Exogenous melatonin does not improve the freezability of Blanca Andaluza goat semen over exposure to two months of short days

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.

The Combined Effect of Melatonin Implant and Removal of Buck Seminal Plasma on Cryopreservation During the Nonbreeding Season

This study aimed to determine how melatonin (MT) and seminal plasma affected the freezability of buck sperm during the nonbreeding season. Semen was collected from eight bucks before (pre-MT) and after (post-MT) MT application in the nonbreeding season. Individual ejaculates were collected from the bucks, split into two equal groups according to the removal of seminal plasma (SP) (-) or nonremoval of SP (+). For washing, the groups of ejaculates were centrifuged, and the supernatant was separated, SP (-) and SP (+) ejaculates were diluted, then frozen. Semen samples were examined for sperm motility, plasma membrane integrity, defective acrosomes, DNA fragmentation, and mitochondrial membrane function at the native and post-thaw stages. When the general average post-thaw motility (p < 0.01), plasma membrane (p < 0.05), acrosome (p < 0.05), and DNA integrity rates (p < 0.05) and mitochondrial membrane potential (MMP) (p < 0.01) were evaluated, it was seen that MT administration caused a statistically significant improvement. The dramatic effect of nonremoval of seminal plasma on motility and plasma membrane integrity is more clearly observed in individual semen samples frozen in the pre-MT group (p < 0.05). Also, it was observed that removing seminal plasma in the post-MT group caused even milder post-thaw acrosome damage compared with the SP (+) group (p < 0.05). The effect of removing seminal plasma was not observed in terms of DNA integrity and MMP rates in pre- and post-MT groups. As a result, it was concluded that MT application and removal of seminal plasma in the nonbreeding season result in improvement in the freezability of buck semen.

Effect of Acute Melatonin Injection on Metabolomic and Testicular Artery Hemodynamic Changes and Circulating Hormones in Shiba Goats under Sub-Tropical Environmental Conditions

The beneficial effects of melatonin were investigated to mitigate various detrimental effects and toxicity on reproductive performance. The present study aimed, for the first time, to explore the effect of intravenous melatonin injection on testicular artery hemodynamics (TH) and metabolomic changes, reproductive hormones in heat-stressed bucks. Ten bucks were randomly split into two groups (five each): (1) the melatonin group, treated with a single intravenous dose of melatonin solution containing 10 mg melatonin each, and (2) the control group, which was treated with 10 mL of the vehicle without melatonin. Changes in the TH at the level of the supra testicular artery (STA) were assessed by triplex ultrasonography just before (0 h) and at 0.5, 2, 7, 24, and 168 h after melatonin or vehicle administration. Doppler velocity parameters of peak systolic velocity (PSV; cm/s), end-diastolic velocity (EDV; cm/s), and time average maximum velocity (TAMAX; cm/s) were measured. Doppler indices (resistive index; RI and pulsatility index; PI), systole/diastole (S/D) ratio and total arterial blood flow volume (TABFV; ml/minute) were measured. Peripheral concentrations of FSH, LH, inhibin, melatonin, testosterone (T), estradiol (E2), and cortisol were measured just before injection (0 h) and at 0.5, 2, 7, and 24 h and daily up to day 7 post administration in both groups. Results revealed reductions in the RI values and increases in the TABFV in the melatonin group compared to the control one, especially 2 h after administration. Significant increases in concentrations of FSH, T, E2, and melatonin and decreases in cortisol and inhibin in the melatonin group compared to the control one. Plasma metabolomic analysis at 2 h indicated the up-regulation of L-glutamine, L-arginine, sorbitol, D-glucose, ascorbic acid, and ornithine and the down-regulation of D-xylose, D-arabitol, ribitol, and oleic acid in the melatonin versus the control group. In conclusion, acute administration of melatonin (10 mg IV) enhanced testicular artery blood flow and plasma reproductive hormones in the Shiba goat under heat-stress circumstances.

Expression of Aquaglyceroporins in Spermatozoa from Wild Ruminants Is Influenced by Photoperiod and Thyroxine Concentrations

This work identified the presence of AQPs in frozen-thawed sperm of wild ruminants and assessed the influence of the interaction between photoperiod and thyroxine on AQP expression, and on testosterone secretion. Thyroxine and melatonin were administered to ibexes. In a second experiment, performed in mouflons, circulating thyroxine was reduced via treatment with propylthiouracil (PTU), and an artificial long day (LD) photoperiod established. In the ibexes, the melatonin treatment increased the blood plasma testosterone concentration, reduced the cryoresistance ratio (CR) for sperm viability and the presence of an intact acrosome, and increased the percentage of sperm with AQP7 in the acrosome and of AQP3 and AQP10 in the midpiece. In the mouflons, neither the PTU treatment, the LD, nor the combination of both affected the CR of any sperm variable. The percentage of sperm with AQP3 increased in the post-acrosome region but decreased in the tail in the LD+PTU group. The percentage of sperm with AQP10 in the principal piece and endpiece was lower in the PTU+LD group than in the control and LD groups. The influence of photoperiod/melatonin on AQP expression might be indirectly exerted through changes in the testosterone concentration, and thus ultimately affect sperm cryoresistance.

