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The Reproductive System in Animals

By

Harry W. Momont

, DVM, PhD, DACT, Department of Medical Sciences, School of Veterinary Medicine, University of Wisconsin-Madison

Last full review/revision Aug 2020 | Content last modified Sep 2020
Topic Resources
Table
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Approximate Gestation Periods

Domestic Animals

Days

Cat

65

Cattlea

Angus

281

Ayrshire

279

Brahman

292

Brown Swiss

290

Charolais

289

Guernsey

283

Hereford

285

Holstein

279

Jersey

279

Limousin

289

Shorthorn

282

Simmental

289

Dog

62–64b

Donkey

365

Goat

150

Horsec

335–342

Llama, Alpacac

335–365

Pig

114

Rabbit

31

Sheep

150

Wild Animals

Days

Bear (Black)

210

Bison

280

Camel

365-400

Chimpanzee

236

Coyote

63

Deer (Mule and White-tailed)

200

Elephant

660

Elk, Wapiti

255

Giraffe

425

Gorilla

270

Hare

36

Hippopotamus

240

Leopard

95

Lion

108

Marmoset

150

Monkey (Macaque)

180

Moose

235

Muskox

255

Muskrat

29

Nutria, Coypu

130

Opossum

12

Otter

270–300d

Panther

90

Porcupine

210

Pronghorn

250

Raccoon

63

Reindeer

225

Rhinoceros (African)

480

Seal

330

Shrew

20

Skunk

63

Squirrel (Gray)

40

Tapir

390

Tiger

103

Walrus

450

Whale

450

Woodchuck

31

Wolf

63

Farmed Fur Animals

Days

Chinchilla

111

Ferret

42

Fox

52

Mink

European

41

American

40–75

a Individuals may range ±7–10 days from these averages.

b Gestation period is 58–72 days from breeding at unknown stage of estrus; from day of ovulation (which can be determined by progesterone or LH monitoring), gestation period is 62–64 days.

c Individuals may range 20 days from these averages.

d 180+ days due to delayed implantation

Table
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Approximate Incubation Periods

Domestic Birds

Days

Chicken

21

Duck

28

Muscovy duck

35

Goose

28

Guinea fowl

28

Turkey

28

Caged and Game Birds

Days

Budgerigar

18

Finch

14

Parrot

26

Pheasant

24

Pigeon

18

Quail

16

Swan

35

Table
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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.

The reproductive system provides the mechanism for the recombination of genetic material that allows for change and adaptation. Manipulation of this system in breeding management programs allows the rapid and dramatic alteration of the conformation and productivity of domestic animals. Theriogenology is the veterinary clinical specialty that deals with reproduction.

The reproductive system is incredibly complex in both its anatomy and physiology, and all aspects must be considered when resolving reproductive problems. The differences in the reproductive system between the sexes and among species are extensive. Both sexes have primary sex organs and primary regulatory centers. Gonads and function-adapted, tubular genital organs constitute primary sex organs in both sexes. The pituitary gland and the hypothalamus are the primary regulatory centers; thus, the regulatory function is, in part, neuroendocrine in nature. In pregnant females, the fetoplacental unit has a significant role in maintaining and terminating pregnancy.

For the temporal and physiologic features of the reproductive cycles of selected species, see Table: Approximate Incubation Periods and see Table: Approximate Incubation Periods and see Table: Features of the Reproductive Cycle.

For More Information

Also see pet health content regarding the reproduction system in dogs, cats, and horses.

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