"We define competitive feeding systems as those in which an animal can obtain more feed by winning a fight," say the researchers at the Prairie Swine Centre. "However, this does not necessarily mean that you will observe a lot of fighting in such a system. Often, the majority of fighting will occur within a couple of hours after mixing."

Once a sow’s dominance status has been established by aggression (fighting), it is often maintained by very subtle agonistic behaviour. These behaviours include threats through head movements and body posture by the dominant animals, and, for subordinate sows, moving in such a way as to avoid dominant animals. One study even referred to the social order among sows in a group to be one of ‘avoidance’ rather than ‘dominance’ (Jensen, 1982).

However, if a sow is able to obtain more feed by any of these means, it is a competitive feeding system. Some feeding systems, such as gated stalls and electronic sow feeding (ESF( stations, protect a sow while she is eating and eliminate the possibility of obtaining more feed by fighting.

Competition is a characteristic of the social system within a group of animals. In its simplest form, we have dominant/subordinate relationships among the animals. The definition of dominance is that it results in priority of access to limited and defendable resources.

Pig producers are generally comfortable with group housing if the resource (feed) is not limited, e.g. finishing pigs fed ad-lib.

But sows are almost always limit-fed to control their body condition, and so there is the possibility of competition.

"Our management of competitive systems is such that we attempt to reduce the dominant sows’ ability to control the resource. We do this in two ways: social and physical management.

"We will look at different competitive systems and how they can be managed most effectively," the researchers add.