Use of melatonin in sperm cryopreservation of farm animals: A brief review

Melatonin (MT) is a potent antioxidant with useful applications in several fields. Due to the capacity to scavenge free radicals and enhance cellular endogenous antioxidant defenses, MT is widely used in sperm cryopreservation to protect against oxidative stress-induced damage in frozen-thawed sperm. In this article, there is a review of positive effects of MT supplementation in cryopreservation of sperm from domestic ruminants and swine. There is direct or indirect scavenging of free radicals, preventing lipid peroxidation (LPO), and reducing oxidative stress, therefore, protecting membrane and DNA integrity, enhancing post-thaw antioxidant and enzymatic functions to maintain mitochondrial functions and activity, and regulating ATP production and utilization leading to maintenance of sperm quality, motility, and viability. In addition, MT reportedly inhibits sperm apoptosis, potentially by enhancing sperm viability and modulating abundances of mRNA transcripts.

The influence of exogenous melatonin on antioxidative status in seminal plasma and spermatozoa in French Alpine bucks during the nonbreeding season

Research data regarding exogenous melatonin effects on buck semen antioxidative status during the breeding and nonbreeding seasons are scarce or missing. The aim of this study was to investigate the effect of melatonin implants on the activity and ratios of antioxidative enzymes and on malondialdehyde concentrations in the seminal plasma and spermatozoa of French Alpine bucks during the 3 mo of the nonbreeding season. Two groups of randomly assigned bucks were either treated with melatonin (n = 6) or served as controls (n = 6). Semen samples were collected weekly, seminal plasma was separated from spermatozoa, and activities of glutathione peroxidase (GSH-Px), glutathione reductase (GR), superoxide dismutase (SOD), catalase (CAT), and the concentration of malondialdehyde were determined. The melatonin-treated bucks had significantly higher CAT/SOD and GSH-Px/SOD ratios, but a significantly lower GR/GSH-Px ratio in seminal plasma and spermatozoa during the different periods of the nonbreeding season. In conclusion, exogenous melatonin influenced the activities of all ratios and some single antioxidative enzymes tested in bucks' seminal plasma and spermatozoa. Here we provide the first evidence derived from an intervention, that is, melatonin treatment, which affects antioxidative enzymes ratios in the semen of bucks, and could thus be recommended as an indicator of oxidative stress severity and antioxidative status of semen.

Administration of melatonin improves testicular blood flow, circulating hormones, and semen quality in Shiba goats

Despite the role of melatonin in the regulation of the sleep-wake cycle and seasonal-reproduction, the present study investigated, for the first time, the potential role of melatonin on testicular blood flow (TBF) in goats. Twelve sexually mature male Shiba goats were exposed to a single s.c. injection of either melatonin suspended in one ml of corn oil (melatonin group; 36 mg/goat; n = 5) or one ml of corn oil (control group; n = 7). Monitoring the changes in TBF was done one week before (W-1), at the time of injection (W0), and once a week for 8 weeks after injection using color-pulsed Doppler ultrasonography. Concentrations of FSH, LH, inhibin, testosterone (T), estradiol (E2), and insulin-like growth factor-1 (IGF-1) in plasma were determined by radioimmunoassay. Melatonin and nitric oxide (NO) concentrations were measured using enzyme immunoassay kits. Moreover, semen collection and evaluation of some sperm parameters were performed once a week. Results revealed decreases (P < 0.05) in the Doppler indices (resistive index, pulsatility index) of the testicular arteries from W2 till W6 in the melatonin group. FSH, LH, and inhibin concentrations did not change between the two groups, while T, E2, IGF-1, NO, and melatonin concentrations increased (P < 0.05) in the melatonin group compared to the control. Estradiol and NO concentrations increased (P < 0.05), coinciding with decreases in the values of Doppler indices. Notable (P < 0.05) improvements in most parameters of semen quality were seen in the melatonin group. In conclusion, melatonin induced a stimulatory effect on TBF in Shiba goats and possibly, it could be a potential to improve male goats fertility.

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.

