Effects of exogenous melatonin treatment on out-of-season ram fertility

Sperm melatonin receptors, seminal plasma melatonin and semen freezability in goats

Goat bucks are seasonal breeders that show variation in sperm quality, endogenous melatonin (MLT), and presumably in the expression of MLT receptors on the sperm throughout the year, which may modify sperm freezability. The aim of this study was to determine whether sperm freezability is associated with (i) endogenous melatonin levels in seminal plasma and (ii) the expression of sperm plasma membrane melatonin receptors (MT1, MT2). To evaluate this, spermatozoa from seven Saanen goat bucks were cryopreserved throughout the year in Mexico using a standard freezing protocol. Seminal plasma MLT concentrations were determined by ELISA and the expression and localization of MT1 and MT2 were detected by immunocytochemistry and confirmed by western blotting. The recovery rate of progressive motility after thawing was higher in spring than autumn and winter; in contrast, the F pattern (CTC assay) was higher in winter than in the other seasons. A proportional increase in the AR pattern (CTC assay) was smaller in winter than in the other seasons and the proportion of sperm showing high plasma membrane fluidity was higher in spring than in summer and autumn. The seminal plasma MLT concentrations showed no significant interseasonal differences. The MT1 receptor was immunolocalised at the apical region of the sperm head, while MT2 was mainly localised in the neck. The relative expression of MLT receptors showed significant differences between summer and winter for all bands, except at 75 kDa of MT2. In conclusion, there was an association between the relative expression of MT1 and MT2 receptors throughout the year and sperm freezability in goat bucks in México. Post-thaw sperm quality is enhanced in semen samples collected during breeding season.

Evaluation of the effect of melatonin implantation in rams and eCG dose in ewes synchronized by a CIDR-eCG protocol on reproductive performance of Lacaune sheep breed during non-breeding season

Sustainable production of milk is favorable in dairy sheep industry, which necessitates year-round reproduction of rams and ewes even during non-breeding season. Hence, protocols facilitating reproduction of rams and ewes during non-breeding season are of importance for this purpose. Therefore, the present study was conducted to investigate the effect of melatonin implantation in rams and administration of 400 IU eCG (E400) versus 300 IU eCG (E300) in ewes on reproductive performance of Lacaune sheep breed during non-breeding season. Rams were allocated to two groups including untreated (control, CON; n = 36) and melatonin-treated (MEL; n = 37). A subset of rams from CON (n = 7) and MEL (n = 7) groups were used for assessment of scrotal circumference, kinematic and functional characteristics of sperm, total antioxidant capacity (TAC) of semen and circulating testosterone on Days 0 (the beginning of study) and 60 (60 days after melatonin implantation). Further, the study had a 2 × 2 factorial design with four experimental groups including 1) ewes treated with E300 and introduced to CON rams (E300CON; n = 17 rams and 172 ewes), 2) ewes treated with E300 and introduced to MEL rams (E300MEL; n = 18 rams and 177 ewes), 3) ewes treated with E400 and introduced to CON rams (E400CON; n = 19 rams and 192 ewes), and ewes treated with E400 and introduced to MEL rams (E400MEL; n = 19 rams and 190 ewes). Melatonin implantation improved scrotal circumference, concentration, progressive motility, velocity, mitochondrial membrane potential and viability of sperm, TAC of semen, concentration of testosterone and fertility of rams (P < 0.05). Besides, E400 compared with E300 enhanced synchronization of estrus and fertility in ewes (P < 0.05). In conclusion, melatonin implantation promoted reproductive performance in Lacaune rams, and increase in dose of eCG improved reproductive performance in Lacaune ewes.

