FDA Approves CIDR For Sheep, Makes Breeding Easier

By Jane Fyksen, Crops Editor
Wednesday, November 25, 2009 3:10 PM CST

The U.S. Food and Drug Administration (FDA) has approved the EAZI-Breed CIDR Sheep Insert (progesterone solid matrix) for inducing estrus in ewes during seasonal anestrus.

This progesterone Controlled Intravaginal Drug Release (CIDR) is a steroid hormone that allows out-of-season breeding in sheep. It can also be used to tighten up a lambing season.

Data supporting FDA’s approval of this sheep CIDR was gathered in collaboration with a USDA program supporting approval of new animal drugs for “minor species” of agricultural importance -n a category into which sheep fall and one that’s meant very few new drug approvals have been forthcoming for sheep.

“Members of the U.S. sheep industry have long cited this type of product as their top priority need,” says Meg Oeller, director of the Center for Veterinary Medicine’s Office of Minor Use and Minor Species (MUMS) Animal Drug Development. “And through efforts with our partners at (USDA) and the pharmaceutical firm, the FDA can now point to an approved drug product that is fulfilling a real need in the sheep industry. It represents the true spirit of the MUMS Act.”

Clinical researchers funded by special grants conducted the studies to support the effectiveness, target animal safety, human food safety, and environmental safety of the progesterone CIDR. The pharmaceutical company was able to use the data in conjunction with its own information to complete the new animal drug application. EAZI-Breed CIDR Sheep Insert is manufactured by Pharmacia and Upjohn, a division of Pfizer.

UW-Madison sheep specialist Dave Thomas says the sheep industry has been trying to get an estrus induction tool approved for many years, and that there’s been a lot of research and estrus induction via off-label product use. With this CIDR approved, manipulating estrus in ewes just got easier and legal for producers to use without veterinarian prescription.

However, he sees “limited use” of this new CIDR in Wisconsin’s sheep industry, although for “certain specific uses, it’s a necessity,” he points out.

Sheep are seasonal breeders, and most commercial flocks will continue to take their lead from Mother Nature and put the rams in with the ewes in the fall to lamb in the spring. However, there are various applications for which the ability to use this CIDR will make life much easier for the shepherd.

Some producers might rely on this CIDR to lamb once a year in the fall, perhaps splitting the flock to spread out lambing and marketing of lambs. It’ll also come in real handy for those on accelerated lambing programs (three to five lambings every two years). Thomas sees its use coupled with artificial insemination also, which, in itself, can be an “expensive” and not an easily accomplished venture with sheep. And, as noted, the CIDR might also be used to synchronize estrus of ewes for in-season breeding, so that lambing doesn’t stretch out as much as it otherwise might. This could be coupled with either AI or natural service. Purebred breeders who have a certain high-caliber ram they want to use in their flock may want to insert CIDRs in ewes in order to AI, or if foreign genetics is being imported (as semen).

CIDRs might also be used in the booming dairy sheep industry, in order to “spread out the capital investment of the parlor over more months of milking,” notes Thomas, however, adding again that he suspects only some of the larger dairy-sheep flocks are apt to use it. Here in Wisconsin, most of the dairy sheep enterprises are pasture-based, and not particularly interested in breeding out of season and thus having to rely on expensive harvested feeds fed in confinement. What’s more, many sheep cheeses are sold on their “natural” grass-based production.

How does a CIDR work? Progesterone is produced by the site of ovulation on the ovary and tells the ewe she’s pregnant so the ovaries won’t initiate any new eggs. When a CIDR is inserted, the ewe body says, “Aha, I’m pregnant” and she doesn’t produce any eggs. Then, when the CIDR is pulled, her body says “I’m not pregnant,” and hormones kick into gear, resulting in ovulation. CIDRs are left in five days and ewes will come into heat within 48 hours of when they’re removed, notes Thomas.

Using a CIDR won’t increase or decrease the prolificacy of a ewe (i.e. how many lambs she’ll have). Thomas notes, though, that a CIDR can be used in a breed of low natural prolificacy in combination with follicle stimulating hormone (FSH) at the time the CIDR is removed; that may increase prolificacy. “In almost all cases,” Thomas notes, there’s no need for FSH, as most breeds are prolific (multiple births) and producers have been striving for prolificacy in their flocks through culling and selection as well.

However, when used out of season, 60 to 80 percent of the ewes will respond and very likely get bred. It doesn’t anywhere near as well with ewe lambs, even ones born in the fall which the producer is hoping to breed in the spring. That’s because they need a long-day photo period (i.e. to go through a summer).

As noted, there might be interest in tightening up the lambing season in flocks relying on the usual fall matings. Naturally, shepherds can expect to see 70 percent of their ewes breed in the first cycle. Using CIDRs in those ewes might increase that to 85 to 90 percent, he surmises.

During a spring mating, the effect will be much larger, he notes. Typically 20 to 30 percent of a flock shooting for out-of-season lambing will get bred in the spring. Using a CIDR might raise the percentage of ewes getting bred in the spring (for fall lambing) to 60 to 80 percent.

Thomas shared a paper with Agri-View by Keith Inskeep, presented earlier this month at the 15th Great Lakes Dairy Sheep Symposium in Albany, N.Y. It was at this meeting that Pfizer announced approval of CIDRS for use in sheep in the U.S. Thomas says Inskeep did much of the experimental work that resulted in the approval of CIDRs for the sheep industry. Inskeep is with West Virginia University in Morgantown.

Inskeep says “the survival and re-growth of the sheep industry require that producers increase efficiency of operation with the use of improved technologies so that they are better poised to take advantage of the improved consumer demand. Many of these technologies are used routinely by producers outside the U.S. However, limited usage of previously approved reproductive management products by U.S. producers, coupled with a long-term decline in sheep numbers in the U.S., have made pharmaceutical companies reluctant to seek approval for commercial use of new products in this country.”

As mentioned, lamb production is a seasonal enterprise for most producers. “Typically, ewes are bred in the fall—when reproductive activity and ovulation rate are greatest—and lamb in the spring. As a result, there are wide monthly fluctuations in both the numbers of lambs available and in the prices received by producers,” Inskeep points out. Seasonal lambing patterns affect prices, as many producers are marketing lambs during the same time period. Further, the inconsistent supply reduces the efficiency of lamb processors and results in periods of low availability to the consumer. Likewise seasonal production of milk can affect functionality and profitability of a sheep cheese enterprise.”

Inskeep details that sheep are seasonally polyestrous animals, meaning that the ewe displays estrus (“heat”) every 16 to 18 days during a limited breeding season. The onset of the breeding season in Wisconsin is associated with decreasing day length (after summer solstice) and temperature. The peak of the breeding season, as represented by the greatest proportion of the flock showing cyclic estrous activity or by the greatest ovulation rate (and thus the greatest expected pregnancy rates and litter sizes) is in October and November.

Breed, age, and nutritional status affect the exact time of onset and duration of the breeding season. Among breeds, the Southdown and Cheviot exhibit a relatively short breeding season, while the Dorset, Rambouillet, Merino and Finn-sheep exhibit extended breeding seasons. The black-faced breeds, Hampshire and Suffolk, have breeding seasons intermediate in length. Many of the hair sheep breed types, such as the Katahdin, Barbados Blackbelly, Virgin Island White and West African Hair Sheep are considered year- round breeders.

By using CIDRs, producers, no matter the breed of sheep they raise, have a much better chance of getting ewes bred out of season. They can also synchronize ewes to reduce the work involved with AI and/or to tighten up the lambing season, which is also a workload issue.

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