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Estrus Synchronization with CIDRs
by Darrel J. Kesler


  • The CIDR is approved by FDA to synchronize estrus in dairy heifers. It is an effective method that is convenient to use.
  • Alterations of the protocol to improve efficacy are being evaluated; however, only the approved protocol—administration of PGF 2a on day 6 and removal the next day—has been sufficiently tested.
  • Utilization of estrus synchronization will facilitate the management of breeding heifers via AI.
  • Approval for use in dairy cows is being sought.
  • Additional uses of the CIDR are being created: use with Ovsynch for AI or ET recipients, use with Ovsynch for treatment of cystic ovarian disease, treatment after insemination to enhance the establishment of pregnancy, and treatment for synchronization of the return estrus.


Although estrus synchronization and artificial insemination (AI) have been cited over the past several decades to have significant impact on reproductive performance of replacement heifers and increase profitability in dairy operations, utilization is limited. A national survey sponsored by the National Association of Animal Breeders (NAAB) revealed that only 55 to 63% of the dairy heifers in the U.S. were being bred by AI even though the USDA Holstein Sire Summary estimates a Net Merit Dollars advantage of $72 per lactation for a cow sired by an average first-evaluation AI sire compared with a cow sired by an average first-evaluation natural service bull. Therefore, estrus synchronization is a valuable reproductive tool for dairy producers and the near ideal methods now available can be used to help dairy producers gain the value of AI.


A new reproductive tool–the CIDR/PGF 2a estrous synchronization protocol–was approved by the U.S. FDA in 2002. The CIDR insert, an intravaginal progesterone insert, used in conjunction with PGF 2a synchronizes estrus in replacement dairy heifers. The CIDR insert was developed in New Zealand and has been used there and many other countries for several years.

The CIDR insert is “T” shaped. The wings of the insert collapse to form a rod that can be inserted into the vagina using an applicator. The CIDR is left in the vagina for seven days. An injection of PGF 2a is administered on day 6 and the insert is removed on day 7; however, many academic researchers are suggesting that the PGF 2a be administered at the same time the insert is removed. On the end of the insert opposite the wings, a tail is attached that facilitates removal at the end of the administration period. The backbone of the CIDR is a nylon spine covered by a progesterone (1.38 g) impregnated silicone skin. During the seven days in the vagina the CIDR releases a relatively constant dosage of progesterone. Upon removal of the insert, progesterone is quickly eliminated. Retention rate of the insert during the seven day period is exceptionally high: greater than 95%. Blood progesterone concentrations after insertion, during the seven days in situ, and after removal are illustrated in the following three figures.

During the seven days of CIDR treatment progesterone diffusion from the CIDR insert does not affect spontaneous luteolysis. Assuming all heifers have a 21 day estrous cycle there will be two populations of females after six days of CIDR treatment: females without corpora lutea and females with corpora lutea more than six days after ovulation. All females, therefore, have corpora lutea that are potentially responsive to an injection of PGF 2a . Although most research suggest that only about 90% of corpora lutea in heifers more than six days after ovulation regress promptly to an injection of PGF 2a, only about 60% of the females will have corpora lutea at the time of PGF 2 " treatment. Therefore, about 95% of the females treated with CIDR/PGF 2a procedure are synchronized to exhibit estrus within a few days of CIDR insert removal. More than 95% of the treated females will be synchronized to exhibit estrus if estrous behavior is monitored for five days after removal of the CIDR insert.

The studies that supported the approval of the CIDR insert in the U.S. were published (Lucy et al., 2001). These studies included 260 dairy heifers from four sites across the U.S. demonstrated that the protocol is efficacious (Table1). There are limited data available generated in the U.S. because the product was just approved by FDA.

Table 1 . Synchrony, conception rates, and pregnancy rates of dairy heifers administered the CIDR + PGF 2a procedure. a

PGF 2a
Synchronization Rate
Conception Rate
Pregnancy Rate

aModified from Lucy et al. (2001).

The following are recommendations that should be followed when using the CIDR/PGF 2a estrous synchronization protocol.

