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Altresyn (Canada)

This page contains information on Altresyn for veterinary use.
The information provided typically includes the following:
  • Altresyn Indications
  • Warnings and cautions for Altresyn
  • Direction and dosage information for Altresyn


This treatment applies to the following species:
Company: Ceva Animal Health

(altrenogest solution 2.2 mg/mL)

DIN 02454882


Oral Progestin


Active Ingredients

altrenogest 2.2 mg/mL

Altresyn® contains the active synthetic progestin, altrenogest.

The chemical name is 17-alpha-allyl-17 beta-hydroxyestra-4,9,11-trien-3-one.

The chemical structure is:

Each mL of Altresyn® contains 2.2 mg of altrenogest in an oral solution.


Altresyn® produces a progestational effect in mares and gilts.

Altresyn Indications

Horses: Altresyn® is indicated for suppression of estrus.

Suppression of estrus allows for a predictable occurrence of estrus following drug withdrawal. 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.

Swine: Altresyn® is indicated for suppression of estrus in sexually mature gilts.

Altresyn® mimics the action of progesterone and blocks the cyclical release of gonadotrophins and thus the development of estrus. Following cessation of treatment, pituitary inhibition ceases and normal development and maturation of the follicles returns, leading to a return to estrus and ovulation. The predictable return to estrus (generally 5-7 days following cessation of treatment) allows for estrus synchronization in a pool of cycling gilts.

Altresyn® is indicated for suppression of estrus in sexually mature gilts to:

1. Permit synchronization of estrus in cycling gilts.

2. Improve breeding unit organization by facilitating batch management (all in, all out system) of the breeding gilts.

3. Reduce the pre-breeding gilt pool size.

Dosage and Administration

Horses: Administer orally at the rate of 1 mL per 50 kg (110 lbs) body weight (0.044 mg/kg) once daily for 15 consecutive days. Administer orally by dose syringe or suitable plastic syringe on to the posterior-dorsal surface of the tongue. The recommended dose may alternatively be added to the usual ration.

Dosage Chart:

Approximate Weight kg/lb

Dose in mL

350kg / 770lb


400kg / 880lb


450kg / 990lb


500kg / 1100lb


550kg / 1210lb


600kg / 1320lb


Extensive clinical trials have demonstrated that estrus will be suppressed in approximately 95% of the mares within three days; however, the post-treatment response depends on the level of ovarian activity when treatment was initiated. Estrus in mares exhibiting regular estrus cycles during the breeding season will be suppressed during treatment; these mares return to estrus four or five days following treatment and continue to cycle normal estrus following withdrawal.

Response in mares in the transition phase between winter anestrus and the summer breeding season depends on the degree of follicular activity. Mares with inactive ovaries and small follicles failed to respond with normal cycles post-treatment.

Swine: Top dress on gilts daily ration at the rate of 15 mg of altrenogest per gilt per day for 14 consecutive days. The recommended daily dose represents 6.8 mL of Altresyn®.


Horses: Suppression of estrus to:

1. Facilitate attainment of regular cycles during the transition period from winter anestrus to the physiological breeding season.

To facilitate the 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.

2. Facilitate management of the mares exhibiting prolonged estrus during the transition period.

Estrus will be suppressed in mares exhibiting prolonged behavioural estrus either early or later during the transition period. Again, the post-treatment response depends upon the level of ovarian activity. The mares with greater ovarian activity initiate regular cycles and conceive sooner than the inactive mares. Altresyn® may be administered early in the transition period to suppress estrus in mares with inactive ovaries to aid in the management of these mares or to mares later in the transition period with active ovaries to prepare and schedule the mare for breeding.

3. 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 Altresyn® 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.


Horses: Altresyn® is contraindicated in pregnant mares and in mares having a previous history of uterine inflammation (i.e. a Grade II or greater uterine biopsy result), or current uterine inflammations (i.e. acute, subacute or chronic endometritis). Altresyn® therapy may exacerbate an existing uterine inflammation into a fulminating uterine inflammation. The safety of this drug in pregnant mares has not been established. Various synthetic progestins, including altrenogest, when administered to rats during the embryonic stage of pregnancy at doses many fold greater than the recommended equine dose caused foetal anomalies, specifically of the female genitalia.

Swine: Altresyn® is contraindicated in gestating gilts or sows and is not to be administered to breeding boars since it could interfere with their fertility.


Horses and Swine: The effect of this drug on post-treatment reproductive performance has not been fully documented. Swine: Over dosing may lead to a delay in the return to estrus. Under dosing may lead to a greater risk of cystic ovaries or failure of estrus suppression.


Horses: This drug is not to be administered to horses that are intended to be slaughtered for use in food.

Swine: Treated animals must not be slaughtered for use in food for at least 42 days following the latest treatment with this drug.

1. Pregnant women or women who suspect they are pregnant should not handle this product. Women of childbearing age should exercise extreme caution when handling this product. Accidental absorption could lead to a disruption of the menstrual cycle or prolongation of pregnancy.

2. Users/handlers should avoid skin contact. Wear protective gloves of non-porous material, such as vinyl, polyethylene or neoprene when handling this product. In case of accidental spillage on the skin, wash off immediately with soap and water.

3. People who have conditions that can be exacerbated by exposure to progesterone and sexual steroids should not handle this product. Consult a physician for individual advice.



Store at or below 25°C.


1 litre plastic bottle.

Ceva Animal Health Inc., 6-1040 Fountain St. N., Cambridge, ON N3E 1A3

1 800-510-8864

®Altresyn is a registered trade mark of Ceva Santé Animale, France


Last revised: 2016-05-26

CPN: 1221125.0

Telephone:   519-650-9570
Toll-Free:   800-510-8864
Fax:   519-650-9576
Every effort has been made to ensure the accuracy of the Altresyn information published above. However, it remains the responsibility of the readers to familiarize themselves with the product information contained on the Canadian product label or package insert.

Copyright © 2021 Animalytix LLC. Updated: 2020-12-31