There are many options as to why a pig hasn’t been bred (or stayed bred in some cases). The funny thing to me is that so many times I see people saying they must get a new boar because their gilt or sow won’t become pregnant. Why people just assume it is the fault of the boar is a question I will never understand. I have found that more times than not, it is an issue with the gilt/sow and not a problem with the boar. This doesn’t mean it can’t be the boar, but from my personal experience, it is usually something else. The other thing I see a lot surrounding this discussion are people immediately blaming a genetic or hereditary issue with the pigs (boar or sow). Again – I am often confused by this reasoning. Why? Because I have found that 95% of problems arise from something that has nothing to do with genetics. It relates to feeding, nutrients, toxins, bacteria, viruses, temperature, climate, housing, and the health of the pig.

Let’s dive into some of the common reasons you may see reabsorptions, abortions, miscarriages, stillborn piglets, mummified piglets, early farrowing, smaller litters, or weak piglets with no will to thrive.

A quick overview is important: When raising animals, you have probably heard the saying “sometimes things just happen”. That saying is correct in that there are times when something goes wrong in the gestation of the piglets and a sow or gilt may lose one or all of her piglets. Knowing what may cause these things to occur is going to help prevent more problems with future litters. When a premature farrowing occurs, it can usually be associated with a nutritional, genetic, or environmental stress.

According to the University of Missouri, an abortion rate of 2% is normal on a farm. When you see an increase in abortions within an entire herd, an infections agent is usually suspected.

Some things to note are:

1. When a severe illness in a gilt or sow occurs in the first ½ of the pregnancy, the fetus’ may be reabsorbed.

2. If an infection occurs in the second ½ of the pregnancy, the abortion, mummified piglets, stillborn piglets, or weak piglets with no will to thrive can be seen.

*disclaimer * The IPPR is not a veterinarian. * To prepare this educational guide, a number of different veterinarians were consulted as well as research done by veterinarians, but no one involved with the making of this guide is a licensed veterinarian. This information is intended to provide a general overview of some of the things that can affect successful reproduction in swine. There are things that differ across the United State and to know what the best protocol for your pigs in your location will be, please consult your local veterinarian directly.

Weight/Body Condition

A common problem when dealing with pigs that are unable to get pregnant is that they are overweight! The desire to feed your pigs additional food at times (or quite often as they like to trick you into thinking they are starving) can cause a lot of overfeeding and overweight issues. Pigs are smart – don’t let them train you to give them snacks or additional feed.

A sow that is fat or overweight can have issues getting bred as well as issues during delivery. Issues during delivery can arise from larger than normal piglets and a smaller than normal birth canal. Fat deposits can build up within the birth canal and create difficulty for the piglets to get out.

A boar that is overweight can also experience breeding issues as he is going to have a difficult time getting into position, he may have additional fat deposits that prevent a successful mating from occurring, or he may just lack the drive or desire to breed.

The opposite can also be true. Pigs that are underweight are also likely to have issues. What a lot of people do not realize is that if a sow/gilt is underweight, their body will actually “reabsorb” the piglets in an effort to save the sow. This can happen at any time throughout the pregnancy.

Pigs can be underweight for a variety of reasons:

1. A sow just weaned her piglets, and they depleted her health.

a. If this is the case, then the best thing is to leave her in a pen without the boar and give her body the chance to bounce back and recover from the depletion of nutrients due to nursing.

b. A sow that had the piglets left on her and nursing too long. Making sure to wean the piglets when it is healthy for the sow is extremely important for the longevity and overall health of your sow. Most people raising IPP are doing so in a small farm or homesteading type of setting and the longevity of their animals is of utmost importance.

2. The pig (boar or sow) isn’t getting enough feed either overall or based on the climate, weather conditions, time of year, etc.. Depending on where you live, most people will need to vary their feed amounts at certain times of the year to better accommodate their animals and make sure they are getting the necessary nutrients their bodies require. Depending on whether it is cold, snowy, warm, crazy hot, beautiful grazing conditions with a lot of nutrient dense grasses/legumes, or all of the grasses are dead or dying due to extreme heat or cold, etc. the animals you are caring for will require different amounts of feed and protein in their diets.

3. Too many pigs in one pen. Having to many pigs in a pasture area will mean that the pigs who are not dominant will not get as much or sufficient feed. (this means that some of them will be overweight, and some will be underweight). Maintaining a good number of pigs is important.

Poor Management

Poor management can be a number of things that can lead to your gilt or sow having difficulty getting bred or staying bred.

