The Administration of Altrenogest in Mares

Altrenogest is a progestin of the 19-nortestosterone group commonly used to suppress or synchronize estrus in horses. It is used extensively in the reproductive management of mares to control the reproductive cycle, help maintain pregnancy, and help with behavior modification. Altrenogest has been demonstrated to maintain pregnancy in oophorectomized mares and may be of benefit in mares that abort due to subtherapeutic progestin levels.

Altrenogest is a progestin of the 19-nortestosterone group commonly used to suppress or synchronize estrus in horses. It is used extensively in the reproductive management of mares to control the reproductive cycle, help maintain pregnancy, and help with behavior modification. Altrenogest has been demonstrated to maintain pregnancy in oophorectomized mares and may be of benefit in mares that abort due to subtherapeutic progestin levels.

Altrenogest is used for suppression of estrus. The mare will experience a predictable occurrence of estrus following drug withdrawal. This allows a regular cycle during the transition from winter anestrus to the physiological breeding season in mares with active ovaries. By managing the reproductive cycle, horse owners have more control over breeding procedures and the timing of the arrival of foals.¹

Suppression of estrus allows for regulation of the equine menstrual cycle and a predictable occurrence of estrus.² This facilitates the attainment of regular cyclicity during the transition from winter anestrus to the physiological breeding season. Suppression of estrus will also facilitate management of prolonged estrus conditions. Suppression of estrus may be used to facilitate scheduled breeding during the physiological breeding season.

Indications

Altrenogest is typically indicated in the following circumstances:

• Facilitation of regular cycles during the transition period from winter anestrus to the physiological breeding season. To facilitate attainment of regular cycles during the transition phase, mares should be examined to determine the degree of ovarian activity. Estrus in mares with inactive ovaries (no follicles greater than 20 mm in diameter) will be suppressed but these mares may not begin regular cycles following treatment. However, mares with active ovaries (follicles greater than 20 mm in diameter) frequently respond with regular post-treatment estrus cycles.
• Facilitating management of the mare exhibiting prolonged estrus during the transition period. Estrus will be suppressed in mares exhibiting prolonged behavioral estrus either early or late during the transition period. Again, the post-treatment response depends on the level of ovarian activity.
• Permit scheduled breeding of mares during the physiological breeding season. To permit scheduled breeding, mares which are regularly cycling or which have active ovarian function should be given altrenogest solution daily for 15 consecutive days beginning 20 days before the date of the planned estrus. Ovulation will occur 5 to 7 days following the onset of estrus as expected for non-treated mares. Breeding should follow usual procedures for mares in estrus. Mares may be regulated and scheduled either individually or in groups.³

Dosages and Routes of Administration

Since it has been determined that exposure to altrenogest may cause reproductive system disorders and other adverse effects in humans who become exposed to the drug, precautions must be taken when handling or administering altrenogest.

It is essential that people administering altrenogest products take appropriate precautions to prevent exposing themselves or other people to the medication. Product labeling directs the use of impermeable, non-porous protective gloves when handling these drug products. These gloves should be nitrile, butyl, vinyl, polyethylene or neoprene.

People who should not handle altrenogest products include:

• Women who are or suspect they are pregnant.
• Anyone with thrombophlebitis or thromboembolic disorders or with a history of these events.
• Anyone with cerebral-vascular or coronary-artery disease.
• Women with known or suspected carcinoma of the breast.
• People with known or suspected estrogen-dependent neoplasia.
• Women with undiagnosed [unexplained] vaginal bleeding.
• People with benign or malignant tumors which developed during the use of oral contraceptives or other estrogen-containing products.
• Anyone with liver dysfunction or disease.³

Altrenogest is commonly available in oral and injectable forms. While observing the precautions outlined above, altrenogest in either form may be administered per your veterinarian's instruction.

Side Effects

No recognized side effects are reported in equines when Altrenogest is used according to label directions.

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