The effect of sperm concentration in the ejaculate on morphological traits of bull spermatozoa

Experiments were performed on 75 ejaculates obtained from 19 bulls representing different cattle breeds used at the Masovian Centre for Animal Breeding and Reproduction in ?owicz. Fresh ejaculates were measured in respect to their volume and sperm count in the ejaculates was determined. The ejaculates were classified based on the criterion of sperm concentration and divided into five groups. Sperm morphometric measurements were taken from each bull and assessment of semen morphology was done on the basis of examination under a microscope using preparations made from fresh ejaculates. For each slide, morphometric measurements were taken of 15 randomly selected spermatozoa characterised by normal morphology and well visible under the microscope. Additionally, in each preparation morphometry of 500 spermatozoa was evaluated, numbers of spermatozoa with normal morphology and morphological abnormalities were recorded and these were categorized into spermatozoa with major and minor defects. An insignificant correlation was observed between the sperm concentration in the ejaculate and morphological traits, dimensions and shapes of bull spermatozoa. The less concentrated ejaculates contained spermatozoa with a slightly larger head circumference and a more elongated head shape in comparison with the spermatozoa in the more concentrated ejaculates. The highest frequency of morphologically malformed spermatozoa, both in the case of primary and secondary alterations, was observed in ejaculates with sperm concentration of no more than 1000 x 10(3)/mm3.     

Evaluation of males spermiogram in domestic pigs

A microscopic assessment was used to estimate sperm morphological structure in 405 ejaculates from 70 boars according to Blom classification. The classification of spermiogram quality according to a new 6-degree scale was also established. We found, that male spermiograms in domestic pigs were characterized by a large variability both between and within breeds. The estimation of semen quality, only with regard to the mean frequency of occurrence of particular morphological forms of spermatozoa, was not effective for evaluation of individual boar or group of boars. However, the method was effective to evaluate individual ejaculates. The quality classification of the spermiogram enabled to evaluate usefulness of ejaculates graded as good and average for insemination.     

Genetic correlations between production and semen traits in pig

Genetic correlations between production traits (average daily gain from birth till the end of the field test and ultrasonically predicted lean meat content at the end of the field test) and semen traits (semen volume, sperm concentration, motility, percentage of abnormal spermatozoa, total number of spermatozoa and number of functional spermatozoa) were estimated from a large dataset (44 500 observations for production traits and more than 150 000 ejaculates from 2077 boars). The boars belonged to the breeds Duroc, Piétrain and Large White or were crossbreds between them. All estimated genetic correlations were low (maximal absolute value 0.13). Therefore, selection on production traits is expected to have only low effects on semen traits.     

Urinary losses of spermatozoa during ejaculation are negligible in boars

Boars that had a catheter implanted surgically in the urinary bladder (n = 10) were used to determine the magnitude of retrograde flow of spermatozoa into the urinary bladder during ejaculation (Experiments 1 and 2) and the post-ejaculatory retention of spermatozoa in the urethra (Experiment 2). The overall mean (+/- SD) total number of spermatozoa in the ejaculates of boars used in Experiments 1 and 2 was 62 +/- 25 x 10(9) and 65 +/- 33 x 10(9), respectively. The overall mean adjusted total number of spermatozoa in the post-ejaculation urine of boars was 106 +/- 537 x 10(6) in Experiment 1, and 41 +/- 242 x 10(6) in Experiment 2. The overall mean percentage of retrograde flow of spermatozoa into the urinary bladder was 0.15 +/- 0.78% for the boars used in Experiment 1, and 0.03 +/- 0.16% for boars used in Experiment 2. In Experiment 2, the overall mean percentage of urethral loss of spermatozoa was 0.45 +/- 1.02%, and the overall mean percentage of total urinary losses was 0.48 +/- 1.03%. These findings demonstrate that in boars, in contrast to bulls, rams, dogs, and cats, urinary losses of spermatozoa during ejaculation are negligible.     

