CHAPTER 170 Prevention of Estrous Behavior in Performance Mares
Veterinarians are often asked by owners to control or eliminate a mare’s estrous behavior. Owners may describe mares as less attentive or less cooperative during estrus so that they do not perform well. For these reasons many owners may prefer to prevent estrous behavior altogether.
PERSISTENT ESTRUS
Persistent estrus is commonly seen in the early spring transitional period and is physiologically a normal phenomenon in the mare. Transitional mares may have irregular periods of estrus or, alternatively, prolonged periods of estrus. The unacceptable behavior associated with this transitional period often subsides once the mare moves into the ovulatory season and estrus cycles become predictable. If the transition period becomes prolonged, hormonal treatments may be beneficial. Treating a transitional mare that has moderate-sized ovarian follicles (greater than 25-mm diameter) with progesterone (Table 170-1) supplementation for 14 days often results in a normal estrus and ovulation following discontinuation of treatment. A transitional mare with one or more follicles larger than 35 mm may respond to ovulation-inducing agents such as deslorelin or human chorionic gonadotropin (Table 170-2). Signs of estrus should cease in 2 or 3 days.
Table 170-2 Drugs, Routes, and Doses of Ovulation-Inducing Agents Used for Estrus Suppression
Drug | Route | Dose |
---|---|---|
Human chorionic gonadotropin (hCG) | IV or IM | 2500 to 3500 international units |
Deslorelin implant (Ovuplant) | SC | One 2.1-mg implant |
BioRelease deslorelin (BETPharm) | IM | 1.5 mg |
IM, intramuscular; IV, intravenous; SC, subcutaneous.
PELVIC PAIN DURING ESTRUS
Pneumovagina As a Cause of Pelvic Pain
Pneumovagina resulting from poor perineal conformation is common in performance mares. Lean, fit performance mares lack perineal fat, which may result in tipping of the vulva and a predisposition to pneumovagina. Chronic pneumovagina is irritating to the vestibulovaginal mucosa and may induce signs of chronic irritation, including frequent urination, vulvar discharge, and rubbing the tail or perineum. In addition, a characteristic hypersensitivity of the flanks and hindquarters to the touch may be seen. Such mares may uncharacteristically kick out when touched or become increasingly aggressive and agitated. Vaginoscopic examination often reveals vaginitis and cervicitis. Ultrasonography may reveal hyperechoic foci in the uterus, consistent with air contamination. Such mares benefit from placement of a Caslick’s suture in the vulva, with irritation and agitated behavior typically subsiding promptly thereafter.