Rhythmicity in testicular melatonin and its correlation with the dynamics of spermatogenic cells in an annual reproductive cycle of Clarias batrachus under natural photo-thermal conditions

Melatonin, the pineal hormone, is synthesized and secreted rhythmically in accordance with various environmental cues especially photo-thermal conditions. The reproductive physiology of seasonal breeders is synchronized with the surroundings by melatonin as a neuroendocrine mediator to acts as an important factor in fish reproduction. However, the data on the participation of melatonin in male reproduction and the putative interaction with the process of spermatogenesis in fish is scarce till date. So, major objectives of the current study are to determine for the first time, the relationship, if any, between seasonal levels of melatonin and testicular development and maturation of the germ cells, and also the involvements of specific meteorological parameters in spermatogenesis under natural photo-thermal conditions. We measured the concentration of circulatory and testicular melatonin; value of gonadosomatic index (GSI), relative percentages of different developing spermatogenic cells, area and perimeter (size and shape) of seminiferous lobules along with the level/duration of rainfall, water temperature and day length in six reproductive phases throughout an annual cycle in adult male catfish (Clarias batrachus). Intra-testicular and serum melatonin concentration showed a similar seasonal pattern with a peak during "functional maturity" phase and trough during "slow spermatogenesis" phase. Correlation as well as regression analyses also supported this positive relationship. Interestingly, intra-testicular melatonin also showed a significant positive correlation with GSI and relative percentage as well as lobular size of mature stages (spermatid and spermatozoa) of germ cells in an annual cycle. Furthermore, meteorological factors exhibited as critical cues to regulate the dynamics (in %) of spermatogenic cells and the level of testicular melatonin throughout the annual gonadal cycle. Our results corroborated by principal component (PC) analysis and showed very clearly that active "functional maturity" state is characterized by GSI, testicular melatonin, relative abundance and lobular size of mature spermatogenic stages as key internal oscillators; and studied environmental variables as the external clues for the regulation of spawning process. Collectively, the present data revealed that there is a relationship between melatonin levels and testicular growth and development of germ cells in Clarias batrachus under natural photo-thermal conditions.

Effects of Melatonin Implants on Reproductive Performance of Dairy Sheep and Dairy Goats

This study investigated the effects of melatonin implants in female and male before the breeding season on the reproductive performance of Tahirova sheep and Turkish Saanen goats. Seventy-five sheep and 53 goats (including 6 rams and 4 bucks) were used in the research. Melatonin implants (18 mg) were applied to half of the female and male animals, one to females and three to males. The rate of estrus was determined as 100% in the melatonin (M) and control (C) groups. The non-return rate, conception rate and lambing rate were close in both groups of ewes and rams groups (P>0.05). The rate of estrus was 100% in the melatonin and control groups of does and bucks groups in Turkish Saanen goats. The non-return rate in does was 75.0±9.02% in M group and 92.0±5.53% in C group (P=0.0101), the non-return rate was 83.3±6.92% in group M and 84.2±8.59% in group C for bucks (P=0.5570). For ewes, the duration from ram introduction to first estrus, conception and lambing was significantly lower in group M than in group C (P≤0.05). Litter size of M in ewe and ram groups were 1.70±0.08 and 1.59±0.09, respectively, whereas it was 1.62±0.10 and 1.74±0.10 in C group, respectively. The birth weight significantly differed between ewe groups (P=0.0017). For goats, the duration from buck introduction to first estrus, conception and lambing was similar in the groups of does and bucks (P>0.05). Litter size of M in doe and buck groups were 1.57±0.11 and 1.53±0.12, respectively, and 1.46±0.11and 1.50±0.09 in C group, respectively (P>0.05). While the live weight and body condition score (BCS) of ewes were significantly affected by melatonin implants (P≤0.05), the live weight and BCS of does were not affected. In conclusion, it might be said that melatonin implants obtained better results for reproduction in Tahirova sheep than Turkish Saanen goats.

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.

