls. Ejaculates from five Angus bulls were collected, extended, and cryopreserved at 10, 20, 20 or 40 × 10⁶ sperm per dose in color-coded 0.5-mL French straws. Multiparous cows (n = 4866) from ten Brazilian farms were synchronized for first-service timed artificial insemination (TAI). Bull identification and straw color were recorded at TAI. Pregnancy per TAI (P/TAI) did not differ between sperm doses (43.8, 45.3, 43.8 and 47.1% for 10, 20, 20 or 40 × 10⁶ sperm respectively; P = 0.31) nor was there an interaction between bull and dose (P = 0.53). The P/TAI differed between bulls and ranged from 40.7 to 48.1% (P < 0.01). The overall P/TAI between the two control groups were not different (45.3 vs 43.8%); however, the numerical variation within bull ranged from 0.5 to 4.9 percentage points. Numerous CASA and FC post-thaw sperm characteristics differed among bulls (P < 0.05), but these characteristics did not explain the fertility difference between bulls. Principal component analysis provided a multivariate description of the CASA and FC data, where three principal components (Prin1, Prin2, and Prin3) accounted for a combined total of 88.7% of the data variability. The primary components of each PCA axis were flow cytometric measures of sperm viability and DNA fragmentation (Prin1), and CASA-derived sperm movement patterns (Prin2) and motility (Prin3); however, the relative influence of these characteristics varied by bull. Although fertility differences between bulls were detected, neither sperm per dose nor post-thaw in vitro sperm analyses (CASA and FC) were able to explain the observed differences in field fertility between bulls, further illustrating the difficulties in predicting bull fertility.

Protein biomarkers for male artificial insemination subfertility in bovine spermatozoa

Background

Although artificial insemination (AI) technique is an established biotechnology for bovine reproduction, the results of AI (conception rates) have a tendency to decline gradually. To our annoyance, moreover, AI‐subfertile bulls have been occasionally found in the AI centers. To resolve these serious problems, it is necessary to control the sperm quality more strictly by the examinations of sperm molecules.

Methods

We reviewed a number of recent articles regarding potentials of bovine sperm proteins as the biomarkers for bull AI‐subfertility and also showed our unpublished supplemental data on the bull AI‐subfertility associated proteins.

Main findings

Bull AI‐subfertility is caused by the deficiency or dysfunctions of various molecules including regulatory proteins of ATP synthesis, acrosomal proteins, nuclear proteins, capacitation‐related proteins and seminal plasma proteins.

Conclusion

In order to control the bovine sperm quality more strictly by the molecular examinations, it is necessary to select suitable sperm protein biomarkers for the male reproductive problems which happen in the AI centers.

Sperm superoxide dismutase is associated with bull fertility

Decreasing mammalian fertility and sperm quality have created an urgent need to find effective methods to distinguish non-viable from viable fertilising spermatozoa. The aims of the present study were to evaluate expression levels of ?-tubulin 2C (TUBB2C), heat shock protein 10 (HSP10), hexokinase 1 (HXK1) and superoxide dismutase 1 (SOD1) in spermatozoa from Holstein bulls with varying fertility using western blotting and to analyse the biological networks of these key sperm proteins using a bioinformatics software (Metacore; Thomson-Reuters, Philadelphia, PA, USA). The rationales behind this study were that the sperm proteins play crucial roles in fertilisation and early embryonic development in mammals and ascertaining the biological networks of the proteins helps us better understand sperm physiology and early mammalian development. The results showed that expression of SOD1 was higher in spermatozoa from high fertility bulls (PPin vivo bull fertility. The findings are important because they illuminate molecular and cellular determinants of sperm viability and the identified protein markers can be used to determine bull fertility.

Maintaining integrity of germline DNA: individuals age, species do not

All life forms are under constant assault, resulting in an accumulation of damage within each individual, in both somatic and germline cells. The obvious causes are: (1) mutations from radiation, chemical reactions like peroxidation and errors in replicating genetic material; (2) injury due to environmental insults, such as chemical alteration of proteins by reactive oxygen species; (3) epigenetic errors, such as failure of appropriate maintenance methylation of cytosines of DNA; and (4) numerous other problems, including retroviral invasions, inflammation and unhealthy microbiomes. Collectively, these phenomena constitute aging and/or certain disease states. Nature has developed numerous mechanisms to counteract these problems, such as proofreading enzymes, ubiquitous antioxidants and apoptotic death of unfit cells. However, none of these is completely effective. Although individuals accumulate damage, species usually do not become increasingly damaged; however, this could be one of the mechanisms for eventual extinction or evolution to a different species, the apparent fate of essentially all species. Nevertheless, germline DNA appears to remain sufficiently pristine to maintain fairly stable phenotypes over many generations. How do species avoid accumulating damage when composed of individuals that do? One broad answer seems to be reproductive redundancy followed by elimination of defects through the death of gametes, embryos, fetuses, neonates and postpubertal individuals, with the culling pressure increasing as potential parents age. Another major force appears to be evolutionary pressure; individuals that best fit the environment out-reproduce those that fit less well. What is impressive is that older and older parents continue to have offspring that are nearly as pristine as those of younger parents, even though their germline cells have continued to age. Although the offspring of old parents are not as fit, on average, as those of young parents, differences are small and, in some species, compensated for by superior parenting with accumulated experience. To conclude, it appears that species do not age, even though they are composed of individuals whose somatic and germline cells have aged.

Semen effects on insemination outcomes in sows

Sows (n=1205) were artificially inseminated with semen from single sires (n=166). Semen was previously analysed for sperm concentration, motility, velocity, morphology (using DIC microscopy) and membrane integrity, sperm clump score, temperature on arrival and pH. Percent normal sperm influenced both numbers of pigs born alive (P<0.01) and litter size (P<0.05) which, in turn, was also influenced by abnormal sperm head morphology (P<0.05) and retained distal cytoplasmic droplets (P<0.01). Percent stillbirths were influenced by sperm flagellar beat cross frequency (P<0.05) and semen arrival temperature (P<0.05).

