Vulva Biting

Pig veterinarian, Mark White, describes the causes, prevention and treatment in a Health Bulletin from NADIS.
calendar icon 8 December 2010
clock icon 6 minute read

Figure 1. Mild vulva biting in group based sows

Figure 2. Severe vulva biting can lead to problems at farrowing

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

Figure 4. Small stable group – here in cubicles – may be less vulnerable to vulva biting

In 1999, close confinement of sows during pregnancy in stalls or by way of a tether was banned in the UK. 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 NADIS surveillance data suggesting that at any one time 1.5 to 2.0 per cent of sows seen have active (i.e. recent) damage to their vulvas. 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.

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 and as such, there will be a greater blood supply to the tissues exacerbating the haemorrhage.


Assuming non-fatal haemorrhage occurs, the healing process will lead to scarring which can interfere with subsequent farrowing, leading to obstructions 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 possibly 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.


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:
    1. Long thin pens
    2. Inadequate feed distributors
    3. Poor feeder design especially with ESF freedom
    4. Small pellets of feed on deep straw
    5. Underfeeding
    6. Single daily feeding
  2. Social environment shortcomings including:
    1. Large group sizes (more than 10 sows)
    2. Uneven sizes of sows within the group
    3. Unstable or dynamic groups
    4. Presence of a boar within the pen
    5. High stocking density/low space provision
  3. Other contributing factors have been identified as:
    1. High rates of return to service – presumably increasing activity and producing swelling of the vulva
    2. Inadequate access to water points either due to layout of the pens or inadequate space/number of drinkers
    3. Chilling and draughts

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.

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, and
  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, and
  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 heat pulp either within the diet or as a separate supplement, and
  3. bed sows on good quality barley straw – sows will tend to eat this and be more satiated as well as drawing a modest nutritional benefit.


Badly injured sows should be removed to a single hospital pen. Medication 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.

December 2010

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