Evaluation of potential reproductive seasonality in brown brocket deer (Mazama gouazoubira) bucks

Photoperiod is the main cue that controls seasonal reproduction in deer from temperate regions, like secretion of testosterone by the testis, neck enlargement, and testis development. However, little is known about its effect on the reproduction of tropical deer species. This research aimed to assess the potential seasonality of the brown brocket deer (Mazama gouazoubira) by melatonin treatment. Reproductive parameters such as testicular volume, neck circumference, and semen quality were evaluated from day 0 to 90, and fecal androgen metabolites (FAM) from day -28 to 91. Melatonin treatment was administered from day 0 to 60. In total, seven individuals were used in the study. Four animals were allocated to the treated group (TG) and three to the control group (CG). The neck circumference and some seminal parameters did not show a significant difference between CG and TG and along the experimental period. High FAM levels were observed for the TG on days 7, 14, 21, 35, 84, and 91 (p < 0.05). The mean testicular volume was reduced from day 0 to 30 (p < 0.05) and from day 0 to 90 (p < 0.05), with no increase in the mean testicular volume from day 30 to 60 (p > 0.05). Sperm motility was the highest on day 60 compared with day 0 (p < 0.05). Although not statistically different, membrane integrity and major defects tended to be higher and lower, respectively, in the TG compared with the CG. For these parameters, the incremental change (%) per individual showed that males from the TG tended to have a higher percentage during the melatonin treatment, hence melatonin might affect these seminal characteristics. These findings suggest that exogenous melatonin might enhance FAM levels and sperm motility.

Daily and seasonal rhythmic secretary pattern of endocrinological profiles in mithun bull

Mithun (Bos frontalis) is a unique domestic free-range bovine species available in North Eastern hilly (NEH) regions of India and is reared for its protein rich meat. Mithun suffers severe non-cyclical population fluctuations; however, it is not yet declared as endangered species. Mithun follows some sort of seasonality based on the calving trend and semen production, although it is a perennial breeder. However, there is need to study the rhythmic changes of endocrine profiles to understand the hormone flow pattern in mithun to select the suitable time for blood collection to assess the exact endocrine profiles and to select the suitable time for natural breeding or semen collection by artificial methods for further research, conservation and propagation of its germplasm. Therefore, the present study was designed to evaluate the reproductive as well as metabolic endocrinological profiles in 24:00 h in intact adult mithun bulls during different seasons (winter, spring, summer and autumn) to know the rhythmic changes and flow pattern of the endocrinological profiles to improve its reproductive efficiency. Experimental mithun bulls (n = 6; age: 5-6 years; body condition score: 5-6 out of 10, classified as good) were selected for the study. Endocrinological profiles, follicle stimulating hormone (FSH), luteinizing hormone/interstitial cell stimulating hormone (LH/ICSH), testosterone, cortisol, thyroxine (T4), insulin like growth factor-1 (IGF-1), prolactin and melatonin (MT) were estimated at 04:00 h interval for one whole day in four seasons. The analysis was completed in two different ways as different times of collection (08:00, 12:00, 16:00, 20:00, 24:00 and 04:00 h) and day (08:00 to 16:00 h) & night time (20:00 to 04:00 h) collections. Repeated measures ANOVA analysis revealed that the bulls in winter and spring had significantly (p < 0.05) higher FSH, LH, testosterone, T4, IGF-1 and MT than those in summer whereas the bulls in summer had significantly higher cortisol and prolactin than those in winter and spring seasons. Similarly FSH, LH, testosterone, T4, IGF-1 and MT were significantly (p < 0.05) higher in night than in day time collections whereas cortisol and prolactin were significantly (p < 0.05) higher in day than in night time collections in different seasons. Correlation analysis revealed that FSH, LH, testosterone, T4, IGF-1 and MT had significant (p < 0.05) positive correlation with each other whereas these had significant (p < 0.05) negative correlation with cortisol and prolactin. The study concludes that season and time of blood collection had significant effect on the endocrinological profiles in mithun bulls. Estimation of FSH, LH, testosterone, T4, IGF-1 and MT during night time and cortisol and prolactin during day time was more appropriate to get correct value of the endocrinological profiles. Spring and winter have significantly greater beneficial effects than summer on reproduction and artificial breeding programs in mithun species in the semi-intensive management in the present location.

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.

