5 causes of pig infertility and how to avoid them

There are many reasons for poor conception rates within a breeding herd, and the explanations for an individual animal to be “not in pig” are likely to be multifactorial.

It is unlikely that there will be one silver bullet that will solve infertility issues overnight.

Vet Max Wood, from Larkmead Veterinary Group and winner of the Young Farm Vet of the Year at the 2020 National Pig Awards, explains the different factors that can cause infertility.

1. Health and disease

The most logical place to start when it comes to infertility is disease status.

There are some diseases that have a direct negative impact on fertility, such as porcine reproductive and respiratory syndrome (PRRS) and parvovirus, but other conditions, such as flu, can also be detrimental.

A sow with a fever will struggle to conceive while her body tries to fight infection.

See also: What to consider before a switch to five-week pig weaning

Periodic health screening and comprehensive, tailored vaccination programmes, ensure the breeding herd can perform to its potential.

Pyometra, a non-infectious uterine infection, will also prevent the animal from conceiving.

Possible causes of pyometra include damage to the cervix and soft tissue during farrowing, inappropriate body condition, and low vitamin E and selenium levels.

Polycystic ovaries occur in about 10% of anoestrus cases (where pigs don’t exhibit heat).

It is not clear what causes polycystic ovaries, but stress leading to high cortisol levels and hormone treatment misuse are thought to be causative. Early weaning could also be a contributing factor.

Post-mortem examinations at slaughter can point towards some of these non-infectious causes. The ovaries can be examined for size and structure, and the uterus for any signs of infection.

2. Body condition and nutrition

The body condition of dams at service and conception is very important. The most common cause of anoestrus sows is poor body condition following weaning.

Follow a rising plane of nutrition through lactation as the metabolic needs of the sow increase. Ensure the environment is optimum, particularly temperature, to ensure maximum feed intake.

The presence of mycotoxins, principally zearalenone, within the diet should always be considered when investigating causes of poor fertility.

3. Gilts

Gilts need a little extra TLC to perform well. They should remain on a grower ration until around 80kg, before moving to a specialist gilt ration.

Three weeks before their first service (when gilts weigh about 140kg), they should receive ad-lib quantities of feed to cause a reproductive flush, which subsequently improves egg numbers and quality. 

For the best lifetime performance, gilts should be served at 220-240 days, weighing 140-150kg liveweight with a backfat of 18mm.

Target a conception rate of 95%, with a farrowing rate of 5% more than the herd average for sows.

4. Seasonal infertility and environmental influences

The increased length of days during summer – where day length can’t be artificially controlled – reduces oestrus in the sows.

This is a hark back to wild boar ancestry – it is advantageous not to have litters in the depths of winter.

Some herds can expect a 20-25% reduction in fertility performance, partly from sows failing to cycle and partly from sows cycling without displaying signs of oestrus.

Prostaglandin hormone injections administered 24 hours after weaning may be useful in severely affected herds.

Temperature also has an influence – extremes of temperature, both hot and cold, will have a negative effect on performance. Heat, in particular, makes sows more lethargic, but wallows and shade can combat this.

6. Stress

When an animal is stressed, the stress hormone cortisol is released.

This triggers the “fight or flight” response which stimulates a degree of self-preservation, where resources are directed away from reproduction. High cortisol levels may also give rise to polycystic ovaries.

Minimising stress throughout the weaning, service, and early gestation periods will improve rates of conception.