Effect of melatonin treatment on semen parameters and endocrine function in Black Racka rams out of the breeding season

Administration of melatonin nanoparticles improves testicular blood flow, echotexture of testicular parenchyma, scrotal circumference, and levels of estradiol and nitric oxide in prepubertal ossimi rams under summer heat stress

Environmental heat stress (HS) impairs reproductive efficiency in farm animals. This study investigated, for the first time, how the melatonin and melatonin nanoparticles treatment affected the testicular hemodynamics, testicular volume, echotexture [Pixel intensity (PIX) and integrated density (IND)], scrotal circumference, serum concentration of testosterone (T), estradiol (E2), nitric oxide (NO), and total antioxidant capacity (TAC) in prepubertal Ossimi ram lambs in hot climatic conditions. The lambs undergoing examination had a temperature humidity index (THI) of 87.05 ± 1.70, indicating severe HS condition. Fifteen prepubertal Ossimi ram lambs were exposed to a single s.c injection of either nano melatonin (nano melatonin group; 20 mg/ram; n = 5) or melatonin suspended in two ml of corn oil (melatonin group; 40 mg/ram; n = 5) or two ml of corn oil (control group; n = 5). Blood collection and ultrasonographic assessment of the testes and supratesticular arteries (STAs) were conducted immediately before treatment (W0) and once weekly for six successive weeks after nano melatonin and melatonin injection (W1-W6). Results revealed decreases (P < 0.05) in the Doppler indices (resistive index; RI and pulsatility index; PI) of the testicular arteries at most time points of the study in the nano melatonin and melatonin groups. PIX of testicular parenchyma was significantly increased (P ˂ 0.05) in the treated groups compared to the control one. IND of testicular parenchyma increased significantly in the nano melatonin group compared to the melatonin and control groups. Testicular volume and scrotal circumference significantly increased (P < 0.05) in nano melatonin and melatonin groups compared to the control one. T concentration did not significantly (P > 0.05) change in the treated groups compared to the control group. E2, NO, and TAC concentrations increased (P < 0.05) in the treated groups compared to the control one. In conclusion, this study extrapolated that administrations of melatonin or nano melatonin can ameliorate the effects of environmental HS in prepubertal Ossimi ram lambs with a more protective effect and lower dose of nano melatonin.

Impact of melatonin administration on sperm quality, steroid hormone levels, and testicular blood flow parameters in small ruminants: A meta-analysis

Background and Aim

The impact of exogenous melatonin on the sperm quality of small ruminants is controversial. Therefore, this study aimed to synthesize previous findings on the influence of melatonin injection on sperm quality, steroid hormones, and testicular blood flow in small ruminants.

Materials and Methods

Thirty studies were analyzed by computing the raw mean difference (RMD) as the effect size between the control and melatonin treatment groups, using the inverse of the variance for the random-effect model of the method of moments by DerSimonian and Laird. We assessed heterogeneity among studies using Q test. I2 statistic was used to classify the observed heterogeneity. We used Egger's regression method to indicate publication bias.

Results

Melatonin injection (p < 0.05) affected sperm concentration (RMD = 0.42 × 109/mL), morphology (RMD = 2.82%), viability (RMD = 2.83%), acrosome integrity (RMD = 4.26%), and DNA integrity (RMD = 1.09%). Total motility (RMD = 5.62%), progressive motility (RMD = 7.90%), acrosome integrity (RMD = 8.68%), and DNA integrity (RMD = 2.01%) of post-thawed semen in the melatonin-treated group were also increased (p < 0.05). Similarly, treatment with melatonin (p < 0.05) enhanced total motility (RMD = 5.78%), progressive motility (RMD = 5.28%), curvilinear velocity (RMD = 4.09 μm/s), straight-line velocity (RMD = 5.61 μm/s), and average path velocity (RMD = 4.94 μm/s). Testosterone (RMD = 1.02 ng/mL) and estradiol 17-ß levels (RMD = 0.84 pg/mL) were elevated (p < 0.05) in the melatonin-injected group. Melatonin implantation ameliorated testicular blood flow, as indicated by a significant reduction (p < 0.05) in the resistive index (RMD = 0.11) and pulsatility index (RMD = -0.15).

Conclusion

Melatonin administration can increase the reproductive performance of small male ruminants.

