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The introduction of automatic sorting scales for finishing pigs has led to a trend towards utilizing this equipment in pen layouts with several hundred pigs in one group. Such systems are well established in North America, but there is still limited information regarding pen design, performance, pig welfare and many other aspects.

As so often happens with new technology, the advantages are oversold, while the disadvantages are sometimes conveniently ignored. Having said that, there is no doubt that large-group autosort systems (LGAS) have many benefits to the producer and the pig. However, any downside to the system needs to be understood and solutions found to minimize their impact on the bottom line.

First, it is important to recognize that the key advantage of LGAS is derived from its ability to automatically select pigs for market and optimize average slaughter weight. This alone can be worth several dollars per pig, while there are also significant labour savings compared to removing pigs from their pen for weighing.

The second big advantage, for both the pigs and the operator, is that pigs in large groups are easier to handle and transport. Research carried out by Dr. Harold Gonyou at the Prairie Swine Centre has shown that there are differences in the way pigs in small and large groups respond to stress. In his trials, pigs housed in large groups took about a third less time to load than those housed in small groups.

Dr. Gonyou observes that pigs raised in large groups are more willing to investigate and travel in addition to interacting better with other pigs. Other research suggests that pork quality is better in pigs raised in large groups, perhaps due to the lower degree of stress prior to slaughter. Work at Iowa State University compared pens of 32 where pigs were not pre-sorted the day before shipping and pigs in groups of 192 that were pre-sorted the day before loading. Utilizing large pens and pre-sorting prior to shipping reduced the physical signs of stress during loading and unloading and reduced transport losses (dead and non-ambulatory pigs) at the plant by a massive 66 per cent.

Slower growth?

By way of downside, there is some evidence that pigs in large groups grow more slowly than those in smaller groups. An investigation at the Prairie Swine Centre compared the performance of pigs in groups of 18 or 108 at two stocking densities. Overall, the average daily gain (ADG) of large-group pigs was 1.035 kg/day, whereas pigs in small groups averaged 1.073 kg/day, a 3.7 per cent difference. Also, pigs in the large groups had poorer scores for lameness and lower leg scores throughout the eight-week study period.

Recently published work from Iowa State also showed a performance disadvantage for pigs housed in large groups. It compared pigs in groups of 34 with pens of 272 pigs and found that ADG and overall growth were higher in pigs housed in the smaller groups (Table 1). The percentage difference in growth rate was also 3.7 per cent. It should be noted that in both these trials an autosort system was not used.

The Iowa State researchers also examined health, in particular the number of body lesions and the number and types of treatments carried out during the trial. They found that there were a significantly higher number of lesions in pigs housed in large groups. Also, more pigs were treated in the large pens (198 versus 158 over the trial) and consequently a higher drug cost was incurred for the large pens ($127.63 versus $95.47).

Competition

If pigs in large groups are disadvantaged, is this likely to be worse where group size is very large and an autosort system is used? While there is no research data that directly supports this suggestion, work at Prairie Swine Centre observing the behaviour of pigs in LGAS pens indicates that some pigs may have difficulty adapting to the system. The challenge for pigs in LGAS pens is that they have to go through the autosort scale to get to a “feed court” where they can eat and drink. Some pigs have difficulties learning to do this, while once in the feed court they are also subject to more competition such that less-dominant pigs may prefer to avoid that area.

The work at PSC compared groups of 250 or 650 pigs with LGAS with conventional pens of 60 pigs. Pigs in the LGAS systems modified their eating behaviour by eating five meals per day compared to the 10-15 for pigs in the smaller pens, suggesting that the process of entering the feed court was less attractive than eating from a feeder placed in an open pen space.

The researchers noted that some pigs had difficulty learning to enter and leave the feed court several times a day. They recommended that management should ensure that an adequate number of feeder spaces are provided, that there is sufficient room for pigs to move around in the feed court and that there are suitable training procedures to facilitate the use of the autosort scale.

One final disadvantage of large groups, with or without LGAS is that it is harder to identify sick and disadvantaged pigs. This means that a high level of stockmanship ability is essential in order to avoid higher mortality rates.

Overall, the success of large-group systems is strongly influenced by pen layout and the quality of management because inadequacies in these areas will impact pig growth and health. The key to developing improved systems will be to better understand how factors such as group size, feed court layout and training methods affect pig behaviour and performance.

Performance of finisher pigsin small or large pens

Large Small

No. pens 12 96

Start Wt. (kg) 28.8 29.2

End Wt. (kg) 102.7 106.5

ADG (g/day) 800 830

Overall gain (kg) 73.9 77.3