Features of the Reproductive Cycle

Cattle

10–12 mo, usually first bred at approx. 14–15 mo

Polyestrous all year; 21 d (18–24)

18 h (6–24)

Insemination from midestrus until 6 h after end of estrus

20–60 d

Ovulation occurs 10–12 h after end of estrus.

Sheep

6–9 mo

Seasonally polyestrous, early autumn to winter; 17 d (14–20)

24–36 h

18–20 h after onset of estrus

Next autumn

Ovulation occurs near end of estrus.

Goat

5–7 mo

Seasonally polyestrous, early autumn to late winter; 21 d

24–48 h

Daily during estrus

Next autumn

Many intersexes are born in hornless strains.

Pig

6–7 mo

Polyestrous all year; 21 d (19–23)

40–60 h

Daily during estrus

4–10 d after weaning

Ovulation usually occurs approx. 40 h after onset of estrus.

Horse

10–24 mo

Seasonally polyestrous, early spring through summer; approx. 21 d (19–23)

5–7 d

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

9 d (4–14)

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

Alpaca

12–18 mo

Polyestrous all year in North America; not applicable

Up to 36 d

When a large, viable follicle is present

Fertile within 15–20 d

Alpacas are induced ovulators.

Dog

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

Monestrous all year; 6–7 mo

9 d (3–21)

Day 2 after ovulation

4–5 mo

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

Cat

4–12 mo

Seasonally polyestrous, spring through early autumn; 14–21 d

6–7 d

Daily from day 2 of estrus

4–6 wk

Induced ovulation occurs 24–48 h after breeding. Pseudopregnancy lasts 40 d. Infertile breedings delay onset of next cycle by approx. 45 d.