What about space per pig?

There is renewed interest regarding the impact of space per pig on both pig performance and the financials associated with this performance. More than 25 years ago Dr Tim Powell and I published a paper examining the economics of space allocation in confinement facilities. Based on the data available at the time, we concluded while individual pig performance (daily gain and feed intake) declines as space per pig is decreased, the economic return to an overall facility increases. This was primarily due to the fact that the reductions in daily gain and feed intake did not result in a worsening of feed conversion.

As a result of this review and a realization of the lack of information on the topic, I conducted a host of space allocation experiments in both partially slatted and fully slatted facilities in the last 15 years of my career at the University of Nebraska. Much of this data ended up being the basis for the National Pork Board summary that resulted in the alometric space equation. This summary, led by Dr Harold Gonyou, concluded that in fully slatted facilities space is not a limit to pig performance when space (in square meters per pig) is defined as body weight to the 2/3 power times 0.0336. This constant of 0.0336 (commonly called the ‘k’ value) has been unofficially adopted as a measure of the impact of space allocation on performance and is often used to ‘correct’ data to model the impact of allocation decisions on production financial estimates.

Why body weight to the 2/3 power? Pigs grow in 3 dimensions – taller, longer and wider. However, when we define pen space we only deal with wider and longer so we need to adapt weight to 2 of the 3 dimensions. As long as we have human care givers working in production facilities I don’t think we need to worry about how tall pigs grow.

There is a renewed interest in the space requirement of growing pigs, primarily since our slaughter weights continue to increase. Much of the literature that went into the Dr Gonyou led effort had final weights of only 220-240 lb. As anyone selling pigs in the US today knows, at most slaughter plants pigs this light would result in underweight discounts, some of which can be severe depending on the slaughter plant.

While weights are not as large as they were in 2014, liveweights of producer sold barrows and gilts last Friday/Saturday averaged 278 lb, well above the 220-240 lb final weight of the available data. There has been recent data led by both Kansas State University and University of Minnesota scientists to relook at the impact of pig weight on performance but now using 300 lb or greater as the final weight.

The new data does suggest that at these heavier weights there appears to be marginal impact on feed conversion in addition to a major impact on daily gain and feed intake as space is restricted. However, there is no evidence of impacts on health or stress levels. The resulting financial models incorporating the new estimates of feed conversion still suggest space allocation decisions should be driven by gain per unit of space, not gain per individual animal.

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