Melatonin implants for out-of-season breeding in ewes: do they advance the breeding season and improve lambing rates vs natural photoperiod? — POSSIBLE

POSSIBLE: Melatonin implants improve out-of-season reproductive performance in ewes, but the cleanest numbers come from trials in which melatonin was an add-on to a progesterone synchronisation protocol, not from melatonin alone against natural photoperiod. In DeNicolo 2008 (PMID: 18082341; New Zealand Romney composite ewes bred out of season), adding melatonin to progesterone plus equine chorionic gonadotrophin (eCG) raised conception from 47% in progesterone+eCG controls (n = 107) to 67% (n = 97) (P < 0.01) and pregnancy from 40% to 55% (P < 0.001), with more lambs born per ewe treated, while melatonin plus progesterone WITHOUT eCG largely failed (oestrus 14%, pregnancy 6%, n = 96). In Duan 2025 (PMID: 40722998), a randomised field test in 170 Hu ewes (85 per group) in seasonal anoestrus found pregnancy 68.23% vs 50.59% and lambing 63.53% vs 47.06% (lambed ewes/total ewes) for a 5-day melatonin implant before a progesterone-sponge plus eCG protocol vs the same protocol without melatonin (P < 0.05, PMC full text, Table 2); the same paper's small 40-ewe Mongolian experiment (20 per group) found pregnancy and lambing both 86.00% vs 56.25%, which did NOT reach statistical significance (P > 0.05) — the abstract presents the field-test percentages alongside the small experiment's description, and the full text governs which numbers belong to which experiment. For melatonin alone vs untreated ewes on natural photoperiod, Mura 2017 (PMID: 28823418; 3,200 Sarda ewes on 16 commercial farms, one 18 mg implant vs untreated) found a significantly higher fertility rate in treated ewes (P < 0.05, highest when treated in April and May), a shorter average time from ram introduction to lambing (P < 0.05), and more ewes lambed by days 160-190 after ram introduction (P < 0.01 to P < 0.05), but its abstract reports no fertility percentages or day counts; and Cevik 2017 (PMID: 29166263; seasonally anoestrous Kivircik and Charollais ewes) found oestrus response and pregnancy rate both significantly higher in melatonin-implanted than control ewes (both P < 0.001, no percentages in the abstract) and states implants induced oestrus approximately four months earlier than the breeding season. Design class (c) for this shelf's own comparison: randomisation is not established for melatonin alone vs natural photoperiod — neither Mura 2017 nor Cevik 2017 states randomised allocation of ewes, and no record states blinding; Duan 2025 is randomised (class (b) on its own) but its control is a synchronisation protocol, not natural photoperiod, so its class is not borrowed for the shelf question. The stamp is POSSIBLE, not LIKELY, because the two pure-comparison records report significance without absolute rates in their abstracts, the quantified benefits are for melatonin as an add-on to progesterone/eCG (and melatonin plus progesterone without eCG failed in DeNicolo), and in Mura 2017 the rams introduced to both groups had themselves received melatonin implants. Tier C is not engaged: pregnancy and lambing rates are the primary outcomes, and a pregnancy-rate primary benefit is not Tier C; no mortality or survival claim is made. One-home cross-points: Kleemann 2014 (PMID: 25132093), in which melatonin was given to RAMS (young Border Leicester rams: ewe pregnancy rate 92.6% vs 5.0% with untreated young rams) is a ram-treatment question, not an ewe-implant claim, and is not carded here; shelf #913 (progesterone sponge vs CIDR synchronisation in ewes) is a different intervention and no record is shared. Drafted Nov 10, 2026 (VetMed build, topic #907); figures from the abstracts and, for Duan 2025, the PMC full text, fetched and verified at drafting.