Improvest® Vaccine

Manufacturer– Zoetis

Product information –According to information from Zoetis, Improvest is an
FDA–approved vaccine that serves as an alternative to physical castration for eliminating boar taint in commercial swine. Improvest is a gonadotropin releasing factor (GnRF, equivalent to GnRH) analog-diptheria toxoid conjugate. The Improvest vaccine effects contraception by inducing production of GnRH antibodies, which in turn block native GnRH from binding to pituitary receptors. As a result, production of pituitary (FSH and LH) and gonadal (estradiol and progesterone in females and testosterone in males) hormones is prevented. The observed effects should be similar to those following ovariectomy or castration. Improvest is manufactured specifically for treatment of domestic boars, but may be effective in a wide range of other taxa. It may be especially useful in reproductive or behavioral management of male artiodactyls, for which there are no alternative contraceptive or behavioral management options.

Dose – According to Zoetis instructions, two injections of 400µg should be given 1 month apart. From the limited data available at this time, subsequent boosters are needed at minimum every 4-6 months.

Latency to effectiveness - As with implants and injections, separation or alternative contraception should be used in females for 1-2 weeks after the second injection (first booster). Males may remain fertile for 2 or more months after the second injection, until residual sperm either degenerate or are passed (as following vasectomy).

Estrous cycles during contraceptive treatment – Unlike GnRH agonists (e.g., Suprelorin®), Improvest does not cause an initial stimulation, or flare, of the reproductive system. Estrous cycles should cease to occur after the second injection is administered.

Duration of efficacy and reversibility – In swine, Improvest becomes effective after initial inoculations, typically given at a one-month interval. The data on duration of efficacy and reversibility for wildlife species are very limited.

Use during pregnancy – Since no data are available on the safety of Improvest in pregnant animals, it should not be used during pregnancy.

Use during lactation – No data are available on the safety of Improvest in lactating females.

Use in pre-pubertals or juveniles – Because Improvest suppresses gonadal steroids, its use may delay epiphyseal closure of the long bones, resulting in taller individuals, similar to the effects of pre-pubertal spaying and neutering in domestic dogs and cats. There are no data available on impact on future fertility when Improvest is used in pre-pubertal animals. Thus, caution should be used when considering treatment of pre-pubertal animals.

Consideration for seasonal breeders – For females, both the initial injection and one-month booster must be completed prior to the anticipated breeding season. For males, both injections must be completed at least 2 months before the anticipated breeding season, since sperm are typically produced in advance of first ovulation.

Precautions – In general, the effects on body weight should be similar to those from ovariectomy or castration. In males, muscle loss may result in overall weight loss if not replaced by fat. In sexually dimorphic species, males may become the size (weight) of females and males may lose secondary sex characteristics (e.g., lions may lose their mane). According to Zoetis, Improvest may cause mild transient local injection site inflammation. All adverse events should be reported to the AZA Reproductive Management Survey and to Zoetis if requested.

Safety – Safety information for this product is available here. Accidental self injection could affect reproductive physiology of both men and women and may adversely affect pregnancy. If self injection is suspected, even in the case of needle stick during the use of the product (loaded syringe with product), contact the Poison Control Center (Toll free: 1-866-531-8896) and refer to the product insert for further information. Improvest mode of action is immunological like a vaccine. The first exposure either by self injection or needle stick may prime the immune system. The risk of a physiological effect is greater after a second or subsequent injection than after a first. After self injection or needle stick injury do not administer the product, and/or any other product with similar action, in the future.

Reporting requirements – All institutions using Improvest are asked to complete a Contraception Survey for the AZA Reproductive Management Center. It is essential that accurate records of doses and intervals be maintained and results reported to the Reproductive Management Center's Contraception Database to contribute to dosage development.

Ordering information – In order to obtain the product, you must call Zoetis at 1-800-366-5288, choose the LIVESTOCK prompt, and ask for Improvest availability for zoos. Currently, Zoetis handles each request for Improvest on a case by case basis.  

For questions about the Contraception Survey, contact:
Ashley Franklin, Program Analyst
AZA Reproductive Management Center
Saint Louis Zoo
1 Government Drive
St. Louis, MO 63110
314-646-4732; fax: 314-646-5534