Reproductive Process in The Horse & Dog

Male Dog Reproductive Tract;


  • Opening at the opposite end of the animal's digestive tract from the mouth.
  • Controls the expulsion of faeces.

Prostate Gland:

  • An organ that surrounds the urethra of a male at the base of the bladder.
  • Controls the release of urine, a glandular portion, which secretes an alkaline fluid  (Makes up part of the semen and enhances the motility and fertility of



  • A membranous sac that serves as the receptacle of a liquid or contains gas.


  • The membranous tube that extends from the bladder to the exterior; and that in the male conveys semen as well as urine.

Sperm Duct (Vas Deferens);

  • The duct that transports the sperm from the epididymis to the penis.

Scrotal Sac;

  • A dual-chambered protuberance of skin and muscle containing the testicles and divided by a septum.


  • The male gonad or reproductive gland, either of two oval glands, located in the scrotal sac.


  • The male organ of copulation and, excretion of urine and spermatic fluid in mammals.

Glans Penis;

  • The head of the penis.

Penis Bone( Os Penis);

  • Not present in humans but aids the dog and other species in penetration during intercourse.

Male Dog Reproductive Tract;

Reproductive tract of a Stallion;

Similarities to the male dog;

Anus (rectum), Prostate Gland, Bladder, Urethra, Sperm Duct (Vas Deferens), Scrotal Sac, Testes, Penis, Glans Penis;   - All as in the Male Dog.

Vesicular Gland;

  • The vesicular gland secretes a significant proportion of the fluid that ultimately becomes semen.

Bulb urethral Gland;

  • During sexual arousal, each gland produces a clear fluid (Pre- ejaculate) used to clear the urethra before ejaculation of sperm to reduce damage and increase sperm count.

Shaft of Penis;

  • Contains the urethra (tube in which sperm and urine are expelled through), and also the spongy tissue cavities that fill with blood to create an erection.

Tail Of Epididymis:

  • Absorbs fluid to make sperm more concentrated.


  • Secures the testis to the most inferior portion of the scrotum.

Spermatic Cord;

  • Cord-like structure in male mammals formed by the vas deferens and surrounding tissue that runs from the abdomen down to each testicle.

One of the first obvious differences between the male horse and dog reproductive system is the size, a stallion's erect penis is around 75cm and the Great Dane Dogs is around 20cm. The dog has a bone in his penis and the horse doesn't, the dog doesn't become erect until he's penetrated the bitch but the horse does. The process of mating can take up to an hour or two with dogs but it takes 5 minutes "approx" with horses.

Female dog Reproductive Tract;


  • These organs produce ova (eggs) for fertilisation and certain hormones such as oestrus.
  • The eggs develop in fluid filled sacs called follicles.


  • These tubes move the eggs from the ovaries to the uterus in about 2 days.
  • The oviducts are the place for fertilisation and maturation of the egg.


  • The dog's uterus is different to the humans due to being in the shape of a "V" and consists of two long horns and a short body this gives the foetus's more room to develop and mature.
  • The foetuses will mature here until parturition.


  • Serves as a channel from the uterus to the vagina.
  • During pregnancy the cervix will close, preventing infection and entry of harmful micro- organisms.


  • Extends from the cervix to the vulva it is muscular and very capable of dilation.


  • External part of and the opening of the reproductive tract made up of soft tissue, two vertical lips and can swell up if the bitch is on heat (ready to mate).

Reproductive tract of female horse;


  • Very much the same in the horse as in the bitch.


  • The vagina is long in the mare (nearly as long as the body of the uterus) and is remarkably distensible in length and circumference, a feature that os very beneficial during pregnancy and parturition.


  • Carries urine from the kidneys to the bladder and outside of the body through the reproductive tract.


  • A tube connecting the uterus to the vagina, closed during oestrus and pregnancy (Good indicator to when the horse is ready to breed or is in foal).

Uterine Horns;

  • The horns lie in the abdomen. This is the part of the reproductive tract where the new foal will attach at only a few days old, where the placenta will form to feed and oxygenate it and where the foal will develop until parturition.

The mare and bitches reproductive tract are very similar in appearance whereas the horses is much larger in size. The bitch's reproductive tract is made for carrying multiple foetuses and so the uterus is very stretchy. The mare is carrying a foal which is much larger to her in comparison to a puppy to a dog and so has a strong and stretchy uterus. Both the horse and dog have uterus's with horns this is an advantage due to carrying either large or multiple offspring.

Task 2;

Role of Hormones in the mammalian reproductive tract;




Gondatrophin releasing hormone (GnRH)

hypothalamus and pituitary

Responsible for the release of Follicle Stimulating Hormone (FSH) and Luteinising Hormone (LH) from the anterior pituitary

Follicle Stimulating Hormone (FSH)

pituitary gland

FSH regulates the development, growth, pubertal maturation, and reproductive processes of the body.

Luteinising Hormone (LH)

Pituitary gland

Controls the length and sequence of the female menstrual cycle.

In males, it stimulates the testes to produce androgen

Testosterone (TT)


Encourages the development of male sexual characteristics

Oestrogen (OR)


Encourages the development of female sexual characteristics

Progesterone (PRO)

mainly by the corpus luteum in the ovary and by the placenta

A Female hormone, Progesterone prepares the lining (endometrium) of the uterus to receive and sustain the fertilized egg and so permits pregnancy.

Oxytocin (OXT)


Used in childbirth and lactation, contracts the uterus during birth and the mammary glands post- pregnancy to produce milk.

