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Health Problems That Affect Fertility

Breeding-herd efficiency requires good fertility. Expected performance in the United States is to have conception rates of 92-94% and farrowing rates of 88-90%. Anything less than these standards indicates a problem with fertility and reproductive performance within the breeding herd. There are a number of potential factors, both infectious and non-infectious, that can affect fertility. Health problems

Breeding-herd efficiency requires good fertility. Expected performance in the United States is to have conception rates of 92-94% and farrowing rates of 88-90%. Anything less than these standards indicates a problem with fertility and reproductive performance within the breeding herd.

There are a number of potential factors, both infectious and non-infectious, that can affect fertility.

Health problems can result in lower fertility, leading to common symptoms including anaestrous (poorer cycling), decreased ovulation rates and embryo survivability, increased number of sows that recycle, and mummies and abortions. These symptoms are due to the following pathogens:

  • Viral agents:
    • Porcine parvovirus (PPV), porcine reproductive and respiratory syndrome (PRRS), swine influenza virus (SIV), porcine circovirus type 2 (PCV2), adenovirus and enterovirus.

  • Bacterial agents:
    • Brucellosis;
    • Leptospirosis;
    • Erysipelas;
    • Bacterial discharges (E. coli and Actinobacillus rossii);
    • Bacterial contamination of semen.
  • Parasitical agents:
    • Eperythrozoonosis.
  • Nutritional deficiency or toxicity:
    • Choline deficiency;
    • Pantothenic acid deficiency;
    • Riboflavin deficiency;
    • Vitamin B12 deficiency;
    • Zinc deficiency;
    • Selenium toxicity;
    • Mycotoxins (contamination in the field, bin or system).
  • Management:
    • Animal density too tight;

    • Chronic environmental and housing stressors;

    • Poor stockmanship and handling (moving animals poorly or moving animals prior to 30 days of pregnancy);

    • Poor heat detection and artificial insemination techniques.

This list demonstrates many possible causes for infertility. A good diagnostic plan is essential to determine the cause of the problem. Sometimes infertility problems are a combination of multiple factors, making it an even greater challenge to specifically diagnose the exact cause.

Good breeding herd and herd history records are essential to demonstrate the problem. Recording significant events in the herd history is also important. Laboratory diagnostics on fetuses from aborted litters can be helpful, but many times unrewarding. Serology can help confirm or rule out specific pathogens, as can a full diagnostic workup including nasal swabs in the case of SIV, and postmortem examinations to evaluate the entire system.

Viral Pathogens

Routine vaccination programs include PPV, multiple species of leptospira and erysipelas. Many farms also vaccinate for swine influenza virus. However, with the ever-changing flu virus, it is difficult to ensure complete protection. The best procedure for SIV is to use a vaccine that contains multiple isolates from the farm or of recently circulating local strains.

PRRS certainly can be a very big concern with infertility; one of the most common signs is abortion. Farms have used a variety of means to control this disease, including eradication procedures to eliminate the virus from their herds.

One of the first methods used was depopulation and repopulation. The most common method has been the use of herd closure. The greatest success has been achieved in herds that have been able to close for at least 220 days, with no outside introductions into the herd once all animals in the herd have been exposed to the virus.

The use of direct PRRS viral exposure to negative replacement gilts and the sow herd has helped to standardize this process, but many herds have been cleaned up simply with closure. If direct virus exposure is used, and staged gilts are exposed at the time of closure, there is little effect on the number of animals produced during the exposure.

One challenge with herd closure is aging parity distribution, which needs attention once the herd is reopened. The herd's age distribution going into the closure is an important consideration.

Other methods for PRRS control are continued introduction of gilts that are negative and exposed with direct virus exposure during their isolation period. This has worked well in hog-dense areas where the likelihood of the herd remaining negative is low.

Vaccination for PRRS is another option and has worked well for some herds.

Biosecurity for all herds is very important due to the fact that most new PRRS strains that gain entrance into a herd will result in the expression of clinical signs.

Darwin Reicks, DVM, of the Swine Veterinary Center, Scott Dee, DVM, University of Minnesota, and Andrea Pitkin, freshman veterinary student at the University of Minnesota, have all demonstrated that 95 DOP filters are an effective barrier for virus entry into herds (pictured on page 50).

The use of air filtration in boar studs has been an effective barrier to PRRS virus, based on field reports the last couple of years. One sow herd has been built with air filtration units using the 95 DOP filters in a pig-dense area, and so far the results have been promising.

PCV2 can also be a concern for reproductive health since it has been demonstrated to be present in herds with fertility problems in sows. Vaccination is becoming very common in developing gilts. At this time, no vaccine has been cleared for use in sow herds, although many herds have been vaccinated with commercial vaccines.

SIV has been a real problem in some herds. The virus continues to change over time, and new strains are circulating in the swine population. This can result in sows running very high fevers and becoming infertile with more recycles, abortions etc. Treating sows with aspirin in the water and Flunixin meglumine (Banamine from Schering-Plough Animal Health) injections will help to control the fever while the herd is breaking. Commercial vaccines are available, but make sure the strains identified on the farm are included in the vaccine. Work with your veterinarian on the products to use.

