Market weight of slaughter hogs has been increasing over the last 30 years. This is no secret in the industry. The USDA reports that slaughter weights have increased from 250 pounds in 1990 to 283 pounds in 2018.
Market weights increase mainly because genetics, nutrition, and housing systems have improved enabling producers to take pigs to heavier weights economically because a heavy pig generates more gross revenue than a lighter pig. Market weights might also increase because of some disruption in pig flow such as an acute disease event, seasonal infertility or a natural disaster.
Regardless of the reason for increased market weights, producers need to ensure they can accommodate the special needs of heavy finishing pigs. As market weight increases, producers need to consider changes in floor space allowances, nutrition, feeder and waterer design, health maintenance programs, pig behavior, and transportation needs to optimize pig performance, health and welfare.
A full discussion of these issues is beyond the space available for this column. However, a comprehensive review of these issues was recently published by Wu and colleagues.
The proper floor space allowance for pigs is an important question especially as pigs are taken to market weights that are heavier than considered when the facilities were designed. Numerous studies have demonstrated that crowding pigs decreases daily weight gain primarily through reductions in daily feed intake with little effect on efficiency of gain.
So what is the proper floor space allowance for heavy market pigs? Recently, five universities (University of Minnesota, Michigan State University, Kansas State University, Ohio State University and University of Missouri) completed a collaborative project that addressed this floor space issue. In this project we asked, "What is the floor space requirement of pigs marketed at 300 pounds?"
In the first experiment, pigs were provided 7.6, 8.6, 9.6, 10.6 or 11.6 square feet of floor space from an initial weight of 59 pounds to a market weight of about 305 pounds. The lowest and highest floor space allowances near the end of the experiment are displayed in Figure 1. Average daily gain ranged from 2.12 to 2.19 pounds and daily feed intake ranged from 5.47 to 5.66 pounds (Table 1). Feed:gain was not influenced by floor space allowance. There was no clear floor space allowance that optimized pig performance.
This lack of response to floor space probably occurred because all pigs had excess space for 60% or more of the study when pigs were light. So, effects of restricted floor space at the end of the experiment when pigs were heavy (crowding) were diluted by the early period growth performance when no crowding existed. To gain a clearer picture of floor space allowances for heavy pigs, we conducted a second experiment.
In the second experiment, pigs were provided the same floor space allowances as Experiment 1, but the initial weight was 292 pounds and the final weight was about 320 pounds. This experiment lasted only two weeks. Average daily gain ranged from 1.89 to 2.43 pounds and daily feed intake ranged from 6.68 to 7.70 pounds. (Table 2). Feed:gain was not affected by floor space allowance. Results of this second experiment suggest that pig performance was optimized at 10.6 square feet per pig at the end of the finishing period.
The floor space allowances used in these experiments were determined using an equation developed by Gonyou and colleagues in 2006 with a "k" value of 0.0336. This equation seems to underestimate floor space requirements by 5% to 10% for pigs marketed at 300 pounds. In practice, producers can use this equation to estimate floor space allowances but need to realize that the equation becomes less accurate as pigs reach heavy weights (above 280 pounds).
In a recent experiment, Lerner and colleagues maximized growth performance of pigs marketed at about 375 pounds with a k value of 0.0383 which equated to 12.7 square feet per pig.
At heavy weights, producers can provide a larger pen which is not very practical or remove some pigs (topping pens) to provide more floor space for pigs. Several researchers have reported that topping pens improves growth performance of the remaining pigs. Carpenter and coworkers determined that either changing pen size or removing the heaviest pig(s) in a pen succeeded in improving performance of the remaining pigs.
In summary, market weights of pigs in the United States have been increasing for years and very well could continue to increase into the future. Pork producers need to think about approaches to provide additional floor space as pigs get heavier near marketing time. Existing equations may underestimate floor space allowances that optimize performance of heavy pigs. The most practical solution to this space challenge is to establish pig removal protocols (topping pens) that alleviate crowding and improve performance of remaining pigs while optimizing the number of pigs marketed at the producer's targeted weight.
We appreciate the financial support of the Pork Checkoff through the Minnesota Pork Board.