Task 3;

Describe the stages of sexual reproduction in selected animals;


Copulation, there are varied methods for horses to breed including natural and artificial insemination. Both methods are effective under different circumstances. For example, a breeder who wishes to breed one horse with another but one is far away may wish to have a mare artificially inseminated by the stallion's sperm that has been collected and sent.

When horses mate, it can take as less as 5 minutes, the male mounts the female, penetrates and ejaculates. The mare must be in heat first in order to conceive, the mare is at her most fertile during the last 24 to 48 hours of her cycle and most breeders will begin mating the horses after the second day in her heat cycle for better chances of pregnancy.  Mares signal oestrus and ovulation by urination in the presence of a stallion, raising the tail and revealing the vulva. A stallion, approaching with a high head, will usually nip and nudge the mare, as well as sniff her urine to determine her readiness for mating.


Once the mating process has finished, fertilisation will happen, this is the union of the male and female zygotes (sperm and egg) during reproduction to form a zygote (resulting cell of the union of the sperm and egg).


Once fertilized, the egg remains in the oviduct for approximately 5.5 more days, and then descends into the uterus. The initial single cell combination is already dividing by this point. The egg will then attach itself to the uterus wall on about the 16th day for the gestational period.


A horse's gestation usually last about 11 months. After implantation, the embryo can be seen on ultra sound at about 21days and a heartbeat should be visible by about day 23. True implantation - invasion into the endometrial of any sort - does not occur until about day 35 of pregnancy with the formation of the endometrial cups, and true formation of the placenta has not commenced until about day 40-45 and not completed until about 140 days of pregnancy. The foetus gender can be determined by day 70 of the gestation using ultrasound. Halfway through gestation the foetus is the size of between a rabbit and an average sized dog. The most sudden foetal development occurs in the last 3 months of pregnancy when 60% of foetal growth occurs.

Parturition (Foaling);

Domestic mares that are due to give birth are usually separated from other horses for the safety of the mare and the unborn foal and to allow humans to interact and interfere with the birth if any problems occur. Labour is very rapid in comparison with most human births as it usually lasts no more than 30 minutes a horse in labour will usually be vocal, kick at her belly, lay on the floor and pace or paw at the floor. A successful birth can happen anything from 3 weeks before or after the mares due date, anything out of these guidelines and a vet may have to be called to induce the horse or assist with the birth and check the late or premature foal for any abnormalities. Observing the mare on a daily basis is the best indication of impending birth. Within one week of birth, the foal will "drop," settling lower in the mare's belly. Her hind end relaxes during the final two weeks and it will appear lower in proximity to her tail. When the mare's vulva relaxes and elongates, foaling is imminent. The foal will appear front hooves or muzzle first (In most cases) and will be passed through the vagina in the placenta.


The male dog will become very excited when introduced to a receptive bitch, sniffing and licking at her vulva. He will mount her rear quarter and penetrate causing two glands directly behind the penis to swell considerably.

In response, the bitch's vulva will clamp around this swelling; this is referred to as a tie, and is the moment when the dog and bitch become "stuck" together. This period typically lasts from fifteen to thirty minutes, and it is at this point that sperm are being delivered to waiting eggs.


Fertilisation in dogs is assisted by copulation due to the swelling of the genitals, assuring the sperm reaches the egg. Fertilisation can then commence by the meeting of the gametes (sperm and egg, male and female sex cells).


Implantation is when the embryo sticks itself to the uterus wall for protection. Implantation in pregnant dogs occurs on around the 19th day, it is different for different breeds of dog.


After implantation to the uterus wall, the embryo will continue to divide from a single celled organism to a foetus. The foetus will continue to grow in the uterus along with others, depending on the breed of dog generally the bigger the dog the bigger the litter size. By day 22 the foetuses will be developing spinal cords and eyes, this is the stage where the puppies are most susceptible to defects. Gestation will usually last around 63 to 65 days in a dog.


The first stage of parturition in a dog can take anything from 8- 18 hours, it is helpful to know how many puppies the dog is expecting as the birth of each puppy and the labour in between can last from half an hour to 4 hours. If the dog is expecting more puppies and has gone longer than 4 hours, a vet should be called as she is probably struggling. About 98% of the time, dogs will give birth successfully, by themselves.

Firstly, dogs copulation period is very varied and can take hours, horses are more predictable as their copulation is around 5 minutes.

Fertilisation in both species is very similar, as in humans, the gametes meet and creates a zygote. Except dogs genitalia will swell to ensure the delivery of the sperm to the egg.

Implantation happens in a similar manner in both animals but at different times. The horse on the 16th day and the dogs on about the 19th day.

In the horse, the gestation period is significantly longer considering most horses only give birth to one foal. The average litter size of a dog is 4-5 and this is surprising as the gestation period is so short.

Parturition in the dog can be naturally, a lot more time consuming in comparison to the horse due to having multiple offspring although dogs tend to be assisted more by humans and so this could be a contributor to the fast delivery of a large litter of puppies.


  • Unknown. (1999).

Definition of luteinising hormone.


  • Kelly Roper. (unknown).

Dog heat cycle and breeding.


  • Unknown. (Unknown).

Female dog reproductive System


  • unknown. (unknown).

inheritance and horse reproduction.


  • Unknown. (Unknown).

The Reproductive Tracts.


  • Stephen Champion, BSc (Hons) BVM&S MRCVS, Veterinary Surgeon. (Unknown).

The Reproductive Organs of the Female Horse.