Bovine spermatozoal head size variation and evaluation of a separation technique based on this size

The objectives of this study were to determine the variation of head areas of normal spermatozoa attributable to breed, individual bull and ejaculate and to verify separation of X and Y chromosome-bearing spermatozoa and separation effectiveness. Spermatozoa were evaluated using video enhanced contrast microscopy combined with video intensified fluorescent microscopy and the polymerase chain reaction (PCR). In Experiment 1, spermatozoal head areas were measured from 2 ejaculates collected from bulls of 3 beef and 2 dairy breeds. No differences in head areas were found between breeds or between bulls within breeds; variation was observed among ejaculates from individual bulls across breeds. In Experiment 2, spermatozoa from 5 ejaculates were separated on individual SEPDEVICEs (Patented). Head area, fluorescent intensity and PCR of spermatozoa retained in the SEPDEVICEs suggested a separation based on size in 1 of 5 samples. Ejaculate variation in head areas affected separation efficiency.     

Glutathione content in the semen of bulls of the lowland black-white breed

Glutathione concentration in the semen was determined in 113 ejaculates obtained from 30 bulls of the lowland black-white breed. The quantitative and morphological characteristics of the studied sperm samples indicated considerable individual differences but always within normal range. Glutathione content was determined in the plasma and in isolated spermatozoa by the method of Saville (Analyst, 1958, 83, 670). A high glutathione level in the spermatozoa (31 nmols in 10(9) cells) and in plasma (28.8 microM) was found. A positive correlation was demonstrated (p less than 0.05) between the level of the peptide in plasma and its level in spermatozoa. It was found that the glutathione level in spermatozoa was higher in the ejaculates with the cell count below the average level.     

Variability in relationships between semen quality and estimates of in vivo and in vitro fertility in boars

The present experiment was designed to characterize relationships between common semen quality and fertility estimates for three boars known to differ in farrowing rate, number of pigs born alive, and monospermic penetration rate. The approach chosen to accomplish this was to monitor semen quality from these boars and use their semen alternately for either artificial insemination or in vitro fertilization for 40 weeks. This strategy relied on the variability in semen quality parameters that normally occurs in an individual boar over time. When comparisons were made among boars, farrowing rates, numbers of pigs born alive, and monospermic penetration rates were significantly different, but progressive motility, normal head and tail morphology, and acrosome morphology were not. However, when comparisons were made among ejaculates within individual boars, there were significant effects of semen quality on both in vivo and in vitro fertility. For boar 3495, the proportion of spermatozoa exhibiting progressive motility and distribution of spermatozoa in a percoll gradient had a positive linear effect on number born alive and monospermic penetration rate, respectively. For boar 2901, quadratic equations best described changes in litter size as a function of progressive motility and normal acrosomes. In addition, monospermic penetration rate increased linearly as normal acrosomes and the proportion of spermatozoa recovered from a percoll gradient increased. For boar 4291, the relationship between progressive motility and number born alive and between normal acrosomes and number of pigs born alive were also quadratic. However, a significant linear relationship was present only between normal acrosomes and monospermic penetration rate. These results demonstrate that simply relying on the means of common semen quality estimates from some boars has limited value in terms of being used as a prospective indicator of their in vivo or in vitro fertility. In contrast, characterization of relationships between semen quality and fertility estimates is useful for estimating differences in the fertility of ejaculates from individual boars. However, both quantitative and qualitative differences in these relationships among boars are present and a given semen quality estimate that is a good predictor of in vivo or in vitro fertilization for one boar, may not be applicable for others.     

Changes in the morphology of spermatozoa during their passage through the genital tract in dairy bulls with normal and impaired spermat ogenesis

An investigation was conducted on changes in sperm morphology along the excurrent duct of bulls. The study comprised 20 bulls with proven fertility and normal semen picture, and 10 bulls with pathologic semen. The morphology of spermatozoa was evaluated on ejaculates and on postslaughter collected contents from the excurrent duct. The incidence of pathologic sperm heads decreased along the duct in both groups of bulls. The main decrease generally occurred in caput epididymidis. In bulls with pathologic semen, the decrease continued in lower regions of epididymis and was deferens. The rate and pattern of sperm removal seem to primarily depend on the quality of spermatozoa entering the excurrent duct. The removal was clearly selective and is assumed to be associated with phagocytosis of spermatozoa mainly in the efferent ductules and proximal part of caput epididymis. Proximal cytoplasmic droplets were present on almost all sperm in the efferent ductules. The incidence decreased during passage along the genital tract. Migration of cytoplasmic droplets from a proximal to a distal position took place between regions C and D of the caput epididymidis. The incidence of middle-piece abnormalities decreased during passage along the genital tract, while the incidence of sperm tail abnormalities increased in the corpus and cauda epididymidis in all bulls.     