Effect of exogenous melatonin implant on post-thaw semen quality of buffalo bulls

Melatonin is an intracellular antioxidant of sperm membrane that protects the cells from lipid peroxidation. Yet, its role as an antioxidant on semen quality of buffalo bulls is still obscure. The present study was undertaken to assess the effect of exogenous melatonin implant (18 mg/50 kg bodyweight) on post-thaw sperm characteristics, oxidative stress, endocrinological profiles and fertility of buffalo bulls. Six apparently healthy breeding Murrah buffalo bulls were randomly selected at bull farm, Guru Angad Dev Veterinary and Animal Sciences University for the present study and divided into two groups viz. control (n = 3) and melatonin implanted group (n = 3). A total of 120 ejaculates were collected from bulls of both groups (n = 60 each) throughout the study period. Most beneficial effects of melatonin implants were observed during post-implantation period. The percentages of post-thaw sperm total and progressive motility, viability and mitochondrial membrane potential were higher (p < .05) in melatonin implanted buffalo bulls compared to controls during post-implantation period. Following melatonin implantation, MDA production in post-thaw semen was lower (p < .05) in melatonin implanted group than in control group. Plasma melatonin and testosterone concentrations were higher (p < .05) in buffalo bulls implanted with melatonin as compared to their control counterparts. No differences (p > .05) in plasma LH concentrations were observed in both groups. First service pregnancy rate was 43.3% using semen of melatonin implanted bulls and 30.0% with semen of controls (p > .05). Thus, melatonin was able to protect sperm membrane against oxidative damage and improve post-thaw semen quality, thereby resulting in higher fertilizing potential of spermatozoa.

Melatonin Administration Enhances Testicular Volume, Testicular Blood Flow, Semen Parameters and Antioxidant Status during the Non-Breeding Season in Bafra Rams

Our objectives were to investigate the effects of exogenous melatonin on testicular volume (TV), testicular blood flow (TBF), and semen quality in Bafra rams during the non-breeding season. One group of rams (MEL, n = 5) received a 36 mg melatonin implant twice, with 30 days in between, while the other group (CON, n = 5) served as the control. TBF, TV, and semen quality parameters were determined at three-week intervals starting three weeks before until twelve weeks after the first melatonin implant. Testicular blood flow was determined in the supratesticular (STA) and marginal testicular artery (MA) using color Doppler ultrasound. Semen was collected and evaluated, and the total oxidative status (TOS) and total antioxidative status (TAS) was determined using an ELISA. The MEL group had increased (p < 0.05) TV between the sixth and twelfth week after the start of treatment. Overall, the MEL group had lower resistance and pulsatility indexes (p < 0.05) between the third and ninth week, although there was no difference (p > 0.05) between the two groups in most semen quality parameters. However, TAS concentrations increased (p < 0.05) in the MEL group compared with the CON. The results of this study show that exogenous melatonin in the non-breeding season significantly increased both TBF and TV in Bafra rams. Therefore, giving rams implants with 36 mg melatonin twice at least one month prior to the non-breeding season is expected to improve testicular size and function and reproductive capacity.

The Role of Melatonin to Ameliorate Oxidative Stress in Sperm Cells

It is widely accepted that oxidative stress (OS) coming from a wide variety of causes has detrimental effects on male fertility. Antioxidants could have a significant role in the treatment of male infertility, and the current systematic review on the role of melatonin to ameliorate OS clearly shows that improvement of semen parameters follows melatonin supplementation. Although melatonin has considerable promise, further studies are needed to clarify its ability to preserve or restore semen quality under stress conditions in varied species. The present review examines the actions of melatonin via receptor subtypes and its function in the context of OS across male vertebrates.

Melatonin Supplementation for the Cryopreservation of Canine Sperm

Antioxidants can be used in sperm cryopreservation protocols to reduce oxidative stress that occurs due to the cryopreservation process. The aim of this study was to evaluate the effects of melatonin supplementation on quality and oxidative stress parameters in cryopreserved canine sperm. Eighteen sperm ejaculates were collected from 6 Frenchie Bulldog males (3 collections per male). Sperm motility parameters, membrane integrity, and sperm morphology were analyzed before the cryopreservation process. The extender used in cryopreservation was composed of Tris-egg yolk and ethylene glycol 5% was added as a cryoprotectant. The cryoprotective medium was supplemented with 1.0, 1.5, 2.0, 2.5, and 3.0 mM melatonin, and the control group (without melatonin). Post-thaw sperm was evaluated as described for fresh sperm and oxidative stress parameters (lipid peroxidation, catalase, and superoxide dismutase). Post-thaw sperm motility parameters, membrane integrity, sperm morphology, and oxidative stress parameters did not differ (p > 0.05) among the control group and samples supplemented with melatonin. The results of this study showed that melatonin supplementation had no positive or negative effect on the parameters evaluated. Thus, it is suggested that different concentrations of melatonin be tested to assess its effectiveness as an antioxidant in the cryopreservation process in canine sperm.