Raising the young boar and sow together: When you get a new breeding pair as young piglets, there is the tendency for people to leave the pair together all the way through adolescents. This is not a good idea for two reasons: the pair can start to cycle earlier than you want and the gilt gets bred too young or they start to see each other as friends and don’t react and breed when they start to cycle. For this reason, it is recommended that young boars and gilts are separated by 3 or 4 months of age. This will eliminate any early “oops” and also allow the gilt to see the boar as dominant when they are put back in together. If this has already happened to you, it is possible to separate the boar and gilt for a month or two and then put them back in together. If the problem is that the pigs view each other as more of friends than a breeding pair, this time apart is very often what is needed to create the “spark” and have them breed.

Missing the heat cycle: For reasons of one variety or another some people prefer to only put their gilt/sow in with the boar when they believe she is cycling and then remove her immediately upon the completion of breeding. If you pull a sow out of the pasture too early, you can completely miss the part of her cycle where she is ovulating. Maybe he bred her 2 days ago and you haven’t seen anything since, so you separate them, but they are only on day three and she just ovulated, meaning you moved her out too soon. Just because you don’t see them breeding, doesn’t mean it hasn’t happened. If you need to separate them after breeding, I recommend waiting at least 3 – 4 days following last time you see them breeding before you separate them just to make sure you aren’t pulling her out too soon. Some boars like to breed early in the morning or late at night when the temperature is cooler. Some boars are shy and will breed when they don’t have a lot of things going on around them. And some boars don’t care and will breed regardless of the time of day or what is happening around them on the farm. While it would be the easiest if all the boars were like the last option, that just isn’t the case. Learning the signs of what to look for to evaluate if a breeding has taken place will help but isn’t completely fool proof. Some of the signs can include stickiness and wetness along her vaginal region, your boar nudging your sow and staying close to her most of the time, your boar jumping on her and attempting to breed, or the boar doing a low guttural grunt that more resembles a growl then a grunt. One thing to think about is that you sow is going to start jumping on your boar and getting antsy a couple days prior to her cycling. She may even grunt or growl at him. This is usually indicative that she is going to cycle in a couple of days. An experienced boar is going to know the difference between her smells and actions and will be less likely to be swayed by her. A mature boar may even get annoyed with her antics and chase her away for the day or two before she starts to cycle. Once she actually starts to cycle though, he will change his mind and be more than happy to have her attention. A young boar on the other hand is not as likely to understand the differences in the smells given off by a sow’s hormones or understand her actions. He may in fact try to breed her in those early days (she will likely not stand for him). This is sometimes confusing to people and is one of the big reasons that I am an advocate for putting the two together when you want them to breed and leaving them together until you know for sure she is bred and even waiting until she is close to farrowing before separating her again.

Young Boars: One thing I would like to make note of at this point is the difference in behavior of young boars and mature boars. As I just stated above, mature boars are more likely to understand the differences in smells of the gilt/sow, whereas a young boar is not. This carries over into the next heat cycle as well. Once a gilt/sow is bred, her hormones will change. Heat cycles usually happen 21 days apart and even if a gilt/sow is bred the previous cycle, she may give off hormones 21 days later (when she would technically be cycling but isn’t because she is bred). These hormones smell different then when she isn’t cycling and can sometimes be confusing to boars. Most gilts/sows do not smell the same as when they are cycling but aren’t the same as when they are not cycling A mature boar usually will have figured out the difference and understand that she isn’t receptive to him and doesn’t want to be bred. BUT – a young boar is not. That means that he may think she is cycling when she is in fact bred. This will cause her to chase him, get annoyed with him, and they may even fight because of his unwanted attention.
He may nudge her belly as a way to see if she is receptive to him. A lot of people get incredibly nervous about this behavior. Usually, they figure it out sooner than later and all is good, and he stops with his behavior, but sometimes that isn’t the case. This stomach nudging could potentially lead to her having a miscarriage, but that isn’t common. I recommend keeping an eye on them and if he continues with that behavior or it gets more excessive, then I would recommend separating them. The thing to remember though is that it is better for him to learn and understand the differences in her smells, hormones, and actions at an immature age as compared to when he is older and much larger. I prefer to leave my pigs together for this reason. This same change of smell and hormones is not as likely to happen every 21 days and usually only happens the first 21 days following being bred, but it is going to happen again near the time of her delivery. Again – most mature boars understand the differences in the gilt/sow’s smells and will not bother her and will leave her alone, but a young boar is highly likely to be confused. As before, it is better for him to learn now and understand the differences for the rest of his life, then to continually be pulled out and never fully learn or understand what is happening. If this is the case, then your boar will likely continue that behavior his whole life and you will have to separate him from your sow earlier then you normally would in order to prevent the loss of the piglets. Remember – pigs are very smart and will usually learn quickly if given the opportunity.

