Etiology

• Seasonal - especially long-haired breeds (short breeding season).
• Unknown ovariohysterectomy.
• Disorders of sex development Disorders of sexual development (presence of ovarian dysgenesis, ovotestes, etc).
• Ovarian disorders (progesterone-secreting cyst; ovarian neoplasia Ovary: neoplasia, etc).
• Systemic abnormalities   →   debility, eg diabetes mellitus Diabetes mellitus.
• Prolonged suppression of estrus Estrus suppression with progestagen therapy or testosterone.
• Pregnancy or pseudopregnancy Pseudopregnancy.  
• Delayed puberty Delayed puberty.
• Environmental factors: excessive cold, insufficient light, overcrowding, poor nutrition.

Predisposing factors

General

• Breed: some purebred longhaired queens, eg Persian Persian longhair may not mature until 12-18 months old.
• Bodyweight: most queens will have first estrus when 2.3-2.5 kg (usually at about 7 months old).
• Season: autumn/winter born kittens may not become sexually mature when the next breeding season arrives in the spring (too young and lightweight), and may only show their first estrus the following breeding season, ie at 12-16 months old.
• Queens needs social contact with other cats to mature. Other breeding queens or a male nearby will stimulate estrus. Timid queens may need housing alone to prevent estrus suppression.
• Neutered male may mount and mate queens, thereby stimulating ovulation and pseudopregnancy Pseudopregnancy.

• Age: queens will normally have estrous cycles until approximately 14 years old.

Pathophysiology

• Ovariectomy Laparoscopy: ovariectomy    →   lack of ovarian hormones.
• Systemic disease may   →   hypothalamic-pituitary-gonadal axis abnormality.
• Ageing and pregnancy   →   normal physiological processes.
• Exogenous testosterone or progestogens   →   chronic suppression of ovarian activity.