Do different portions of the boar ejaculate vary in their ability to sustain cryopreservation?

Previous studies have shown sperm quality post-cryopreservation differs depending on the fraction of the seminal plasma boar spermatozoa are fortuitously contained in. As such, spermatozoa contained in the first 10 mL of the sperm-rich fraction (portion I) have better sustained handling procedures (extension, handling and freezing/thawing) than those contained in the ulterior part of a fractionated ejaculate (second portion of the sperm-rich fraction and the post-spermatic fraction, portion II). However, those studies were performed using pooled samples. In the present study, individual ejaculates were used. Split ejaculates (portions I and II) from five boars were frozen and thawed using a conventional freezing protocol, followed by computer-assisted motility and morphology analysis (CASA and ASMA, respectively), as well as an Annexin-V assay for spermatozoa from each boar and ejaculate portion. Significant differences between portions were observed in all ASMA-derived variables, except in one boar. Also significant differences were observed between boars and ejaculate portions in sperm quality post-thaw. We identified, however, boars showing best results of motility and sperm membrane integrity post-thaw in portion I, while in other boar the best results was observed in portion II. It is concluded that the identification of the ejaculate portion more suitable to sustain cryopreservation in each individual boar may be a readily applicable and easy technique to diminish variation in sperm freezability among boars.     

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.     

Assessment of plasma membrane and chromatin structure of sperm from transgenic and non-transgenic boars

The aim of this study was to determine the apoptotic changes and chromatin damage in non-transgenic and transgenic boars carrying the human α1,2-fucosyltransferase gene. Five ejaculates were collected from six transgenic (TG) and six non-transgenic (NTG) boars. Five ejaculates were collected from six transgenic (TG) and six non-transgenic (NTG) boars both crossbreds of Polish Landrace and Large White. Two fluorescence methods were employed to measure apoptosis: an assay to assess the early changes in sperm membrane integrity using fluorophore YO-PRO-1 and an assay for phosphatidylserine (PS) translocation across the plasma membrane using fluorescein-labeled Annexin-V. The chromatin damage was assessed based on the sperm chromatin structure assay method. No significant differences in the proportion of all detected subpopulations of spermatozoa were found between TG and NTG boars. Similarly, the analysis of the chromatin structure revealed no statistical differences in the sperm chromatin damage between TG and NTG boars. In conclusion, the presence of the human α1,2-fucosyltransferase gene in the genome of TG boars did not cause any spermatogenesis process disturbances leading to the increased production of apoptotic spermatozoa. Moreover, the low level of sperm with damaged chromatin in TG boars confirms the high stability of the spermatogenesis process in the TG boars analyzed.     

Bull selection and use in northern Australia. Part 2. Semen traits

Detailed semen evaluations were carried out on approximately 363 Santa Gertrudis, 5/8 Brahman and Brahman bulls on 12 different properties across northern Australia, as part of systematic breeding soundness examinations. A subset of bulls (n=245) were subsequently mated in groups, to cows and heifers at bull:female ratios of 2.5-6.0%, with the paternity of resulting calves being determined by microsatellite DNA testing. Motility traits of semen and spermatozoa were moderately repeatable and correlated with each other, but were unrelated to calf output. The percentage of morphologically normal spermatozoa in ejaculates was moderately to highly repeatable (e.g. r=0.10-0.64). The most common morphological abnormalities seen were mid-piece abnormalities, in particular, distal mid-piece reflex associated with a cytoplasmic droplet. Semen quality, particularly percent normal spermatozoa, was consistently related to calf output. In general, bulls with <50% normal spermatozoa sired few calves while bulls with the highest calf outputs had >70% normal spermatozoa. The presence or absence of heparin binding proteins in semen did not influence calf output. Semen from 93% of tested bulls was positive for heparin binding proteins. These results confirm that examination of semen, in particular, evaluation of percent morphologically normal spermatozoa, should be included in the breeding soundness examination of bulls.     

