Seminal selenium concentrations and spermatozoal abnormalities in beef bulls

The relationship between seminal selenium (Se) concentration and spermatozoal abnormalities in 24 Angus and 12 Simmental bulls maintained on a Se adequate diet was studied. Two semen samples were collected by electroejaculation 50 days apart from each bull. Measurements of primary and secondary spermatozoal abnormalities, seminal Se concentration, and blood plasma Se concentration were determined at each semen collection. The mean (chi +/- SD ) Se concentration of semen (0.535 +/- 0.267) was approximately 8 fold greater than the Se concentration of blood plasma (0.069 +/- 0.066) and the values were similar for both collections. Spermatozoa concentration was correlated (r = 0.50; P<.01) with seminal Se concentration; however, seminal Se concentration was not highly correlated (P<.01) with primary spermatozoal abnormalities (r = -0.29) and secondary spermatozoal abnormalities (r = 0.16). This study indicates that the Se concentration of semen is high relative to blood plasma in bulls maintained on a Se adequate diet; however, the seminal Se concentration is not highly correlated with spermatozoal abnormalities.     

SDS-polyacrylamide gel electrophoresis of buffalo bulls seminal plasma proteins and their relation with semen freezability

The objective of this study was to evaluate the protein profiles of seminal plasma in buffalo bulls and to examine their correlation with semen characteristics. Semen of 10 buffalo bulls were collected by a bovine artificial vagina. Semen characteristics (motility, morphology, viability and concentration) were recorded. A part of the semen sample (1 ml) was diluted by tris-egg yolk-glycerol extender, packed in French straws and was frozen in liquid nitrogen. The straws were later thawed and semen characteristics were compared with those of the fresh semen. Seminal plasma was harvested by centrifugation; treated with cold ethanol and then, underwent SDS-polyacrylamide gel electrophoresis (PAGE). Twenty five protein bands were identified on the gel, of which those of <35.5 kDa were prominent (72% of the bands). Of these protein fractions, 24.5 kDa was significantly correlated with sperm progressive motility in fresh and viability in frozen-thawed semen while 45 kDa bands were correlated with abnormal morphology in frozen-thawed semen; 55 kDa protein fractions were correlated with sperm viability of fresh semen. Progressive motility, viability and abnormal sperm morphology of frozen-thawed semen were highly correlated with these parameters in the fresh semen. In conclusion, seminal plasma protein fractions in buffalo bulls are similar to those reported in other animal species and have some correlations with semen characteristics before and after freezing.     

Relationship of seminal vesicle size and measures of libido in yearling beef bulls

Ninety-five yearling beef bulls were given routine Breeding Soundness Examinations, two libido tests and palpated rectally for internal genital disease and measurement of seminal vesicle size. Finger tips were premeasured, and then used as "glandometers". The bulls were examined at the end of a 140-day performance test. Sixteen lines of breeding were examined including 13 Hereford, 2 Angus and 1 Red Angus. Average age was 384 days and average weight was 961 lbs. Line and breed differences (P<.05) were observed for scrotal circumference, scrotal circumference score and second libido test. Similar differences were observed for SV length (P<.01), depth and volume both (P<.05). There were no significant correlations between seminal vesicle (SV) size and libido scores. There were, however, significant correlations between SV size and scrotal circumference (P<.05), BSE score (P<.01), body weight (P<.01), and semen morphology score (P<.05). Proximal droplets and midpiece abnormalities, respectively, were the most common spermatozoal abnormalities observed in semen from this group of bulls.     

Impact of seminal and serum zinc on semen quality and hormonal status: A population-based cohort study of Russian young men

