Estrus Phases in Dogs and Cats

Estrus Phases in Dogs and Cats

Estrus Cycle Phases:

Anestrus:

• Characteristics: Ovarian inactivity, uterine involution, no attraction to males, small vulva, no discharge.

• Cytology: Predominantly parabasal cells, occasional neutrophils.

• Duration: 1–6 months.

Proestrus:

• Characteristics: Attracts males but not receptive, serosanguineous discharge, mild vulvar enlargement.

• Cytology: Shift from parabasal to superficial cells, presence of RBCs.

• Duration: 3 days to 3 weeks (average 9 days).

Estrus:

• Characteristics: Receptive to males, diminished discharge, peak vulvar edema.

• Cytology: Predominantly superficial cells, decreasing RBCs.

• Duration: 3 days to 3 weeks (average 9 days).

Diestrus:

• Characteristics: Refractory to males, diminished discharge, resolution of vulvar edema.

• Cytology: Reappearance of parabasal cells, frequent neutrophils.

• Duration: 2–3 months (pregnancy or pseudo-pregnancy).

Cytological Changes and Their Meanings:

• Parabasal Cells: Indicate anestrus or diestrus, low estrogen influence.

• Intermediate Cells: Early estrogen influence, proestrus phase.

• Superficial Cells: High estrogen influence, fertile period during estrus.

Assessment:

• Vaginal Cytology: Essential for determining the stage of the cycle.

• Hormonal Assays: Progesterone and LH testing to time breeding accurately.

Treatment:

• Hormonal Management: Progesterone levels for ovulation timing.

• Antimicrobials: For infections if present.

For more details, visit the Merck Veterinary Manual.