Administration of slow release exogenous melatonin modulates oxidative stress profiles and in vitro fertilizing ability of the cryopreserved mithun (Bos frontalis) spermatozoa

Mithun (Bos frontalis) is a unique domestic free range bovine species of North Eastern hilly regions of India. The present study was designed to assess the seasonal effect of slow release exogenous melatonin (MT) implant on semen quality parameters (SQP) and in vitro zona binding ability (IVZ) of spermatozoa. The experimental animals were divided into Gr I: Control (n = 5) and Gr II: Treatment (n = 5; melatonin implant @ 18mg/50 kg bwt). A total of 20 semen samples/group in winter, spring, autumn and summer seasons (n = 160), twice per week were collected. Following cryopreservation, samples were evaluated for motility parameters (forward progressive, mobility & velocity by computer assisted sperm analyser (CASA), viability, acrosome integrity, plasma membrane and nuclear abnormality, functional status of mitochondria, enzymatic, antioxidant and oxidative profiles, and IVZ. The study revealed significant (p < 0.05) improvement in total motility, viability, acrosome-, plasma membrane-, and nuclear-integrity, and antioxidant profiles; with highest values in spring and lowest in summer season in the fresh semen in Gr II than the Control. A significant (p < 0.05) improvement in motility parameters, membrane potential of mitochondria, antioxidant profiles and reduction in sperm and nuclear abnormalities, leakage of intracellular enzymes and oxidative stress and IVZ index & binding percentage in post-thaw semen samples in melatonin supplemented than in un-supplemented control group was observed. It can be concluded from the study that slow-release melatonin supplementation can be effectively utilized to improve the antioxidant profiles and reduction of oxidative stress, with cascading beneficial effects on semen quality parameters and fertility status of the mithun bull.

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.

Efficiency and demographics of a high-yield dairy ewe farm with two managing systems involving five or 10 lambings per year

This study assessed milk productivity, demographic characteristics and workload distribution on a single high-yield dairy ewe farm in Spain (Avila, Spain; continental climate, latitude of 40.90 N, altitude of 900 m) over a 7-year period considering a transition from a herd management system involving five lambings per year (5LY) to a system involving 10 lambings per year (10LY). The 5LY system was practiced on the farm from 2010 to 2012 and the 10LY system from 2014 to 2015, with 2009 and 2013 being considered transition years. During this period, 27 415 lactations were recorded from an average of 3746 Lacaune sheep/year. Several productivity parameters were higher in 2014 to 2015 than in 2010 to 2012: milk yield/lactation (370±156 v. 349±185 l), lactation length (218±75 v. 192±75 days) and dry period length (53.5±38.3 v. 69.1±34.8 days) (all P<0.0001). During 2014 to 2015, investment in new lambing facilities was possible, workload was distributed more uniformly throughout the year, workload per worker was smaller, rate of ewe culling was lower (35.39±0.53% v. 42.51±7.51%), ewe longevity was greater and higher-order lactations were more numerous (P<0.0001). On the other hand, during 2010 to 2012, daily production was higher (1.73±1.66 v. 1.70±0.62 l/day; P=0.038), the interlambing period was shorter (283±50 v. 302±44 days; P<0.0001) and lambings/ewe per year were greater (1.42±0.01 v. 1.30±0.01; P<0.05). These results suggest that a 10LY herd management system can be compatible with profitability, productivity and good animal and worker's welfare on a high-yield dairy farm, and may even be associated with better outcomes than a 5LY system.

Effects of melatonin implantation on the fertility potentials of Kivircik and Charollais ewes and rams during the non-breeding season

This study examined the effect of melatonin implantation during the non-breeding season on the reproductive performance of ewes and the testicular dimensions of rams. In seasonally anestrus Kivircik and Charollais ewes and rams were subjected to melatonin. Estrus response was significantly higher in treated than control ewes of both breeds (p<0.001). The pregnancy rate was significantly lower (p<0.001) in the control than in the treated animals. The twinning rate was significantly lower in melatonin implanted Kivircik than Charollais ewes (p<0.05). The testicular dimensions after 42 days of melatonin treatment increased in both breeds. Scrotal length (SL) increased in Kivircik and Charollais rams (p<0.01). The increase in scrotal circumference (SC) was more marked in the Charollais (P<0.01) than in the Kivircik rams. There was a large increase in testicular volume (TV) in both Kivircik (p<0.01) and Charollais (p<0.001) rams. This study shows that melatonin implants can be applied to induce estrus in ewes approximately four months earlier than breeding season. Melatonin implantation in the non-breeding season significantly increased testicular dimensions in Kivircik and Charollais rams thus increasing their reproductive potential.

