Melatonin advances and condenses the onset of seasonal breeding in Greek dairy ewes

The combination of melatonin implants and prostaglandin F2α improves lamb production in a late-autumn mating season

To determine the effect of the combination of melatonin implants and prostaglandin (PG) F2α on reproductive performance in the late breeding season (Dec at the northern hemisphere), 500 Lacaune ewes were divided into four groups. On day 0 (7 Nov), 150 ewes were treated with a melatonin (M) implant. From that group, 64 ewes (M + 1PGF group) were injected with 10-mg prostaglandin (PG) F2α 34 d after melatonin implantation (11 Dec). The remaining 86 ewes (M group) were treated with melatonin, only. Another group of 75 ewes (2PGF group) was treated with double injection of PGF2α (9 days between the first and second application) (2 and 11 Dec), and 75 non-treated ewes (C group) were the control group. The remaining 200 ewes of the flock were not considered in the study. Rams (n = 23) were introduced on 11 Dec. The percentage of prolificacy, lambing and fecundity rates were calculated. Lambing rate did not differ among groups (M: 79%; M + 1PGF: 78%; 2PGF: 69%; C: 71%). The M + 1PGF group had a higher % of prolificacy than the 2PGF group (P < 0.10) and the C group (P = 0.06) (M: 1.65 ± 0.07; M + 1PGF: 1.74 ± 0.09; 2PGF: 1.54 ± 0.08; C: 1.54 ± 0.07 lambs/lambing) (P < 0.05), and a higher fecundity than the 2PGF group (P < 0.05) and the C group (P < 0.10) (M: 1.30 ± 0.09; M + 1PGF: 1.36 ± 0.11; 2PGF: 1.07 ± 0.10; C: 1.08 ± 0.09 lambs/ewe). Ewes implanted with melatonin had significantly higher prolificacy (1.69 ± 0.06 lambs/lambing) (P < 0.05) and fecundity (1.33 ± 0.07 lambs/ewe) (P = 0.01) than did ewes that did not receive melatonin (1.54 ± 0.04 and 1.08 ± 0.04, resp.). In conclusion, melatonin implants increased the number of lambs born per ewe in a late-autumn mating season, and the effect was greatest if it was given in combination with PGF2α administration at ram introduction.

The effect of melatonin treatment in combination with progestagen pessaries on reproductive performance of ewes during the anoestrous period

The objective of this study was to compare the effects of melatonin implants combined with intravaginal, progestagen-impregnated pessaries with the conventional treatment of progestagen pessaries followed by pregnant mare serum gonadatrophin (PMSG) on the reproductive performance of ewes during the anoestrous period.

A commercial flock of 179 seasonally anoestrous Chios crossbred ewes was used. The ewes within the flock were randomly allocated to one of two groups. Ewes of group MP (melatonin + pessaries) received melatonin implants on 20 March (50 days before the target breeding date of 10 May) and were treated with intravaginal progestagen pessaries 35 days later (25 April). Ewes of group PP (pessaries + PMSG) were also treated with pessaries on 25 April. After 14 days the pessaries were removed from both groups and 500 i.u. PMSG was injected (i.m.) into ewes of group PP only. Fertile rams were introduced into both groups 24 h after sponge removal. Pregnancy rate and litter size were determined by ultrasound scanning 80 days after ram introduction.

Pregnancy rate at first oestrus was significantly higher in group MP than in group PP (57 v. 40%, P < 0·05). The overall conception rate during two oestrous cycles was significantly higher in group MP than in group PP (78 v. 59%, P < 0·02). The groups did not differ significantly in the mean number of foetuses per pregnant ewe that conceived during the first or second oestrus after pessary removal (1·78 and 1·87, respectively). The total number of foetuses per treated ewe was higher in group MP than in group PP (1·39 v. 1·10) as a consequence of the difference in pregnancy rate.

