Reproductive System Overview - Anatomy & Physiology

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Introduction

Reproduction is a sequence of events beginning with the development of the reproductive system in the embryo. After the animal is born, it must grow and achieve puberty by aquiring the ability to produce fertile gametes. This ability must be accomplished by reproductive behaviour and copulation. After copulation, the sperm and egg meet, fertilization occurs and development of the preattachment embryo follows. The conceptus attaches to the uterus by a specialised organ called the placenta. It allows the conceptus to grow and develop to term. The fully developed foetus is born and the female giving birth to it must lactate to provide nourishment for the neonate. During or after lactation the dam must re-establish cyclicity before she can become pregnant again.

Development to Puberty

Female Reproductive Tract

The female reproductive tract comprises of the ovaries, oviduct, uterus, cervix, vagina and external genitalia in all domestic species. However many species variations do occur. The female reproductive tract is located ventral to the rectum seperated from it by the the rectogenital pouch. This anatomical feature allows the female tract to be palpated, manipulated and ultrasounded par rectum in some of the larger species i.e Cows and Mares.

Male Reproductive Tract

Species Cattle Sheep Swine Horses Birds
Mature Male BULL RAM BOAR STALLION Rooster/Cock/Tom
Castrate Male STEER WETHER BARROW GELDING CAPON

Reproductive Behaviour

During Embryogenesis, sexual differentiation occurs, during which the brain is programmed to be either male or female. In most mammals, reproductive behaviours are sexually differentiated. For example, mounting,erection and ejaculation are typically male behaviours, while standing to be mounted (lordosis),crouching and elevated locomotion are typically female behaviours. These behaviours are endocrine controlled, the presence of gonadal steroids (Oestrogen and Testosterone) is obligatory for normal reproductive behaviour.


The purpose of reproductive behaviour is to promote the opportunity for copulation and thus increase the probability that sperm and oocyte will meet. In the female, sexual receptivity occurs only during Oestrus and is characterized by distinct behaviour and mating posture. In the male, reproductive behaviour can occur potentially any time. Sexual arousal in the male involves a cascade of endocrine and neural events that result in erection of the penis, mounting of the sexually receptive female, intromission and ejaculation. Erection of the penis involves specific neural and biochemical events that culminate in the penis vasodilating. Ejaculation is a reflex that is initiated by stimulation of the glans penis and concludes with expulsion of semen.



MALE

Consists of:


FEMALE

Consists of:

Fertilisation, Implantation and Early Embryonic Development

Gestation

Species Mare Cow Ewe Sow Bitch Queen Guinea Pig Gerbil Mouse Hamster Chinchilla Ferret
Gestation Length (days) 330-340 280-285 147-150 115 63-64 63 60 22-26 21 16 105-115 43



Parturition

The step in the reproductive process that immediately precedes lactation, uterine involution and return to cyclicity. It is initiated by the foetus and involves a complex cascade of endocrine events that promote myometrial contraction, dilation of the cervix, expulsion of the foetus and expulsion of the extraembryonic membranes.

The Puerperium

Immediately following parturition, the female enters a period of reproductive repair called the Puerperium and begins lactation. For a period of time these two processes overlap.

  • During the puerperium uterine involution and return to ovarian function occurs.
    • Involution is the reduction in size and remodelling of the endometrium so that the uterus can initiate and sustain another pregnancy.
  • The time required for complete uterine involution and ovarian activity to resume varies among species.


The four major events of the puerperium are:


In many polyoestrous animals, the shortest possible puerperium is desirable because eligibility for a subsequent pregnancy is of high economic importance.


Lactation

Mammary gland development is initiated prenatally in the female foetus and continues through puberty and pregnancy. The anatomy and distribution of mammary glands is diverse among mammals. Secretion of milk does not begin until shortly (hours) before parturition. Lactation provides the neonate with the opportunity to nurse and be nourished with minimal energy expenditure. It also provides immunoprotection for the neonate because initial mammary secretions (colostrum) contain antibodies that provide passive immunity. Lactation continues until the neonate is weaned. After weaning, the mammary glands undergo involution and return to a non-secretory state.


Key words

Schematic Diagram to show the Stages of Mammary Development,Copyright RVC 2008
  • Mammogenesis: the development of mammary tissue
  • Lactogenesis: the onset of milk secretion
  • Galactopoesis: the maintenance of lactation
  • Milk ejection: the expulsion of milk from alveoli
  • Involution: termination of milk secretion and mammary gland regression.



Links to Associated Pathology

  • Information on Hypocalcaemia 'Milk Fever' can be found here
  • Information on Mammary Neoplasia can be found here
  • Information on Mastitis can be found here


Reproductive Technologies


Camelids (LLamas & Alpacas)

Alpacas and Llamas have a long gestation period of ~11 months. They are almost always monotocious, giving birth to a single cria.


Small Domestic Mammals

Species Rabbit Chinchilla Chipmunk Gerbil Guinea Pig Golden Hamster Mouse Rat
Reproductive Pattern No True Oestrous Cycle Seasonally Polyoestrous:Breeds November-March Seasonally Polyoestrous:Breeds March-September Polyoestrous Polyoestrous Polyoestrous Polyoestrous Polyoestrous
Length of Oestous Cycle Every 4 days 30-35 days 14 days 4-6 days 15-16 days Every 4 days 4-5 days 4-5 days
Type of Ovulation Induced:Occurs Within 10 hours of Mating Spontaneous Spontaneous Spontaneous Spontaneous Spontaneous Spontaneous Spontaneous
Gestation Period 28-32 days 111 days 28-32 days 24-26 days 63 days 15-18 days 19-21 days 20-22 days
Average Litter Size 2-7 2-3 2-6 3-6 2-6 3-7 6-12 6-12
Type of Young at Birth Altricial Precocial Altricial Altricial Precocial Altricial Altricial Altricial
Weaning Age 4-6 weeks 6-8 weeks 6-7 weeks 3-4 weeks 3-4 weeks 3-4 weeks 18 days 3 weeks
Age of Sexual Maturity 5-8 months 8 months 12 months 10-12 weeks 6-10 weeks 6-10 weeks 3-4 weeks 5-6 weeks


Key Words

  • Altricial: newly born young are relatively immobile, have closed eyes, lack hair, and must be cared for by the adults. Altricial young are born helpless and require care for a comparatively long time.
  • Precocial: young have open eyes, have hair, large brains and are immediately mobile and somewhat able to defend themselves against predators.


The main reproductive characteristics of the following species:


Exotics


References

  • P.L Senger: Pathways to Pregnancy and Parturition,2nd Edition
  • David E. Noakes,Timothy J. Parkinson,Gary C. W. England,Geoffrey H. Arthur: Arthur's Veterinary Reproduction and Obstetrics
  • Bairbre O'Malley:Clinical Anatomy and Physiology of Exotic Species
  • Dyce, Sack and Wensing: Textbook of Veterinary Anatomy, 3rd Edition
  • Konig and Liebich: Veterinary Anatomy of Domestic Mammals, 3rd Edition
  • Victoria Aspinall, Melanie Cappello: Introduction to Veterinary Anatomy & Physiology
  • Gina Bromage: Llamas and Alpacas: A Guide to Management
  • R.J. Roberts,Lydia Brown: Aquaculture for Veterinarians - Fish Husbandry and Medicine (Pergamon Veterinary Handbook)

Creators of Reproductive Anatomy and Physiology Pages

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