BackgroundTrace elements are important factors in human reproductive health. Among them, special attention is paid to zinc, which is an essential trace element and is necessary for the normal functioning of the male reproductive system and the process of spermatogenesis. The aim of the study was to investigate the association between seminal and serum zinc concentrations and semen quality and reproductive hormone levels in population of Russian young men.MethodsThe study population consisted of 626 young Russian men (median age 22.5 years), recruited from the general population, regardless of their fertility status. Each participant provided semen and blood sample, information about his lifestyle and ethnicity. Semen quality (sperm concentration, motility and morphology), reproductive hormone levels (testosterone, estradiol, LH, FSH and inhibin B), and serum and seminal zinc concentrations were evaluated. The semen samples were analyzed according to the WHO laboratory manual (WHO, 2010). Serum hormones were measured by enzyme immunoassay, zinc concentrations were determined using spectrophotometry and direct colorimetry without deproteinization.ResultsZinc was present in the seminal plasma in a significantly higher concentration than in the blood serum (median serum Zn concentration was 23.6 μmol/L vs seminal Zn concentration 1571.8 μmol/L). The seminal zinc concentration was positively related to the total sperm count, sperm concentration, progressive motility and normal morphology (Spearman’s test: 0.221; 0.286; 0.269; 0.183, respectively, p < 0.001), while the serum Zn concentration was negatively related to serum testosterone and estradiol levels (r = −0.249 and r = −0.096, respectively, p < 0.001−0.05). It was found that the seminal Zn content in men with normal semen quality was higher compared to men with lowered semen quality (means: 6.37 and 5.03 μmol/ejaculate, respectively, p < 0.001). Similarly, the semen volume, total sperm count, sperm concentration, progressive motility, normal morphology and the serum testosterone level in men with the seminal Zn deficiency were lower than in men with the normal seminal Zn content.ConclusionBased on the results of our population-based study, seminal Zn levels were closely associated with semen parameters in young men, so Zn deficiency may be an important risk factor for lowered semen quality. Seminal Zn determinations should be considered as a useful tool in addition to other parameters in assessing male fertility.     

Effect of prostaglandin F2 alpha on libido, seminal quantity and quality of buffalo bulls

Four mature Murrah buffalo bulls on a regular semen collection schedule of twice a day, two days per week, were injected with 30 mg prostaglandin F2 alpha THAM salt(PGF) intramuscularly 30 minutes prior to each alternate first ejaculation for six weeks. Effects of PGF on time to initial false mount on the decoy, time to ejaculation after two false mounts (reaction time), seminal volume, sperm concentration, total sperm output, motility of fresh and thawed semen and the semen doses obtained per collection were evaluated. Treatment caused significant (P < 0.01) reduction in the time to first false mount and the reaction time for the first ejaculations but had no effect (P > 0.05) on these for the second ejaculations. Values for other quantitative and qualitative parameters did not differ (P > 0.05) due to PGF treatment. It is concluded that PGF at the dosage and frequency of administration used may be of some value in improving libido in low-libido bulls but does not alter the reproductive capacity of buffalo bulls.     

Relationship between contents of lipocalin-type prostaglandin D synthase on the surface of infertility sperm and in seminal plasma

Lipocalin-type prostaglandin D synthase (L-PGDS) is localized in Leydig cells, sperm, and epithelial cells of the epididymis. The present study was to determine the correlation between content of this enzyme in seminal plasma and on the surface of sperm. We analyzed 90 semen samples. L-PGDS in seminal plasma was analyzed by an ELISA procedure. L-PGDS on sperm was analyzed by flow cytometry. The semen donors were categorized in three groups: normal, oligospermic, and azoospermic. According to results obtained, L-PGDS may have the ability to improve progressive motility of sperm, and L-PGDS in seminal plasma and on sperm surface may impact male fertility in the female reproductive tract. Published in Russian in Biokhimiya, 2007, Vol. 72, No. 2, pp. 255–259.     

Polymorphism of growth hormone gene and its association with seminal and sexual behavioral traits in crossbred cattle

The decline in the male reproductive ability in terms of sexual behavior and seminal traits might lead to nonavailability of required number of bulls in a progeny testing program. The present study was conducted in 493 crossbred cattle (Bos taurus × Bos indicus) bulls to study polymorphisms of growth hormone (GH) gene and its association with seminal and sexual behavioral characteristics. A 428-base pair fragment of GH gene spanning over the fourth exon, fourth intron, and fifth exon was amplified and digested with AluI restriction enzyme. Bulls were found to be polymorphic, with two variants, LL and LV, and higher genotypic frequency for LL being 0.88. Twelve nucleotide changes and a single nonsynonymous substitution of Leucine by Valine were observed from GH1 (L) to GH2 (V). Statistical analysis revealed that the genotype of the GH gene had a significant effect on libido score, reaction time, Flehmen response, requirement of mounting stimulus, sperm mass activity, number of semen doses per collection, individual fresh sperm motility, postthaw sperm motility, acrosome integrity, hypo-osmotic swelling test, live and dead count, total morphological abnormality, and head abnormality of sperm in crossbred bulls. Growth hormone gene might be considered a candidate gene for seminal and sexual behavioral traits in crossbred cattle.     

