Check-List for Mixing Pigs

The big error made by most stockpeople is to fail to allow sufficient space for submissive's to avoid dominants and not allowing the dominants in each group to get the challenges over with, so as to create minimal damage and stress to either party, according to Mr Gadd. The answer to this is not to assume that if the to-be mixed groups have existed satisfactory at an acceptable and approved stocking density, that they will be able to do so on being mixed.

"You must allow them more space, and at least +20 per cent is suggested," says Mr Gadd. This is why smaller groups settle down better than larger groups in relatively constricted pens, such as in a typical flat decked nursery, and why much larger groups can often be mixed with no discernible trouble in straw-based yards where there is much more gateway space, or if needs be 'sleepway' space for the first night or two. This is another example on the 'big pen' concept.

'Sufficient space' certainly involves voiding/exercise and resting ares but also includes feeding space. In the feeding space it is preferable to have two drinkers (or more) rather than just one. The majority of aggressive incidents occur at or near feeders and this is why an extra feeder or temporary trough/hopper seems to help.

If it is practicable, reduce the feed allowance slightly for the to-be mixed and recipient pigs, say by one third, from the morning of mixing day. However, do not overdo this as it will increase aggression at mixing. The aim is to get all the pigs slightly hungry, but not overly so.

If withholding some food prior to mixing, extra trough space is vital as two-thirds of aggressive acts are directed at pigs trying to approach the feeder. Feeder seeking is so important that subordinate pigs can attack dominants. To avoid this, put in a temporary feeder/trough so the chased away pigs can gain access to it.

The best time to introduce the pigs is just before dusk, certainly by late afternoon. It is best to move pigs quickly but gently as stressed pigs are more aggressive, especially in new surroundings.

Once the pigs are moved now, you can allow ample feed.

After pigs are moved immediately spray them with lavatory freshener aerosol or detergent. "Sump oil is far too messy," says Mr Gadd.

If using bedding, re-bed amply just before mixing. Also, place some of the to-be-mixed pigs faeces in the voiding area.

Another thing to check is drinker flow and adequacy. Submissive pigs will be last to eat and so they tend to fill up on water as they wait and this itself may induce tail–biting.

Do not batch too evenly, especially young pigs out of the nursery. A four-kilo range is better than identical weights for smaller pigs and maybe up to a six–kilo difference for older pigs. Why so much of a difference? This allows dominance to get established more quickly and then the pen settled down sooner. At 21 to 28 days, a one-kilo range may be good within each batch of, say, 20.

It is also important to check you are not exceeding stocking density, which can be a common error. "Try to put in one less pig per pen if practicable, ie de–stock by 15 per cent," says Mr Gadd. Try to remember that mixed pigs need fleeing space.

In typical intensive nurseries, small groups (under 20) mix better than large ones, and 12 is better still.

In larger groups, ie 'big pens', now gaining favour, once group size reaches 50 to 100 animals, the drop–off in weight gains after mixing begins to disappear.

Rechecking ventilation. Getting the two groups to 'rub together' in the first night is important, so an ample warm and dry sleeping area helps this natural socialisation. Submissive animals tend to 'sleep out', get cold and stressed and may tail–bite the next day. A temporary cover or lid across the pen has been known to help but do not place it flat – raise only one end by a few centimeters to circulate the air over the sleeping pigs.

To conclude, the most important thing to do is observe your pigs. Mixing can awaken a latent persistent tail–biter. “Often, I find a small female. Watch for this pig, which must be removed and penned with others displaying a similar trend, whereas in large units, a sedative can be given. Such pigs rarely convert well, and whether to keep such individuals is debatable,” adds Mr Gadd.

General Check-List for Mixing Sows

Cater for the least dominant sow in the group, advises Mr Gadd. If you get the conditions right for her, not only will she benefit materially but the whole group will settle down more quickly. "Farm for the most timid sow" is sound advice.

Allow a minimum of 3.5 square metres per sow.

Adequate fleeing space seems vital. MAFF reports that 75 per cent of aggressive sows will not chase another sow beyond 2.5 metres (range: 0 to 20 metres). While the jury is still out on ideal pen shape, it could be that a larger, narrow pen could allow more fleeing space than the same stocking density in a square or near-square shape. While the latter is generally favoured, if you give them enough space, it probably does not matter.

A specially designed mixing pen may be a useful idea, especially where a gilt has to be introduced into an established group. The pen should be straw-bedded and floors provide adequate grip, i.e. not a soft, spongy undersurface.

The mixing pen can be used for about 24 hours. Aggression is worst in the first four hours from introduction, so periodic suspension is wise during this time – say once an hour.

Pen size should be matched to age and weight of the animals housed.

A mixing pen adds six per cent to the breeding units capital cost; about 0.5 per cent to total production cost per year (for a 500-sow herd).

Ad-lib feeding reduces aggression. Competition for food is a significant trigger. If you can, provide sugar beet pulp from single space feeders.

Both wet-feeding and, to a lesser extent, trickle feeding, minimise aggression.

Despite careful measurement of subsequent performance in one trial, when sows were mixed from one week to six weeks after service (to cover the implantation period in depth), there were no significant differences in total born, born-alives or total litter weight born.

However, it is still current advice not to mix sows during the implantation period, and the writer can quote several cases where returns to service and poor litter size responded quickly when it was suggested that it was a good idea to move batch introduction of new gilts into the herd’s farrowing profile, rather than their introduction into what is called dynamic breeding groups. This could be valuable in outdoor breeding paddocks even though, paradoxically, there is much more room for escape.

Mixing in the evening may be beneficial, suggests the author.

Adding fresh straw at mixing tends to delay the settling of peck-order as the more dominant sow’s attention is distracted for a while. However adding fresh straw at evening or late-afternoon may be beneficial in aiding socialisation. It depends, in Mr Gadd's experience, on whether the sow genotype is basically placid, the space available and the frequent presence of a familiar stockperson. If some or all are borderline, fresh straw helps, he says.

Avoid re-mixing sows whenever possible; if so, a mixing pen as described is very worthwhile, concludes Mr Gadd.