University of Illinois scientists map a three-year course of research designed to develop an economic model of wean-to-finish building systems.

Wean-to-finish (W-F) systems have been a building phenomenon. Popularity has mushroomed since their introduction to the Midwest in the early 1990s.

The boom is unique because it has been built on producer trial and error. A number of researchers agree that scant controlled research has been done to justify stocking and management protocols.

In the first year of a three-year program at the University of Illinois, animal scientist Mike Ellis and graduate student Bradley Wolter are working together to look for answers to W-F production dynamics.

“Our goal at the end of this whole venture is to create a decision-making model that takes into account all of the economic factors involved with W-F,” explains Wolter.

Evolving into Wean-to-Finish

There is plenty of research data on production parameters in conventional nurseries and growers, says Wolter. But that information is 20 years old. And so are many of the facilities.

In contrast, W-F barns are newer and the environment is so different, raising pigs in one place from early weaning to market, he says.

For example, research at the University of Illinois showed that large group sizes don't work well in conventional nurseries, observes Wolter. Performance is reduced 5-7%.

Illinois research evolved into looking at the impact of group sizes in W-F units. Groups of 25, 50 and 100 pigs/pen were tested from 17 days of age to 255 lb. average market weight. Floor space was 7.3 sq. ft./pig for all three groups. Feeder space and waterer allowance/pig were constant across all group sizes.

At the end of eight weeks, pigs in groups of 50 and 100 head were lighter and recorded 3% lower average daily gain and feed: gain conversion rates but similar average daily feed intake. This supports conventional nursery and European research results, says Wolter.

But from eight weeks to finish, the larger pig groups had similar growth performance.

For the overall study, pig performance was nearly identical for all group sizes, Wolter points out. (See Table 1.)

In all, growth performance from weaning to market weight was not affected by group size. Carcass value was unaffected by group size.

Wolter stops short of recommending that pigs be raised in large group, W-F barns. “I think it is a management decision based on a number of factors, particularly pig flow,” he says. “Unless you've got a substantial pig flow where you can fill a barn within a short period of time, if you feed to a pig mean weight, you could end up overfeeding the heavy pigs and underfeeding the lighter pigs.”

Table 1. Effect of Group Size on Pig Performance from Weaning to Market in a Wean-to-Finish System
Group Size
Pig Performance* 25 50 100
Avg. start wt., lb. 13.0 13.0 13.0
Avg. end wt., lb. 256.7 256.0 256.2
Daily gain, lb. 1.44 1.43 1.45
Daily feed intake, lb. 3.88 3.87 3.88
Feed: gain 2.70 2.70 2.70
Days on test 168 167 166
Carcass percent lean 53.4 53.7 53.8
* No significant (P > 0.05) differences were observed.

Wolter says he hears some employee concerns about being nibbled while working in large group pens of market-size hogs. Behavior was not studied, but increased aggression was not observed during the study, he adds.

Some preliminary data suggest as group size increases, there is more “free” space in a pen because pigs share space for movements and resting.


The next stocking density issue Wolter studied was double-stocking 17-day-old pigs for 10 weeks in pens of 104 head versus 52 head.

The research trial was carried out in United Feeds' 1,800-head, tunnel-ventilated, W-F barn. Some pens were left empty to break double groups out at the end of the 10-week double-stocking period.

Single-stocked pigs got 7.8 sq. ft./pig, the double-stocked group were allotted half that — 3.9 sq. ft./pig. At the end of the 10-week trial, the double-stocked group showed a significant reduction in performance, weighing 87 lb. versus 94 lb. for the single-stocked group, states Wolter. The crowded pigs had 8% lower average daily gain, but other parameters were similar (see Table 2).

From week 10 to slaughter (250 lb.), pigs that were previously double-stocked rebounded, gaining like the single-stocked pigs, but they were 4% more efficient. Double-stocked pigs took just two more days to slaughter than their single-stocked counterparts and had similar lean percentages, comments Wolter. (See Table 2.)

“We found that the pigs that were double-stocked did somewhat compensate when you look at their growth,” he says.

The double-stocking experiment was repeated recently at a southern Illinois W-F farm. Performance was compared for pens of 27 versus 54, 17-day-old weaned pigs for 10 weeks post-weaning.

Table 2. Effect of Stocking Rate on Pig Performance from Weaning to Market in a Wean-to-Finish System
Stocking Rate
Pig Performance Single Double
Weeks 1 to 10 Post-Weaning
(Double-Stocked Period)
Avg. weaning wt., lb. 13.0 13.0
Avg. 10-week wt., lb. * 94.0 87.6
Daily gain, lb. * 1.20 1.11
Daily feed intake, lb. * 1.75 1.73
Feed: gain 1.75 1.73
Week 11 Post-Weaning to Market
Avg. market wt., lb. 251.3 249.7
Daily gain, lb. 1.74 1.77
Daily feed intake, lb. 5.10 5.02
Feed: gain * 2.94 2.82
Days from weaning to market * 157 159
Mortality, % 1.5 1.8
Percent lean, % 54.3 54.6
* Significantly (P < 0.05) affected by stocking rate.

Despite the fact that this group differed from the one reported above (genetics, facility and management), the results were almost identical to those of the previous double-stocking trial, remarks Wolter.

At the southern Illinois farm, by the end of the 10-week trial period, there was about a 7-lb. (7%) difference in body weight in favor of the single-stocked group. That 7-lb. difference carried over to finishing, cutting the difference in performance to 3.5% in favor of the single-stocked pigs.

“Still, we have good confidence that there certainly is an economic advantage to double-stocking pigs,” he stresses, “because of the tremendous opportunity to increase your throughput and lower your total fixed costs of production.

“But it is a difficult decision because you have to think how you are going to manage those extra pigs after you revert to single-stocking,” he points out.

Eric Parr, research manager at the United Feeds research farm at Sheridan, IN, says double-stocking also presents biosecurity, stress and transportation issues associated with moving the extra pigs.

Feeder Space

In a third trial, feeder space was doubled to evaluate pig performance from weaning to eight weeks post-weaning for groups of 108 pigs/pen. Two, six-hole, wean-to-finish feeders were positioned in the center of each pen; the control pens only had one feeder that contained feed.

Through week 6, doubling feeder trough space had no affect on growth performance. From week 6 to 8, pigs on the doubled feeder space had about 10% higher average daily gain and were close to 2 lb. heavier than the control group pigs (69.74 lb. vs. 67.98 lb.) at the end of week 8, says Wolter.

Cooperative Research Efforts

The wean-to-finish project at the University of Illinois is a multidisciplinary project involving animal scientists Mike Ellis, Stan Curtis, Gilbert Hollis and Floyd McKeith; ag economist Gary Schnitkey, ag engineer Gary Riskowski, veterinarian Larry Firkins and Doug Webel, swine nutritionist from United Feeds.

The graduate students participating include Bradley Wolter, Brendan Corrigan and Jake DeDecker.

Producer collaborators on the research include Art Lehman, Brauer Pork, Maschhoff Pork, Oasis Farms and United Feeds.

Supporting the project is funding from the Illinois Council on Food and Agricultural Research.