Biting and damage to the anus of growing pigs is a rare but extremely damaging condition that is normally categorised along with tail, flank and ear biting as a vice. As with these other forms of aberrant behaviour, the causes are often multiple and complex and can be particularly difficult to control.
Whilst the condition is not frequently seen, it occurs most often in the middle growing period of 20-60kg. Close observation may identify a single culprit as the instigator of it. The condition is seen irrespective of tail docking, being seen in all situations from pigs with undocked tails to those with the shortest dock.
It can be described more as a nibbling rather than the more devastating biting damage that is done to the tails but can become quite extensive as blood is revealed. It will occur in both sexes but in gilts can extend to include damage to the prepubertal vulva. The condition does not appear to be associated with oestrous onset in young gilts.
A further trigger for biting is a rectal prolapse. These are frequently attached by pen mates and one blood is drawn the behaviour can become frantic and spread to other pigs not affected by prolapses.
As with all vice patterns there are many factors which may trigger anal biting but the most common appears to be:-
1) High stocking density - close to legal maximum limits.
2) Variable temperatures.
3) High levels of competition for feed and water, not necessarily related to overall space provision.
4) Concurrent disease. As with most vice problems, diseased pigs tend to be "unhappy" pigs and are more prone to aberrant behaviour.
Where anal biting is triggered by previous rectal prolapse, the trigger factors for that - which include fast growth, overcrowding, temperature variation, scour and straining, and pneumonia - should also be considered.
In its mildest form, damage to the anus will heal without consequence. However, as the level of damage increases, the consequences become more serious. Straining as a result of damage can produce rectal prolapses with further more extensive damage and the well recognised consequences such as classic rectal stricture or even evisceration.
In early cases of anal damage, the pig is likely to become faecally incontinent but as severe damage heals, it can form a stricture similar to that seen with rectal prolapses and the result is that the pig is unable to pass faeces and gradually "blows up" whilst losing condition, becoming hairy and often jaundiced (yellow). The abdominal distention can be very marked.
Spinal abscesses that can occur as a result of tail biting do not tend to occur with anal biting.
Gilts suffering concurrent vulva damage may be compromised as future breeders.
There is little treatment that can be given other than in mildly affected pigs isolation and supportive antibiotics. Where severe, humane destruction is necessary. Surgical repair whilst feasible is uneconomic. Rapid identification and isolation of a single culprit will minimise the extent of the problem. It is not appropriate to move that pig to another pen both due to risk of repeat offence and the risk of antagonism to that pig from new pen mates.
By its very nature, anal biting tends to be sporadic in incidence and generally rare enough that it usually only occurs as a one off episode.
Attention to basic husbandry to minimise the trigger factors involved in all vice problems, are an essential part of disease control problems. Should anal biting become a recurrent problem in the herd, then a full review of the circumstances must be undertaken with the veterinary surgeon to identify and correct any inadequacies.
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