Merck Manual

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Features of the Reproductive Cycle

Features of the Reproductive Cycle

Species

Age at Puberty

Cycle Type and Length (Range)

Duration of Estrus

Best Time to Breed

First Estrus After Parturition

Comments

Cattle

10–12 months, usually first bred ~14-15 mo

Polyestrous all year; 21 days (18–24)

18 hours (6–24)

Insemination from midestrus until 6 hr after end of estrus

20–60 days

Ovulation 10–12 hours after end of estrus.

Sheep

6–9 months

Seasonally polyestrous, early fall to winter; 17 days (14–20)

24–36 hours

18–20 hr after onset of estrus

Next fall

Ovulation near end of estrus.

Goat

5–7 months

Seasonally polyestrous, early fall to late winter; 21 days

24–48 hours

Daily during estrus

Next fall

Many intersexes born in hornless strains.

Pig

6–7 months

Polyestrous all year; 21 days (19–23)

40–60 hours

Daily during estrus

4–10 days after weaning

Ovulation usually ~40 hours after beginning of estrus.

Horse

10–24 months

Seasonally polyestrous, early spring through summer; ~21 days (19–23)

5–7 days

Last few days of estrus, just before ovulation; should be bred at 2-day intervals

4–14 (9) days

Ovulation usually 1–2 days before end of estrus. Double ovulation occurs in ~20% of estrous periods, but twins rarely progress to term.

Alpaca

12–18 months

Polyestrous all year in North America; Not applicable

Up to 36 days

When a large, viable follicle is present

Fertile within 15–20 days

Alpacas are induced ovulators.

Dog

6–24 months; earlier in smaller breeds, later in larger breeds

Monestrous all year; 6–7 mo

9 days (3–21)

Second day after ovulation

4–5 months

Proestrous bleeding 7–10 days. Ovulation usually 1–3 days after onset of estrus. Ova shed before first polar body has been extruded (primary oocyte).

Cat

4–12 months

Seasonally polyestrous, spring through early fall; 14–21 days

6–7 days

Daily from day 2 of estrus

4–6 weeks

Induced ovulation 24–48 hours after breeding. Pseudopregnancy lasts 40 days. Infertile matings delay onset of next cycle ~45 days.