CIDRs (Controlled Internal Drug Release) are an intravaginal progesterone insert used in the beef cattle, dairy cattle, goat and sheep industries. CIDRs have also been used in gazelles bred in captivity (6).  The progesterone is released at a controlled rate into the bloodstream after insertion. In all species, CIDRs are used for the synchronization of estrus. This can be highly beneficial in large herds because with the synchronization of estrus, groups of cows and heifers can be bred at the same time in a narrow window.   In beef cattle specifically, CIDRs advance the first estrus in anestrus postpartum beef cows and in prepubital beef heifers (4, 7). 



How a CIDR works

Breeding Protocols

What is a CIDR Made of?

Molecular Action


Species Dosages

Product Information








CIDRs are coated with progesterone.  Progesterone is a naturally produced steroid hormone by the corpus luteum of mammalian ovaries. In vivo, progestrone functions to maintain pregnancy. Progesterone provides a potent suppression of estrus, making it important for estrus synchronization in herds of animals. When the CIDR is removed at the end of a treatment period, a rapid drop in concentration of systemic progesterone occurs in each animal. Thus promoting a synchronized estrus effect within the herd, and allowing for artificial insemination of the herd to take place (3, 5, 8).


Lactating Dairy Cows
"Fast Back" Breeding Program using a CIDR insert (5). This breeding protocol is for lactating dairy animals that failed to concieve after one round of artificial inseminiation, and is not used in combination with prostaglandins. Prostaglandins would terminate the pregnancy if one had occured (8). (This protocol is not extensively used because of its inherent impracticality.)

Breeding protocol for heifers utilizing a CIDR insert and prostaglandins (5). Prostaglandins regress a current corpus luteum (if one is present) to ensure that the CIDR insert is the only source of progesterone, so that when the insert is removed all animals return to estrus regardless of the stage of the ovary at the start of the protocol (8).

Current research has shown that follicular wave emergence may be more synchronous following treatment with estradiol in combination with progesterone, rather than relying solely on the progesterone from a CIDR insert to induce dominant follicle regression in cattle (2).

Recent studies have also looked at the use of GnRH with a CIDR protocol, however, it was found that this experimental design did not result in higher pregnancy rates after artificial insemination (4).

A study done in Argentina, looked at the effectiveness of using CIDRs in addition to an ovsync protocol. The investigators found that CIDR inserts did not increase pregnancy rates, but found that they decreased the amount of pregnancy loss (1).

Other research is looking at expanding the use of CIDRs to non-domestic species, such as the brown brocket deer and mohor gazelle (6, 9).


Calendar of CIDR Usage

with and without Lutalyse






The CIDR is designed as a T shaped nylon spine molded with a silicone rubber skin, which contains progesterone. The wings of the CIDR insert have the ability to be folded together in order to insert intravaginally. Once inserted, the wings return to their original T shape position and apply pressure to the vaginal walls to hold the insert in place. The CIDR insert is removed following the treatment period by pulling the plastic tail that protrudes from the vulva (5).

Current research is looking at modifying a CIDR to reduce the initial and residual progesterone load, while maintaining intended preformance (7).


Progesterone is released from the skin of the insert, causing the animal’s blood progesterone concentrations to increase rapidly. Maximum concentrations are reached within an hour after insertion (2). Progesterone acts according to the same mechanism as a typical steroid hormone. Progesterone diffuses through the cell membrane and the nuclear membrane, binding to the progesterone receptor in the nucleus, thus causing a change in cell physiology (8).


Administration of a CIDR is intravaginal. For best results, wash the applicator with disinfectant between uses, and clean the area of the vulva thoroughly. Put the body of the insert into the applicator, with the tail in the slot. Apply lubricant to the tip, and position the insert with the tail on the underside of the applicator and curling down. Open the labia and slide the applicator in at a slight upward angle, then depress the plunger and withdraw the applicator slowly. (It is possible to cut the excess tail so other cows are less likely to pull it out.) To remove, pull gently on the tail and dispose of properly (5).



Manufacturer: Eazi-breed and CIDR are registered trademarks of InterAg, Hamilition, New Zealand, and are distributed by Pfizer.  (From

Packaging: CIDRs come in a plastic pouch. There are 10 inserts in each pouch. The plastic applicator is packaged separately (5)


A package of 10 Cattle CIDR inserts: $133.25 USD (5)
The Long Applicator for Eazi-Breed CIDR Cattle Inserts: $15.75 USD (5)

A package of 100 Sheep CIDR inserts: $404.76 USD (3)
The Long Applicator for Eazi-Breed CIDR Sheep Inserts: $25.49 USD (3)


Taken from product insert:

Human Warning: Avoid contact with skin by wearing latex gloves when handling the inserts. Keep this and all medications out of the reach of children.

Environmental Warning: Store removed EAZI-BREED CIDR Cattle Inserts in a plastic bag or other sealable container until they can be properly disposed in accordance with applicable local, state and Federal regulations.

Residue Warning: Neither a pre-slaughter withdrawal interval nor a milk discard time is required when this product is used according to label directions.

Do Not Use:






1. Bartolome, J. A., J. J. J. van Leeuwen, M. Thieme, O. G. Safilho, P. Melendez, L. F. Archbald, and W. W. Thatcher. 2009 ''Synchronization and resynchronization of inseminations in lactating dairy cows with the CIDR insert and the Ovsynch protocol.'' Theriogenology 72:869-878.

2. Colazo, M.G., Kastelic, J.P., Whittaker, P.R., Gavaga, Q.A.''Fertility in beef cattle given a new or previously used CIDR insert and estradiol, with or without progesterone.'' Animal Reproduction Science. 81 (2004) 25-34

3. General Veterinary. General Veterinary Pty. Ltd., 1999-2009. Web. <>.

4. Leitman, N. R., Busch, D. C., Wilson, D. J., Mallory, D. A., Ellersieck, M. R., Smith, M. F., Patterson, D. J. ''Comparison of controlled internal drug release insert-based protocols to synchronize estrus in prepubertal and estrous-cycling beef heifers''. J. Anim Sci. 2009 87: 3976-3982

5. Pfizer Animal Health. Pfizer, Inc., 2008. Web. <>.

6. Pickard, A.R., T. Abáigar, D. I. Green, W. V. Holt and M. Cano. ''Hormonal characterization of the reproductive cycle and pregnancy in the female Mohor gazelle (Gazella dama mhorr). Reproduction. (2001) 122, 571-580.

7. Rathbone, M.J., Bunt, C.R., Ogle, C.R. ''Reengineering of a commercially availiable bovine intravaginal insert (CIDR insert) containing progesterone''. Journal of Controlled Release. 85 (2002) 105-115

8. Senger, P.L. Pathways to Pregnancy and Parturition. 2nd ed. Current Conceptions, Inc., 2005.

9. Zanetti, E. d. S., B. F. Polegato, and J. M. B. Duarte. 2010. ''Comparison of two methods of synchronization of estrus in brown brocket deer (Mazama gouazoubira).'' Anim. Reprod. Sci. 117:266-274.