Failure to Cycle

Failure to Cycle



Basic Information image



Definition


Failure to show estrous behavior when expected during the breeding season



Synonyms




• Noncycling mare


• Anestrus



Epidemiology



Species, Age, Sex


Sexually mature mares



Risk Factors




• Iatrogenic from the use of hormones


• Long-term chronic infections, such as pyometra



Geography and Seasonality




• From October to February (Northern Hemisphere), most mares present physiologic anestrus.


• Mares that foal between January and early March under the natural photoperiod (Northern Hemisphere) are more predisposed to lactational anestrus, especially if they are in poor body condition.



Associated Conditions and Disorders


Poor body condition, negative energy balance, endometritis, photoperiod, pregnancy loss, pyometra



Clinical Presentation



Disease Forms/Subtypes




• Lack of ovarian activity


• Prolonged luteal activity


• Behavioral


• Iatrogenic



History, Chief Complaint




• Absence of estrous behavior when expected during the breeding season


• Absence of follicular development during the breeding season



Physical Exam Findings


Good/poor body condition, ± vulvar discharge



Etiology and Pathophysiology




• Lack of ovarian activity


• Seasonality (winter anestrus): Decreased gonadotropin-releasing hormone (GnRH) secretion from increased melatonin secretion during darkness

• Lactational anestrus: In mares that foal from January to March under the natural photoperiod and/or that are in poor body condition, the condition is likely related to the suppressive effect of the photoperiod on GnRH secretion and/or negative energy balance

• Gonadal dysgenesis (63,XO; 65,XXX, 64,XY)

• Ovarian tumors (eg, granulosa theca cell tumor [GTCT]): Production of inhibin suppresses follicular activity through follicle-stimulating hormone suppression

• Anabolic steroid treatment: Suppresses pituitary gonadotropin secretion

• Prolonged luteal activity


• Persistent corpus luteum (CL): Can remain functional for up to 60 to 90 days if untreated

image Pyometra: Failure to release prostaglandin F2α (PGF2α) because of extensive damage to the endometrium

image Insensitivity to released PGF2α: Diestrus ovulation after the tenth day postovulation

image Pseudopregnancy: Embryonic death after the first luteal response to pregnancy (typically days 14 to 15 days postovulation)

• Pregnancy: Persistent progesterone production by the CL after maternal recognition of pregnancy or progestogens from the fetoplacental unit

• Behavioral


• Silent estrus: Absence of estrous behavior in spite of normal cyclicity

• Iatrogenic


• Progestins: Suppress estrous behavior by inhibition at the level of the brain

• Oxytocin treatment for estrus suppression: Prolongs luteal activity


Diagnosis image



Differential Diagnosis


See Etiology above



Initial Database




• Teasing: No signs of estrous behavior


• Transrectal palpation and ultrasound:


• Follicular activity, CL, no uterine edema, tight cervix: Prolonged luteal function

• Small inactive ovaries, no uterine edema, no CL, relaxed cervix: Lack of ovarian activity

• Asymmetric ovaries, no uterine edema, cervix relaxed: GTCT

• Follicular activity, uterine edema, relaxed cervix: Silent estrus

• Uterine contents

image Conceptus: Pregnancy

image Intrauterine fluid: Pyometra or endometritis


Advanced or Confirmatory Testing




• Inhibin, testosterone, and progesterone serum concentrations for GTCT


• Inhibin >0.7 ng/mL, testosterone >50 to 100 pg/mL, and progesterone <1 ng/mL in a nonpregnant mare are suggestive of GTCT
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Jul 24, 2016 | Posted by in SMALL ANIMAL | Comments Off on Failure to Cycle

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