Some Thoughts on Mixing Pigs

Wendell Berry in the ‘Unsettling of America’ writes…’the standards of cheapness and convenience, which are irresistibly simplifying and therefore inevitably exploitative, have been substituted for the standard of health (of both people and land), which would enforce consideration of essential complexities.’ To put this into context, Wendell is writing at this point about the fact that ‘the consumer wants food to be as cheap as possible’ and ‘the producer wants it to be as expensive as possible.’ In the brackets the text could be paraphrased ‘people and pigs’. I recommend this book to anyone who has a genuine calling to, as he succinctly puts it,’ living out of the possibility of kindly use’ in terms of the way we farm, through understanding and imagination. This is in contrast to the institutional and organisational solutions that have, narrowly defined and simplified actions.

Industrial principles can override essential complexities yet the key to success within industrial production is to understand and to bring to bear benefits inherent in such complexities. For this collection of thoughts, I am indebted to Bobbie Watchorn née Fryers for allowing me to read her degree dissertation, written in 1976 in which she herself acknowledges research as far back as 1949.

For some time, I have believed that mixing pigs whether sows or their progeny, at various stages of their respective production cycles incurs a production cost in degrees of lost performance. Some mixing is unavoidable but most is dictated by industrial thinking. Measurement of this assumed loss is scant and unavailable, hence this piece is just some thoughts on the subject.

The breeding herd.

My belief for the breeding herd is based on the service group being a herd within the (total) herd. The ‘ideal’ group size for feeding pigs, below, is 10 to 20 and I suspect that this holds true for the service group of sows. It is quite common practise on larger herds to have three separate parts of each service group. There will be the replacement gilts in a group of their own, or on smaller herds they will be housed separately throughout the first gestation in order to manage their development. This is because the gilt will continue to develop towards adulthood possibly through to their second parturition. The sow will be split between small and large which usually equates to parities 2 and 3 in the smalls group and parities 4 and above in the larger animal group. This works reasonably well if the individual service group mirror the herd in parity distribution as parity 1, service to weaning will make up around 24% of the herd, parities 2 and 3 a further 42% and parity 4 and above the remaining 34%. The most important thing about getting the replacement flow and the service group balance correct is that cohorts of animals move through the herd production cycles undisturbed and avoid any introduction of sows outside the cohorts causing maladaptive behaviour leading to stress. Part of achieving this uncompromised flow is a strict management of breeding failure (which is another subject) where the practise of re-serving returns is kept to a minimum level or not at all. The benefit is the mitigation of social upheaval that can contribute to reduced overall output performance. Each parity cohort stays together, apart from any culls and mixes with only one other cohort (in a 1 to 5 parity structure) at the beginning of 4 of the 5 production cycles in a lifetime. This can also contribute to less culls, and reduced sow mortality.

The feeding herd.

The first hierarchy begins to become established in the litter once all the piglets have arrived. The sibling hierarchy will remain as long as siblings are retained in the same group therefore if litters are mixed after weaning pigs become members of more than one hierarchy simultaneously. These complexities need understanding in order to mitigate as much as possible the loss of feed efficiency through stress. Bobbie Watchorn puts it like this ‘A knowledge of the maximum number of individuals which can form a linear-type dominance hierarchy would seem to be important. It could be argued that this number might also represent the maximum number of animals which can organise themselves into a behaviourally stable group, and that this should therefore be the maximum number of animals kept in any one pen.’

Pigs of similar social rating tend to continually antagonize one another whereas groups of varied social rating establish more settled dominant/subordinate hierarchy’s. Grading pigs into batches at weaning seems to ensure an on-going insecurity in the batch. Any further introduction/removal of pigs leads to further stress. Research suggests that pigs belonging to a single stable hierarchy is limited by the pigs’ capacity to remember the identity of the other members of the hierarchy. This supports the importance of size variation within the group.

In her 1976 dissertation, Bobbie Watchorn cites reasonably comprehensive research that suggests the ideal group size is between 10 and 20 pigs for establishing a stable hierarchy. Husbandry will play a large part in achieving and maintaining success at these levels. However, a good proportion of indoor finishing accommodation is based on the ‘ideal’ population range. Currently weaned pigs are commonly graded into large groups and the group size reduces as they move through. An increasing number of producers are also grading into gender groups. Mixing is therefore considerable.

I have long suspected that long narrow pens, in terms of shape, are detrimental to social stability in feeding herd groups because they increase the encounters between pigs in the pen. Pigs like their personal space just as much as me and you. Bobbie Watchorn highlighted the fact that pigs ‘maintain a “personal field” only in front of their heads and often rest side by side in physical contact with one another’.

Much discussion has taken place in recent years on the subject of phase feeding of grouped slaughter generation pigs. This has even more relevance if the grouping is based on the above as it optimizes the efficiency gains from reduced and improved management of grouping these pigs.

There is much more to discuss in regard to the on-going welfare of the pig which ironically Bobbie Watchorn also covers in her work from 1976, but this piece has simply concentrated on some thoughts on the mixing of pigs.

I wish to express my gratitude to Bobbie Watchorn for allowing me to read and use her work.


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