Reproductive performance of hair ewes and rams implanted with melatonin previous to the anestrus season in northwest Mexico

Ovine reproductive behavior depends on annual photoperiodic cycle and its impact on endogenous melatonin secretion. In this regard, exogenous melatonin administration previous to the physiological anestrus period could modify the reproductive performance of sheep in the northwest of Mexico. Two independent studies were performed to evaluate such hypothesis in hair sheep implanted with melatonin prior to the anestrus season in latitudes 24° and 25° of Mexico. Study 1 involved 15 rams assigned to one of three treatments receiving 0mg (n=5), 18mg (n=5), or 36mg (n=5) of melatonin subcutaneously. Study variables were measured monthly since implantation (d0) and included testosterone concentration, scrotal circumference, mass motility, individual motility, and sperm concentration. Study 2 included 50 ewes assigned to one of two treatments receiving 0mg (n=25) or 18mg (n=25) of melatonin subcutaneously. In ewes, progesterone concentration and the frequency of females in anestrus were measured during the implantation (-30d), as well as at the beginning (0d) and at the end (45d) of the mating period, while pregnancy rate was determined by ultrasonography 45d after. Continuous variables were analyzed using a mixed effects model considering treatment, time, and the treatment by time interaction as fixed effects. Animal nested within treatment was the random effect. Binary variables were analyzed using the chi-square test. In males, melatonin improved testosterone and sperm concentrations (P<0.05), while in females, a 28% higher pregnancy rate was observed in implanted ewes (P<0.05). Therefore, melatonin enhanced reproductive parameters in both sexes and its exogenous administration previous to the anestrus season in northwest Mexico could be more effective in rams.

Improvement of the Seminal Characteristics in Rams Using Agri-Food By-Products Rich in Phytomelatonin

The aim of this study was to evaluate the effect of a phytomelatonin-rich diet, including by-products from the food industry, on ram sperm quality and seminal plasma composition. Melatonin content in several by-products before and after in vitro ruminal and abomasal digestion was determined by HPLC-ESI-MS/MS. Finally, 20% of a mix of grape pulp with pomegranate and tomato pomaces was included in the rams' diet, constituting the phytomelatonin-rich diet. Feeding the rams with this diet resulted in an increase in seminal plasma melatonin levels compared with the control group (commercial diet) in the third month of the study. In addition, percentages higher than those in the control group of morphologically normal viable spermatozoa with a low content of reactive oxygen species were observed from the second month onwards. However, the antioxidant effect does not seem to be exerted through the modulation of the antioxidant enzymes since the analysis of the activities of catalase, glutathione reductase and glutathione peroxidase in seminal plasma revealed no significant differences between the two experimental groups. In conclusion, this study reveals, for the first time, that a phytomelatonin-rich diet can improve seminal characteristics in rams.

Photoperiodic-dependent histomorphological changes in the excurrent duct system of helmeted guinea fowl subjected to short day (8L:16D), long-day (16L:8D) light/dark cycles and exogenous melatonin

In the present study, the influence of varying photoperiods [short day light 8L:16D, long day light 16L;8D] and exogeneous melatonin on the excurrent duct system of male helmeted guinea fowl was investigated using histo-morphological and histometric approaches. A total of twenty-eight (28) guinea fowl birds were randomly divided into Group I: Short daylight (SD; 8 HL), Group II: (SD +1mg/kg melatonin; 8 HL+ Mel), Group III: Long daylight (LD; 16 HL) and Group IV: (LD +1mg/kg; 16 HL + Mel)] and comprises of seven birds (n=7) per group. At the end of the 8 weeks of experimentation, the excurrent ducts were excised and processed for routine histological examination and the variations in histo-morphometrical parameters were determined using the GIMP2 software. Histologically, apart from the moderate cellular degeneration observed in efferent duct epithelia of the SD subgroups: (8 HL and 8 HL + Mel), there was remarkable spermatozoa presence in the lumens of the epididymal duct and ductus deferens of both 16 HL and 16 HL + Mel groups. The histo-morphometric data (luminal, ductal diameters and epithelial heights) were significantly increased (p <0.05) in the excurrent ducts of guinea fowl exposed to 16 HL and 16 HL + Mel, as compared to other groups. There was significant decrease (p <0.05) in stereocilia height (SH) in 16 HL compared to 8 HL sub-groups of lower segments. Although, a non-significant (p >0.05) increase in SH was observed in melatonin-treated groups, regardless of photoperiod. Taken together, these sets of data from this study indicate the importance of artificial light and exogenous melatonin in the control of seasonality of reproduction and which could be used to influence the reproductive cycle of the guinea fowl.

