When we talk about pigs and aggression, one of the topics that invariably arise is the idea that as a pig matures, you will start to see an increase in aggression. By about 1-2 years, conventional wisdom tells us that the pig will start to challenge anyone who appears 'weak’, strangers, etc, as the pig tries to move up the ranks of the herd. Is this really what’s happening though? A critical analysis of pig behavior tells us that pig aggression is likely much more complex. Ontogenetic shifts in behavior may play a considerable role in what we currently attribute to maturity-related aggression in pet pigs.
Before we get to that though, let's first consider what we already know about how pigs behave in a herd and why our understanding of changes in pet pig behavior in the maturing pig may be incorrect:
1) Piglets begin establishing hierarchies as early as 24 hours old! These squabbles between day-old newborns can be FEIRCE. In fact, piglets are born with 8 very sharp ‘needle teeth’, and commercial hog farms routinely clip these teeth to reduce the incidence of facial cuts that piglets inflict upon each other when fighting! They DO NOT wait until they are ‘mature’ to begin fighting with herd-mates and littermates to establish hierarchies.
2) Studies show that normal pig hierarchies are fairly stable – the piglets don’t challenge the older pigs *just* because they reach maturity (Boars are an exception, but pet pigs should be neutered!). Even if a piglet grows larger than her mother, the hierarchy tends to remain stable, unless one of the senior members of the herd is removed. If a pet pig truly views you as her ‘leader’, she should not automatically begin challenging you at 2 years of age *just because* she reached 2 years of age.
In fact, there is an interesting disconnect when we use the term ‘maturity’ and aggression in pigs. In general, when considering the concept of an animal that becomes ‘aggressive’ at maturity, we are referring to sexual maturity. Indeed, an intact boar WILL become aggressive as he becomes sexually mature. But potbellied pigs mature VERY early – boars can and do breed at just a few months old and females can breed by 4 – 6 months old. So if we are talking about sexual maturity and the presence of aggression, our time-frame for the development of aggression towards people should be 3-6 months old, not 1-2 years old as conventional wisdom tells us. Of course, pigs that are kept as pets should be spayed/neutered for MANY reasons, and in fact, most pet pigs are – so what might account for the idea that pigs begin showing dominance-related aggression as they reach maturity?
I believe that ontogenetic changes in behavior should be given serious consideration when exploring why so many pigs seem to become aggressive as they get older. Ontogenetic changes – or behavioral changes in response to the same stimuli as an animal gets older – occur in many species of animals. These shifts in behavior optimize survival chances for the animal.
Behavioral shifts in response to the same stimulus as an animal matures occur in a wide variety of species and may include a corresponding change in color or pattern as the animal ages.
The Leopard Gecko: Juveniles (left) have bright warning coloration, and a recent study showed that these youngsters are more likely to bite when harassed; that is, they exhibit a defensive anti-predator strategy. As these lizards mature, their coloration changes from bright, conspicuous warning coloration ("I BITE!") to a pattern that is designed for camouflage. Indeed, the adult geckos prefer to hide/flee when threatened, utilizing an escape strategy that coincides with the change in color/pattern and are very reluctant to bite.
Fawns are born with a spotted coat; they are unlikely to be fast enough to flee effectively, and certainly cannot respond by fighting; instead they innately respond to threats by hiding. As they mature and become larger and faster, they will either flee (or in some cases, if cornered: fight) when they are threatened.
If we understand that many animals that display ontogenetic shifts in behavior, also display differences in color/coat pattern between young animals and adults that reflect these behavioral differences, what might that tell us about pigs?
Consider the natural coat of the pig: Adults are generally a uniform brownish color. Piglets are born with stripes; similar to the spots of a fawn, this mottled coat is designed to help a small piglet avoid detection. Small piglets have little chance of successfully utilizing a defensive strategy against a larger predator. Their best bet for survival lies in first, avoiding detection, and barring that, fleeing. Adult pigs have formidable size and weaponry; fighting back is a viable way to avoid predation for a large pig when cornered.
Often, I hear that a pet pig ‘suddenly became aggressive or violent’ as it reached a year or two – presumably because it wanted to ‘move up the pecking order’. It’s easy to assume that if no aggression was noted previously. However, very often, there WERE signs of fear from the pig when it was younger, that either went unnoticed or were ignored by the owner.
A piglet that shies away from strangers, moves subtly away from guests or freezes in the presence of children is utilizing innate behaviors that a young pig would in times of fear. As the pig gets bigger, suddenly the RESPONSE to the fearful event changes, even though the underlying cause is the same. And suddenly an owner may be faced with a large, adult pig that charges guests, snaps at children and bites when cornered.
It’s now understood, even with domestic dogs, that behaviors that may have been previously attributed to dominance as a dog matures can more often be attributed to behavioral shifts in response to the same fearful stimulus. Puppies, like many young animals, are quite defenseless; cowering, moving away or freezing is most often how they deal with fearful situations. As a dog matures, he suddenly has size and weaponry (sharp teeth) that allow him to adopt a defensive strategy of fighting to try and deal with frightening stimuli. The underlying emotion, FEAR, hasn’t changed; however the animal’s response to fearful situations HAS changed.
So why does it matter? Aggression is aggression, right? Perhaps. But if we as a pig-parenting community are misidentifying root causes of behavioral problems, we may well be further exacerbating those problems. If age-related aggression truly was because these pigs were trying to ‘move up the ranks’, and could be resolved by responding through force or being ‘top pig’, then it shouldn’t continue to be such a prevalent issue for pig-parents. If, however, the aggression we commonly see as pigs age is rather an age-related shift in how the pig reacts to a fearful situation, responding with force or punishment is likely to result in an increase in aggression.
We must continue to try and better understand porcine behavior and natural history in order to better address, and hopefully avoid, these common pitfalls; both for our own sake as well as for our porcine companions.