Progestogen-Based Estrus Synchronization in Sheep and Goats: Practical Use of CIDR and Vaginal Sponges

Progestogen-based synchronization remains one of the most useful approaches for controlling estrus in sheep and goats because it can be applied in both cycling and anestrous females. For the practicing veterinarian, the value of these protocols lies in their ability to temporarily control the luteal phase, coordinate follicular activity, and provide a more predictable period for breeding or artificial insemination¹. 

How Progestogen Devices Control Estrus 

The physiological principle is straightforward. Intravaginal devices containing progesterone or synthetic progestogens maintain elevated circulating progestogen concentrations, creating an artificial luteal phase. This suppresses gonadotropin secretion and prevents estrus and ovulation while the device remains in place. 

When the device is removed, circulating progesterone declines. The hypothalamic–pituitary axis can then resume activity, allowing synchronized follicular development and subsequent estrus expression¹. 

Commonly used devices include controlled internal drug release (CIDR) devices, fluorogestone acetate (FGA) sponges, and medroxyprogesterone acetate (MAP) sponges^1,2. Although they share the same basic physiological objective, they differ in duration of application, hormone-release characteristics, and residue considerations. 

Shorter Protocols and Practical Handling¹ 

Short-term programs lasting approximately five to seven days have increasingly replaced traditional longer regimens. The supplied evidence indicates that shorter exposure can be associated with improved fertility outcomes, reduced vaginal discharge, and lower overall hormone exposure. 

For field practice, this makes protocol duration an important consideration rather than simply a scheduling detail. The veterinarian must account for the timing of device placement and withdrawal in relation to the planned mating or AI program. 

Device-based synchronization also requires repeated animal handling. Therefore, the reproductive advantage needs to be considered alongside the labor and technical input required to manage the flock. These factors become particularly important in production systems where handling facilities or labor availability are limited. 

Role of eCG at Device Withdrawal 

Progestogen treatment may be combined with equine chorionic gonadotropin (eCG) at device withdrawal to support follicular maturation and improve ovulatory responses¹. This becomes particularly relevant during the non-breeding season, when endogenous gonadotropin secretion is naturally reduced. 

The choice to incorporate eCG should therefore be considered in relation to the reproductive state and season rather than viewed as an automatic component of every progestogen protocol. The supplied content also highlights international variation in eCG availability and regulatory considerations, contributing to interest in alternative approaches and reduced-dose strategies¹. 

What Can Be Expected in Well-Managed Flocks? 

Progesterone-device protocols provide relatively consistent biological control across different reproductive states. During the breeding season, reported fertility outcomes commonly exceed 60% and frequently range from 70% to 90%. Under seasonal anestrus or less favorable nutritional and management conditions, additional gonadotropin support may be required to achieve comparable pregnancy outcomes^1,3. 

Controlled comparisons of CIDR or sponge protocols combined with eCG or GnRH have reported overall fertility exceeding 60%, often falling between 70% and 85%, depending on breed, season, and adjunct treatment⁴. 

These figures should be interpreted within the context of flock management rather than as guaranteed outcomes for individual animals. 

Practical Clinical Insight 

When considering a CIDR or sponge-based program, assess: 

• Reproductive state: cycling versus anestrous females. 

• Protocol duration: short-term programs may reduce hormone exposure and vaginal discharge. 

• Need for gonadotropin support: particularly during seasonal anestrus. 

• Handling capacity: device insertion and withdrawal require organized flock management. 

• Production objective: intensive breeding, accelerated lambing, fixed-time AI, or genetic improvement may justify the additional technical input. 

Progestogen devices provide strong control over the reproductive cycle, but their success still depends on the physiological and management conditions of the females being treated. Appropriate protocol selection and disciplined flock management remain essential for translating synchronization into useful reproductive outcomes. 

References 

1. 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 

2. Knights M, Singh‐Knights D. Use of controlled internal drug releasing (CIDR) devices to control reproduction in goats: A review. Animal Science Journal. 2016 Sep;87(9):1084-9. https://www.researchgate.net/profile/Marlon-Knights/publication/269931577 

3. Texeira TA, Da Fonseca JF, de Souza-Fabjan JM, de Rezende Carvalheira L, de Moura Fernandes DA, Brandão FZ. Efficiency of different hormonal treatments for estrus synchronization in tropical Santa Inês sheep. Tropical animal health and production. 2016 Mar;48(3):545-51. https://www.academia.edu/download/88652528/2016-TEIXEIRA-Efficiency-of-different-hormonal-treatments-for-estrus.pdf 

4. Martinez-Ros P, Rios-Abellan A, Gonzalez-Bulnes A. Influence of progesterone-treatment length and eCG administration on appearance of estrous behavior, ovulatory success and fertility in sheep. Animals. 2018 Dec 26;9(1):9. https://www.mdpi.com/2076-2615/9/1/9