Coping with Oxidative Stress in Reproductive Pathophysiology and Assisted Reproduction: Melatonin as an Emerging Therapeutical Tool

Infertility is an increasing global public health concern with socio-psychological implications for affected couples. Remarkable advances in reproductive medicine have led to successful treatments such as assisted reproductive techniques (ART). However, the search for new therapeutic tools to improve ART success rates has become a research hotspot. In the last few years, pineal indolamine melatonin has been investigated for its powerful antioxidant properties and its role in reproductive physiology. It is considered a promising therapeutical agent to counteract the detrimental effects associated with oxidative stress in fertility treatments. The aim of the present narrative review was to summarize the current state of the art on the importance of melatonin in reproductive physiology and to provide a critical evaluation of the data available encompassing basic, translational and clinical studies on its potential use in ART to improve fertility success rates.

Melatonin promotes the growth and development of lambs by increasing growth hormone and testosterone, targeting on apoptosis signaling pathway and intestinal microflora

Melatonin is an indole-like neuroendocrine hormone. A large number of studies have shown that melatonin can improve production performance of ewes, but it is not clear in lambs. In this study, the growth and development of the 2-month-old lambs implanted with melatonin were monitored for 60 days. The results showed that the growth rate of body weight and body skew length of lambs with melatonin treatment were significantly improved compared to the controls. The similar results were also observed in red blood cell count, hematocrit, red blood cell volume distribution width, the levels of growth hormone, testosterone, immunoglobulin A, immunoglobulin M and albumin. In addition, the cross sectional area of muscle fibers and adipose cells of lambs with melatonin implantation were also significantly increased compared to the controls (P<0.05). To further explore the potential mechanisms, the muscle and adipose tissue were selected for transcriptome sequencing. KEGG enrichment results showed that melatonin regulated the expression of genes related to apoptotic signaling pathway in muscle and adipocytes. Since the intestinal microbiota are involved in the nutritional balance and animal growth, the 16SrRNA sequencing related to the intestinal microbiota was also performed. The data indicated that the structural differences of fecal microflora mainly occur in the pathways of Cardiovascular disease, Excretory system and Signaling molecules and interaction. In brief, melatonin promotes the growth and development of lambs. The potential mechanisms may be that melatonin increased the growth hormone and testosterone mediated apoptosis signaling pathway and regulated intestinal microbial flora. Our results provide valuable information for melatonin to improve the production of sheep husbandry in the future.

Melatonin improves testicular haemodynamics, echotexture and testosterone production in Ossimi rams during the breeding season

The objective was to determine effects of a single parenteral dose of melatonin on testicular blood flow indices, testicular echogenicity and plasma testosterone concentrations in rams during the physiological breeding season. We hypothesized that melatonin enhances testicular blood flow, echogenicity and plasma testosterone concentrations during the breeding season in rams. During the breeding season, 12 sexually mature Ossimi rams were randomly allocated to either a melatonin group (n = 8) that received 18 mg of melatonin in 1 ml of corn oil (injected SC) or a control group (n = 4) that received 1 ml corn oil only. Blood collection and ultrasonographic assessment of the testes and supratesticular arteries were conducted immediately before treatment (W0) and once weekly for 6 weeks after melatonin injection (W1-W6). Mean plasma testosterone concentrations were greater (p < .05; at least 1 ng/ml) in the melatonin-treated group compared to the control group from W4 to W6 after treatment. A decrease (p < .05) in both resistive index (RI) and pulsatility index (PI) began 1 week after melatonin injection (W1) and persisted until the end of the experiment, with mean RI and PI values in the melatonin group lower (p < .05) than those in the control group on W3 and W4. Furthermore, plasma testosterone concentrations in melatonin-treated rams were inversely correlated to both RI and PI (r = -.7 and -.6, respectively, p < .01). Testicular echogenicity decreased (p < .05) 1 week after melatonin injection (W1) and remained lower (p < .05) in the melatonin-treated group compared to the control group until the end of the study (W6). In conclusion, melatonin administration significantly altered testicular blood flow and echogenicity and increased plasma testosterone concentrations in Ossimi rams during the breeding season.

