Boar infertility

Occurrence: Worldwide.
Age affected: Boars.
Causes: Lameness/ leg weakness; mismanagement; infectious infertility.
Effects: Sows return at 3 weeks.


Infertility in the boar is caused by a number of factors. These can include failure of sperm production, production of abnormal sperm, overuse of the boar, physical abnormalities of the male genital tract which prevent delivery of semen at mating, physical or psychological factors which prevent mating and, finally, infection of paternal origin which destroys the products of conception. The production of normal sperm can be affected by genetic factors, age (boars are not fertile until at least 5 months of age and semen quality declines in old animals), high body temperature (fever can cause poor semen quality and even aspermia), high environmental temperatures and infection of the testes and accessory sex glands. Those with ruptured penises also cannot mate. Boars may be reluctant to mate if ill or if lame and some boars will not mate for psychological reasons. This is particularly common in young boars. Finally, infection with agents such as PRRS, leptospiras and Brucella suis and contamination from faecal or preputial organisms can cause death of the products of conception.

Mode of transmission

Many types of boar infertility result from structural, genetic, behavioural or management factors and are not transmissible. The infections causing infertility because of fever, such as influenza, are described elsewhere, but some transmissible infections such as leptospira (e.g. serogroup Pomona) may invade the testes and be present in the semen. This is also the case with some viruses such as PRRS. One important infection causing infertility is swine brucellosis, in which B. suis can infect though contact or venereally and colonises the testes and accessory sex glands, to be present in the semen.

Clinical signs

The most important clinical sign to indicate infertility in boars able to mate is the return of the sow to oestrus at around 21 days as it confirms that a mating has been unsuccessful. Where infection of the genital tract is responsible, vulval discharge may have occurred in the sow. There may be swelling or atrophy of the testes which suggest that semen production could be impaired. Ejaculate obtained in an artificial vagina may be grossly or microscopically abnormal and contain blood or pus or be yellowish if it contains urine. The failure of a boar to mount is obvious in supervised matings, but may present as returns to service where there is no supervision. The fitness of the boar for service must then be assessed by clinical examination and testing for libido when investigating returns to service. The reason for failure to serve should be determined, illness should be diagnosed, lameness identified, psychological factors investigated and the state of the penis assessed. Where returns to service are not associated with failure to service, the possibility of overuse and service late in oestrus should be considered and confirmed from service records and observations of service technique. The records may demonstrate the infertility of an individual boar. Clinical signs of systemic disease such as erysipelas may be present and reduce libido, or the animal may simply be too ill to rise as in acute influenza, the signs of which are clear. Lameness is commonly seen in boars unable to mate or to complete mating and hind limb lameness is particularly important. Infertile boars may show pain on attempting to mate, particularly when the penis is ruptured or ulcerated. Finally, the boar may refuse to serve the sow for psychological rather than physical reasons and may show fear, aversion or simple lack of interest.

When boars are used in studs to collect semen for home use or sale, the semen should be assessed before use. Contaminated semen should be rejected. Ejaculates from boars suspected of infertility should be assessed for volume, colour, consistency and presence of all major semen fractions. Microscopical examination for sperm count, sperm morphology and motility, the presence of pus and blood should be carried out, also laboratory examination for bacterial contamination or pathogens. Poor semen quality may result from past high environmental temperature or fever. Where semen parameters are normal, the possibility of maternal failure or the presence of infectious conditions capable of causing early embryonic death should be considered.

Postmortem lesions

Where there is inability to serve, the presence of arthritis can be identified. In Brucella suis infection, there may be lesions in the spine and in the testes. Abscesses and cystitis may be present in the reproductive tract. Fibrous adhesions resulting from trauma or earlier infections may be present. Abnormality or damage to the penis may be evident and the testes may be abnormal in size or appearance. Microscopical examination of the testicular tissues can identify faults in the maturation of sperm. The lesions of systemic diseases such as erysipelas and influenza may no longer be present by the time that semen quality is seen.

Treatment and prevention

Boars may be treated for lameness, illness and for physical injuries which prevent service. Libido may be improved in young boars by close supervision to overcome fear or incompetence. The effects of high environmental temperature on libido can be reduced by wallows, water sprays, shade and by serving in the early morning. Overuse can be prevented by allowing no more than two services per week. Where poor semen quality is present, priority must be given to maintaining services. Affected boars should be replaced by normal animals. If too few boars are available, artificial insemination (AI) can supplement or replace natural service. Boards which cannot serve may recover after treatment or rest but should be culled if they do not. Semen quality is more difficult to improve. Bacterial infections f the genital tract may be treated with antimicrobials. The effects of high environmental temperature or fever on semen quality take up to six weeks to develop, and are not immediately reversible. Boar infertility may be prevented by careful examination at selection, use when mature, careful training of young boars, prompt treatment of infection, provision of cool but not cold accommodation, attention to flooring to reduce lameness and supervision of service. Sufficient boars should be available to ensure continued natural service or the supply of good quality semen for AI.

Special note

Boar semen quality used in trade is governed by regulation in many countries, especially those of the EU.