Effects of sperm concentration at semen collection and storage period of frozen semen on dairy cow conception

The present study was based on data obtained from artificial inseminations (AIs) performed with cryopreserved semen from elite bulls used in the Norwegian breeding program. Semen was diluted to standardize the number of spermatozoa to 18 million per AI dose. The aim of the study was to investigate whether the net sperm concentration at semen collection and the storage period in liquid nitrogen have any effect on probability of conception in dairy cattle. We demonstrated that the natural range of sperm concentration at semen collection within some of the bulls was associated with the probability of conception. However, no primary trend among bulls was found on the effect of sperm concentration at semen collection. This appears to be due to differences among bulls in their response to the dilution ratio of seminal plasma to extender. The effect of storage time was investigated in semen that had been stored between 1000 days and 2400 days in AI straws in liquid nitrogen at the AI center. Our findings showed that use of semen with the longest storage period, i.e. 1951-2400 days, resulted in a more than one percentage point lower probability of conception than semen with a shorter storage period. In conclusion, the net sperm concentration at semen collection, which affects the dilution ratio of seminal plasma to extender, should be considered individually among bulls to achieve optimal reproductive performance. Furthermore, this study gives support to the idea that a measurable degree of damage to the spermatozoa could occur during the preservation time in liquid nitrogen.     

Dynamics of exogenous kallikrein-stimulated bovine sperm motility in the presence of seminal plasma kallikrein

Sperm motility is known to be activated and maintained by kallikrein contained within the seminal plasma. We studied the relationship between the levels of seminal plasma kallikrein activity and in vitro exogenous kallikrein-induced sperm motility enhancement. Semen samples were collected from Holstein-Friesian bulls and grouped on the basis of the initial total sperm motility into Group I with > 60 % (mean 75.3 +/- 1.8 %, n = 25), and Group II with < 60 % (mean 51.2 +/- 1.7%, n = 25). Seminal plasma kallikrein activity was measured with the aid of the specific chromogenic substrate S-2266. In Group I the mean activity was 0.983 +/- 0.042 microkat/L, and in Group II it was 0.805 +/- 0.063 microkat/L (P < 0.05). Then each semen sample was divided into a control and an experimental subgroup treated with 16.7 microkat/L of hog pancreatic kallikrein. Total sperm motility was monitored at 1-h intervals. It was found that the addition of exogenous kallikrein stimulated the sperm motility in both groups but in the 4th h after treatment the difference in sperm motility between the experimental and control subgroups of Group I was 12.4 % whereas in Group II it was 21.7 %. We concluded that adding exogenous kallikrein in vitro to semen samples with lower kallikrein activity in the seminal plasma enhanced total sperm motility more than adding it to ejaculates with higher levels of endogenous kallikrein activity.     

Cholesterol concentration in seminal plasma as a predictive tool for quality semen evaluation

The aim of this study was to investigate the relationship between lipid composition of bovine serum and seminal plasma, seasonality, and semen quality. The experiment was carried out in two groups of Simmental breeding bulls: Group I (ages 2 to 4 yr) and Group II (ages 5 to 10 yr). Blood samples were collected from jugular vein, and bovine semen was sampled with an artificial vagina once per season. Serum concentrations of total cholesterol, high-density lipoprotein cholesterol (HDL-C), low-density lipoprotein cholesterol (LDL-C), triacylglycerols, nonesterified fatty acids (NEFAs), and lipoprotein electrophoretic patterns were determined. Seminal plasma concentrations of total cholesterol, HDL-C, and LDL-C were assayed. Serum concentration of triacylglycerols in young bulls was significantly higher in winter compared with that in autumn, whereas serum NEFA concentration was significantly higher in autumn compared with that in other seasons. Serum concentration of total cholesterol, LDL-C, and LDL lipoproteins in older bulls was significantly higher in winter than in spring. Seminal plasma concentration of total cholesterol in young bulls was significantly higher in spring compared with that in summer, whereas in older bulls it was significantly higher in winter compared with that in autumn samples. Sperm volume of both groups was significantly higher in summer compared with that in autumn and winter. Sperm motility in young bulls was lowest in summer and differed significantly from the values recorded in other seasons. The changes observed in seminal plasma cholesterol concentration were associated with extracellular lipid use and appeared to be applicable as a biochemical marker of sperm quality.     