Influence of Boars on the Relationship between Fertility and Post Thawing Sperm Quality of Deep Frozen Boar Spermatozoa*

The aim of this investigation was to evaluate the possibility of selecting boars for deep freezing by means of laboratory tests on frozen-thawed spermatozoa. Thirty-one randomly selected frozen ejaculates from four boars were investigated by a thermoresistance test after thawing in boar seminal plasma and in OLEP. Extracellular ASAT activity was measured in samples from 30 of the ejaculates after thawing in OLEP and in isotonic glucose solution. Twenty of the ejaculates were utilized for fertility tests by artificial insemination of 37 gilts preceding the laboratory investigation. Three of the boars proved fertile with frozen semen. One of these boars seemed to yield superior fertility to the other two boars. No fertility was obtained with frozen spermatozoa from the fourth boar. Prior to the freezing trial this boar had been used for fresh semen inseminations giving higher pregnancy rates than the average of Swedish A.I.-boars. This boar was therefore considered a case of “low freezability”. In the laboratory tests the samples from this boar showed the lowest motility after 3 hrs.’ storage at 37°C, the highest relative decrease of motility during the thermoresistance test, the highest release of ASAT after thawing in OLEP and the highest relative release of ASAT. Analyses of variance indicated significant and almost significant variation among boars in relative decrease of motility during the thermoresistance test and in relative release of ASAT. The results indicate that the boars were the main cause of variation in fertility as well as in outcome of the laboratory tests. These results do not permit a complete evaluation of the relationship between fertility and outcome of the applied laboratory tests. However, the results indicate a possibility of detecting boars producing spermatozoa with low freezability by means of laboratory tests.     

Quantification of bull sperm characteristics measured by computer-assisted sperm analysis (CASA) and the relationship to fertility

Two experiments were conducted to evaluate semen quality of bulls housed under controlled conditions at a large AI facility and relate results to fertility. In Experiment 1 semen was collected from six 6-yr-old bulls twice daily at 3- to 4-d intervals for 3 d. In Experiment 2 eleven 6- to 11-yr-old bulls were used. Extensive breeding information was available and semen was collected as in Experiment 1 but replicated 4 times. Standard semen analysis and computer-assisted sperm analysis (CASA) with the Hamilton Thorne IVOS, model 10 unit, were performed on 36 first and second ejaculates in Experiment 1 and on 44 first ejaculates in Experiment 2. Sixteen fields (2 chambers with 8 fields per chamber) were examined per sample. In Experiment 1 the correlation between estimated sperm concentration by spectrophotometry and CASA was 0.91 (P < 0.01). Among bulls the range in the percentage of motile spermatozoa was 52 to 82 for CASA versus 62 to 69 for subjective measurements made by highly experienced technicians. Thus, CASA, with high repeatability, provided a more discriminating estimate of the percentage of motile sperm cells than did the subjective procedure. Bull effect was much greater than any other variable in the experiments. Chamber differences were small and so the results for the 2 chambers with 8 fields each were combined. One to five CASA values were correlated with bull fertility, defined as 59-day nonreturn rates corrected for cow and herd effects. The percentage of motile spermatozoa accounted for a small fraction of the total variation in fertility (r2 = 0.34). However higher r2 values (0.68 to 0.98) were obtained for 2 to 5 variables used in the multiple regression equations. The results are promising, and further testing will determine more precisely which of these CASA variables are most useful in estimating bull fertility potential.     