Overcrowding: Having too many pigs in one pasture is going to put undue stress on your sows and this stress can prevent them from getting pregnant or cause early reabsorption.

Moving Time: Moving your pigs too close to breeding could affect them getting bred especially if the move had a lot of added stress associated with it. One example of this would be if someone purchases a sow and moves her directly into the boar’s pen. (or if someone wants to do an outside breeding and takes their sow to a new farm to get bred). If the sow was set to cycle within a couple of days, there is a good chance that she may not take that cycle due to the stress she is under. If doing a 30-day quarantine, which is highly recommended, this will give your sow time to settle in and decreases her overall stress. Along this same line is when a sow gets bred and then immediately travels to a new home. It is best to allow the sow to settle and then move her. Giving her an additional 30 – 60 days will allow you to not only be sure she is bred, but also allow her body time to fully settle before she travels. The stress of traveling can also affect a sow when she is close to farrowing. The sow’s body may reabsorb or abort the piglets depending on the length or severity of the stress involved.

Inexperience: When a gilt has her first cycle it may be what is termed a Pseudo-cycle. This means that her hormones are changing, and she may even stand for a boar, but she may not actually ovulate. When no eggs are released, no pregnancy can occur. Many people are quick to get angry with the gilt and immediately assume that something is wrong with her, but in reality, this is a normal occurrence. The other thing to remember and consider is that a gilt has no idea what is happening to her. Although breeding is a natural thing, it is still stressful and confusing to some gilts more than others. Some gilts have a difficult time relaxing and continually turn to see why the boar is jumping on her or nudging her belly. Some may in fact just get angry with the boar when he continues to “bother” her (and remember a new boar is going to be confused too, so this leads to a learning curve for both of them).

Breeding too Young: Most gilts will start to cycle at about 6 – 10 months of age, but when a gilt gets bred too early it can lead to fertility issues that carry though their lifetime. A gilt that is bred too early is also more likely to have smaller litter sizes and weaker piglets for the remainder of their lifetime.

Bacteria

Bacterial infections can be a cause of infertility in swine and can affect both sows and boars depending on the type of infection. Most common causes of infertility due to bacterial infections are usually found in gilts or sows, but there is a slight chance that the semen from a boar can be infected with bacteria. The infection can be passed on to the gilt or sow through the semen and can also be prevalent when doing Artificial Insemination.

Most bacterial infections can be treated with antibiotics provided by your veterinarian, but for the health of your pigs and upcoming litters, practicing good sanitation and preventing the infection in the first place is extremely important. Having a place to farrow that is free of feces is essential as well as having clean living areas that allow breeding to take place without contamination entering the uterus during mating.

Some of the more common bacteria that affect the fertility of swine are:

• Leptospirosis
• Brucellosis
• Escherichia coli (E. coli)
• Erysipelas

Some bacterial infections can be prevented using vaccinations. Whether a farm does or does not use vaccinations is completely dependent on their personal beliefs, research on the pros and cons, and talking to a veterinarian, and knowing whether there may be extenuating  
circumstances such as living near a commercial hog farm, having a high number of feral hogs in your area, or if your property was a pasture or pig farm in the past. Many types of bacteria and viruses can live in the soil or be transferred through the air or carried on visitor clothing. Having a good biosecurity protocol is important for the overall health of your farm.

Parasites

Pigs that aren’t treated for parasites can develop a heavy worm load. A heavy worm load can not only cause stress on the pig itself, but can also affect the pig’s overall health and body condition. Gilts or sows with parasites that are left untreated will have difficulty getting bred and carrying their litter to a healthy delivery.

Viruses

Viruses can play a part not only in whether your sow is able to get pregnant, but also in whether she stays pregnant, aborts, delivers mummified piglets, has smaller than normal litter sizes, or delivers weak piglets who lack a will to thrive.

A few of the common viruses are:

1. Parvovirus: Rarely do pigs present with signs or symptoms when infected with Parvovirus, but the virus is able to cross the placenta and affects the fetus. Depending on when the gilt/sow becomes infected will determine what most commonly occurs. Infection in the 1st half of the pregnancy will result in more mummy fetuses. Whereas an infection that occurs in the 2nd half of the pregnancy is more common to cause stillbirths, delivery of weak piglets, and possibly infertility in the sow going forward. Parvo does affect gilts more commonly than sows.

