By Dr Jacolette Jansen, Charles Street Veterinary Consultancy
Internationally there has been pressure on pig farmers to do away with dry sow stalls – either in its totality or only for a specified period of time. For many farmers the thought of converting to group housing is a terrifying concept. Since this has become a social issue many researches have started evaluating the effects of group housing on sows.How do sows interact in groups?
Fighting occurs between pigs which are unfamiliar to each other. Fighting also establishes the relative social ranking between animals, which reduces the need for outright aggression to settle future disputes. Aggressive interaction may continue between familiar animals, but at lower levels unless resources such as food become limited.
Social rank in sows has been shown to be positively correlated with age, weight and parity. It is therefore recommended that different sub-groups be formed when placing animals in groups. Different sub-groups to form include pregnant gilts, first parity sows and groups according to body condition. This is of greater importance when sows are grouped in small (six to eight) animals.
Resident sows (those who have been in the group longest) tend to initiate and win fights more than sows coming into a new group. Pre-exposure of animals can shorten the duration of fighting or even reduce the tendency to fight. This means that the more stable the group remains through different cycles the less fighting will occur in subsequent cycles. Newly mixed sows should therefore be supervised and the importance of good stockmanship can’t be overemphasised.
There is little evidence for an ideal group size at which fighting and aggression can be minimised or even eliminated. The expectation is that the number of fights will increase if there are more hierarchy positions to settle.
Commercial experience has suggested though that aggression is reduced when sows are mixed together into larger groups.
Static and dynamic groups
Static groups are defined as groups where after the initial mixing/grouping of sows, the group remains stable with no addition of new sows. These groups can either be big or small groups.
Dynamic groups are defined as groups where new sows are continually added and taken out of the group. Traditionally these groups are large groups. It is important to know that these animals are at different stages of their production cycle and therefore have varying nutritional needs.
• Floor feeding – this system can only be used for small groups (six to eight sows). Food is dispensed onto the floor and all the sows eat simultaneously. Fighting does occur during feeding times and submissive sows tend to withdraw from eating. Partitions can be placed between the feeding spaces but the disadvantage is that these take up more of the available space which can cause more aggressive behaviour amongst sows.
• Individual stall feeding – some housing systems allow for a communal area where sows can move freely but feed is dispensed for the number of sows in the group in individual stalls. Only one sow can enter a stall and when she has consumed her feed she can move out of the stall. These systems have the advantage that sows do not fight while feeding and it still allows for free movement. It is however an expensive housing option.
• Single space feeders – sows eat throughout the day and night. Some sows will dominate over submissive sows and body condition of sows should be evaluated throughout gestation. Fall out sows should be removed from the group.
• Electronic sow feeding station – theses feeding stations are only viable when having sows in large groups and especially dynamic large groups. Each sow can be fed according to her nutritional requirement as sows are fitted with transponders. Sows are fed singly and while a sow is eating the other sows can’t enter the feeding station. Different systems are available but these can commonly accommodate the needs of up to 60 sows.
There are numerous possibilities for the group housing of pregnant sows. Each farm will have to evaluate its own system and customs and only then can a specific group housing system be considered. Adaptations to current buildings or the construction of new buildings can only be done once all possibilities have been evaluated.