Introducing sows to groups

• Small stable groups which stay together, barring mishaps, until farrowing.
• Large dynamic groups where sows are added and removed on a regular basis – usually weekly.
• Groups built up over a period of 2-3 weeks to a group size of say 40 and then maintained as a stable group until farrowing. Note that in systems where the group is built up over several weeks there are likely to be significant levels of aggression at each introduction.

• Agression is most commonly seen during the development of the pecking order which occurs when sows are first mixed.
• It is important that the housing system and management practices cater for the establishment of the pecking order within the group.
• Once the pecking order has been established there is normally less severe aggression displayed as the less dominant animal in any confrontation will generally back down. However it is important that resources such as feed access and lying area are not limited since this could affect the welfare of timid sows within the group.
• Pens used for newly mixed sows should aim to minimise the results of aggression allowing sows to establish the hierarchy with minimum damage.

• Ideally a minimum space allowance of 3.5m2 (37½ sq. ft) per sow is required to ensure adequate space for normal sow behaviour.
• Note this represents more space than the commercially accepted requirements for lying and dunging/exercise areas.

• The distance required for an individual to get away is of crucial importance.
• For example in a situation of unrestricted space in a straw yard with dynamic grouping the distance over which sows were pursued following aggressive interactions varied from 0 to 20m (66’), with 75% of encounters resulting in chase distances of less than 2.5m (8’2").

• These can play an important part in pecking order formation. When two animals confront each other the ability of the less dominant individual, once beaten, to get out of sight of the other can quickly end any aggression.
• Ideally barriers should be provided within the pen at mixing. Barriers should be flexible e.g. big bales or a suspended partition of colliery belting, not fixed items which could in themselves cause injury.

• Pen design should ensure there are no sharp edges or protuberances e.g. drinkers or feed troughs.
• Sows should not be mixed in cubicle systems. Sows can be trapped in the cubicle during bouts of aggression and may be injured.

• The timing of mixing should fit in with management routines. There is some evidence that mixing in the evening may be beneficial but it is more important that stockpersons are available to oversee the operation.
• The use of an ad lib feeding system at mixing is likely to be beneficial
• Other management aids are likely to be of limited use. Tranquillisers and masking sprays have limited useas the need as the need for formation of the pecking order is not removed.
• The addition of fresh straw at mixing is only likely to delay normal onset of mixing behaviour.
• age for the formation of a group is at weaning. Mixing around implantation stage – generally 13-35 days after conception – should be avoided as stress at this time can result in higher levels of return to service.
• Avoid re-mixing sows wherever possible. If it is practical mix sows back into their original group post weaning.
• There is some evidence to suggest that physical contact, e.g. through a gate, between a dynamic main group and the sub-group to be introduced into it, may reduce the level of aggression at introduction.

• A rectangular pen is ideal with a central flexible barrier around which sows can pass each other easily.
• Space allowance should be a minimum of 3.5m2 (37½ sq. ft) per sow.
• The pen should be straw bedded and floors should provide adequate grip.
• Any fixtures in the pen e.g. feeders, drinkers, should be well protected to minimise the risk of injury.
• Ad lib feeding is recommended to minimise aggression.
• Pen size should be matched to group size required in the main dry sow housing system.
• The pecking order should be established within 1-2 days.

• In dynamic group systems the weekly sub-group should have an established hierarchy prior to being added to the main group, i.e. use of a specialised mixing pen is recommended.
• The size of the sub-group is important and should not be less than 3 animals according to the best information available. The size of the overall group is not critical.
• In deep straw yards where the sub-group is added to the larger group, layout is not critical as long as there is adequate lying space, and extremes of pen shape are avoided.
• Breaking up the lying area with divisions around the perimeter – forming a specific area for each sub-group – can be beneficial particularly in non-bedded systems.
• Penning a new group in an area which has been closed off for a few days prior to the addition of the new sub-group can help in the establishment of that group’s territory.
• In competitive feeding systems e.g. floor feeding, it is particularly important that newly introduced sows can compete effectively for resources e.g. lying space, feed, water etc. The housing/feeding system should be designed such that there is adequate space/feeding places for all stock.
• Herd performance is likely to be better where sub-groups are mixed into the main group at least 5 weeks after service, i.e. after implantation is complete.
• Gilts and small sows can have difficulty competing within a mixed group. It is generally recommended that they are housed separately.