Exogenous melatonin advances the ram breeding season and increases testicular function

Governed by melatonin, ovine reproductive seasonality limits production outcomes due to periods of decreased reproductive efficiency. Though it is established that slow-release melatonin implants improve out of season reproductive performance in the ewe, the comprehensive effects of exogenous melatonin in the ram remain inconclusive. This study aimed to ultimately clarify the ability of exogenous melatonin to alter ram reproductive function during the non-breeding season and the subsequent breeding season. Hence, we investigated the effect of exogenous melatonin on reproductive endocrinology, semen quality and production, testicular size and libido in Merino and Poll Dorset rams (n = 31, using a subset of 18 rams for analysis of semen production and quality). Melatonin treatment resulted in elevation of melatonin in seminal plasma from 1-8 weeks post-implantation and in blood plasma at 6 weeks post-implantation. The blood plasma testosterone of implanted rams was greater than controls at both 6 weeks post-implantation and during the following breeding season. Implanted rams exhibited increased testicular size and number of sperm per ejaculate from 3-12 weeks post-implantation but did not demonstrate any change in sperm motility or morphology in response to treatment. Compared to their control counterparts, melatonin-treated Poll Dorset rams exhibited a lower percentage of sperm DNA fragmentation during several weeks of the non-breeding season. Though melatonin increased the likelihood of ejaculate collection in Poll Dorset rams (P < 0.05), libido was otherwise unaffected by treatment. Melatonin did not alter seminal plasma concentrations of inhibin A or Anti-Mullerian hormone, however, for the first time in the ram we have shown Anti-Mullerian hormone to be positively correlated with the number of sperm per ejaculate and sperm motility (r = 0.464 and 0.3242 respectively, P < 0.001), and inhibin A to be correlated to the number of sperm per ejaculate (r = 0.1786, P = 0.0135). These results indicate that melatonin is able to both systemically upregulate reproduction and act directly upon testicular function in the ram.

Melatonin-improved buffalo semen quality during nonbreeding season under tropical condition

The role of melatonin in protecting spermatozoa from different kinds of injury has been widely reported. The present study aimed to test whether treatment of buffalo bulls with melatonin could ameliorate sperm function during nonbreeding season under tropical condition. Ten Murrah buffalo bulls were randomly allocated into control and treated groups of equal numbers of bulls to study the effect of melatonin on semen characteristics, seminal plasma constituents, blood plasma hormonal levels, and antioxidant enzyme activities during nonbreeding season. Treated bulls were implanted with melatonin (18 mg/50 kg of body weight) for a period of 2 mo. During this period, semen was collected twice a week, and blood samples were collected weekly to determine plasma concentration of melatonin and LH and activities of antioxidant enzymes. During nonbreeding season, melatonin implantation improved semen characteristics by increasing (P < 0.05) percentages of sperm with forward motility, viability, total motile sperm, and rapid motility, average path, curvilinear, and straight-line velocity and amplitude of lateral head displacement and decreasing (P < 0.05) percentages of abnormal sperm and linearity index as compared to the control group. Furthermore, melatonin implantation increased (P < 0.05) seminal plasma concentrations of total protein, albumin, and cholesterol and decreased (P < 0.05) seminal plasma aspartate aminotransferase activity. In addition, melatonin-implanted bulls exhibited an increase (P < 0.05) in red blood cells superoxide dismutase activity compared to untreated bulls. In conclusion, melatonin implantation successfully improved semen quality of buffalo bulls during nonbreeding season under tropical condition.