Effects of deep-horn AI on fertilization and embryo production in superovulated cows and heifers

The primary objective of this study was to determine the effect of site of semen deposition on fertilization rate and embryo quality in superovulated cows. The hypothesis was that deposition of semen into the uterine horns would increase the fertilization rate compared with deposition of semen into the uterine body. The secondary objective was to evaluate the effect of uterine environment on fertilization rate and embryo quality. It was hypothesized that subclinical endometritis at the onset of superstimulation would decrease the fertilization rates and embryo quality. In experiment 1, 17 superovulated heifers were randomly assigned to receive artificial insemination (AI) into the uterine body or uterine horns. The total number of fertilized structures and fertilization rate from superovulated heifers was increased (P = 0.04 and P = 0.02, respectively) when semen was deposited into the uterine horns compared with the uterine body. Other embryo characteristics did not differ based on the site of semen deposition. In experiment 2, 14 lactating dairy cows were superovulated twice and were randomly assigned to receive AI into the uterine body or deep into the uterine horns using a crossover design. Neither fertilization rate nor any other embryo characteristics were improved when semen was placed deep into the uterine horns compared with the uterine body. In experiment 3, 72 superovulated lactating dairy cows were randomly assigned to receive AI into the uterine body or uterine horns. Before initiation of superstimulatory treatments, an endometrial cytology sample was collected from each cow. Ova/embryos were collected by a nonsurgical technique at 70 ± 3 days in milk. Similar to experiment 2, neither fertilization rate nor any other embryo characteristics differed based on the site of semen deposition in experiment 3. The percentage of cows with subclinical endometritis did not differ between treatments. Interestingly, there was a tendency (P = 0.09) for a reduction in embryo recovery rate and a reduction (P = 0.01) in the fertilization rate for cows with subclinical endometritis. In conclusion, deposition of semen into the uterine horns rather than into the uterine body did not improve the fertilization rate or embryo quality in superovulated cows. Subclinical endometritis decreased the fertilization rate in superovulated cows.

Assessment of in vitro sperm characteristics and their importance in the prediction of conception rate in a bovine timed-AI program

The aims of this study were to assess in vivo fertility and in vitro sperm characteristics of different sires and to identify sperm variables important for the prediction of conception rate. Multiparous Nelore cows (n = 191) from a commercial farm underwent the same timed artificial insemination (timed-AI) protocol. Three batches of frozen semen from three Angus bulls were used (n = 9). A routine semen thawing protocol was performed in the laboratory to mimic field conditions. The following in vitro sperm analyses were performed: Computer Assisted Semen Analysis (CASA), Thermal Resistance Test (TRT), Hyposmotic Swelling Test (HOST), assessment of plasma and acrosomal membrane integrity, assessment of sperm plasma membrane stability and of lipid peroxidation by flow cytometry and assessment of sperm morphometry and chromatin structure by Toluidine Blue staining. For statistical analyses, Partial Least Squares (PLS) regression was used to explore the importance of various sperm variables in the prediction of conception rate. The following in vitro sperm variables were determined to be important predictors of conception rate: total motility (TM), progressive motility (PM), TM after 2 h of thermal incubation (TM_2 h), PM after 2 h of thermal incubation (PM_2 h), Beat Cross Frequency after 2 h of thermal incubation (BCF_2 h), percentage of rapidly moving cells after 2 h of thermal incubation (RAP_2 h), intact plasma membrane evaluated by HOST, intact plasma and acrosomal membranes evaluated by flow cytometry, intact plasma membrane suffering lipid peroxidation, major defects, total defects, morphometric width/length ratio, Fourier_0 and Fourier_2 and Chromatin Heterogeneity. We concluded that PLS regression is a suitable statistical method to identify in vitro sperm characteristics that have an important relationship with in vivo bull fertility.

Triennial Reproduction Symposium: the obstacle course to successful establishment of pregnancy in domestic livestock species

The 2012 Triennial Reproduction Symposium (TRS), "Impediments to Fertility in Domestic Animals," was held immediately before the Joint Annual Meeting of the American Society of Animal Science, American Dairy Science Association, Canadian Society of Animal Science, Western Section of the American Society of Animal Science, and the Asociación Mexicana de Producción Animal in Phoenix, AZ, in July, 2012. The theme of the symposium highlighted key impediments or opportunities in the process of creating a pregnancy, beginning with male and female gametes and ending with a viable fetus. The 2012 TRS was designed to focus on areas of current and exciting investigation across a variety of species and to include 8 presentations from a mix of established and early-career scientists. The TRS was also the venue for presentation of the 2012 L. E. Casida Award for Graduate Education; the recipient was R. D. Randel (Texas A&M University). The symposium provided an excellent opportunity for reproductive biologists to consider the broad spectrum of factors that limit fertility in domestic species and contemplate the current status of knowledge relative to several of the significant obstacles to pregnancy.

