The Sow Reproductive tract

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How much do you really know about the sow reproductive tract? For instance, did you know sow is the term used for a female adult pig? Maybe you did; perhaps you didn’t. The truth is we are always learning, and there is much to learn about sows and their reproductive tract.

pig's nose sticking out from a pen

The Importance of a the Sow Reproductive Tract

You may have heard of women being able to carry more than three babies at a time. These phenomena happen and are usually astounding to another individual. These women have got nothing on pigs.

Now we don’t mean that in any negative way! Females in all species are amazing for being able to produce young, grow, and care for them. But when we talk about amazing reproductive systems, we have to mention the pig.

A female pig or sow is one of the most prolific breeders. A single sow can produce between 10-12 piglets in one litter (more than the infamous octomom!). If they are in an organized management system, they can even have two litters a year.

Meaning any given sow can give birth to up to 24 piglets in one year! That’s a lot of piglets and a lot of moming for the sow to do! Making them one of the fastest reproducing livestock in the world.

the sow's reproductive tract

A List of Sow Reproductive Tract Terminology

When it comes to breeding or reproductive information in the veterinary industry, it’s a whole other world. It even comes with its own language and has its own area of veterinary medicine. 

Below is a list of common terminology used:

  • Agalactia– without milk.
  • Barrow– male pig who has been castrated.
  • Boar– intact male boar used for breeding purposes.
  • Cervicitis– inflammation of the cervix.
  • Conception rate- recorded in a percentage. 
  • Corpus luteum– The body that produces progesterone. 
  • Cryptorchid– a male pig whose testes have not fully descended through the inguinal canal.
  • Embryo– multicellular organism that develops in the uterus after fertilization.
  • Endometritis- inflammation of the lining of the womb.
  • Erythema– redness of the skin.
  • Follicle Stimulating Hormone (FSH)- the hormone that stimulates the growth of eggs. 
  • Farrowed- the term used for a sow that has given birth. 
  • Fetus- developing piglet from 30 days to maturity.
  • Gilt- young female pig that has yet to farrow a litter.
  • Implantation- attachment of the embryo to the uterine wall 12-14 days post-mating.
  • Irregular return– an oestrus cycle that lasts longer than 22 days.
  • Luteinizing Hormone (LH)- hormone controlled by the pituitary gland that triggers the ovary to release an egg to become fertilized. 
  • Mammary system– the sow’s udders consisting of two rows of 5-7 teats.
  • Mastitis– inflammation of the mammary gland.
  • Mating- the act of copulation.
  • Mummified pigs– piglets that died within the uterus, causing tissues and fluids to be reabsorbed, causing black shrunken skeletal remains. 
  • Non-Productive Days (NPD)-  all the days that the sows and gilts are not pregnant or suckling.
  • Oestrus/heat- a period in which the sow will stand for the boar to mate.
  • Oestrus cycle– 19-22 days interval where one oestrus occurs, and another begin. 
  • Orchitis- inflammation of the testicle.
  • Oxytocin– a hormone whose function is to release milk from the glands and cause the uterus to contract. 
  • Parity – the term used to describe the number of times a female has farrowed.
  • Prolactin- the hormone that initiates and maintains milk production.
  • Progesterone- the hormone that maintains pregnancy. 
  • Pyometra- pus-filled uterus. 
  • Regular routine– an oestrus cycle between 19-22 days. 
  • Scrotum– sack made of pliable skin which will contact in the cold and relax in the heat. It houses the testes. 
  • Seminal vesicles– glands that provide fluid and nourishment for the sperm.
  • Sperm- the male reproductive cell.
  • Spermatic cord– the fibrous cord that contains the vas deferens which suspend the testicles. 
  • Stillborn pigs– piglets who died before birth.
  • Teat necrosis– death to the teat tissues. 
  • Uteri- plural for uterus.
  • Uterus- the womb that consists of two horns that will contain the fetuses.
  • Urethritis- inflammation of the urethra.
  • Vas deferens– the muscular tube that propels the sperm at the time of ejaculation.
  • Testicle– the gland that produces the sperm.
pigs running on a farm

Swine’s Anatomy

Now that we discussed some common terminology let’s discuss the anatomy of the sow and boar’s reproductive tract and what each organ’s job is. 

The main structures of the sow’s reproductive tract are the ovaries. The ovaries are two small structures that produce follicles, release eggs, and produce hormones. The ovaries are housed in the pelvis.

The oviduct is the tube that connects the ovaries to the outside world. This is also the site where fertilization will take place. 

The sow has two uterine horns, which are 2-3 feet long. They are used as a passageway for sperm to reach the oviduct in order for fertilization to occur. During the heat cycle, the uterine horns become dilated. 

During mating, sperm is deposited in the cervix. The cervix is the area between the vagina and the uteri. During the heat cycle, the cervix will become dilated, but otherwise, it is constricted. 

The outer portion of the reproductive tract is called the vulva. This area will become red and swollen before the heat cycle. This is a physical way to tell if the sow is in heat or not. 

Between the cervix to the vulva is the vagina, which provides lubrication, as well as sensation. This area is where the piglets will travel to meet the outside world as well as urine which is connected via the urethra – the bladder is where urine is housed. 

Primary and Secondary Signs of Estrus in Sows

The most reliable sign of estrus and primary sign is if the sow will stand for the boar. Sows will only stand for a boar to mount them if they are in heat. Boars release pheromones in their salivary glands that result in the standing reflex for the sow. 

Secondary signs of estrus in sows include:

  • Red or swollen vulva
  • Grunts and growls
  • An increased amount of vaginal mucus
  • Mounting other sows
  • Inappetance
  • Restlessness

Sexual Behaviour in Pigs

The length of heat varies between sows being 12 hours on the shorter end and can last for 60 hours on the longer end. Because of this variation, it is best to mate the sow up to two times to ensure better timing. 

If artificial insemination (AI) is being performed, then it is best to observe the sow for secondary estrus.  AI should be done 12 hours after with a secondary AI 18 hours later. 

It is a visual representation of the anatomical parts of the sow’s reproductive tract.


There is a lot that goes into the mating of pigs. Timing is everything in this section of veterinary medicine, and it must be done right. Without proper evaluation, clinical signs, and observation, it would be harder to tell when the sow is in heat. 

If you enjoyed this article – why not read about A Comprehensive Guide About the Things, You Weren’t Told Before You Got a Pet Pig – Part Two