The isolation of females from males to promote a later male effect is unnecessary if the bucks used are sexually active

It has been suggested that female goats in permanent contact with males become refractory to their presence, and need to be previously separated from them for 40-45 days if the presence of bucks is to induce reproductive activity, ovulation and oestrous during seasonal anoestrous. The present study examines the reproductive response (ovulation and oestrus) and reproductive performance of does isolated from bucks for different periods before their reintroduction to male company. A total of 103 Payoya and Blanca Andaluza does were distributed into six treatment groups that required their isolation from males for different periods: 0 days (N = 29), 5 days (N = 15), 10 days (N = 14), 20 days (N = 16), 30 days (N = 14) and 39 days (N = 15). After this period they were introduced to sexually active bucks (ensured to be in this condition by keeping them under long days light treatment for three months), and oestrous activity was recorded daily by direct visual observation of the marks left by the marking harnesses worn by these males. Ovulation was confirmed via the plasma progesterone concentration (measured in blood samples taken twice per week). The ovulation rate was assessed by transrectal ultrasonography. Fecundity, fertility, prolificacy and productivity were also determined. The sexual behaviour of the males towards the females was also monitored on Days 0, 1, 2, 3, 4, 8 and 9 after their meeting with the latter. The length of the female isolation period had no effect on the percentage of does that responded to contact with the males, nor did it affect the oestrous response, fecundity, fertility or productivity. The males, however, undertook more ano-genital sniffing and nudging with the 5 day group females compared to those of the other groups (P < 0.05). However, the sexual behaviour of the males changed as the days passed, with ano-genital sniffing becoming less common, and nudging, licking, sneezing and mounts with intromission more frequent on Days 8 and 9 than on Day 0, 1 and 2 after the sexes were reunited (P < 0.05). These results show that the isolation of females is not necessary for an efficient male effect if the bucks used are sexually active. In addition, the sexual behaviour of the bucks changes as the time in contact with the does increases, but in general is not affected by the duration of female isolation.

Morphometry and subpopulation structure of Holstein bull spermatozoa: variations in ejaculates and cryopreservation straws

Sperm quality is evaluated for the calculation of sperm dosage in artificial reproductive programs. The most common parameter used is motility, but morphology has a higher potential as a predictor of genetic quality. Morphometry calculations from CASA-Morph technology improve morphological evaluation and allow mathematical approaches to the problem. Semen from 28 Holstein bulls was collected by artificial vagina, and several ejaculates were studied. After general evaluation, samples were diluted, packaged in 0.25 ml straws, and stored in liquid nitrogen. Two straws per sample were thawed, and slides were processed and stained with Diff-Quik. Samples were analyzed by a CASA-Morph system for eight morphometric parameters. In addition to the "classical" statistical approach, based on variance analysis (revealing differences between animals, ejaculates, and straws), principal component (PC) analysis showed that the variables were grouped into PC1, related to size, and PC2 to shape. Subpopulation structure analysis showed four groups, namely, big, small, short, and narrow from their dominant characteristics, representing 31.0%, 27.3%, 24.1%, and 17.7% of the total population, respectively. The distributions varied between animals and ejaculates, but between straws, there were no differences in only four animals. This modern approach of considering an ejaculate sperm population as divided into subpopulations reflecting quantifiable parameters generated by CASA-Morph systems technology opens a new view on sperm function. This is the first study applying this approach to evaluate different ejaculates and straws from the same individual. More work must be done to improve seminal dose calculations in assisted reproductive programs.

Effects of a long-day light programme on the motility and membrane integrity of cooled-stored and cyropreserved semen in Shetland pony stallions

Increasing day length in spring stimulates reproductive functions in horses. In this study, we have analysed the effect of artificial long days on the quality of cooled-stored and cryopreserved semen in Shetland stallions. Stallions of the treatment group (AL, n = 8) were exposed to 16 h light and 8h darkness from 15th December to 20th March while control stallions (CON, n = 7) were kept under natural photoperiod. Semen was collected once weekly and processed for cooled-storage and cryopreservation once per month. Total and progressive motility and percentage of membrane intact spermatozoa were analysed at 24, 48 and 72 h of cooled-storage and after freezing-thawing, respectively. Total and progressive motility and membrane integrity decreased during cooled-storage for 72 h in each month and both groups (p < 0.001). All these parameters were lower in CON versus AL stallions (p < 0.05) and the decrease was more pronounced in group CON (storage time x group p < 0.05). Differences between groups decreased throughout the observation period from January (p < 0.05 between groups) to July (e.g. total motility after 72 h of cooled-storage in January for group AL 80 ± 3 and group CON 49 ± 12%, respective values in July, 83 ± 2 and 72 ± 6%). Neither total and progressive motility nor percentage of membrane-intact and morphologically defect spermatozoa in frozen-thawed semen differed between groups and months. In conclusion, motility of cooled-stored semen was reduced in January and increased in stallions kept under a long day light programme for at least 30 days.