Shortened daily photoperiod during the non-breeding season can improve the reproductive performance of camel bulls (Camelus dromedarius)

The effects of a shortened photoperiod on the reproductive performance and hormones of mature dromedary camel bulls (Camelus dromedarius) were evaluated. A group of 6 bulls were blindfolded to induce a daily photoperiod that was ∼2.55 h shorter than the natural day length (10.83L:13.17D), whereas 6 others served as the control group. The trial started in June and continued for 10 weeks during the non-breeding season. The reproductive performance of all animals was evaluated weekly during this time and also during the breeding season, starting in December and continuing for 10 weeks. Camel bulls in the treatment group showed a significant (p < 0.05) increase in testicular volume, scrotal circumference, sexual desire, reaction time, and mating ability scores, and serum melatonin and testosterone concentrations, relative to the control group, during the non-breeding season. In addition, sexual desire and reaction time and mating ability scores were significantly (p < 0.05) higher in the treatment group than in the control during the breeding season. There was no significant difference between the treatment groups in both seasons and the control group in the breeding season regarding semen volume, sperm cell concentration, total motility, progressive motility, plasma membrane integrity, and viability. Shortening the daily photoperiod by blindfolding can improve the reproductive performance of dromedary camel bulls during the non-breeding season and the following breeding season. This simple, inexpensive, and easily applicable method can enable breeders to collect semen of acceptable quality during the non-breeding season.

Effects of melatonin implants on the reproductive performance and endocrine function of camel (Camelus dromedarius) bulls during the non-breeding and subsequent breeding seasons

This study aimed to evaluate the effects of melatonin implants on the reproductive performances and hormone levels of dromedary (Camelus dromedarius) bulls during the non-breeding and subsequent breeding seasons. Fourteen mature dromedary bulls were divided into a control group (n = 7) and a group that was implanted with melatonin (n = 7) twice, at the beginning of the study and 35 days later. The trial started on the 17th June and continued for 10 weeks during the non-breeding season. Reproductive performances of animals in the control and melatonin groups were evaluated weekly during the non-breeding season [control non-breeding (CNB) and melatonin non-breeding (MNB) groups, respectively] and evaluated again during the subsequent breeding season [control breeding (CB) and melatonin breeding (MB) groups, respectively], which started on the 6th December and continued for 10 weeks. MNB bulls had greater (P ≤ 0.05) scrotum circumference and testicular volume, sexual desire, reaction time and mating ability scores, and serum melatonin and testosterone concentration values (24.91 ± 0.26 cm, 271.00 ± 7.81 cm³, 2.31 ± 0.13, 2.03 ± 0.22, 2.26 ± 0.09, 23.90 ± 0.05 pg/mL and 2764.51 ± 137.02 pg/mL, respectively) than the CNB group (23.63 ± 0.05 cm, 199.21 ± 3.27 cm³, 1.00 ± 0.00, 0.00 ± 0.00, 1.00 ± 0.00, 9.46 ± 0.08 pg/mL and 1872.41 ± 264.89 pg/mL, respectively). The scrotum and testes, reaction time score, proportion of bulls refusing to mount, and serum melatonin values were significantly higher in MB than CB bulls (P ≤ 0.05). Progressive motility (PM), average pathway velocity, straight-line velocity, curvilinear velocity (VCL), linearity, straightness (STR), wobble, beat cross frequency (BCF), livability, and DNA integrity were significantly higher in MB than CB bulls (P ≤ 0.05). PM, VCL, STR, amplitude of lateral head displacement, BCF, and livability were significantly higher in MNB than CB bulls (P ≤ 0.05). In conclusion, melatonin implants improved the reproductive performance of bulls during the non-breeding and subsequent breeding seasons.

Exogenous melatonin influences distribution of French Alpine buck spermatozoa in morphometrically distinct subpopulations during the non-breeding season

The aim of this study was to establish subpopulations of spermatozoa in bucks using the principal component (PC) and cluster analysis according to morphometric head and tail variables, and to determine differences in proportions of subpopulations between exogenous melatonin-treated and control bucks. The bucks (n = 12) were assigned to two groups comprising six bucks each. By the end of March, four melatonin implants were inserted in the bucks in the experimental group. Semen was collected weekly using an artificial vagina from March to May (the non-breeding season). Analyses were performed in stained smears by SFORM computer-assisted program for eight head and five tail variables. The PC analysis revealed four components with the most important value for each (head outline, head ellipticity, mid-piece length and width). Cluster analysis indicated there were three subpopulations (average-sized spermatozoa- C_1; small and less-elliptic - C_2; big and elliptic - C_3). Melatonin-treated bucks had a greater proportion of C_1 spermatozoa and a lesser proportion of C_2 spermatozoa during May (P < 0.05). To the best of our knowledge, this is the first study where PC and cluster analyses were performed on buck semen with head and tail variables analyzed together, in the same analysis, to evaluate spermatozoa population. Also, this is the first analysis of morphometric variables for assessing the influence of melatonin on spermatozoa subpopulations. The positive effect of melatonin on the proportions of spermatozoa in subpopulations could have been a consequence of the decreasing the proportion of the subpopulation with the least head and tail sizes and ellipticity.