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.

New evidence of melatonin receptor contribution to ram sperm functionality

The present study analysed the involvement of melatonin, acting via its receptors (MT1 and MT2), in ram sperm functionality. Indirect immunofluorescence assays revealed no changes in the distribution or intensity of MT1 receptors, whereas different subpopulations were established for MT2 receptors in control, in vitro capacitated and acrosome-reacted ram spermatozoa. Chlortetracycline staining revealed the following correlations between the pattern of staining for MT2 receptors in: (1) non-capacitated (NC) sperm rate and the proportion of spermatozoa with equal immunostaining intensity in the acrosome and post-acrosome (r = 0.59, P < 0.001); (2) in capacitated (C) sperm rate and the proportion of spermatozoa with stronger reactivity in the acrosome (r = 0.60, P < 0.001); and (3) in acrosome-reacted (AR) sperm rate and the proportion of spermatozoa with more intense staining on the post-acrosome (r = 0.67, P < 0.001). Incubation of swim-up-selected samples with either 1 μM melatonin or MT1 and MT2 receptor agonists (2-phenylmelatonin 1 µM and 8-Methoxy-2-propionamidotetralin (8M-PDOT) 1 µM and 10 nM) at 39°C and 5% CO2 for 3 h resulted in a higher proportion of the NC pattern compared with the control group (P < 0.05), whereas treatment with MT1 and MT2 receptor antagonists (luzindole 1 µM and 4-phenyl-2-propionamidotetralin (4P-PDOT) 1 µM and 10 nM) decreased the proportion of spermatozoa exhibiting the NC pattern (P < 0.001) concomitant with an increase in those exhibiting the C pattern (P < 0.01). In conclusion, melatonin exerts a modulating effect on ram sperm functionality, primarily via activation of the MT2 receptor.

Melatonin in sperm biology: breaking paradigms

Melatonin is a ubiquitous molecule, present in a wide range of organisms, and involved in multiple functions. Melatonin relays the information about the photoperiod to the tissues that express melatonin-binding sites in both central and peripheral nervous systems. This hormone has a complex mechanism of action. It can cross the cell plasma membrane and exert its actions in all cells of the body. Certain melatonin actions are mediated by receptors that belong to the superfamily of G-protein-coupled receptors (GPCRs), the MT1 and MT2 membrane. Melatonin can also bind to calmodulin as well as to nuclear receptors of the retinoic acid receptor family, RORα1, RORα2 and RZRβ. The purpose of this review is to report on recent developments in the physiological role of melatonin and its receptors. Specific issues concerning the biological function of melatonin in mammalian seasonal reproduction and spermatozoa are considered. The significance of the continuous presence of melatonin in seminal plasma with a fairly constant concentration is also discussed.

Effect of stimulation with a gonadotropin mixture on reproductive outcome in nulliparous ewes bred during seasonal anestrus and early breeding season

