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Overview of the Reproductive System

By Harry W. Momont, DVM, PhD, DACT, Clinical Associate Professor, Department of Medical Sciences, School of Veterinary Medicine, University of Wisconsin-Madison

Reproductive System Introduction
Overview of the Reproductive System
The Gonads and Tubular Genital Tract
Infertility
Principles of Therapy of the Reproductive System

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 Gestation Periods and Approximate Incubation Periods and Features of the Reproductive Cycle.

Approximate Gestation Periods

Domestic Animals	Days	Wild Animals	Days
Cat	65	Bear (Black)	210
Cattle^a		Bison	280
Angus	281	Camel	365-400
Ayrshire	279	Chimpanzee	236
Brahman	292	Coyote	63
Brown Swiss	290	Deer (Mule and White-tailed)	200
Charolais	289	Elephant	660
Guernsey	283	Elk, Wapiti	255
Hereford	285	Giraffe	425
Holstein	279	Gorilla	270
Jersey	279	Hare	36
Limousin	289	Hippopotamus	240
Shorthorn	282	Leopard	95
Simmental	289	Lion	108
Dog	62–64^b	Marmoset	150
Donkey	365	Monkey (Macaque)	180
Goat	150	Moose	235
Horse^c	335–342	Muskox	255
Llama, Alpaca^c	335–365	Opossum	12
Pig	114	Panther	90
Sheep	150	Porcupine	210


Fur Animals	Days	Pronghorn	250
Chinchilla	111	Raccoon	63
Ferret	42	Reindeer	225
Fox	52	Rhinoceros (African)	480
Mink		Seal	330
European	41	Shrew	20
American	40–75	Skunk	63
Muskrat	29	Squirrel (Gray)	40
Nutria, Coypu	130	Tapir	390
Otter	270–300^d	Tiger	103
Rabbit	31	Walrus	450
Wolf	63	Whale (Sperm)	450
		Woodchuck	31
See also Selected Physiologic Data of Laboratory Animals ^a.
^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

Approximate Incubation Periods

Domestic Birds	Days	Caged and Game Birds	Days
Chicken	21	Budgerigar	18
Duck	28	Finch	14
Muscovy duck	35	Parrot	26
Goose	28	Pheasant	24
Guinea fowl	28	Pigeon	18
Turkey	28	Quail	16
		Swan	35

Features of the Reproductive Cycle

Species	Age at Puberty	Cycle Type	Cycle Length	Duration of Estrus	Best Time to Breed	First Estrus After Parturition	Comments
Cattle	10–12 mo, usually first bred ~14-15 mo	Polyestrous all year	21 days (18–24)	18 hr (6–24)	Insemination from midestrus until 6 hr after end of estrus	20–60 days	Ovulation 10–12 hr after end of estrus.
Sheep	6–9 mo	Seasonally polyestrous, early fall to winter	17 days (14–20)	24–36 hr	18–20 hr after onset of estrus	Next fall	Ovulation near end of estrus.
Goat	5–7 mo	Seasonally polyestrous, early fall to late winter	21 days	24–48 hr	Daily during estrus	Next fall	Many intersexes born in hornless strains.
Pig	6–7 mo	Polyestrous all year	21 days (19–23)	40–60 hr	Daily during estrus	4–10 days after weaning	Ovulation usually ~40 hr after beginning of estrus.
Horse	10–24 mo	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 mo	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 mo; earlier in smaller breeds, later in larger breeds	Monestrous all year	6–7 mo	9 days (3–21)	Second day after ovulation	4–5 mo	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 mo	Seasonally polyestrous, spring through early fall	14–21 days	6–7 days	Daily from day 2 of estrus	4–6 wk	Induced ovulation 24–48 hr after breeding. Pseudopregnancy lasts 40 days. Infertile matings delay onset of next cycle ~45 days.

Resources In This Article

Table 1

Approximate Gestation Periods
Table 2

Approximate Incubation Periods
Table 3

Features of the Reproductive Cycle

Reproductive System Introduction
Overview of the Reproductive System
The Gonads and Tubular Genital Tract
Infertility
Principles of Therapy of the Reproductive System

The Gonads and Tubular Genital Tract

Veterinary Manual

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Overview of the Reproductive System

Approximate Gestation Periods

Approximate Incubation Periods

Features of the Reproductive Cycle

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Overview of the Reproductive System

Approximate Gestation Periods

Approximate Incubation Periods

Features of the Reproductive Cycle

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