Monitoring of libido and semen quality parameters in melatonin-treated French alpine bucks during the non-breeding season

The aim of this study was to investigate the effects of exogenous melatonin on libido and semen quality parameters in bucks during the non-breeding season. Twelve bucks of the French alpine breed from 1.5 to 4 years of age were assigned into melatonin (MG) and control (CG) groups, with 6 bucks in each group. The experimental period was 3 months (March-May), divided into six periods of 15 days each. The bucks in the MG group received four melatonin implants at the end of March. Two semen samples were taken from the bucks by artificial vagina once per week and their libido estimated. Volume and spermatozoa concentration, their mass motility and motility, proportion of live and total abnormal and forms with abnormal head and tail were determined in the obtained ejaculate samples. The total number of spermatozoa and functional spermatozoa fraction in the ejaculate was also calculated. The MG bucks had significantly higher mass motility and motility of spermatozoa in the first half of April, and a higher proportion of live spermatozoa in the first and second half of April (p < .05). Differences in libido intensity were not significant. The results indicated that the application of melatonin significantly improved the qualitative parameters of semen in bucks, as seen in increased mass motility, motility of spermatozoa and proportion of live spermatozoa shortly following melatonin insertion. Therefore, the results of the current study are novel regarding the use of melatonin treatment during the non-breeding season to improve the qualitative parameters of ejaculates in bucks.

Comparison of sexual performance and testicular characteristics of melatonin treated Kivircik and Charollais rams during the non-breeding season

ABSTRACT This study was conducted to investigate the effects of melatonin implantation on basic testicular characteristics and reproductive performance of Kivircik and Charollais rams and ewes during the non-breeding season. In this study, 8 Kivircik and 6 Charollais rams were used. Rams were implanted with 54 mg melatonin according to the manufacturer's instructions. At melatonin implantation and at ram introduction the reproductive performance and testicular characteristics were evaluated. Throughout the experimental period, rams were permanently kept outdoors under conditions of natural day length and at ambient temperature. The effects of exogenous melatonin treatments on the reproductive performances of rams and ewes, estrus response, pregnancy rate, litter size and twinning rate of ewes were evaluated in all groups. Libido values were significantly higher in Charollais rams compared to Kivircik rams (P<0.001). Testicular volume (TV) was increased in both ram breeds. Scrotal length (SL) was also increased in both Kivircik and Charollais rams (P<0.01). In conclusion, we showed that the treatment of rams with slow release melatonin implants increased scrotal diameters and testicular volumes in both Kivircik and Charollais rams. Furthermore, melatonin implantation improved the reproductive performances of ewes naturally mated with these melatonin implanted rams during non-breeding season.

Melatonin MT₁ and MT₂ Receptors in the Ram Reproductive Tract

Some melatonin functions in mammals are exerted through MT₁ and MT₂ receptors. However, there are no reports of their presence in the reproductive tract of the ram, a seasonal species. Thus, we have investigated their existence in the ram testis, epididymis, accessory glands and ductus deferens. Real-time polymerase chain reaction (qPCR) revealed higher levels of m-RNA for both receptors in the testis, ampulla, seminal vesicles, and vas deferens, than in the other organs of the reproductive tract (p < 0.05). Western blot analyses showed protein bands compatible with the MT₁ in the testis and cauda epididymis, and for the MT₂ in the cauda epididymis and deferent duct. Immunohistochemistry analyses revealed the presence of MT₁ receptors in spermatogonias, spermatocytes, and spermatids, and MT₂ receptors in the newly-formed spermatozoa in the testis, whereas both receptors were located in the epithelial cells of the ampulla, seminal vesicles, and ductus deferens. Indirect immunofluorescence showed significant differences in the immunolocation of both receptors in spermatozoa during their transit in the epididymis. In conclusion, it was demonstrated that melatonin receptors are present in the ram reproductive tract. These results open the way for new studies on the molecular mechanism of melatonin and the biological significance of its receptors.