To evaluate the effect of gonadotropic stimulation on the reproductive response of nulliparous acyclic female sheep during mid-anestrous and early breeding season, fall-born ewe lambs of mixed breeding (N=191; ∼7 months old; study 1) and yearlings (Dorset X Texel (DT), N=120, study 2) were assigned randomly during May to July to be either pre-treated with progesterone using CIDR-g (0.3g of progesterone) devices for 5 days or to also receive gonadotropins (240IU eCG and 120IU hCG, 3mL i.m. injection of P.G. 600(®)) at CIDR-g removal. Study 3 was conducted with nulliparous acyclic DT yearling ewes (N=104) in late August and was similar to study 2 except that a group of control ewes that were not treated was included. Gonadotropic stimulation increased estrous response (P=0.0002), pregnancy rate to the first service period (P=0.0007), proportion of ewes lambing (P=0.03) and the lambing rate (P=0.01) in fall-born ewe lambs (study 1), but did not modify reproductive outcome in yearling females (study 2) during mid-anestrus. During the transition into the breeding season (study 3), progesterone pre-treatment increased the pregnancy rate and the proportion of ewes lambing to first service after ram introduction (P=0.003 and P=0.02, respectively). However, gonadotropic stimulation of progesterone pre-treated yearlings did not modify reproductive performance variables. In conclusion, gonadotropic stimulation improved reproductive outcome in fall-born ewe lambs bred during the mid-anestrous period, but did not affect reproductive outcome in yearling females.

Influence of dry period length on reproductive performance and productivity of Lacaune dairy sheep under an intensive management system

Intensive management is almost the only way to ensure dairy farm profitability. The dry period length (DPL) is a key factor in the productivity and health of dairy cows, but whether the same is true of dairy sheep is unclear. This study investigated the effects of DPL on the performance of Lacaune sheep under intensive management. We recorded 8136 lactations from 4220 ewes on one farm for the period 2005-2010, and data from a total of 6762 complete lactations 1-4 were included in the study. The length of the dry period following the current lactation was studied. The larger the total milk yield (MY) and daily milk yield (DMY), the shorter was the DPL before the next lactation. DPL correlated with MY (r=-0·384), DMY (r=-0·277) and the lambing-to-conception interval (LC; r=0·201, P<0·0001) in the global analysis of all lactations (lactations 1-4). The influence of previous-DPL (P-DPL), or the length of the period prior to the start of the next lactation, was studied for 4318 lactations. P-DPL was classified into five intervals: very short (P-DPL-XS), 1-30 d; short (P-DPL-S), 31-60 d; medium (P-DPL-M), 61-90 d; long (P-DPL-L), 91-120 d; and very long (P-DPL-XL), >120 d. P-DPL positively correlated with lambing-to-next conception interval (LNC; r=0·095, P<0·0001) for lactations 1-4. LNC was significantly shorter for P-DPLs that were very short, short, or long (P-PDL-XS, 144·2±67·8 d; P-PDL-S, 149·1±57·2 d; P-PDL-L, 152·0±53·7 d) than for groups with very long or medium P-PDLs (P-DPL-XL, 161·5±62·9 d; P-DPL-M, 169·0±74·8 d; P<0·0001). Moreover, P-DPLs that were very short, long, or very long were associated with the lowest milk yields (P-PDL-XS, 377±215 l; P-PDL-l, 370±168 l; P-PDL-XL, 396±196 l). These yields were significantly lower than the yields for short and medium P-DPLs (P-DPL-S, 432±187 l; P-DPL-M, 436±191 l; P<0·0001) when averages of lactations 1-4 were analysed. These results indicate that lactations with larger MY are followed by a shorter dry period, and that a dry period of 30-90 d leads to larger yields in the next lactation. The best LNC was associated with the shortest Previous-DPL. Hence, 30-60 d should be the optimal dry period length for Lacaune sheep under intensive conditions.

Influence of age at first lambing on reproductive and productive performance of Lacaune dairy sheep under an intensive management system

