Ivory Towers: Four legs good, bad and resistant

DO PIGS have personalities? This important question is tackled in the paper 'Individual behavioural characteristics in pigs' by M J C Hessing, A M Hagelso, J A M van Beek, P R Wiepkema, W G P Schouten and R Krukow, published in the current (September 1993) issue of Applied Animal Behaviour Science. And the answer is that they do, much as George Orwell predicted.

Quite apart from the inherent interest of the matter, it may have important implications for pig- breeding. 'For instance', they write, 'putting only dominant animals in a group is asking for trouble. A mixture of dominant and subordinate ones may be more appropriate. If such a reasoning makes sense it might be worthwhile composing groups of pigs in intensive husbandry on better grounds than is the case now.'

With this in mind, they set out to determine behavioural characteristics of pigs that were easy to identify and stable over time.

Stage One: 218 piglets from 20 sows had their ears tattooed for identification purposes. At one week of age, two or three piglets from one litter were were placed in a metal crate with an identical number from another litter. This 'Social Confrontation Test' continued for 30 minutes, during which a tally was kept for each pig of the occurrence of sniffing, threatening, biting, head knocking, fighting, chasing, fleeing, withdrawal and passive behaviour, as well as noting which piglets started any fights.

A score for aggressive behaviour was then obtained by adding the numbers for threatening, head knocking, biting, fighting and chasing. On the basis of these figures, pigs were classified as Aggressive (A) or Non-Aggressive (NA).

Stage Two: A repeat of Stage One, a week later.

Stage Three: 'The Backtest'. Each pig was restrained on its back for 60 seconds with a hand placed loosely over its head. The tester kept a record of how many times it tried to escape and its number of 'vocalisations'. This was done once in the first week and twice in each of the second and third weeks. On the basis of these results, all piglets were then classified as Resistant, Non-Resistant or Doubtful (R, NR or D).

Stage Four: At ten weeks of age, the piglets were mixed and relocated into large groups, and the same behavioural elements as in Stage One were measured. To aid identification, the pigs had numbers painted on their backs.

A statistical analysis now confirmed the testers' hypotheses. 84 per cent of the pigs classified as A or NA in the first social confrontation test displayed the same behaviour a week later. The aggressive pigs from stages one and two tended to be resistant in the third stage.

Aggression and resistance in the first three stages both proved to be good predictors of aggression in the wider social context of stage four. They conclude: 'The present work demonstrates that in pigs consistent individual behavioural characteristics exist . . . experiments have been started to reveal how, in pigs, an optimum group composition can be realized based on their individual characteristics.'

The researchers are optimistic that this approach will bring positive results, following earlier research by D von Holst who demonstrated in 1986 the stress- reducing effects of social support in tree shrews.

There is no information at present on whether aggressive or non-aggressive pigs produce better-tasting bacon.