Sperm Morphology and Preparation Method Affect Bovine Embryonic Development

This study was conducted to evaluate the effect of sperm separation methods of semen samples collected from bulls subjected to scrotal insulation on embryonic development after in vitro fertilization (IVF) and to determine whether IVF results would be affected by various heparin concentrations. Morphologically abnormal semen samples were obtained and cryopreserved from Holstein bulls following scrotal insulation for 48 hours. Standard protocols using the Percoll gradient (90%/45%) method and the swim-up method were used to separate spermatozoa fractions in experiment I. The pellet (A(p)) and the 45% layer (B(p)) were isolated from the Percoll separation, while for the swim-up separation, the supernatant (A(s)) and the interphase (B(s)) were isolated. The overall blastocyst rate for our laboratory control semen was 23.1 +/- 2.1% for Percoll separations (A(p) and B(p)) and 18.2 +/- 2.0% for swim-up (A(s) and B(s)) separations. This rate was higher (P <.01) than the rate observed for the semen from the bull that had the greatest response to scrotal insult 5 days prior to the insult, when it was 9.2 +/- 2.1% for the Percoll separation and 20.7 +/- 2.3% for the swim-up separation, while semen from 27 days after scrotal insulation (D +27) resulted in no blastocyst formation for the Percoll separation and a 4.2 +/- 2.1% rate for the swim-up separation. In experiment II, semen was sampled from the bulls that responded in the greatest and least degrees to scrotal insult 5 days before scrotal insulation (D -5) and on days 23 (D +23) and 34 (D +34) after scrotal insulation. These samples were exposed to IVF mediums with 3 different heparin concentrations (0.1, 1.0, and 10 microg/mL). There was a significant difference (P <.05) in developmental scores between the D -5 (1.08 +/- 0.08), D +23 (0.9 +/- 0.08), and D +34 (0.8 +/- 0.08) samples, but no differences were observed in blastocyst formation based on the number of cleaved embryos. Increasing the heparin concentration resulted in higher (P <.01) embryonic developmental scores. In conclusion, when semen samples with high percentages of abnormal spermatozoa are used for IVF, semen separation preparation methods affect results. Our results show that the separation methods used under these conditions were inadequate in their ability to provide potentially competent sperm for IVF. However, selecting appropriate sperm separation procedures could improve in the IVF embryonic development of semen from bulls used in artificial insemination. Also, an increase in the heparin concentration was able to partially overcome deficiencies, which suggests that morphologically abnormal spermatozoa undergo capacitation despite possible structural changes to the plasma membrane.

Alleviation of reproductive toxicity of gossypol using selenium supplementation in rams

The objective of this study was to evaluate the reproductive toxicity of gossypol and the possible counteracting effect of selenium supplementation in rams. Twenty-five mature crossbred (Barki × Rahamni) rams were randomly divided into 5 equal groups. The first group served as a control (no gossypol in diet). The second and third groups received diets containing free gossypol of 9 and 14 mg·kg(-1) BW·d(-1)(low level and high level of gossypol), respectively. The fourth and fifth groups received the same diets given to the second and third groups, respectively, with an oral administration of 1 mg selenium (as sodium selenite) daily for each animal. Results showed reductions in ejaculate volume (P = 0.028), percentage of dead sperm (P = 0.003), total functional sperm fraction (P < 0.001), and blood serum concentration of testosterone (P < 0.001) in the presence of both levels of gossypol inclusion. Furthermore, high level of gossypol reduced forward motility (P < 0.001) and semen initial fructose concentration (P = 0.002) and increased abnormal-head sperm (P = 0.003) and blood serum concentration of triiodothyronine (P = 0.006). Regardless of selenium supplementation, increasing level of free gossypol in diet resulted in a significant decrease in the percentage of forward motility (P = 0.037) and significant increases in the mean values of sperm concentration (P < 0.001), total sperm output (P = 0.002), percentage of total abnormal sperm (P = 0.058), and abnormal-head sperm (P = 0.016). On the other hand, regardless of levels of gossypol inclusion, selenium supplementation resulted in significant increases in libido (P < 0.001), mean values of ejaculate volume (P < 0.001), percentage of forward motility (P = 0.019), total sperm output (P < 0.001), total functional sperm fraction (P < 0.001), semen initial fructose concentration (P = 0.031), and blood serum concentrations of both testosterone and triiodothyronine (P < 0.001). In conclusion, free gossypol in diet induced adverse effects on semen quality in rams, but selenium supplementation successfully counteracts most of the hazardous effects of gossypol on semen characteristics.

Association between myeloperoxidase concentration in equine frozen semen and post-thawing parameters

Despite improvement of techniques, semen of 20% of stallions remains unfreezable. Recent studies focused on the impact of reactive oxygen species and oxidant enzymes on semen characteristics. Myeloperoxidase (MPO) is a pro-oxidant enzyme contained in and released by neutrophils during degranulation or after cell lysis. It is responsible for the formation of hypochlorous acid, a strong oxidant agent, which could damage spermatozoa. The aim of this study was to determine the relation between MPO concentration and characteristics of frozen semen from stallions. Thirty-five straws from different stallions were analysed. Post-thawing spermatozoal concentration, and progressive and total motility were determined by Computer-Assisted Semen Analysis. Freezability was determined according to post-thawing progressive motility (above or below 15%). Percentage of alive spermatozoa and abnormal forms was determined after Eosin-Nigrosin and Diff-Quick(®) staining, respectively. Post-thawing MPO concentration was measured by enzyme-linked immunosorbent assay (ELISA). Our study shows that frozen thawed semen contains large amounts of free MPO. We also observed that post-thawing MPO ELISA assay can be used as an indicator of equine semen freezability. High MPO concentration samples showed lower total and progressive motility. A higher proportion of abnormal head shape associated with acrosome reaction was observed in our late examinations of the high concentration MPO group. Our results show that MPO adversely affects total and progressive motility of equine semen. A negative correlation between normal motile forms and MPO concentration was also observed. The effect of MPO on dead or abnormal forms remains to be precised.

Flow cytometry for the assessment of animal sperm integrity and functionality: state of the art

Flow cytometry is now a recognized methodology within animal spermatology, and has moved from being a research tool to become routine in the assessment of animal semen destined to breeding. The availability of 'bench-top' flow cytometers and of newer and versatile markers for cell structure and function had allowed the instrumentation to measure more sperm parameters, from viability to reactiveness when exposed to exogenous stimuli, and to increase our capabilities to sort spermatozoa for potential fertilizing capacity, or chromosomal sex. The present review summarizes the state of the art regarding flow cytometry applied to animal andrology, albeit keeping an open comparative intent. It critically evaluates the present and future capabilities of flow cytometry for the diagnostics of potential fertility and for the development of current reproductive technologies such as sperm freezing, sperm selection and sperm sorting. The flow cytometry methods will probably further revolutionize our understanding of the sperm physiology and their functionality, and will undoubtedly extend its application in isolating many uncharacterized features of spermatozoa. However, continuous follow-up of the methods is a necessity owing to technical developments and the complexity of mapping spermatozoa.

