Vulva Biting

Author: Mark White BVSc LLB DPM MRCVS
Reviewed: Mark White BVSc LLB DPM MRCVS 2016
Published: 2010

At the end of the 20th Century close confinement of sows during pregnancy in stalls or by way of a tether was totally banned in the UK (except for short periods for feeding, veterinary examination etc).

The ban has subsequently been extended to the whole of the EU although in many countries close confinement of pregnant sows is still permitted for the first 4 weeks after service. Whilst intended as a measure to improve sows' welfare by allowing greater freedom to express 'normal' behaviour, it has allowed far greater interaction between sows and in particular aggressive interaction. As a result, damage to the vulvas of sows by way of biting has become a significant problem on some farms with surveillance data suggesting that at any one time 1.5-2% of sows seen have active (i.e. recent) damage to their vulvas. Many more have healed scars in the vulval tissue. Many different feeding systems are used but vulva biting is seen with all types of feed provision (e.g ESF, drop feeders, individual feeders etc). It is more prevalent in indoor situations but can be seen outdoors. This paper will summarise the condition and look at possible causes and measures that can be taken to alleviate the extent of the problem.

Fig 1: Mild vulva biting in group based sows

Clinical Presentation

The first sign often noted within a yard or pen is blood staining on the bodies or noses of sows or on the walls of the pen. Closer observation will reveal damage to the vulva of one or more sows that can range from a mild lesion with minimal bleeding up to virtual shredding of the vulva and major haemorrhage. In extreme cases the haemorrhage can lead to collapse or even death of the sow but this is unusual. In most instances the sow demonstrates little evidence of distress. As a general rule, the more swollen the vulva is, the more likely it will be bitten eg as farrowing approaches and as such, there will be a greater blood supply to the tissues exacerbating the haemorrhage.

Fig 2: Severe vulva biting can lead to problems at farrowing


Assuming non-fatal haemorrhage occurs, the healing process of deep wounds will lead to scarring which can interfere with subsequent farrowing, leading to obstruction and stillbirths or if more severe, tearing of the vulva during farrowing. Scarring may also interfere with subsequent service - especially if natural service is used - and the deformation created can lead to dysfunction of the protective mechanism of the urogenital tract potentially leading to ascending infection of the bladder and kidneys (cystitis/ pyelonephritis) or the vagina and uterus. Serious systemic illness or infertility will be natural consequences. Sows that have been previously bitten are more likely to return to service at the next litter.

It is very rare for biting damage to extend into the anus and recto-anal function is not usually disturbed.

Fig 3: Large dynamic groups can be more vulnerable to vulva biting even if feed distribution is good


A wide range of factors have been identified which have been implicated as trigger factors although there is rarely one single factor involved.

Vulva biting is an act of aggression by other sows. As such, genetically determined behaviour may play a part; behaviour patterns may relate to breeds, families or individuals that are naturally aggressive and will attack each other.

Any factor which increases swelling of the vulva may make it more attractive to other sows; thus, late pregnancy, oestrus and extraneous hormonal stimulation - such as occurs with the mycotoxin zeralenone - may all render the sow more vulnerable to being bitten. However, features related to environment and management can often act as trigger factors.

1. Pen design and feed availability - Any factor which inhibits all sows gaining access to feed can frustrate and lead to aggression. Such factors may include:

  • Long thin pens
  • Inadequate feed distributors
  • Poor feeder design especially with ESF freedom
  • Small pellets of feed on deep straw
  • Underfeeding
  • Single daily feeding

2. Social environment shortcomings including:

  • Large group sizes (more than 10 sows)
  • Uneven sizes of sows within the group
  • Unstable or dynamic groups
  • Presence of a boar within the pen
  • High stocking density/low space provision

3. Other contributing factors have been identified as:

  • High rates of return to service - presumably increasing activity and producing swelling of the vulva
  • Inadequate access to water points either due to layout of the pens or inadequate space/number of drinkers
  • Chilling and draughts
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Prevention and Control

Prevention and control of vulva biting can be very challenging particularly if structural environment is implicated. Vulva biting is a direct consequence of loose housing allowing sows to interact with each other.

Fig 4: Small stable group - here in cubicles - may be less vulnerable to vulva biting

At the planning stages aim to:

  1. Maintain small stable groups of sows
  2. Use well designed ESF feeders for larger groups to avoid queuing, frustration and bullying
  3. Ensure feed is well distributed within the pen to reduce bullying at feeding time
  4. Ensure plentiful access to water
  5. Select stock for low levels and aggression

On a day to day basis:

  1. Group sows by size avoiding mixing large bully sows with small timid younger ones
  2. Do not have the boar within the pen permanently
  3. Use large feed pellets in straw yards floor fed
  4. Feed sows twice daily
  5. Remove any known aggressive sows to individual pens immediately
  6. Manage bedding and feed bins to minimise mycotoxin contamination
  7. Provide adequate bedding and thermal protection

Additional measures to reduce aggression can include increasing gut fill by:

  1. Raising the fibre level of the dry sow diet
  2. Adding sugar beat pulp either within the diet or as a separate supplement
  3. Bed sows on good quality barley straw - sows will tend to eat this and be more sated as well as drawing a modest nutritional benefit


Badly injured sows should be removed to a single hospital pen. Individual treatment with broad spectrum antibiotics and analgesics may be appropriate. Animals should be clearly identified as potential problems at farrowing and if necessary surgical excision of a scarred obstructed vulva (episiotomy) should be performed rather than allowing the vulva to tear naturally.


Little information is available on the financial costs of vulva biting to the pig industry although premature culling is an inevitable consequence in badly damaged sows.

Of far greater significance is the welfare cost to the sow which should always be a primary concern to the stockman and pig farmer.

Comments made in this paper are based on the practical clinical experiences of the author working in the field and opinions expressed are derived from those experiences; others may have different experiences.




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