What Medicine Brings a Mare into Heat?
The primary medicine used to bring a mare into heat, known as induction of estrus, is Prostaglandin F2α (PGF2α) analogs. This hormone effectively restarts the mare’s estrous cycle, allowing for controlled breeding.
Understanding the Mare’s Estrous Cycle
The mare’s estrous cycle is a complex process influenced by seasonal changes and hormones. Mares are seasonally polyestrous, meaning they cycle regularly during specific times of the year, typically spring and summer, and enter a period of anestrus (absence of cycling) during the winter months. The length of the cycle is approximately 21 days. Understanding the phases of the cycle is crucial for successful breeding management.
- Estrus (Heat): The period when the mare is receptive to breeding, lasting approximately 3-7 days.
- Diestrus: The period between heats, lasting approximately 14 days.
- Anestrus: The period of reproductive inactivity, typically during the winter.
- Transition Period: The period leading up to and following the breeding season, characterized by irregular cycles.
Prostaglandin F2α (PGF2α) Analogs: The Primary Choice
- Mechanism of Action: PGF2α analogs work by causing regression (destruction) of the corpus luteum (CL) on the ovary. The corpus luteum produces progesterone, a hormone that maintains pregnancy. By eliminating the CL, progesterone levels drop, allowing the mare to return to estrus.
- Commonly Used Medications: Common brands include Lutalyse (dinoprost tromethamine) and Estrumate (cloprostenol sodium). These are synthetic analogs of PGF2α.
- Administration: PGF2α analogs are typically administered via intramuscular injection.
- Timing: Mares usually come into heat within 2-5 days after administration.
Benefits of Using PGF2α Analogs
- Cycle Synchronization: Allows for precise timing of breeding, particularly useful in artificial insemination (AI) programs.
- Estrous Cycle Management: Helps to manage mares with prolonged diestrus or other cycle irregularities.
- Induction of Parturition: Can be used, under veterinary supervision, to induce labor in late-term pregnant mares. (Note: this is a separate application from inducing estrus, but relevant to PGF2α’s effects)
- Shortened Transition Period: Sometimes used, in conjunction with light manipulation, to help mares transition into the breeding season earlier.
Important Considerations and Precautions
- Health Status: Mares should be in good general health before administration.
- Pregnancy Status: PGF2α analogs are abortifacients and should never be administered to pregnant mares unless abortion is the intended outcome.
- Veterinarian Supervision: It is essential to consult with a veterinarian before administering PGF2α analogs to ensure proper dosage and monitoring.
- Side Effects: Potential side effects can include sweating, abdominal cramping, increased defecation, and restlessness. These are usually transient.
- Human Safety: PGF2α analogs can cause bronchospasm in humans, particularly in individuals with asthma. Wear gloves and avoid direct contact with the medication.
Alternative Medicines and Treatments
While PGF2α analogs are the primary choice for inducing estrus, other treatments may be used in conjunction or when PGF2α is contraindicated.
- Domperidone: Useful for stimulating prolactin release and potentially promoting cyclicity, particularly during the transition period.
- Regu-Mate (altrenogest): A synthetic progestin that can be used to suppress estrus. When discontinued, mares typically come into heat. However, it’s usually used to maintain pregnancies and is less ideal for inducing heat quickly than PGF2a.
- Light Manipulation: Exposing mares to artificial light for a prolonged period (e.g., 16 hours per day) can stimulate their reproductive cycles. Often used in conjunction with drug therapies.
Common Mistakes to Avoid
- Administering PGF2α to Pregnant Mares: This can result in abortion. Always confirm that the mare is not pregnant before administering the drug.
- Ignoring Underlying Health Issues: Address any underlying health problems before attempting to induce estrus.
- Incorrect Dosage: Administer the correct dosage as prescribed by a veterinarian.
- Failure to Monitor: Monitor the mare closely for side effects after administration.
- Using Expired Medication: Ensure that the medication is not expired.
- Assuming PGF2α will work on mares in anestrus: PGF2α is most effective on mares that have a functional corpus luteum. It won’t work on mares deep in anestrus.
Practical Applications in Breeding Management
Using medicine to manipulate the mare’s estrous cycle is crucial for modern breeding management. This allows breeders to plan breeding dates around desired foaling dates. It ensures that a stallion’s book is kept full. It allows for better management of the mare’s health during pregnancy and beyond. Therefore, understanding what medicine brings a mare into heat is paramount to maximizing breeding success.
| Treatment | Primary Purpose | Mechanism | Common Use |
|---|---|---|---|
| ———————– | —————————- | ———————————————————– | ————————————————————– |
| PGF2α Analogs | Induce estrus | Regression of the corpus luteum | Cycle synchronization for AI or live cover |
| Domperidone | Stimulate cyclicity | Prolactin release | Transition period management |
| Regu-Mate (altrenogest) | Suppress estrus | Synthetic progestin | Managing mares who have early embryonic loss |
Frequently Asked Questions (FAQs)
Can PGF2α analogs be used in all mares?
No. PGF2α analogs should not be used in pregnant mares or mares with certain health conditions, such as acute respiratory disease. A veterinarian should always evaluate the mare’s health history before administration.
How quickly will a mare come into heat after receiving PGF2α?
Most mares will come into heat within 2-5 days after administration. However, individual responses can vary.
What are the common side effects of PGF2α in mares?
Common side effects include sweating, abdominal cramping, increased defecation, and restlessness. These are usually transient and resolve within a few hours.
Can I administer PGF2α analogs myself?
While it is possible to learn to administer intramuscular injections, it is strongly recommended to consult with a veterinarian before administering PGF2α analogs. They can determine the appropriate dosage and monitor for any adverse reactions.
What if a mare does not respond to PGF2α?
If a mare does not respond to PGF2α, it could be due to several factors, including pregnancy, anestrus, or the absence of a functional corpus luteum. Further evaluation by a veterinarian is necessary.
What is the role of light manipulation in inducing estrus?
Light manipulation can stimulate the mare’s reproductive cycle by suppressing melatonin production, which is normally elevated during the winter months. This can help to advance the breeding season.
Is it ethical to manipulate a mare’s estrous cycle?
When done responsibly and under veterinary supervision, manipulating a mare’s estrous cycle can be a safe and effective way to manage breeding. It is essential to prioritize the mare’s health and well-being.
Are there any natural alternatives to PGF2α for inducing estrus?
While some herbal remedies are purported to influence the estrous cycle, their efficacy is not well-established, and they should not be considered a substitute for veterinary-prescribed medications. Light manipulation, however, is a natural alternative.
What is the ideal body condition score for a mare undergoing breeding management?
Mares should ideally be in a moderate to good body condition score (5-7 on a 9-point scale) for optimal reproductive performance.
Can stress affect a mare’s response to PGF2α?
Yes, stress can negatively impact a mare’s reproductive function and potentially affect her response to PGF2α. Minimize stress factors as much as possible.
How does the mare’s age affect the response to medicine that induces heat?
Older mares may respond less reliably to medications such as PGF2α due to decreased ovarian function. This is not always the case but is a factor to consider.
What testing should I perform before using medicine to induce a mare to cycle?
A thorough reproductive exam performed by a veterinarian, including ultrasound of the reproductive tract and possibly hormone testing, will ensure that medicine that induces heat can be used safely and to its greatest effect.