Characterization of a monoclonal antibody to a conserved epitope on human seminal vesicle-specific peptides: a novel probe/marker system for semen identification

A novel sperm-coating antigen from the human seminal vesicles was discovered. We identified a monoclonal antibody MHS-5, recognizing an epitope with characteristics of a forensic semen marker: conservation in all vasectomized or normal semen samples tested (421); absence in all human tissues or biological fluids other than semen; and immunolocalization on the surface of ejaculated sperm. Western blots of ejaculates allowed to liquefy for 5 min demonstrated the MHS-5 epitope to be located on peptides of a wide range of molecular masses from 69 to 8 kDa. After 15 h of semen liquefaction, immunoreaction peptides of higher molecular mass were undetectable in semen, while peptides of lower molecular mass from 8 to 21 kDa retained antigenicity. Three peptides of 10, 11.9, and 13.7 kDa were the most immunoreactive species in semen liquified for 15 h. Using the MHS-5 monoclonal, an enzyme-linked immunosorbent assay (ELISA) was developed sensitive to 1 ng of seminal protein. This assay showed that the MHS-5 antigen was undetectable in semen of common domestic animals and monkeys but was present in chimpanzee, gorilla, and orangutan semen. ELISA of homogenates from human organs and reproductive tissues demonstrated the antigen only in samples of seminal vesicles. Epididymal sperm obtained at vasovasostomy lacked the MHS-5 epitope, a fact that, together with immunolocalization on ejaculated sperm, demonstrated that the MHS-5 antigen functions as a "sperm-coating antigen." The MHS-5 monoclonal detected semen in sexual-assault evidence obtained six months previously and in mixtures of semen with vaginal or cervical fluid. Assay systems employing the MHS-5 monoclonal may be useful for identification of semen in sexual-assault casework. The MHS-5 epitope resides on novel seminal vesicle-specific peptides whose functions, aside from sperm coating, are uncharacterized.     

Two-dimensional polyacrylamide gel electrophoresis of bovine seminal plasma proteins and their relation with semen freezability

The objective of this study was to evaluate the low weight (10-30 kDa) protein profile of bovine seminal plasma using two-dimensional polyacrylamide gel electrophoresis (2D-PAGE) and to determine if any of these proteins was associated with semen freezability. Seminal plasma was collected from 16 bulls of high or low semen freezability. Twelve protein spots were identified from the 2D gel (15%); six of these were present in all samples. Of the 12 proteins found, three spots, present in all samples, 3 (15-16 kDa), 5 (16-17 kDa), and 7 (10-12 kDa) had nonsignificant variation among bulls, regardless of their freezability classification. Four proteins were more abundant (P<0.05) in seminal plasma samples collected from bulls with high semen freezability than in samples of bulls with low semen freezability: the spots 3 (15-16 kDa, pI 4.7-5.2), 7 (11-12 kDa, pI 4.8-4.9), 11 (13-14 kDa, pI 4.0-4.5), and 23 (20-22 kDa, pI 4.8-5.2). On the other hand, spot 25 (25-26 kDa, pI 6.0-6.5) was more abundant (P<0.05) on seminal plasma samples from bulls with low semen freezability. The N-terminus sequence of protein 7 was identical to the acidic seminal fluid protein (aSFP). Protein 23 (after trypsin digestion) had structural similarity to bovine clusterin. We concluded that there were differences in the seminal plasma protein profile from bulls with low and high semen freezability; aSFP, clusterin, proteins 3 and 11 may be used as semen freezability markers; and protein 25 was related to low semen freezability.     