Water and feed-grade medications, such as tetracyclines, can be used to treat secondary bacterial infections due to the SIV virus infection.

The diagram above (Table 1) demonstrates an example of a vaccination schedule, detailing the type of products to use and timing of vaccinations, as well as a weekly organizer of activities.

Bacterial Pathogens

Common bacterial infections that lead to infertility include erysipelas, salmonella and ileitis. When these conditions are present, animals will become clinically sick and fertility will drop. Treating these infections and vaccinating are often the best ways to prevent these problems.

Erysipelas treatment with injectable penicillin, boostering vaccination (make sure to use an extended duration product) and using tetracycline in the feed are ways to control this problem.

Salmonella can be treated with ceftiofur sodium (Naxcel Sterile Powder or Excenel from Pfizer Animal Health), along with vaccination and tetracycline in the feed.

Ileitis can be treated with injections of tylosin (Tylan, now a generic drug), or lincomycin (Lincocin from Pfizer Animal Health), vaccination (Enterisol Ileitis from Boehringer Ingelheim Vetmedica, Inc.) and water medication of tylosin, lincomycin or tiamulin (Denagard from Novartis Animal Health).

Bacterial Discharges

Discharges caused by bacterial infections can be a problem in herds and tend to occur more in the summer because environmental conditions are conducive for growth of these organisms. This coincides with seasonal infertility.

Whenever you see bacterial discharges, review the breeding technique to ensure sows aren't being serviced too late in the heat cycle, when they are more prone to contamination. Their systems change from estrogen control to progesterone control during that time.

Also, review the breeding process to ensure pipettes are being handled properly and lubricants haven't become contaminated.

Another possibility for bacterial infection is poor technique when assisting sows at farrowing. This contamination and infection often doesn't show up until breeding. Review farrowing procedures to make sure this isn't a problem. Tetracycline can be used in the feed to help treat these problems.

Prevent these management problems by making sure sows are in good standing heat when bred. Keep the environment and equipment as clean as possible.

Bacterial contamination of semen can destroy semen in storage. If problems are suspected, check with your boar stud to see if they are routinely culturing semen samples and testing processing methods. Stored semen can also be cultured to check for problems. The shorter the storage time, the less likely semen will be damaged even if contaminated.

Review age of semen and delivery schedule and adjust ordering schedule to ensure semen is as fresh as possible.

Eperythrozoonosis can still be an infertility problem, although it is less of a concern today and not commonly diagnosed. Most herds have eradicated external parasites, which helped to spread this agent within herds.

Any pathogen that can produce an elevated body temperature can produce infertility. A good example is SIV, which causes high fevers resulting in infertility. A number of pathogens can result in fevers. Occurrence will vary with the herd's health and vaccination status.

Internal Gilt Replacements

Due to concerns with the introduction of new pathogens, such as PRRS and PCV2, some herds have turned to raising their own replacement gilts on site. This can be done by herd closure or by greatly reducing the number of introductions of grandparent gilts brought on-site. The only introduction to the fully closed herds would be semen, which is the safest form of internal multiplication.

With this approach, it is very important that the proper matings occur. Using a genetic improvement plan is important, as well as making sure that the semen used to develop replacements is the proper semen to maintain a high genetic value. It is important to monitor the estimated breeding values (EBV) of the boars used to produce the next generation of replacement gilts. If the genetics are not properly managed, this can potentially result in bigger costs to the herd than disease.

Tagging replacement gilts at birth will ensure that only the correct gilts are considered as replacements. Figure that roughly 60% of replacement female candidates will meet selection criteria. Grandparent females should represent approximately 10% of the sow herd.

Environmental Factors

Environmental conditions are another factor. Higher barn temperatures can definitely impact fertility with increased returns both at regular and irregular time frames. The use of cool cells has greatly reduced the impact of high temperatures. Some boar studs are using air conditioning along with filtration to control temperature.

In tunnel-ventilated barns, especially in late summer and fall, days are shorter and nighttime temperatures begin to drop. If the ceiling inlets are not reopened in time, the cool cell end of the barn can drop to very cool temperatures because the controllers read the average temperature of the barn. They continue to get cooler on the cool cell end because the curtain opens and lets 50°F air in and the fan end of the barn just gets warmer.

This situation sets up a repeating cycle unless the ceiling inlets are opened on the fan end of the barn to allow some attic air in to balance out the temperatures. This chilling at the cool cell end of the barn results in stress, and can cause the animals to develop any number of diseases, and they are therefore more likely to show infertility problems.

There is also debate about the use of timed lighting, but the cost of running lights and timers for 16 hours is not that high, so most lighting systems attempt to mimic the longest day. A guide to the amount of light needed is if you can read the paper, you have enough.

Seasonal Problems

Entering the fall, most producers focus on the seasonal effects on fertility. In the northern hemisphere, seasonal infertility is associated with sows bred from July through September. This seasonal infertility results in fewer sows farrowed and fewer pigs born in early winter — November through January.

This trend has a well-established pattern, which is even reflected in the market price of hogs slaughtered in the May through July period. Understanding this pattern is important, because many times this may be the most or only profitable time of the year. If producers prepare for this pattern, they can capitalize on it.