Factors affecting fertilisation and early embryo quality in single- and superovulated dairy cattle

Data on fertilisation and embryo quality in dairy cattle are presented and the main factors responsible for the low fertility of single-ovulating lactating cows and embryo yield in superovulated dairy cattle are highlighted. During the past 50 years, the fertility in high-producing lactating dairy cattle has decreased as milk production increased. Recent data show conception rates to first service to be approximately 32% in lactating cows, whereas in heifers it has remained above 50%. Fertilisation does not seem to be the principal factor responsible for the low fertility in single-ovulating cows, because it has remained above 80%. Conversely, early embryonic development is impaired in high-producing dairy cows, as observed by most embryonic losses occurring during the first week after fertilisation. However, in superovulated dairy cattle, although fertilisation failure is more pronounced, averaging approximately 45%, the percentage of fertilised embryos viable at 1 week is quite high (>70%). Among the multifactorial causes of low fertility in lactating dairy cows, high feed intake associated with low concentrations of circulating steroids may contribute substantially to reduced embryo quality. Fertilisation failure in superovulated cattle may be a consequence of inappropriate gamete transport due to hormonal imbalances.

Two-stage genome-wide association study identifies integrin beta 5 as having potential role in bull fertility

Background

Fertility is one of the most critical factors controlling biological and financial performance of animal production systems and genetic improvement of lines. The objective of this study was to identify molecular defects in the sperm that are responsible for uncompensable fertility in Holstein bulls. We performed a comprehensive genome wide analysis of single nucleotide polymorphisms (SNP) for bull fertility followed by a second-stage replication in additional bulls for a restricted set of markers.

Results

In the Phase I association study, we genotyped the genomic sperm DNA of 10 low-fertility and 10 high-fertility bulls using Bovine SNP Gene Chips containing approximately 10,000 random SNP markers. In these animals, 8,207 markers were found to be polymorphic, 97 of which were significantly associated with fertility (p < 0.01). In the Phase II study, we tested the four most significant SNP from the Phase I study in 101 low-fertility and 100 high-fertility bulls, with two SNPs (rs29024867 and rs41257187) significantly replicated. Rs29024867 corresponds to a nucleotide change of C → G 2,190 bp 3' of the collagen type I alpha 2 gene on chromosome 4, while the rs41257187 (C → T) is in the coding region of integrin beta 5 gene on chromosome 1. The SNP rs41257187 induces a synonymous (Proline → Proline), suggesting disequilibrium with the true causative locus (i), but we found that the incubation of bull spermatozoa with integrin beta 5 antibodies significantly decreased the ability to fertilize oocytes. Our findings suggest that the bovine sperm integrin beta 5 protein plays a role during fertilization and could serve as a positional or functional marker of bull fertility.

Conclusion

We have identified molecular markers associated with bull fertility and established that at least one of the genes harboring such variation has a role in fertility. The findings are important in understanding mechanisms of uncompensatory infertility in bulls, and in other male mammals. The findings set the stage for more hypothesis-driven research aimed at discovering the role of variation in the genome that affect fertility and that can be used to identify molecular mechanisms of development.

Evaluation of sperm functional attributes in relation to in vitro sperm-zona pellucida binding ability and cleavage rate in assessing frozen thawed buffalo (Bubalus bubalis) semen quality

The objective of this study was to evaluate sperm functional attributes in relation to in vitro sperm-zona binding ability and cleavage rate in assessing frozen thawed buffalo (Bubalus bubalis) semen quality. Frozen-thawed forty-eight ejaculates from eight Surti buffalo bulls (six ejaculates/bull) obtained by artificial vagina were used. Frozen semen from each bull was thawed, pooled, and subjected for sperm functional (six replicates) and in vitro fertilization (four replicates) tests. The progressive forward motility, plasmalemma functional integrity assessed by fluorogenic [6-carboxyfluorescein diacetate (CFDA), and propidium iodide (PI)], hypoosmotic swelling (HOS), and hypoosmotic swelling-Giemsa (HOS-G) test, mitochondrial membrane potential, sperm nuclear morphology, the number of sperm bound to zona and cleavage rate differed significantly (P<0.05) between bulls. When the animals were grouped based on cleavage rate (group I, >40% cleavage rate, n=5, and group II, <40% cleavage rate, n=3), in vitro fertility parameters and all the sperm functional attributes except sperm nuclear morphology differed significantly (P<0.05). The proportions of sperm with functional plasmalemma in the tail and intact acrosome assessed by HOS-G test (25.33, range: 17.48-40.27) were significantly (P<0.001) lower than the functional plasmalemma in the tail assessed by HOS test (39.80, range: 27.85-54.67). The number of sperm bound to zona had significant correlations with the mitochondrial membrane potential (r=0.90, P<0.01) and plasmalemma integrity (fluorogenic, r=0.74 and HOS, r=0.79, P<0.05) and HOS-G, r=0.87, P<0.01). The cleavage rate had significant (P<0.05) correlations with the mitochondrial membrane potential (r=0.70) and plasmalemma integrity measured by HOS-G test (r=0.68). The present study indicates that these attributes could represent important determinants of buffalo sperm quality influencing cleavage rate.

Comprehensive proteomic analysis of bovine spermatozoa of varying fertility rates and identification of biomarkers associated with fertility

BACKGROUND

Male infertility is a major problem for mammalian reproduction. However, molecular details including the underlying mechanisms of male fertility are still not known. A thorough understanding of these mechanisms is essential for obtaining consistently high reproductive efficiency and to ensure lower cost and time-loss by breeder.

RESULTS

Using high and low fertility bull spermatozoa, here we employed differential detergent fractionation multidimensional protein identification technology (DDF-Mud PIT) and identified 125 putative biomarkers of fertility. We next used quantitative Systems Biology modeling and canonical protein interaction pathways and networks to show that high fertility spermatozoa differ from low fertility spermatozoa in four main ways. Compared to sperm from low fertility bulls, sperm from high fertility bulls have higher expression of proteins involved in: energy metabolism, cell communication, spermatogenesis, and cell motility. Our data also suggests a hypothesis that low fertility sperm DNA integrity may be compromised because cell cycle: G2/M DNA damage checkpoint regulation was most significant signaling pathway identified in low fertility spermatozoa.

