Kansas pork producer’s queries about proper stocking density and mixing procedures in grow-finish led a team of Kansas State University (KSU) scientists to conduct a research trial to determine the impact of mixing late-finishing pigs two weeks before marketing on growth performance.

The trial proved that mixing pigs from two finishing barns two weeks prior to slaughter did not impact overall performance, and that increasing pig density had a larger impact on performance than mixing pigs, according to lead researcher Megan Potter, DVM, who is now a research associate at the Abilene (KS) Animal Hospital.

A total of 512 finishing pigs from two, 1,200-head commercial research barns located in northeast Kansas were compared in a 15-day trial.

Four sets of mixing parameters were studied in 32 single-sex pens in a single barn. Pigs were housed with either 12 or 20 pigs/pen (eight pens/treatment) as follows:

  • Non-mixed pigs with 12 north barn pigs (control);
  • Mixing six north barn pigs with six south barn pigs;
  • Mixing 10 north barn pigs with 10 south barn pigs; and
  • Mixing 10 north barn pigs with 10 more north barn pigs (Figure 1).

“The Kansas producer moved close-to-market-weight pigs from one finishing barn to a second barn so he could empty one of the barns for refilling. He wasn’t sure if he was negatively affecting production by moving and mixing pigs, which increases aggression tendencies,” Potter explains. “He wondered whether it would be better to leave them in their original pens and let them grow.”

All pigs were fed a common diet. No Paylean (Elanco Animal Health) was fed to pigs in this study.

Impact on Performance

As Figure 1 indicates, at Day 0-8 after pigs were mixed between the two barns, average daily gain was decreased vs. the control, non-mixed pens, adds fellow researcher Bob Goodband, animal scientist at KSU.

Pigs fought to reestablish their social order. But during the second part of the trial, from Day 8-15, pigs recuperated, and average daily gain in the mixed pens of 12 pigs actually exceeded that of the control pens, he points out. “If you are going to mix pigs, they are not going to grow very fast the first week after they are mixed, but if you give them two weeks’ time, they will bounce back,” he explains.

Pigs mixed between the two barns and penned 20/pen had decreased gains in both the first and second week of the trial. Pigs mixed just within one barn and penned at 20 pigs/pen also produced inferior gains.

Figure 2 compares final market weights for the four treatment groups, and shows that pigs in pens of 12 mixed between the two barns had compensatory growth, allowing them to equal the market weights of the control group, Potter says.

“These data indicate, in the two-week period prior to marketing, increasing the number of pigs/pen had a larger effect on performance than mixing pigs. Although performance was negatively affected immediately after mixing, overall performance of mixed pigs was not different than that of non-mixed pigs. Therefore, given adequate time to adjust to a new environment and to establish a new social order, mixing pigs does not appear to affect overall performance,” she remarks.

Avoid Sorting

Goodband says the practice of sorting pigs when filling grow-finish barns is not as common as it used to be. Producers used to sort pigs into pens based on whether they were heavy, medium or lightweight.

Having recently visited a Kansas hog farm where sorting was still practiced, he reports: “On this farm, they were doing a lot of sorting, and they were short on labor to begin with, so when they stopped, they found it saved them hours of time.”

Instead of sorting, producers should gate-cut pigs into pens and allow for natural weight variation, he says. “Then as pigs approach market weight, you can top off the heaviest pigs in each pen instead of getting into a situation where you end up pulling one whole pen of pigs and leaving that pen open until the rest of the pigs in the barn are marketed,” Goodband stresses.

By not sorting pigs going into the finisher, pigs finish 3 to 4 lb. heavier than their sorted counterparts, based on some earlier KSU research, Goodband says.

If you’ve got a normal range of variation of big and little pigs in a pen, it becomes easy to go into a pen and sort the 2-4 heaviest pigs for marketing (topping), he says.

Even when pigs were tightly sorted to reduce variation, KSU research shows that at the end of finishing, the level of variation within a pen was really not much different than if they had been gate-cut. “This says pigs will grow to a common variation no matter what you do,” Goodband says.

Topping vs. Sorting

In another study, KSU researchers assigned 25 pigs/pen in three treatment groups (Figure 3), to measure the effects of pen unloading or topping on feed efficiency and average daily gain.

The first group (no topping) was allowed 7.2 sq. ft./pig, the second 7.8 sq. ft./pig (two pigs topped), and the third group was given 8.6 sq. ft./pig (four pigs topped).

The best results were achieved when two pigs were removed from the pen, confirming that topping out market strategies improve finishing performance over sorting pens when pigs are placed in grow-finish, Goodband notes. Topping four pigs out of a pen really didn’t provide any further improvement, as both pen-unloading strategies averaged about $1 more profit/pig compared with the no-topping treatment.

Marketing Tool

The series of marketing projects described were developed over time to emphasize the importance of completing the marketing process.

“Producers are so concerned about lowering feed costs, labor costs and all these other costs of production that they sometimes miss out on the marketing side, and you can lose as much marketing as you saved in feed costs,” Goodband says.

When preparing to market hogs, know your packer’s weight grid, Goodband adds. Calculate which packer best fits your marketing profile by taking slaughter data and plugging it into the marketing program, http://www.asi.k-state.edu/DesktopDefault.aspx?tabid=1229, developed by KSU Extension Swine Specialist Mike Tokach.

Higher Pig Density Doesn’t Pay

Usually, higher pig stocking densities for finishing pigs pays off, but that wasn’t the case in a research experiment conducted by Kansas State University (KSU).

In the trial, 1,201 pigs weighing 63 lb. were placed on test for 99 days to evaluate the impact of increasing stocking density on finishing pig performance, says Megan Potter, DVM, former KSU graduate student.

Pigs were stocked in four treatments: 22, 24, 26 or 28 pigs each, allowing 8.2, 7.5, 6.9 and 6.4 sq. ft./pig, respectively (Table 1).

Overall, average daily gain and average daily feed intake improved as the number of pigs in each pen was reduced, although feed efficiency (F/G) was not affected, Potter says.

Even though throughput was quite a bit less as the stocking densities described in the trial decreased, income over feed and facility cost per pig placed was best when pigs were stocked with 24 pigs/pen, in the middle of the stocking density ranges (Table 1), Potter says.

She says the unique feature to this study was that apparently, factors other than stocking density had a large impact on finishing performance results, which suggests the need for more research.