The effect of melatonin on seasonal reproduction of indigenous and crossbred dairy goats in Greece

The effects of melatonin implants, administered during anoestrus, on the time of onset of oestrus, conception rate and litter size in indigenous (Capra prisca) and crossbred dairy goats were studied on commercial farms in a hill region of northern Greece. In the 1st year, 192 indigenous and 86 crossbred does on one farm (farm 1) were each separated into treated (T) and control (C) groups. The T groups from each breed type were given implants of melatonin on 17 April and 6 May, respectively. Bucks were re-introduced to both T and C groups 5 weeks after implantation. Mean mating dates for indigenous goats were 6 July (s.e. 0·15) (T) v. 13 July (s.e. 0·24) (C). Corresponding dates for crossbreds were 31 July (s.e. 0·61) (T) v. 14 August (s.e. 0·87) (C). Treatment did not significantly affect conception rate. Mean kidding dates (from first service) were 6 December (s.e. 0·18) (T) v. 14 December (s.e. 0·28) (C) for indigenous and 31 December (s.e. 0·64) (T) v. 13 January (s.e. 0·82) (C) for crossbred goats. Litter size was higher in both T groups but the difference was not significant. In the 2nd year the indigenous flock on farm 1 was supplemented by two similar neighbouring farms. Farm 1 had both treated does and control does; farm 2 were all treated and farm 3 were untreated control does. In this year all bucks used on treated does were also implanted. All implants were given on 21 April. Mean mating dates were 21 June (s.e. 0·23) (1/T) v. 9 July (s.e. 0·36) (1/C), and 28 June (s.e. 0·09) (2/T) v. 19 July (s.e. 0·15) (3/C). Conception rate was high in all groups. Corresponding mean kidding dates were 22 November (1/T) v. 11 December (1/C) and 29 November (2/T) v. 22 December (3/C). Litter size was higher (F > 0·05) in T than in C groups.

Controlling reproduction in sheep

Intravaginal progestagen pessaries + pregnant mare's serum gonadotrophin (PMSG) for controlling the oestrous cycle and for inducing out-of-season breeding have been commercially available for many years. However, extremely good mating management is required if acceptable results are to be achieved. More recently the role of the pineal hormone, melatonin, in the regulation of seasonal breeding has been recognized, and this has led to the development of slow-release formulations for use under farm conditions. Early indications are that such preparations can advance the breeding season by about 4 to 6 weeks, with lambing percentages in early (January) lambing flocks comparable with those of traditional (March) lambing flocks.

Recent developments in the use of laparoscopy as an aid to intrauterine insemination and multiple ovulation and embryo transfer (MOET) should play a major role in breed improvement. Intrauterine insemination can markedly improve conception rates following the use of frozen semen compared with the conventional cervical technique, as well as eliminating the incidence of fertilization failure in embryo transfer donors. In addition, laparoscopic collection and transfer of embryos permit repeated collections from the same donor ewes and are much more acceptable than surgical techniques from the welfare point of view.

Independent changes of thyroid hormones in blood plasma and cerebrospinal fluid after melatonin treatment in ewes

The authors measured the effects of exogenous melatonin treatment on the concentrations of total (T) and free (f) fractions of thyroxine (T4) and triiodothyronine (T3) in cerebrospinal fluid (CSF) and blood plasma as well as the expression of their binding/transporter protein, transthyretin (TTR), in the choroid plexus of ewes from May to August. Melatonin implantation in May and July mainly prevented the decrease in plasma for fT3 and TT3 exhibited in untreated group, and induced a limited decrease in TT4 in June. By contrast, melatonin implantation prevented the decrease in CSF fT3 observed in the untreated group. No effect of melatonin was found on the expression of TTR mRNA in the choroid plexus There were a correlations between blood fT4 and CSF TT4 concentrations in both control and melatonin treated group (r(2)-0.4; P < 0.01 vs. r(2)-0.14; P < 0.05), as well as between blood fT3 and CSF TT3 concentrations but only in the melatonin-treated group (r(2)-0.26; P < 0.02). We conclude that T3, the active form of the hormone within the brain, is regulated by melatonin independently of the peripheral changes within the blood. The lack of correlation between plasma fT3 and CSF TT3 in the control group suggests that an increase in local T3 conversion could contribute as an additional source of T3 in the CSF during the period of increasing day length. These data seem to confirm a local nature for recently discovered connections between the pineal melatonin signal and thyroid-dependent seasonal biology in mammals.