CONCLUSION

This is the first comprehensive description of the bovine spermatozoa proteome. Comparative proteomic analysis of high fertility and low fertility bulls, in the context of protein interaction networks identified putative molecular markers associated with high fertility phenotype.

Influence of the male on embryo quality

Early pregnancy failure or loss (EPL) represents a major source of wastage and inefficiency in livestock production systems. Although successful embryo development is dependent upon genetic and epigenetic contributions from both the male and female, potential adverse male affects on embryo quality and development are probably often underestimated. Of adverse male effects which have been identified, those associated with sperm and semen "quality" have been best characterized. In turn, although many factors can adversely impact semen quality, the mechanisms involved are relatively few. This presents opportunities for identifying biological markers for spermatogenic damage, as well as protective measures.

Embryo production from superovulated cattle following insemination of sexed sperm

Two trials were conducted to ascertain fertilization rate, embryo quality and numbers of transferable embryos in superovulated heifers and cows inseminated with sexed sperm. Inseminates contained 2 x 10(6), 10 x 10(6) or 20 x 10(6) total sperm enriched for the X- or Y-chromosome ( approximately 90%) by flow cytometry/cell sorting. Non-sexed inseminates contained 40 x 10(6) total sperm. Donors in each trial were allocated to one of each of the bulls included in that study. Each donor was inseminated with frozen/thawed sperm from the same bull for each treatment in successive courses of superstimulation with twice daily i.m. injections of FSH for 4 d. Heifers and cows were inseminated 12 and 24 h after visually observed standing estrus in Trial 1. In Trial 2, a single timed inseminate was used 70-72 h following PGF(2alpha). Ova/embryos were collected non-surgically 7-7.5 d after insemination. In both trials, fewer ova were fertilized with sexed versus non-sexed treatments and with 2 x 10(6) sexed sperm compared to higher doses (P < 0.05). However, insemination of 20 x 10(6) total sexed sperm of >or=90% purity resulted in similar numbers of transferable embryos of the desired sex compared to that for non-sexed sperm.

Differences between Belclare and Suffolk ewes in fertilization rate, embryo quality and accessory sperm number after cervical or laparoscopic artificial insemination

Ewe breed has been shown to have a major effect on pregnancy rates following cervical AI using frozen-thawed semen. The main objective of this study was to examine the differences between purebred Belclare and Suffolk ewes (multiparous) in fertilization rate, number of accessory sperm and stage of embryo development on day 6 after cervical or laparoscopic AI with frozen-thawed semen. In experiment 1, Belclare and Suffolk ewes were synchronized for 12 days and were either cervically inseminated (year 1: n=28 and 31; year 2: n=16 and 15, respectively) or laparoscopically inseminated (year 2: n=13 and 14). In experiment 2, superovulated Belclare (n=4) and Suffolk (n=13) ewes were laparoscopically inseminated. All ewes were slaughtered 6 days after AI; oocytes/embryos were recovered, morphologically graded and stained to assess the number of cells and accessory spermatozoa. Data from both experiments were combined for statistical analysis. The proportion of ewes with fertilized oocytes was significantly higher following laparoscopic AI compared with cervical AI (54% versus 19%). More Belclare than Suffolk ewes yielded fertilized oocyte(s) after cervical AI (34% versus 10%, P<0.02) but there was no difference after laparoscopic AI (62% versus 60%). From the ewes that yielded at least one fertilized oocyte the proportion of Belclare ewes with embryos at the morula/blastocyst stage was significantly greater than for Suffolk ewes (94% versus 59%, P<0.02). A higher proportion of Belclare than Suffolk ewes had evidence of sperm reaching the site of fertilization following cervical AI (39% versus 15%, P<0.02) but there was no difference after laparoscopic AI (62% versus 64%, P>0.8). Amongst the ewes with evidence of sperm at the site of fertilization, laparoscopic AI resulted in a higher number of sperm per oocyte/embryo or per ewe than cervical AI (P<0.01). These results suggested that the difference in pregnancy rate between Suffolk and Belclare ewes following cervical AI was due to: (i) sperm traversing the cervix and uterus in a higher proportion of Belclare than Suffolk ewes, leading to a higher incidence of fertilization and (ii) the lower developmental competence of fertilized oocytes from Suffolk ewes.

Bovine embryo development after IVF with spermatozoa having abnormal morphology

The study was conducted to evaluate the effects of scrotal insulation on semen samples collected from bulls on embryonic development after IVF. Semen samples were obtained and cryopreserved from four Holstein bulls before and after a scrotal insulation period of 48 h (Day 0). Three types of samples were used for IVF: (1) semen from the test bulls collected 5 d prior to scrotal insulation (pre-insult); (2) semen from Day 13 (2-week post-insult; 2-week PI); and (3) semen from Day 20 (3-week PI). After 18 h of sperm-oocyte co-incubation, the zygotes were cultured for 8 d when a developmental score (0=degenerate, 1=2-cell embryo through 5=blastocyst) was assigned to each embryo. The post-thaw morphological evaluation of sperm samples revealed a decrease (P<0.01) in the percentages of normal spermatozoa in the 3-week PI samples in comparison with the pre-insult samples for Bulls I and III (74-22.3% and 67.7-0.5 %, respectively). The percentage of vacuolated spermatozoa increased significantly for Bull II. The cleavage and blastocyst formation rates and embryo development scores were affected (P<0.01) by the interaction of bull by sample collection time. For Bulls I and III (severe responders) the scrotal insulation effects persisted from the time of cleavage through blastocyst formation. In contrast, the cleavage and blastocyst formation rates for Bulls II and IV were unaffected, despite high percentages of vacuolated spermatozoa present in the post-insult samples for Bull II. In conclusion, the use of scrotal insulation to elevate scrotal temperature was an effective method to obtain semen samples with high percentages of abnormal spermatozoa. The decrease in embryonic development after IVF when using spermatozoa with morphological abnormalities seemed to be multifaceted and related to changes in head morphology.

