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

Abstract

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 use of melatonin and progestagen–eCG to initiate reproductive activity in prepuberal Awassi ewe lambs

“…Our working hypothesis was that a combination of melatonin along with a progestagen-eCG protocol would be more effective in improving reproductive performance in ewe lambs of late-maturity breeds (like Awassi) than either melatonin or induced estrus alone (Laliotis et al 1997;Stellflug et al 1994). For this reason, this study was designed in an attempt to advance puberty and initiate the breeding season in Awassi ewe lambs through hormonal treatments.…”

Efeitos da nutrição na atividade cíclica reprodutiva e nas concentrações plasmáticas de melatonina em ovelhas mantidas em pastagem e submetidas ao efeito macho durante o anestro sazonal.

“…Inúmeros são os trabalhos (ARENDT et al, 1983;ENGLISH et al, 1986;WALLACE et al, 1988;GUERIN et al 1989;DUROTOYE et al, 1991;FORCADA et al, 1995) que têm demonstrado que a melatonina administrada diariamente por injeção, via oral ou através de implantes, é eficaz em induzir ou antecipar a atividade cíclica reprodutiva de ovelhas, em época de anestro sazonal, sem (REKIK et al, 1991) ou com (GÓMEZ BRUNET et al, 1995) auxílio do efeito macho. Alguns estudos demonstraram ainda que os implantes de melatonina, além de aumentar as concentrações plasmáticas de melatonina dos animais tratados em relação aos animais controles (NOWAK et al, 1990) podem promover um aumento da taxa de ovulação e conseqüente incremento da prolificidade (DUROTOYE et al, 1991: REKIK et al, 1991GÓMEZ BRUNET et al, 1995;LALIOTIS et al, 1997), principalmente em condições de baixo escore corporal 14 (ROBINSON et al, 1991;RONDON et al, 1996). Porém, outros trabalhos também evidenciam a falta de resposta em animais que tiveram uma mudança drástica de fotoperíodo antes do tratamento (ELDON, 1993), ou a diminuição de resposta e/ou diminuição da taxa de ovulação após prolongados períodos de exposição aos tratamentos de melatonina (JORDAN et al, 1990).…”