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Space/comfort, after feeding and nourishment, is without doubt a limiting factor for the establishment of a quick, and above all, solid hierarchy.
Although the european law, Dir 88/2001/CE indicates the minimum surface space that must be allowed for animals, the simple availability of these spaces may not be enough to guarantee access to a comfortable zone with regard to space and temperature, adequate dryness and cleanliness, that allows all the animals to stretch out at the same time, rest and get up with normal movements.
First contact
Insistence
Attack #1
Attack #2
Attack #3
Retreat
The changing of the seasons, the increase in weight of the animals or the change of operators can alter the equilibrium between the animals and their environment, which reduces, sometimes even dramatically, the available resting space. In many cases the simple increase in the amount of space can immediately solve the problem, while in other cases it is the actual positioning of the box or the choice of materials that need to be reconsidered.
Maintaining a group together from birth until slaughter is not very usual in pig production, although it could provide certain advantages with regard to social conflicts.
On farms, pigs suffer many groupings that may cause aggressions with dramatic results too. The most intense aggression occurs during the first two hours of the grouping, and this then decreases to lower levels in the following 24-48 hours.
The lack of familiarity is the main cause of the aggression. In fact, the piglets show the same level of aggressiveness towards piglets that are siblings as they do towards siblings from which they were separated at birth. In groups with defined dimensions the conflicts increase in line with the increase of “non-family” pigs in the group. Pigs that have never been in the same group but that have a certain degree of contact through the dividing bars between pens are less aggressive amongst themselves compared to pigs that have never had any contact. When all the pigs from one box are not related to each other by blood, the pig that assumes the dominant position will fight against each pig from the same box to arrive at its position of dominance.
In the case of different litters being mixed, initially only one pig per litter will fight, and the victor will then proceed to attack the pigs of the loser’s litter. As a result the piglets belonging to the victor’s litter tend to reach the same situation of dominance within a box, which does not mean that the more numerous litters have a better chance of gaining dominant positions compared to the litters containing just one pig.
It is generally believed that by homogenizing the groups at the time of introducing into pens, a greater uniformity is achieved when they leave to the slaughterhouse, however, studies have demonstrated that variation in weight is similar in groups whether they were uniform or heterogeneous at the beginning of the fattening phase; other studies have revealed that the growth rate of pigs that are part of heterogeneous groups is equal or greater than that of uniform groups. Post-grouping aggression is actually lower in heterogeneous groups or it is not seen to be influenced by the variation of the weight of the pigs. A hypothesis has been presented which suggests that pigs in groups are perhaps more stable when there is a clear difference in weight.
How can we reduce aggressiveness between animals at the time they are grouped together?
Compared to the space allowed to sows, the area given to pigs/piglets is normally more extensive, because, unlike breeding sows, their weight will increase with time. At least during the initial stages, the getaway space should be assured in the pens intended to be for large groups, since in pens that are still very spread out for 8-12 animals the planning of obstacles and hiding places is not feasible.
In pens with larger dimensions (30-40 animals) it is possible to respect easily the legal recomendations by borrowing an idea from road works. If we choose the correct size, the well-known portable Jersey-type barriers are easy to clean and disinfect, and can be placed inside the boxes and fixed in place by filling them with water.
Equally important for the establishment of a stable hierarchy is the supply of feed and the quality of the animals’ environment. In the weaning phase the feed is offered ad libitum or in a quantity that is sufficient to reduce competition between the animals, however, in some production systems, during the fattening and finishing phases the ration is limited in order to reduce the carcass fat deposition. When the feed is rationed the social competition mainly influences the productivity, in the same way as it influences the availability of space at the trough.
Some studies indicate that the reduction of space at the trough reduces the daily feed intake and the ADG. Attempts to improve growth with more nutritious diets have not produced more favorable results, however, many pigs continue to limit their energy and protein intake. These results suggest that the reduction of intake is more influenced by a metabolic change induced by stress than by the feed restrictions. The presence of hiding zones at the time of grouping reduces aggressions and quickly improves growth.
As far as the animals’ environment is concerned, particular attention should be given to the temperature and to the resting zone, which must be available for all the animals at the same time. The availability of objects for entertainment such as cans, ropes or rubber objects, does not have a positive influence on the reduction of fights, unlike the use of straw as bedding which does have a positive effect. The level and intensity of the fighting is also affected by the intensity of the light and by the time of day at which the animals are grouped: it is recommendable to offer the minimum light allowed or to make any movements of the animals in the last hours of the day.