Relationships between Brucella ovis semen culture and various semen and serology parameters

Semen and blood samples from 154 rams from two Montana range flocks (Flock A, vaccinated for Brucella ovis ; Flock B, nonvaccinated) were evaluated to determine the relationship between Brucella ovis (B. ovis ) semen culture results and various semen and blood parameters. All rams utilized in this study exhibited no palpable ram epididymitis lesions. Thirteen and 25.6% of the rams tested in Flocks A and B, respectively, had positive B. ovis semen cultures. Only age of ram and ram condition scores differed (P<0.05) between flocks. No flock by semen culture interactions were detected (P>0.05) for any of the parameters evaluated. Age of ram, ram condition score, and spermatozoa rate from forward movement were unrelated (P>0.05) to B. ovis culture results. Rams with positive B. ovis semen cultures had lower sperm motility (P<0.05), higher percentage of abnormal spermatozoa cells (P<0.05), higher percentage of spermatozoa head abnormalities (P<0.01), lower percentage of live-normal cells (P<0.05), higher incidence of white blood cells in semen (P<0.01) and higher complement fixation (CF) titers (P<0.01).     

Comparison of electroejaculation and transrectal massage for semen collection in range and yearling feedlot beef bulls

Two experiments were conducted to compare electroejaculation (EE) and transrectal massage (RM) of the ampullary region for semen collection from beef bulls, and to determine the effect of semen collection method on semen traits. In experiment 1, semen was collected either by EE or RM randomly assigned on an alternate basis in 137 range beef bulls unaccustomed to being handled. The maximum time allowed for RM was 4 min and if no semen was obtained, EE was used. In experiment 2, semen was collected from 39 yearling feedlot beef bulls that were accustomed to being handled, by RM followed immediately by EE. The maximum time allowed for semen collection by both methods was 4 min. In both experiments, sperm concentration, percent of progressively motile sperm, percent of sperm staining alive, and sperm morphology were determined. In experiment 1, RM resulted in fewer (P<0.001) successful semen collections and fewer bulls with penile protrusion than EE (80.9% versus 100% and 54.4% versus 91.5%, respectively). The success of RM was not influenced by bull age or breed, or by the veterinarian performing the massage. Transrectal massage required more time (30s, P<0.001) for obtaining a semen sample and resulted in samples with lower sperm concentration (P<0.001), percent motile sperm (P<0.05) and percent live sperm (P<0.001) when compared to EE. In experiment 2, EE and RM were equally effective for obtaining a semen sample (97.4 and 94.9%, respectively), but the proportion of bulls exhibiting penile protrusion during semen collection was lower (P<0.0001) with RM compared to EE. Percent of sperm staining alive was also lower (P<0.01) in samples collected by RM. Sperm morphology (normal sperm, head defects, midpiece defects, proximal cytoplasmic droplets, and detached sperm heads) did not differ between samples collected by EE and RM. In conclusion, semen could be collected by transrectal massage from approximately 80% of range beef bulls and from 95% of yearling beef bulls accustomed to handling. Sperm morphology was not affected by the method of semen collection, but percent of motile sperm and live sperm were lower in samples collected by RM. A reduced ability to stimulate penile protrusion with RM precluded examination of the penis in a large proportion of bulls.     

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.     

Qualitative and quantitative analyses of seminal ribonuclease in reproductive tract fluids of bulls

Bovine seminal ribonuclease (BS RNase) is synthetized in the ampulary gland and seminal vesicles of the bull as shown by indirect immunofluorescence and by using a sensitive sandwich-linked immunosorbent assay (ELISA). The ampullary and seminal vesicle BS RNase concentrations in samples from 15 bulls were 656 μg/ml and 1285 μg/ml, respectively. Seminal plasma BS RNase levels in 22 breeding bulls were slightly lower than in the seminal vesicles—1132 μg/ml. There were no significant differences in the concentration of this enzyme in seminal plasma of 16 bulls ranked as having high and low fertility. Even with its immunosuppressive activity this enzyme does not seem important for the protection of sperm cells in the female reproductive tract.     

