Managing Seasonal Anestrus in Sheep and Goats: Synchronization and Reproductive Strategies

Seasonal anestrus can make planned breeding difficult in sheep and goats, particularly when production systems require mating outside the natural breeding season. During this period, ovarian activity declines and the endocrine system becomes less responsive to synchronization stimuli. For the practicing veterinarian, the challenge is therefore not simply to induce estrus, but to select an approach that addresses the animal’s seasonal reproductive status while fitting the flock’s management and production objectives^1,2. 

Why Synchronization Becomes More Challenging During Anestrus 

Sheep and goats are seasonal breeders, with reproductive activity influenced by photoperiod and melatonin secretion. During shorter-day conditions, melatonin provides photoperiodic information to the hypothalamic–pituitary–gonadal axis. During the non-breeding season, reduced ovarian activity can limit the response to synchronization treatments^2,3. 

This is why protocols that work effectively in cycling females may not provide the same response during anestrus. Nutritional status, body condition score, breed, health and stress can further influence hormonal responsiveness and fertility outcomes⁴. 

Progestogen and Gonadotropin Support 

Progestogen-based protocols are commonly used to establish temporary luteal-phase control, with gonadotropin supplementation frequently incorporated during anestrus. Equine chorionic gonadotropin (eCG) can be administered at progestogen-device withdrawal to promote follicular maturation and improve ovulatory responses when endogenous gonadotropin activity is reduced². 

Reported comparisons of CIDR or sponge protocols combined with eCG or GnRH indicate fertility outcomes exceeding 60%, often ranging from 70% to 85%, although results vary according to breed, season and adjunct treatment. eCG-supported programs may promote higher ovulation rates and can increase litter size, while GnRH-based sequences may provide greater temporal precision for ovulation in some management settings². 

The choice should therefore reflect the reproductive objective. Maximizing ovulatory response and prolificacy may lead to a different protocol preference than achieving predictable ovulation for fixed-time artificial insemination. 

Melatonin as a Seasonal Management Tool 

Melatonin provides another approach because it acts as a reproductive signal associated with shorter day length. Slow-release melatonin implants administered 30–60 days before mating can mimic short-day signals and may advance the breeding season or help restore cyclicity during seasonal anestrus^2,5. 

The supplied data indicate that ovarian activity can be induced in 70–90% of treated females, with more synchronized estrus than in untreated controls. Melatonin-supported programs are generally used alongside progestogen protocols or the ram effect rather than as an isolated synchronization strategy. Reported conception rates range from 55% to 75%, depending on species, breed , and management conditions². 

Its limitations are equally important in clinical planning. Response can vary between animals, onset is delayed, synchronization is less precise than with progestogen–gonadotropin protocols, and implants add cost. Advance planning is therefore necessary². 

Combining Biological and Management Signals 

The male effect can provide an additional stimulus during anestrus. Introduction of a sexually active male can increase GnRH and LH activity and trigger ovulation, although the initial ovulation may be silent². 

Nutritional management can complement these approaches. Flushing, involving a 10–30% increase in energy intake for 2–4 weeks before breeding, primarily improves follicular development and ovulation rather than directly synchronizing estrus^2,6. When combined with the ram effect, it has been associated with improved estrus expression and conception compared with the ram effect alone^2,7. 

Practical Clinical Insight 

When managing seasonal anestrus, assess reproductive status, body condition, nutrition, season, production objective, and available handling capacity before selecting a protocol. Hormonal approaches may provide greater timing precision, whereas melatonin, the ram effect, and nutritional management can provide complementary or lower-intervention options. The most appropriate strategy is one that matches the degree of reproductive control required with the physiological and management conditions of the flock. 

References 

1. Bartlewski PM, Baby TE, Giffin JL. Reproductive cycles in sheep. Animal reproduction science. 2011 Apr 1;124(3-4):259-68. https://www.academia.edu/download/48421160/Reproductive_cycles_in_sheep20160829-29682-1fhrwbs.pdf 

2. Berean D, Bogdan LM, Ciupe S, Cimpean R. Hormonal and Non-Hormonal Estrus Synchronization in Sheep and Goats: Physiological Basis, Efficacy, and Practical Applications. Applied Biosciences. 2026 May 1;5(2):35. https://www.mdpi.com/2813-0464/5/2/35 

3. Duan Z, Liu M, Li J, Liu K, Qi Q, Yu Z, Samoo HA, Wang C, Hou J. Melatonin implantation improves the reproductive performance of estrus-synchronized ewes during seasonal anestrus and enhances the antioxidant and steroidogenic capacities of granulosa and luteal cells. Antioxidants. 2025 Jul 21;14(7):895. https://www.mdpi.com/2076-3921/14/7/895 

4. Araújo AR, Rodriguez NM, Rogério MC, Borges I, Saliba EO, Santos SA, Pompeu RC, Fernandes FE, Monteiro JP, Muir JP. Nutritional evaluation and productivity of supplemented sheep grazing in semiarid rangeland of northeastern Brazil. Tropical Animal Health and Production. 2019 May 1;51(4):957-66. https://www.researchgate.net/profile/Marcos-Rogerio/publication/329730299 

5. Duan Z, Liu M, Li J, Liu K, Qi Q, Yu Z, Samoo HA, Wang C, Hou J. Melatonin implantation improves the reproductive performance of estrus-synchronized ewes during seasonal anestrus and enhances the antioxidant and steroidogenic capacities of granulosa and luteal cells. Antioxidants. 2025 Jul 21;14(7):895. https://www.mdpi.com/2076-3921/14/7/895 

6. Tesfaye A, Asmare B, Abiso T, Wamatu J. Effect of nutritional flushing using long-term energy and protein supplementation on growth performance and reproductive parameters of Doyogena ewes in Ethiopia. Veterinary Sciences. 2023 May 23;10(6):368. https://www.mdpi.com/2306-7381/10/6/368 

7. Makela B, Recktenwald E, Alves FC, Ehrhardt R, Veiga-Lopez A. Effect of pre-conceptional nutrition and season on fetal growth during early pregnancy in sheep. Theriogenology. 2022 Sep 15;190:22-31. https://www.sciencedirect.com/science/article/am/pii/S0093691X2200276X