Sperm morphology and fertility of progeny-tested AI dairy bulls in Sweden

Use of bull semen with high levels of sperm abnormalities, reflecting genital dysfunction, is not recommended for artificial insemination (AI) since it would most likely lead to subfertility. Sperm quality, including sperm morphology, may deteriorate with increasing age of the bull thus becoming a source of concern when using older, progeny-tested AI bull sires. Although a relationship between sperm morphology and fertility after AI in progeny-tested bull sires has been reported, it is yet unclear which sperm abnormalities are most critical. This constituted the core aim of a 22-month long retrospective study in proven (aged 60-84 months at the start of the study) AI sires of the Swedish Red (SR, n=8) and Swedish Holstein (SLB, n=4) breeds where their semen (107 freezing batches in total, built by a single ejaculate (n=3) or pooling two consecutive ejaculates (n=104) collected at 1-3 months interval), were subjected to detailed morphological examinations on wet- and dry, stained smears. Attention was paid to between- and within-bull variations with regard to presence and level of sperm abnormalities. Sperm morphology differed significantly between sires and ejaculates, with 6/12 sires having ejaculates containing >10% of morphologically deviating sperm head shapes, a commonly used threshold for young AI bulls in Sweden. However, with the exception of pear-shaped or narrow-at-the-base anomalies, the mean values for individual defects were always within the limits expected for a normal bull sire, and were therefore considered acceptable. The percentage of morphologically normal spermatozoa was positively related to fertility, whose output differed significantly among bulls. Among sperm abnormalities, the proportion of morphologically deviating sperm head shapes were negatively correlated with fertility, pear-shaped sperm heads in particular. In conclusion, the relationship between sperm morphology and fertility after AI calls for frequent (2-3 months interval) detailed assessments of sperm morphology in AI stud bull sires.     

Effects of the anabolic steroid, boldenone undecylenate, on certain reproductive parameters in bulls

A total of 17 bulls was used to study the effects of boldenone undecylenate on growth and semen characteristics in beef bulls. In trial 1 nine mature mixed-breed beef bulls with satisfactory semen quality were divided into two groups. Group I (n = 5) received boldenone undecylenate (1.1 mg/kg) at 21 d intervals for a total of seven treatments (147 d). Group II (n = 4) served as untreated controls. Semen was collected from each group by electroejaculation on each treatment day and evaluated according to the standards of the Society for Theriogenology. Although neither the percentage of spermatozoa with primary or secondary morphological abnormalities was different, the ejaculates of Group I bulls contained a higher percentage of abnormal spermatozoa than those in Group II. In trial 2, eight mixed-breed bull calves, average weight 140.4 kg, were maintained under drylot conditions in a single paddock. The bulls were divided into two equal groups. Group I (n = 4) received boldenone undecylenate as in Trial 1. Group II (n = 4) served as untreated controls. The bulls were weighed and the scrotal circumference (SC) was measured every 21 d until it reached 30 cm, at which time semen was collected and evaluated as in Trial 1. Group I bulls had a higher percentage of spermatozoa with primary morphological abnormalities than bulls in Group II. Group I bulls had a higher average daily gain (ADG) than Group II bulls and required 21 d longer for the SC to reach 30 cm. Semen quality for all bulls was satisfactory at each sampling day.     

Incidence and ultrastructure of “crater” defect of bovine spermatozoa

The “crater” defect of bovine spermatozoa is a narrow-mouthed invagination of the nuclear membrane that appears as a surface-oriented crater under differential interference contrast microscopy. Craters are most often located directly posterior to the apical ridge or at the acro-some-postnuclear cap junction. Elevated incidence of craters (>20%) is indicative of impaired spermiogenesis and poor seminal quality and, probably, subfertility. In a survey of 316 ejaculates from 46 Alberta beef bulls representing a wide range of breeds and ages and with poorly documented fertility data, 13% of the ejaculates and 28% of the bulls had crater incidence above 20%. Significant differences were not found between crater levels in first and second ejaculates within a day nor among ejaculates collected over three successive collection days. Crater incidence did not differ between ejaculates collected over two collection periods 1 month apart. Differences among bulls were highly significant in all comparisons. It is recommended that more attention be given to the presence of the crater defect during the evaluation of bovine semen and of the reproductive capacity of beef bulls.     

Capacity of boar spermatozoa to bind zona pellucida proteins in vitro in relation to fertilization rates in vivo