Testicular function and semen characteristics of Awassi rams treated with melatonin out of the breeding season

The objective of this study was to evaluate the effect of long-term melatonin treatment applied during the non-breeding season on semen characteristics, endocrine function of testicles and baseline level of insulin-like growth factor-I (IGF-I) in Awassi rams kept in the temperate continental zone of Europe and used as semen donors in an artificial insemination (AI) programme. On 23 February (day 0), slow-release melatonin implants were inserted subcutaneously into rams (n = 8). Control animals (n = 8) received no treatment. In both groups, basic semen parameters (concentration, total motility, fast and slow forward motility, morphology), GnRH-induced testosterone response and basal IGF-I concentration were evaluated on days 0, 47 and 71. No differences were found in concentration of spermatozoa, total motility, and numbers of spermatozoa with fast and slow progressive motility and normal/abnormal morphology between the melatonin-treated and the control group. However, in melatonin-treated animals, basal and GnRH-induced testosterone levels were slightly elevated on day 47 and became significantly higher on day 71 (P < 0.05) as compared to controls. There was no difference in plasma IGF-I levels between the groups. In conclusion, slow-release melatonin applied during the non-breeding season improves testicular testosterone production but does not influence the semen characteristics and the IGF-I level of semen donor Awassi rams used in an AI programme and kept in the temperate continental zone of Europe.

Effect of exogenous melatonin on in vivo and in vitro prostaglandin secretion in Rasa Aragonesa ewes

The effect of exogenous melatonin on prostaglandin secretion was measured on Rasa Aragonesa ewes. Fourteen ewes received an 18 mg melatonin implant (M+) on 10 April and were compared with 13 control animals (without implants M-). Twenty days later, intravaginal pessaries were inserted in all animals to induce a synchronized oestrus (day 0). On day 14, ewes were injected, i.v., with 0.5 IU oxytocin. Plasma 15-ketodihydro-PGF(2alpha) (PGFM) concentrations were measured to assess uterine secretory responsiveness to oxytocin. After euthanasia, pieces of endometrium were collected to determine progesterone content and PGE(2) and PGF(2alpha) secretion in vitro, in the presence or absence of either 20 microg/ml recombinant ovine interferon-tau (roIFNt) or 1 nmol/l oxytocin in the medium. Endometrial progesterone content was similar in the two treatments (M+: 50.25+/-17.34 ng/mg tissue, M-: 43.08+/-11.21 ng/mg tissue). M+ ewes that responded to oxytocin had significantly higher plasma PGFM concentrations between 10 and 80 min after oxytocin administration, a higher mean PGFM peak (P<0.001), higher plasma PGFM levels after the challenge (P<0.05) and higher plasma progesterone concentrations (P<0.01) than control ewes. In the in vitro experiment, M+ and M- control samples secreted similar amounts of PGE(2). The presence of roIFNtau and oxytocin only stimulated PGE(2) production (P<0.05) in M- tissues. Control M+ tissues secreted higher amounts of PGF(2alpha) (P=0.07) and PGF(2alpha) secretion was significantly (P<0.01) stimulated by roIFNtau. Oxytocin produced this effect only in M- samples (P<0.01). In conclusion, although previous studies have demonstrated a positive effect of melatonin on lamb production, PGF(2alpha) secretion is higher in vitro and the PGE(2):PGF(2alpha) ratio is unfavourable in response to IFNtau, which could affect embryo survival. Whether or not these mechanisms are similar in pregnant ewes remains to be elucidated.

Effect of exogenous melatonin and plane of nutrition after weaning on estrous activity, endocrine status and ovulation rate in Salz ewes lambing in the seasonal anestrus

Forty-nine Spanish Salz ewes lambing in the second fortnight of March (20 March +/- 1.5 d) were used to determine the effects of exogenous melatonin and postweaning nutrition on endocrine status, date of first estrus and ovulation rate. Experimental design was a factorial defined by 2 postweaning planes of nutrition, 1.80 (high) and 1.35 (low) times the maintenance requirements, and treatment with a single 18-mg subcutaneous implant of melatonin (M) 32 d after lambing or no treatment control (C). Mean weaning to first estrus interval was shorter in treated than in control ewes (50.8 +/- 4.2 vs 87.6 +/- 6.3 d; P < 0.01). Considering both the treated and control animals together, the ratio between mean night and daytime plasma melatonin levels was significantly correlated with the implant insertion-first estrus interval on Day 5 (0.67; P < 0.01) and Day 35 (0.63; P < 0.05) after implantation. Melatonin implants induced a significant increase of mean LH concentrations at Days 14 and 33 after implantation (P < 0.01) without any significant influence of plane of nutrition. Ovulation rate was higher for treated than control ewes in the second estrus (P < 0.05). An interaction between plane of nutrition and exogenous melatonin on ovulation rate at the second cycle after weaning was detected (P < 0.01), being close to the significance in the first, fourth and fifth cycles (P < 0.1). These results suggest that exogenous melatonin in April may be an effective way of advancing the breeding season and enhancing ovulation rate associated with a low rather than a high plane of nutrition.