• Natural Immunity: The best way to develop natural immunity is for a gilt or sow to come into contact with an infected pig prior to being bred (at least 30 days is best). Animals exposed to the virus’ prior to breeding can develop natural immunity that will last the entire lifetime of the animal.
• Vaccinations: Vaccinations are available for Parvovirus and a Certified Veterinarian should be consulted regarding the proper protocol.

2. Porcine Enterovirus: Like Parvovirus, enterovirus rarely presents with signs or symptoms. If on the rare occasion a pig does present with signs, it is likely diarrhea or pneumonia. This virus again crosses the placenta and affects the developing fetus’ and can cause all of the same problems as the Parvovirus including smaller litter sizes. Enterovirus is also more prevalent in gilts because natural immunity is developed when a pig comes in contact with the feces of other infected pigs. Once natural immunity is present, subsequent fertility is usually not affected. There is no vaccine for enterovirus to protect against the loss of piglets if a gilt/sow develops enterovirus while pregnant.

3. Porcine Reproductive & Respiratory Syndrome (PRRS): Unlike the last two viruses we looked at, this virus does present with signs & symptoms in the infected pig.

• The signs & symptoms can be labored breathing, fever, loss of appetite, pneumonia, reproductive failure, listlessness, redness of body, blue ears, and they may be more susceptible to bacterial infections. Younger pigs are more often affected and there is a high mortality rate.
• A sow infected with PRRS may abort early upon infection due to the primary infection or she may not abort until weeks after being infected due to the virus’s crossing the placenta & affecting the fetuses. Gilts/sows infected will usually present with decreased conception & farrowing rate. Besides abortion of piglets, stillborn piglets, mummies, premature farrowing, and weak piglets may be present.

Infection can be spread through contact, feces, urine, it can be airborne, and it can be found in semen. This means that if you are doing AI, a sow or gilt can be infected if the infection is found in the semen. Improved reproductive performance is usually seen after 3 – 5 months.

Mycotoxins

Most people know that mold or fungi aren’t good for livestock, but they easily overlook the role they can play in fertility. Mycotoxins are caused by mold and fungi and can be found in contaminated grain and straw. Knowing that your feed mill is taking great care not to use contaminated grains and is using good sanitation is as important as making sure your feed bins are kept clean and dry. One more thing to consider is that you don’t bed with damp or moldy straw.

Mycotoxins can affect all animals by impairing their health and growth. Pregnant sows are more likely to experience problems because mycotoxins can cross the placenta and cause stillborn piglets or abortions. Most often a sow infected with mycotoxins will miscarry before anyone knows that she is pregnant. Because this happens without any knowledge of it happening, a lot of times it is overlooked as simple infertility or a genetic problem.

Treatment is to get rid of the feed or bedding that contains the mycotoxins.  There are “binders” that can be added to feed on a routine basis that will help absorb dangerous mycotoxins.  Another type of natural treatment is to use activated charcoal which has been found to be beneficial in absorbing multiple types of mycotoxins.  

Weather/Temperatures

The weather can be a crucial factor in breeding primarily because when the temperatures are extremely hot or cold, neither your boars nor sows may want to breed. Boars are especially affected as they have been found to not be fond of breeding in extreme hot temperatures. Making sure your pigs always have access not only to cool drinking water, but also to a nice wallow and shaded areas is important for the overall health of your pigs and to allow the pigs to stay cool and want to breed.

Old Age

Whether we like it or not our animals get older each year. The average sow will have successful litters into her early teens, but at a certain point her litter size will decrease. Older sows will also take more to maintain their health overall and you may find that it is better to have one litter each year with a sow near 10 years old as compared to the traditional two litters a year. Some things to consider with your older sows is that they need to maintain a healthy weight in order to successfully carry a litter of piglets and you may need to increase their feed while they are pregnant. Making sure they can eat their full amount of feed and aren’t pushed away by younger pigs is going to be important as well. They will eat slower and may not get the full amount of feed if they are in with younger pigs. One way to make sure your older pigs are getting enough grain and minerals in their diet is to keep my older girls (near 10 years old and up) together. They are more inclined to eat at a slower pace and this will ensure they get enough in their diet. This also allows you to be able to give them a bit of additional feed if necessary.
At a certain point, your sow may stop cycling altogether and what your plan for her is, is completely up to you.