The purpose of this study was to determine variation among boars in the percentage of sperm in an ejaculate that express enhanced binding of zona pellucida proteins during treatment for capacitation in vitro, and to determine whether this relates to fertilizing ability in vivo. Ejaculates (n=35) were collected from 12 boars. A sample of each ejaculate was treated for capacitation in vitro. During incubation, the zona binding ability of spermatozoa was assessed at regular intervals with fluorescein-conjugated solubilized zona pellucida proteins (FITC-sZP) and propidium iodide, using a flow cytometer. After incubation, a percentage of the sperm had enhanced FITC-sZP binding. The percentage of viable sperm with enhanced FITC-sZP binding, expressed as a percentage of the total sperm population, increased rapidly over the first 60 min and thereafter reached a plateau after 120-180 min. Averaged over all ejaculates, the percentage at 180 min was 46% (range 27-61%); this percentage was significantly different among boars. However, the variation between ejaculates within a boar was relatively small. There was no significant boar effect on the rate at which the percentage of viable cells with enhanced FITC-sZP binding reached the maximum. In ejaculates (n=14) from four boars (selected from the group of 12), we investigated the increase in the percentage of viable sperm with enhanced sZP binding during treatment for capacitation in vitro in relation to the ability to fertilize in vivo. Sows (n=44) were inseminated 4 h after ovulation with a suboptimal insemination dose (0.5x10(9) spermatozoa). Time of ovulation was determined using transrectal ultrasonography and sows were killed at 120 h after ovulation. The percentage of fertilized oocytes, embryo development, and numbers of accessory spermatozoa were determined. The percentage of spermatozoa that were viable and showed enhanced sZP binding after 180 min of incubation was 48 +/- 12% (range 28-56%). The percentage of fertilized oocytes was 85 +/- 27% and 64% of the sows had 100% fertilized oocytes. The percentage of sows with 100% fertilized oocytes correlated well (P< or =0.05, R2=0.98) with the percentage of viable spermatozoa with enhanced FITC-sZP binding after capacitation in vitro.     

Spermatogenesis, sperm output and seminal quality of Holstein bulls electroejaculated after administration of oxytocin

The 12- to 24-month-old Holstein bulls were electroejaculated twice on each of 3 days per week throughout the study. After a 2-week stabilization period and subsequent 2-week pre-treatment period, 7 bulls were given 50 i.u. oxytocin via the jugular vein 10 min before each first ejaculate for 10 weeks. The 7 control bulls were handled identically but did not receive oxytocin. All bulls were castrated at the end of the study. Oxytocin was without effect on spermatogenesis (P greater than 0.10). Oxytocin did not alter the total number of spermatozoa harvested per collection day (P greater than 0.10), but increased the number of spermatozoa in first ejaculates by an average of 34.2% (P less than 0.025). Oxytocin did not affect sperm quality (P greater than 0.10) as judged by the motility of spermatozoa in fresh semen or by the motility or percentage of spermatozoa with intact acrosomes in thawed semen. It is concluded that 50 i.u. oxytocin enhanced sperm output in first ejaculates of electroejaculated bulls without altering daily sperm production or seminal quality.     

Sources of variation in the morphological characteristics of sperm subpopulations assessed objectively by a novel automated sperm morphology analysis system

There is evidence that the mammalian ejaculate contains distinct subpopulations of spermatozoa and that the variability among these subpopulations may have adaptive and functional significance. This study investigated the precision, reproducibility and operating characteristics of a novel automated sperm morphology analysis system, the Hobson Morphology package, establishing protocols to investigate boar sperm characteristics. Five ejaculates were collected from each of three boars from different genetic lines: Landrace-Meishan introgression, Sireline Large White and Damline Large White. Five semen smears per ejaculate were stained with haematoxylin and eosin. Two hundred spermatozoa per slide were analysed. No significant differences among slides within an ejaculate were detected for sperm tail length (P = 0.770), head width (P = 0.736) and head length (P = 0.615), indicating that both staining and morphology analysis were precise and reproducible. Among the boars, variability in tail length was detected (P = 0.001), but head width (P = 0.114) and length (P = 0.069) did not differ significantly. Multivariate pattern analysis (PATN computer package) highlighted three sub-populations of spermatozoa objectively on the basis of tail length (10.0-22.0 microns, 22.1-73.0 microns and 73.1-130.0 microns). The Landrace-Meishan introgression boar possessed more spermatozoa (P < 0.0001) with tails 73.1-130 microns long. Subsequent analysis of morphology parameters in a pure-bred Meishan boar showed similar measurements for tail length (mean +/- SD; 66.36 +/- 24.70 microns) to the Landrace-Meishan introgression boar (mean +/- SD; 67.09 +/- 21.80 microns). Sperm subpopulations originate during spermatogenesis, when heterogeneous genotypic effects determine the structural features of spermatozoa. The findings of this study confirm that tail length differs between boars and that subpopulations of spermatozoa can be detected within a single ejaculate.