It is believed that warm summer temperatures and changes in the photoperiod (amount of daylight) cause this seasonal infertility. Diseases only compound and potentially magnify this problem.

One other concern is the money producers spend on diagnostics for this seasonal problem, which may not have anything to do with a pathogen. The challenge for veterinarians and producers alike is not to let a health problem go undiagnosed, thinking it will get better later in the fall.

Expect to see a 2-5% decrease in breeding performance due to seasonal infertility if temperatures are controlled with some form of evaporative cooling. If rates exceed that range, there are most likely other problems in the herd. Watch for longer wean-to-first-service intervals, an increase in irregular recycles, more not-in-pig sows and more pseudopregnancies.

False Pregnancies

Pseudopregnancy is one of the most frustrating types of infertility. The definition of pseudopregnancy is the functional corpus luteums (structures on the ovary that form after the egg ovulates and produce progesterone to maintain pregnancy) are maintained beyond expected luteolysis (the process of breaking down the corpus luteums either to come back into heat or at farrowing in the absence of viable fetuses).

There are two types of pseudopregnancies — a short and a long form. The short form may be as little as three days in an extended return to heat cycle. These are often undiagnosed and may be interpreted as an abnormal recycle. The long form is greater than 50 days and commonly diagnosed. Most of these sows visibly appear to be pregnant, and the pseudopregnancy may not be apparent until the sow has gone through an extended gestation period and accumulated many nonproductive days.

If a nonproductive sow day costs $1.50/day, and a sow goes 114 days before detection, these losses can cost $171/sow in direct cost. The lost opportunity of another litter of pigs in that week of production at 10 pigs weaned/litter at a value of $30/pig adds another $300 loss.

Some of these sows have udder development and have even raised nurse pigs without farrowing any piglets themselves.

How does this happen?

The sows really were pregnant, but the fetuses were lost some time between Day 11 and 35 of pregnancy. This makes diagnosing this problem very difficult, because by the time the sows are identified, it is well after the cause. Anything that can affect the fetuses in this time frame — including viral diseases such as PPV, PRRS and SIV — may have caused the losses.

Zearalenone toxicity (a mycotoxin) is another cause, and can develop as both the short and long forms. Zearalenone acts like estrogen and can lead to pseudopregnancy if cycling animals are exposed at Days 11-12 of their cycle. If the source of zearalenone is present for more than 8-9 days during this period, it can lead to a long pseudopregnancy.

Very often sows visibly appear pregnant and will even develop an udder; however, at the time of their normal 114-day gestation period, these signs will disappear and the sow will look open. If these sows are moved back to the breeding area, they will cycle and come back into heat, typically in 5-7 days. The best way to diagnose these sows is with repeated real-time ultrasounds.

Sow Nutrition

When diets are properly formulated, there should be no concerns about nutrient shortages or toxicities that could result in infertility. Test the diet periodically to ensure standard inclusion rates have been met and formulations match what sows are actually getting.

Keep an eye on the age of vitamin ingredients (no more than 90 days); this is the key to making sure what is still active.


The best means to manage seasonal infertility is to compensate for it in the number of females serviced. However, this doesn't help if it results in more crowding and stress, which can also lead to lower fertility rates.

There are many reasons for infertility. A good vaccination protocol to prevent the common infectious agents that can cause infertility is the backbone of prevention.

Having a good biosecurity program is essential to disease control. Providing a good-quality environment will help to reduce the impact of seasonal infertility.

A good recordkeeping program can be a great help in diagnosing fertility problems in a breeding herd.

Table 1. Vaccination Schedule1
Animal Timing Product4 Method of Administration Withdrawal, days
New gilts and vasectomized boars In week post-arrival/at selection Ileitis
Autogenous SIV2
Porcine circovirus type 2
2-weeks post-arrival/at selection Swine influenza virus (SIV)
Autogenous SIV
Last week before entry into herd Dewormer Oral 5
Gilts Entry into main herd IM 21
Vasectomized boars Every 6 months
Every 3 months
Swine influenza virus
Gilts prefarrowing 6 weeks prefarrowing Feedback Oral 0
5 weeks prefarrowing Rotavirus-clostridium perfringens-type C-E. coli
Swine influenza virus (SIV)
Autogenous SIV


4 weeks prefarrowing Feedback Oral 0
3 weeks prefarrowing Feedback IM
1 week prefarrowing Dewormer Oral 21
Sows prefarrowing 6 weeks prefarrowing Feedback Oral 0
5 weeks prefarrowing Feedback
Autogenous SIV
Swine influenza virus (SIV)
4 weeks prefarrowing Feedback Oral 0
3 weeks prefarrowing Feedback
Rotavirus-clostridium perfringens-type C-E. coli


1 week prefarrowing Dewormer Oral 21
Piglets Day 1 Fortified iron (200 mg) IM 30
1Herd is negative for porcine reproductive and respiratory syndrome and Mycoplasmal pneumoni.
2SIV refers to swine influenza virus.
3IM refers to intramuscular (injection).
4Dosage per label instructions.
TAGS: Reproduction