Relationships among spermatozoal abnormalities and the selenium concentration of blood plasma,semen, and reproductive tissues in young bulls

The concentration of selenium (Se) was measured by instrumental neutron activation analysis in samples of blood plasma, semen, and reproductive and non-reproductive tissues obtained from each of 12 young bulls (8 Angus and 4 Simmental). Semen was collected by electro-ejaculation and used for measurements of the frequency of primary and secondary spermatozoal abnormalities. The mean Se concentration (μg/ml) of semen (± SD) was 0.461 (±0.223) compared to 0.061 (±0.014) for blood plasma. Tissue from the testis, caput epididymis and cauda epididymis had mean Se concentrations of from 2.5 to 2.7 μg/g compared to less than 1.8 μg/g in all other tissues except the pituitary gland (3.4 μg/g) and kidney cortex (6.9 μg/g).Correlations of the proportional incidence of spermatozoal abnormalities with Se concentrations in reproductive tissues, semen or blood plasma were low. Although Se may be concentrated in the testis and epididymis, the Se concentration was not related to spermatozoal abnormalities.     

Variation in lipid profiles within semen compartments—the bovine model of aging

Semen lipid composition was examined in young and mature bulls. Given the specific roles of various semen compartments (i.e., seminal fluid, sperm head, and sperm tail) during fertilization, we hypothesized that altered fatty acid and cholesterol composition of a specific compartment might impair semen quality and sperm function. Semen samples were collected from five mature and five young Holstein Friesian bulls during the winter (December–January). Semen was evaluated by computerized sperm-quality analyzer for bulls and was centrifuged to separate the sperm from the seminal fluid. The sperm fraction was sonicated to separate its head and tail compartments. Cold extraction of lipids was performed, and fatty acids and cholesterol were identified and quantified by gas chromatography. Semen physiological features (concentration, motility, and progressive motility) did not differ between mature and young bulls. However, lipid composition within fractions varied between groups, with prominent impairments in the head compartment. In particular, the proportions of polyunsaturated fatty acids, omega-3 fatty acids, and docosahexaenoic acid in the intact sperm; seminal fluid; and sperm head were lower in semen collected from mature bulls than in that from young bulls. The finding suggests an age-differential absorption and/or metabolism through spermatogenesis. Reduced proportions of major fatty acids in mature bulls might reduce membrane fluidity, which in turn might affect the ability to undergo cryopreservation and/or oocyte-sperm fusion through fertilization.     

Semen quality and presence of cytokines in seminal fluid of bull ejaculates

It has been postulated that cytokines play an immunoregulatory role in human semen. The presence and levels of various cytokines, namely the interleukins 6, 10 (IL-6 and IL-10) and tumor necrosis factor alpha (TNFalpha) were investigated in the seminal plasma of six fertile crossbred bulls (Bos taurus x Bos indicus), using specific enzyme immunoassay. Cytokine levels were related to the semen quality of these bulls. A direct significant correlation between the level of IL-10 and individual sperm motility (r=0.84, P<0.036) was observed. The levels of IL-6 and IL-10 were inversely correlated (r=-0.93, P<0.006) and likewise in the same way an inverse correlation between the level of IL-6 and TNFalpha was observed (r=-0.84, P<0.037). These results confirm that cytokines are present in bull semen as has been demonstrated in human semen.     

Effect of season on bovine seminal plasma proteins in Thailand

Although season has been shown to affect bull sperm quality and fertility in some studies, the effect of season on seminal plasma proteins has not been examined. In the present study, seminal plasma proteins were analysed by Fast Protein Liquid Chromatography (FPLC), to separate the phosphorylcholine-binding proteins and heparin-binding proteins from the other proteins. Semen samples were collected from bulls in three seasons: winter, summer and the rainy season. Sperm quality was analysed by flow cytometry and computer assisted sperm analysis, and further aliquots of semen were used to prepare the seminal plasma for FPLC. Meteorological data were available from a location close to the bull station. There were slight differences in sperm kinematics between seasons, but other parameters of sperm quality were not different. Minor differences in the phosphorylcholine-binding proteins were detected according to season, being lower in summer than in winter or in the rainy season, although there were no changes in the heparin-binding proteins. Temperature, humidity and rainfall differed between winter and the rainy season, but no differences were observed between summer and the rainy season except in the temperature humidity index (THI). However, the THI was above the threshold indicative of heat stress in all seasons, which could explain why few seasonal differences in protein composition were detected in this study. Alternatively, the bulls could have been well-adapted to heat stress. In conclusion, there were only slight differences in bull sperm quality and seminal plasma proteins between seasons during this study.