Pregnancy Rates in Lactating Dairy Cows After Presynchronization of Estrous Cycles and Variations of the Ovsynch Protocol

Our objectives were to determine pregnancy rates after altering times of the second GnRH injection, insemination, or both in a combined Presynch + Ovsynch protocol, to accommodate once-daily lockup of dairy cows. Lactating dairy cows (n = 665) from 2 dairy herds in northeastern Kansas were studied. Cows ranged from 24 to 44 d in milk (DIM) at the start of the Pre-synch protocol, which consisted of 2 injections of PGF(2alpha) 14 d apart, with the second injection given 12 d before initiating the Ovsynch protocol. Cows were blocked by lactation number and assigned randomly to 3 treatments consisting of variations of the Ovsynch protocol. Cows in 2 treatments received injections of GnRH 7 d before and 48 h (G48) after the PGF(2alpha) injection. Timed AI (TAI) was conducted at the time of the second GnRH injection (G48 + TAI48) or 24 h later (G48 + TAI72). Cows in the third treatment received the injections of GnRH 7 d before and at 72 h after PGF(2alpha) and were inseminated at the time of the second GnRH injection (G72 + TAI72). Pregnancy was diagnosed weekly by palpation per rectum of uterine contents on d 40 or 41 after TAI. Pregnancy rates differed between herds, but they were consistently greater for G72 + TAI72 than for G48 + TAI48 and G72 + TAI72. Subsequent calving rates were consistent with differences in initial TAI pregnancy rates. Pregnancy loss was least for cows on the G72 + TAI72 treatment. Body condition scores (BCS) ranged from 1.0 to 4.0 when assessed on Monday of the breeding week. An interaction of BCS and herd was detected in which cows in herd 1 having poorer BCS (<2.25) had greater pregnancy rates than cows of greater BCS (>/=2.25), whereas the reverse was true in herd 2 in which overall pregnancy rates were greater. We concluded that inseminating at 48 or 72 h after PGF(2alpha), when GnRH was administered at 48 h after PGF(2alpha), produced fewer pregnancies than inseminating and injecting GnRH at 72 h after PGF(2alpha) for cows whose estrous cycles were synchronized before initiating this variant of the Ovsynch protocol.

Assessment of the morphology of frozen-thawed bull sperm in relation to its cryopreservation for artificial insemination

The morphology of sperm in raw semen was compared with that of the live sperm in semen which had been frozen and thawed. The thawed semen was stained with 6-carboxyfluorescein diacetate and propidium iodide and examined by fluorescence microscopy; smears of the raw semen were stained with eosin and nigrosin. Thirty-four ejaculates from 24 bulls of various breeds were examined. There were fewer abnormal heads, detached heads, coiled tails and proximal cytoplasmic droplets/pseudodroplets in the thawed semen than in the raw semen, there was no change in the number of bent tails, but the number of distal cytoplasmic droplets/pseudodroplets increased. There were no significant differences in morphology between ejaculates which passed or failed the osmotic resistance test after thawing, but failed batches tended to have more distal cytoplasmic droplets/pseudodroplets.

Fertility estimation: a review of past experience and future prospects

Fertility has many components and stages which require that males and females be functionally capable of carrying out all critical stages if each generational reproductive cycle is to be completed. To accomplish this, the male must produce and ejaculate normal fertile sperm. The female must produce, store and ovulate normal fertilizable oocytes. Furthermore, the female must provide a reproductive system compatible with sperm transport, capacitation, and fertilization of the oocytes, embryo and fetal development, and finally birth of healthy young. Reproductive success or failure at several of these points can be estimated quantitatively on a population basis, and in a few situations on an individual basis. It is important that fertility estimates be determined accurately and with precision to be most useful to researchers and managers of animal enterprises. Many studies have underestimated the biological relationship of fertility to other traits because the estimates lacked precision. Many in vitro manipulations of sperm in artificial insemination, of gametes in various assisted reproductive technologies, and of embryos in embryo transfer are utilized in animal breeding programs. Accurate estimation of reproductive efficiency of these in vitro procedures also is important. Conditions surrounding different sets of fertility estimates almost certainly will be different. These conditions should be described as precisely as possible, and appropriate controls included in all experiments. When possible, experiments should be replicated over time and place to determine the repeatability of the various criteria used to estimate fertility and reproductive efficiency. Advances in genomic information and molecular biology should facilitate characterizing more fully inherent potential fertility of animals at birth. In vitro tests will improve, and automated techniques will facilitate making multiple determinations possible on a large scale. Reliability of fertility estimates will increase, with the potential for enhanced animal reproductive performance through more accurate selection, genetic engineering, and enlightened animal care. Simultaneously, it is important to recognize that prediction of future fertility is more hazardous than estimating fertility, as a completely new set of circumstances may occur which are not predictable. Because fertility estimation may be applied under a myriad of conditions, principles and factors affecting fertility will be emphasized in this review as being more useful than a compilation of numerical examples.

Plasma membrane and acrosomal integrity in bovine spermatozoa with the knobbed acrosome defect

Previous studies have shown that bovine spermatozoa with the knobbed acrosome defect have a reduced ability to bind to and penetrate the bovine zona pellucida. Cryopreserved spermatozoa from a normal control bull (N) and two bulls with the knobbed acrosome defect (K1 and K2) were subjected to a hypoosmotic swelling test (HOST) to evaluate the functional integrity of the plasma membrane. A capacitation assay and a calcium ionophore challenge test was used to determine the ability of spermatozoa to undergo capacitation and acrosome reaction (AR), respectively. The mean percentage of spermatozoa responding to the HOST was significantly higher for Bull N (68.8 +/- 2.4) than for Bulls K1 (36.1 +/- 4.6) and K2 (40.2 +/- 4.7). The mean percentage of capacitated spermatozoa (54.0 +/- 1.8) was significantly higher for the treatment group (incubation in capacitating medium) for Bull N than that of the negative control group (29.5 +/- 1.8). However, there was no difference between the treatment and the negative control groups of the bulls with the knobbed spermatozoa (36.5 +/- 1.4 and 27.1 +/- 3.0 for Bull K1 and 47.5 +/- 3.8 and 35.2 +/- 6.6 for Bull K2, respectively). Although the mean percentage of acrosome-reacted spermatozoa (60.7 +/- 1.3) was higher for the treatment group (receiving calcium ionophore) for Bull N than that of the negative control (29.5 +/- 1.3), there was no difference between the treatment and the negative control groups for the bulls with the knobbed spermatozoa (47.8 +/- 3.3 and 49.3 +/- 5.0 for Bull K1 and 58.8 +/- 10 and 59.5 +/- 9.7 for Bull K2, respectively). A positive correlation existed between the proportion of spermatozoa that did not respond to the HOST and that undergoing a spontaneous AR. Results suggest that spermatozoa with the knobbed acrosome defect have impaired plasma membrane function which predisposes them to premature capacitation and spontaneous AR on incubation after thawing.