The present study investigated the effect of age at first lambing (AFL) on the performance of Lacaune sheep under intensive management conditions. Records from 3088 maiden sheep from one farm, for the period 2005-2010, were classified into four experimental groups: group E (early) ewes with AFL ⩽390 d; group M (middle) with AFL of 391-450 d; group L (late) with AFL of 451-510 d; and group A (aged) with AFL ⩾511 d. The higher the number of lactations, the lower were the yield/lactation and yield/Day in Milk. Ewes from group M up to 450 days old lambed 0.2 times more often and had 0.25 more lactations than the ewes from group L; in addition, the former group lambed 0.5 times more often and had 0.49 more lactations than ewes from group A. Group A had the lowest yield per lifetime; the yield followed the sequence: group E (1032 l) >group M (1051 l) >group L (989 l) > group A (859 l) (P<0.0001). Yield/lactation was affected by AFL during the first three lactations (P<0.05). Group E produced significantly less milk in the first lactation than ewes from groups M, L and A. AFL correlated negatively with the number of lactations in life (r= -0.26; P<0.0001) and with total milk yield (r= -209; P<0.0001). The productive performance between the ewes that reached puberty early (n=404) or late (n=2684) in life were different (P<0.0001) with the early sheep having a lower total milk yield (591 v. 1073 l, P<0.0001). In conclusion, the current study indicates that the optimal AFL for the Lacaune breed under an intensive dairy system is between 390 and 450 d. Ewes with AFL earlier than 390 d or later than 450 d are likely to have a shorter productive life and a lower lifetime milk production.

Melatonin prevents capacitation and apoptotic-like changes of ram spermatozoa and increases fertility rate

We recently demonstrated the presence of melatonin in ram seminal plasma and differences in its concentration in this fluid between the breeding and nonbreeding season. In this study, we investigate the hypothesis that in vitro treatment with melatonin affects ram sperm quality, and that this is reflected in the in vitro fertilization (IVF) results. Semen from nine rams was collected during the nonreproductive season and treated with 1 mum, 10 nm and 100 pm melatonin. Samples were incubated at 39 degrees C and 5% CO2, and motility, viability, capacitation status and phosphatidylserine (PS) translocation were assessed before and after melatonin addition, either 1 or 3 hr of incubation. Fertility rate of the melatonin-treated samples was determined by means of IVF. Although melatonin failed to affect both sperm kinematic parameters and viability, the exposure of ram spermatozoa to melatonin has a direct effect, decreasing capacitation and PS translocation at 1 mum, and increasing short-term capacitation at 100 pm, which caused an increased oocyte fertilization rate following IVF. Furthermore, cleavage rate of oocytes fertilized with 100 pm melatonin-treated spermatozoa was higher than that with 1 mum melatonin and control samples (P < 0.1). These results prove that melatonin has a direct effect on ram spermatozoa in the nonreproductive season, which can be explained, at least in part, by the melatonin capacity as a reactive oxygen species scavenger and antioxidant. These findings might help to select the optimal experimental conditions for IVF and to improve sperm preservation protocols.

Effects of melatonin implants during non-breeding season on sperm motility and reproductive parameters in Rasa Aragonesa rams

The effect of melatonin implants administered during non-breeding season in Rasa Aragonesa rams on sperm motility parameters and other reproductive traits was assessed. In a first experiment, two Rasa Aragonesa rams were implanted (with melatonin group M), remaining other two males as control group (C). Semen of each group was collected from 1 May to 23 June, twice or three times a week, and motility parameters were assessed using a computer-assisted sperm analysis system. Melatonin increased the percentage of progressive motile spermatozoa, particularly during 46-75 days after melatonin implantation (p < 0.01). In experiment 2, M and C in vitro fertilization ability had been determined by zona-pellucida binding assays, using spermatozoa from experiment 1, obtained 60-70 days after melatonin was implanted. A significantly higher number of spermatozoa attached per oocyte was observed in frozen-thawed immature ovine oocytes incubated with sperm from M animals than in those incubated with sperm from the C group (p < 0.01). Finally, a field assay (experiment 3) was performed. In this case, five Rasa Aragonesa rams were implanted with melatonin and three remained as control group. Sperm doses from those animals were used for artificial insemination of 2608 Rasa Aragonesa ewes from 39 different farms at non-breeding season. Fertility, litter size and fecundity were studied. Semen from melatonin implanted rams seemed to increase both fertility and fecundity in ewes inseminated with spermatozoa obtained 46-60 days after implantation (p < 0.1). Thus, melatonin treatment in rams during non-breeding season modifies sperm motility parameters and seems to improve the fertilization parameters obtained.