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

Abstract

This experiment was conducted to evaluate the effect of administering hormonal treatments (melatonin and progestagen/equine chronic gonadotropin (eCG)) on advancing puberty in Awassi ewe lambs. Fifty-one 6-month-old ewe lambs of similar body weights (around 28 kg) were randomly assigned into four treatment groups; control (CON; n = 14), melatonin (MEL; n = 13), melatonin plus progestagen-eCG (MELPP; n = 11), and progestagen-eCG (PP; n = 13). Ewe lambs in the PP and MELPP groups were fitted with intravaginal progestagen sponges containing 60 mg medroxyprogesterone acetate for 14 days; 400 IU eCG were administered to each of these ewe lambs on the day of sponge removal. Ewe lambs in the MEL and MELPP groups received subcutaneous melatonin implants (Regulin®, 18 mg melatonin) 36 days before sponge insertion. Hormonal treatment had no effect on ewe lamb body weight change. Estrous behavior was greater (p < 0.001) in the PP and MELPP groups than in the CON and MEL ewe lambs. The duration from ram introduction to onset of estrus was shorter (p < 0.05) in the CON, PP, and MELPP than in the MEL ewe lambs. The number of ewe lambs showing luteal activity was greater (p < 0.001) in the MELPP and PP than in the CON and MEL groups. Lambing rate from mating during the first cycle following ram introduction differed significantly (p < 0.01) among treatments being greater in the MELPP and PP than in the CON and MEL groups. Based on these results, it can be concluded that progestagen-eCG appears to be more effective than melatonin in inducing reproductive activity. However, the majority of ewe lambs in the current study either failed to cycle or stopped cycling following the induced estrus. Such failure in advancing puberty may be related to body weight of ewe lambs at the time of mating.

Induction of ovulation using repeated doses of sulpiride, a dopamine antagonist, in ewe lambs

“…Martinez et al (2015) used a combined stimulation method that resulted in 95% ovulation in the ewe lambs. In a study comparing combined treatment with melatonin treatment alone, ovulation was not observed in ewe lambs treated with melatonin alone but was observed in >90% of the animals treated with melatonin + progesterone and melatonin + progesterone + PMSG (Sawalha et al, 2011). Similar stimulation studies discussed above show that repeated sulpiride administration can produce above‐average stimulation in pre‐pubertal ewe lambs.…”

90 Establishment and characterization of Day 30 equine chorionic girdle and allantochorion cell lines

“…within 6 days (Bartlett et al, 2009). In ruminants, eCG treatment has been less frequently exploited to stimulate early puberty, however, multiple studies showed that it works successfully in sheep (Sawalha et al, 2011). In dairy cattle, a major reproductive issue is the duration of the postpartum anestrus because of the economic consequences on production.…”

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

“…Gonadotropic supplementation did not enhance reproductive performance of the progesterone-treated females, which indicated that the need for gonadotropin stimulation might diminish with advancement into the breeding season. In contrast, gonadotropic stimulation following progestogen treatment advanced the breeding and lambing season of spring-born ewe lambs exposed to rams during the breeding season at 7 months of age (Stellflug et al, 2001;Sawalha et al, 2011). However, these studies did not include a progestogen-only treatment group which precluded an assessment of the requirement for gonadotropic stimulation beyond the progesterone pre-treatment.…”

“…Stimulation with eCG after progestogen priming also induced fertile estrus and advanced ages at first conception and lambing in spring-born lambs (Stellflug et al, 2001;Sawalha et al, 2011). Those data led to the suggestion that gonadotropic support might improve reproductive performance of nulliparous ewes bred during the breeding season.…”