  • Individuals handling the CIDRs should wear latex or nitrile gloves to prevent exposure to progesterone on the surface of the insert and to prevent introduction of contaminants from the hands into the vagina of treated heifers.
  • The inserts were developed for a one-time use and multiple-use, which is not approved by FDA, may cause vaginal infections.


Because the CIDR/PGF 2a procedure may not be optimized, several alterations of the procedure are being evaluated. Although Ovsynch has not been reported to be satisfactory in heifers (per insemination pregnancy rates of 75% and 35% for control and Ovsynch treated heifers), when the CIDR insert was included in the protocol and AI was done at the time of the second injection of GnRH pregnancy rates were exceptional (three studies reported 68% 60%, and 65% pregnancy rates, respectively). Conversely, when estradiol was administered at the time of CIDR insertion, pregnancy rates were reduced. Although more heifers administered estradiol about 24 h after CIDR insert removal express estrus during the synchronized insemination period than non-estradiol treated heifers, fertility is similar and an additional animal handling was required to administer the estradiol. Furthermore, the only estradiol commercially available in the U.S. is estradiol cypionate (ECP). Most studies have been done with estradiol benzoate which is a far shorter acting ester than ECP. In addition, in another study it was reported that estradiol benzoate and ECP are equally effective in stimulating follicular atresia; however, recuitment of a new follicle wave may be delayed in heifers administered ECP. Administration of any estradiol to heifers synchronized with the CIDR, or any other procedure, is not recommended.


Although FDA approved the use of the CIDR for synchronization of estrus in heifers and beef cows and advancement of the first pubertal estrus and first postpartum estrus in beef cattle, it has several additional applications beyond estrus synchronization of dairy cows. The approved protocol includes the injection of PGF 2 a six days after CIDR insertion and CIDR removal the next day; however, this may not be the protocol with maximal efficacy. Other applications evaluated include:

  1. inclusion with Ovsynch for synchronization of heifers and cows,
  2. inclusion with Ovsynch for preparing ET recipient cows,
  3. inclusion with Ovsynch for treatment of cystic ovarian disease,
  4. treatment after insemination to enhance the establishment of that pregnancy, and
  5. treatment for synchronization of the return estrus of cows not conceiving to the first synchronization protocol.

When included with Ovsynch, inserted at the first GnRH injection and removed at the PGF 2a injection seven days later, it has been demonstrated to improve pregnancy rates in anestrous dairy cows (20 more pregnancies per 100) and all cows combined (15 more pregnancies per 100). It improved pregnancy rates in ET recipient cows when it was included with Ovsynch. Embryos were transferred into 94% of the cows administered Ovsynch with or without CIDR treatment. There were 10 more pregnancies per 100 cows treated with the Ovsynch protocol that included the CIDR. Overall, 64% of the ET cows, 94/100 starting the protocol received embryos, became pregnant. When used with the Ovsynch protocol 100% of the cystic cows ovulated subsequent to treatments and 44% became pregnant. Administration on day 7 post-breeding it has been shown to either improve (one study-12 more pregnancies per 100) or have no effect (two studies) on pregnancy rates to the previous breeding. Studies have demonstrated that nonpregnant cows administered the CIDR about 14 to 21 days after breeding express a shorter period of return estrus than untreated cows.


Kesler, D.J. 2002. Synchronization of Estrus in Beef and Dairy Heifers. Urbana, IL: University of Illinois.

Kesler, D.J. 2002. Synchronization of estrus in heifers. Proc. Midwest Dairy Veterinary Symposium.

Kesler, D.J. 2002. Review of estrous synchronization systems: CIDR inserts. Proc. Applied Reproductive Strategies in Beef Cattle Workshop.

Lucy, M.C., H.J. Billings, W.R. Butler, L.R. PGF 2 " Ehnis, M.J. Fields, D.J. Kesler, J.E. Kinder, R.C. Mattos, R.E. Short, W.W. Thatcher, R.P. Wettemann, J.V. Yelich, and H.D. Hafs. 2001. Efficacy of an intravaginal progesterone insert and an injection of PGF 2 " for synchronizing estrus and shortening the interval to pregnancy in postpartum beef cows, peripubertal beef heifers, and dairy heifers. J. Anim. Sci. 79:982.

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