Effect of time of insemination on number of accessory sperm, fertilization rate, and embryo quality in nonlactating dairy cattle

Two experiments were conducted to determine the effect of insemination time on number of accessory sperm per embryo (ovum), fertilization rate, and embryo quality. Semen was collected from three fertile Holstein bulls and cryopreserved in egg yolk-citrate-glycerol. In experiment 1, cows were continuously monitored for behavioral estrus by the HeatWatch estrous detection system and were artificially inseminated (AI) with one 0.5-ml straw (25 x 10(6) sperm) at the onset of estrus (AI 0 h), 12 h after onset (AI 12 h), or received natural service at 0 h (Nat 0 h) from one of three bulls. From 150 inseminations, 115 embryos and ova (AI 0 h: n = 39; AI 12 h: n = 39; Nat 0 h: n = 37) were recovered 6 or 7 d after insemination. Fertilization rates differed between treatments (AI 0 h: 67%; AI 12 h: 79%; Nat 0 h: 98%). Median accessory sperm per embryo (ovum) also differed (AI 0 h: 1; AI 12 h: 10; and Nat 0 h: 27) and paralleled the fertilization rate. Embryo quality was not affected by insemination time or natural service. In experiment 2, cows received AI at 0, 12, or 24 h (AI 24 h) after the onset of estrus as determined by HeatWatch. From 154 inseminations, 117 embryos and ova (AI 0 h: n = 39; AI 12 h: n = 39; AI 24 h: n = 39) were recovered 6 or 7 d after insemination. Fertilization rates did not differ in experiment 2 (AI 0 h: 66%; AI 12 h: 74%; AI 24 h: 82%); however, a trend toward a higher fertilization rate accompanied AI 24 h. Median accessory sperm values increased from AI 0 h (1) to AI 24 h (4). Embryo quality declined with AI at increasing intervals after onset of estrus, as percentages of excellent and good, fair and poor, and degenerate embryos were as follows: 77, 15, 8; 52, 38, 10; and 47, 19, 34 for the 0-, 12-, and 24-h inseminations, respectively. Results indicate AI 12 h after the onset of estrus provides a compromise between potential fertilization failure (AI 0 h) and embryo failure (AI 24 h), despite increased accessory sperm per embryo (ovum) after AI 24 h. Artificial insemination 12 h after onset of estrus should optimize fertility of dairy cattle through an acceptable fertilization rate, number of accessory sperm per embryo, and desirable embryo quality.

Fertilizing characteristics of bovine sperm with flattened or indented acrosomes

Frozen semen from a control bull (C: 89% morphologically normal sperm) and two bulls with acrosomal defects (K1: 92% flattened acrosomes; K2: 82% indented acrosomes) were used to investigate the fertilizing ability of bull sperm with flattened or indented acrosomes. In experiment 1, frozen-thawed sperm were evaluated for acrosomal integrity with fluorescent microscopy. In experiment 2, proteolytic activity of the acrosomal contents of sperm was evaluated through a gelatin digestion assay. In experiment 3, an IVF test system was used to determine the ability of sperm with flattened or indented acrosomes to bind to bovine oocytes and penetrate the zona pellucida. In experiment 4, IVM zona-free bovine oocytes (ZFO) were fertilized and examined to evaluate sperm chromatin decondensation. In experiment 1, bulls K1 and K2 had a lower proportion of sperm with intact acrosomes (0 and 13.6 +/- 4.5%, respectively) than bull C (30.2 +/- 5.6%) after 2h of incubation. In experiment 2, the proportion of sperm with proteolytic activity, as indicated by gelatin digestion around sperm heads, did not differ among bulls (C: 55%, n=410; K1: 43%, n=426; K2: 48%, n=324). In experiment 3, a lower proportion of sperm with flattened (K1) or indented acrosomes (K2) bound to oocytes than sperm from the control bull, C. The percentage of zona penetrated (55%, n=20; 13%, n=23; 4%, n=25) and the mean (+/- S.E.M.) number of sperm penetrating these zona pellucida (19.7 +/- 2.5; 6.9 +/- 1.0; and 2.6 +/- 0.5) was higher (P<0.05) for bull C than for bulls K1 or K2, respectively. In experiment 4, the percentage of ZFO penetrated (95%, n=20; 52%, n=30; 30%, n=33) and the mean (+/- S.E.M.) number of sperm with chromatin decondensation (7.8 +/- 1.6; 0.8 +/- 0.2; and 0.3 +/- 0.1) were also higher (P<0.05) for the control bull, C than for bulls K1 or K2, respectively. Results suggest that although sperm with the flattened or indented acrosomes had a tendency to undergo spontaneous acrosome reaction on incubation after thawing, the proteolytic activity of the acrosomal contents appeared to be normal. Sperm with the flattened or indented acrosomes also appeared to have a reduced ability to fuse with oolemma as demonstrated by confocal microscopy. This would impair the ability to penetrate ooplasm and undergo sperm chromatin decondensation.

The search is on: finding accurate molecular markers of male fertility

Diagnosis of the fertility potential of a semen sample is essential for consistently high reproductive efficiency. The use of subfertile or infertile semen can have devastating consequences for those selling or using the semen. Therefore it is crucial to develop and use accurate diagnostic tests to determine the fertility of males and of individual semen samples. These diagnostic tests must be economically practical and provide consistent results. The goal of this review is to explore areas of fertility diagnostic research, including what we have termed functional and molecular tests, and consider the accuracy of each test. In this article, literature from several species is cited, and it is noteworthy that each diagnostic test may not be valuable in all species. Multiple functional and molecular tests will likely be needed to effectively characterize male fertility in each species.

