Pre-sorting pigs by weight at the beginning of the growing and finishing stage offers no major advantage to producers, according to results from trials at PSCI. Ethologist Dr. Harold Gonyou oversaw the trials. He says while the conclusions might come as a surprise in terms of current production practices, they make sense based on what we know about pigs’ social behaviour. For the producer, it means one less chore.

“You don’t have to worry about spending time sorting your pigs,” Gonyou says. “It’s not that critical to the productivity of the animal.” This shift in popular wisdom comes from management changes in the last 20 years. Back then, the practice of sorting by weight had merit, as pigs that were three or four weeks apart in age might be grouped together. In addition, pigs weren’t given all the feed they could eat. Under such a system, smaller animals were at a definite disadvantage. Today, groups of pigs are typically only a few days apart in age, producing a very uniform range of weights. They are also demand-fed, so they get all the feed they want. Under this system, social interaction becomes more important. It’s better to keep together pigs that know each other and have an established hierarchy. This reduces fighting and other problem behaviour. Two trials were conducted to answer the questions of whether pigs should be sorted by weight, and whether continuous flow or all in-all out pig flow management should have a bearing on the decision. Pigs were classified as Heavy, Medium and Light before being put into pens. Barrows and gilts were handled separately, as it has been established that each gender has different protein requirements and growth rates. For the uniform pens, pigs from a single weight class were grouped together. For the variable pens, pigs of two or more weight classes were included. Researchers kept track of how fast the pigs were growing, how much they were eating, how aggressive they were, how much time they spent at various activities, and how long it took to bring them up to finished weight. There were no adverse effects from having variable weight pens. Uniform and variable weight pens emptied at the same rate under the continuous flow system (an average of 105.5 days). There was no significant difference in the way the pigs behaved. Under the all in-all out system, sorting appeared to slow down the rate of turnover in the pens. Rooms of variable weight pens emptied nearly six days faster, on average, than the rooms with uniform weight pens (110.9 days for uniform pens versus 104.1 days for variable pens). Gonyou says the results from the PSCI trials are consistent with previous studies he has conducted, and there is growing confidence that sorting by weight is unnecessary. In fact, when pen-emptying rate is factored in under the all in-all out systems favoured today, it makes more sense to randomly assign pigs to pens, within gender.

TAKE HOME MESSAGE
Sorting pigs requires labour, and results in remixing, a practice known to reduce feed intake and gains in growing pigs. The practice is not adding value to a continuous flow barn and may be detrimental to room turnover in all in-all out barns.