Fertilizing potential in vitro of semen from young beef bulls containing a high or low percentage of sperm with a proximal droplet

Fertilizing potential of semen containing a high percentage of sperm with a proximal droplet was evaluated using IVF. Design criteria: (a) specified semen with >100 x 10(6) sperm/mL with >40% progressively motile spermatozoa, after collection via electro-stimulation; (b) designated a droplet group, bulls whose semen contained >30% spermatozoa with a proximal droplet and <25% with other morphological abnormalities, and a control group, with <25% abnormalities of any type; and (c) stipulated evaluations at 11 to 13 mo of age and again -4 wk later. At the initial evaluation, when a bull was assigned to the droplet group, the next bull meeting control criteria was designated his pair; 15 pairs in four herds were studied. Semen was extended in egg-yolk citrate, cooled to 5 degrees C over approximately 2.5 h, and held at 5 degrees C. After 20 to 44 h, spermatozoa were processed by swimup, incubated with heparin, and co-cultured with oocytes (35 to 56 oocytes/sample; 18 h). Ova were observed for cleavage approximately 42 h after co-culture, and further development was evaluated on day 8. At first evaluation, cleavage rates were 18 and 46% for droplet and control groups (P < 0.01); semen had 34 to 70% and 0 to 12% droplet spermatozoa. For 10 of 15 droplet bulls, <10% of ova were cleaved whereas cleavage rate was >15% for all control bulls. At second evaluation, only three droplet bulls still had >30% of spermatozoa with a proximal droplet. Cleavage rates increased accordingly; only four droplet bulls had <10% cleaved ova and 10 had >34% cleaved ova. Three control bulls had <10% cleaved ova and nine had > or = 34% cleaved ova. Considering all 60 ejaculates, correlation between percentage of spermatozoa with a proximal droplet and percentage of cleaved ova was -0.49 (P < 0.0 1). Correlations between percentages of motile or normal spermatozoa in field evaluations and outcome in IVF were 0.28 and 0.52. Laboratory evaluations of spermatozoa concomitant with preparation for IVF revealed that only incidence of proximal droplets appeared related to outcome in IVF. We concluded: (a) semen from most yearling beef bulls with a high incidence of proximal droplet spermatozoa had severely compromised IVF fertility; (b) as these bulls matured, the incidence of proximal droplets decreased, and IVF fertilizing potential increased; and (c) semen containing >30% spermatozoa with a proximal droplet is strong evidence that fertilizing potential of the bull will be low until the incidence decreases.

Relationship of seminal traits and insemination time to fertilization rate and embryo quality

The nature of subfertility due to the male or inseminate is as complex as that of the female. Fertilization failure or failure in embryogenesis are both documented to be of seminal origin. Males also differ in the numbers of sperm required to reach their maximum fertilization rate. Males requiring more sperm would be considered to have compensable seminal deficiencies. These include a number of known (viability and morphology) and unknown factors (functional or molecular traits) precluding sperm access to the ovum or ability to engage the ovum sufficiently to initiate fertilization and the block to polyspermy. Differences in fertility among males or inseminates independent of sperm dosage are considered uncompensable. These deficiencies would be associated with fertilizing sperm that are incompetent to maintain the fertilization process or subsequent embryogenesis once initiated, with most failures occurring prior to maternal recognition of pregnancy. Such sperm would preempt fertilization by competent sperm. Chromatin aberrations in morphologically normal or near normal spermatozoa from abnormal semen samples appear to be the best candidates for the uncompensable deficiency. However, recognition of uncompensable or incompetent fertilizing sperm has not been achieved. Six-day-old non-surgically recovered bovine ova/embryos have been used to evaluate compensable and uncompensable seminal deficiencies as well as to test reproductive strategies. These ova/embryos provide information on fertilization status and embryo quality as well as quantitative and qualitative data regarding associated accessory sperm. Thus, they permit the separation of reproductive failure by fertilization from that by embryonic development. Accessory sperm number is positively associated with both fertilization rate and embryonic quality. Early insemination results in low fertilization rates (low accessory sperm number), but good embryo quality, whereas, late insemination results in high fertilization rates (high accessory sperm number), but poor embryo quality. Additional studies will be necessary to substantiate this model; however, if true, future research designed to improve results to artificial insemination should be tested by breeding early in estrus where sperm viability is most limiting and embryo quality is best.

Effect of a deep uterine insemination on spermatozoal accessibility to the ovum in cattle: a competitive insemination study

A competitive insemination study was conducted to determine the effect of a deep uterine insemination on accessory sperm number per embryo in cattle. Cryopreserved semen of a fertile bull characterized by spermatozoa with a semi-flattened region of the anterior sperm head (marked bull) was matched with cryopreserved semen from an unmarked bull having spermatozoa with a conventional head shape. Using 0.25-mL French straws and a side delivery embryo transfer device, deep uterine insemination (0.125 mL deposited in each horn) was performed 2 cm from the uterotubal junction. Immediately after, the uterine body was artificially inseminated using semen (0.25 mL) from an alternate bull and a conventional insemination device. The complete dose (both inseminations) was 50x10(6) total sperm cells consisting of an equal number of spermatozoa from each bull. Single ovulating cows (n = 95) were inseminated at random with either the unmarked semen in the uterine body and marked semen in the uterine horn, or the unmarked semen in the uterine horn and marked semen in the uterine body. Sixty-one embryos(ova) were recovered nonsurgically 6 d post insemination, of which 40 were fertilized and contained accessory spermatozoa. The ratio and total number of accessory spermatozoa recovered was different among treatments: 62:38 (326) for the unmarked semen in the uterine body and marked semen in the uterine horn, and 72:28 (454) for the unmarked semen in the uterine horn and marked semen in the uterine body (P<0.05). Deep uterine insemination using this semen in a split dose and a side delivery device favors accessibility of spermatozoa to the ovum compared with conventional uterine body insemination.