Trials of encouraged-exercise in gestating stall-housed sows improved bone density, bone-breaking strength and piglet survivability, but it had no real impact on lameness or most performance traits.

Proponents of group sow housing systems suggest that the increased pen space will improve the amount of exercise sows get, thereby improving their welfare and their productivity.

But in a rigorous study measuring everything from structural durability and lameness to a number of production characteristics, frequent exercise of gestating sows only improved bone density, and better-conditioned sows lost a smaller percentage of piglets.

Purdue University graduate student Erin Schenck conducted the trials under the direction of Don Lay, research leader with USDA's Agricultural Research Service (ARS). Lay heads up the Livestock Behavior Research Unit, a component of the Center for Food Animal Well-Being, an ARS-Purdue consortium, which carries out joint animal welfare studies at the West Lafayette, IN, campus.

First Study

Schenck's first study evaluated the impact of exercising stall-housed gestating gilts to determine the impact on lameness, lying behavior and muscle weight among other factors.

Gilts in individual stalls were used as opposed to those in group housing, to eliminate confounding factors such as fighting and individual variation in exercise and feed intake.

In the study, at Day 35 of gestation, 51 crossbred gilts were assigned to one of three groups: low-exercise, high-exercise or control group.

The low-exercise group was allowed to walk 402 ft. for five days/week. The high-exercise group was allowed to walk 402 ft. twice a week and 1,409 ft. three days a week. Gilts were walked until Day 110 of gestation and then moved to the farrowing crates.

Schenck says gilts were taught to back out of crates and individually walk or run laps in the 2.5-ft.-wide alleyway around the room in which they were housed. At the end of each lap, females received a sugar cube as an incentive. Gilts were also given light pats on the back to encourage them to continue their exercise regimen.

Body weight was taken at Day 0, 35, 54, 84, 110 and at weaning. Video recorders were used to record birthing intervals and lying behavior. Farrowing data was also recorded. After weaning, performance data was collected, first-parity females were sacrificed, and specific muscle weights were analyzed.

No differences were observed in body weight, body condition scores, lameness scores, muscle weight or most production parameters, says Schenck.

“Although there was no benefit of exercise on lameness, the differences in piglet survivability and lying behavior may provide useful insight into alternative housing for sows,” she adds.

Although not statistically significant, exercised groups had somewhat higher numbers of piglets born live, litter birth weights, fewer stillborns and fewer piglets that died during lactation.

Lying down behavior was recorded for three consecutive days after farrowing. Litter sizes in the farrowing barn were adjusted to 8-10 piglets/sow to equalize lactation stress. Exercised sows took less time to lay down in the farrowing crate, which Schenck postulated as the reason fewer pigs were crushed.

It was previously thought that the slower sows laid down in the crate, the fewer number of pigs would potentially be crushed. “We think with the exercise that sows are actually able to control their bodies a little bit more and lower their hindquarters (faster) so that the piglets can't get underneath them quite as quickly as our control group that didn't get any exercise,” she observes. Figure 1 depicts the stages of lying down behavior.

USDA's Lay says Schenck's observation correlates to findings of research he conducted while at Iowa State University. Meishan sows rarely crushed their piglets because they seemed to quickly lie down, compared to Yorkshire-Landrace sows that took longer to lie down.

In order to look at the longer-term effects of exercise on gestating sows, five Parity 1 sows were rebred. They were exercised as Parity 2 sows, euthanized and performance compared; few differences were noted.

Overall, injuries and lameness scores for both parities studied were in fact highest in the high-exercise treatments, Schenck says.

Second Study

A second part of the exercise study involved measuring the effects on bone density, cartilage and hoof lesion scores.

Cartilage and hoof scores were unchanged for the exercised and control group sows. Cartilage damage was already evident in the year-old females.

But sows in the low-exercise treatments exhibited a greater bone density in the tibia, humerus and radius compared to that of the control group, Schenck comments. The bone density of the humerus and bone-breaking strength were both greater in the low-exercise group.

Group Sow Observations

Schenck says an offshoot of the two studies was to monitor the exercise level of group-housed sows for two days consecutively.

“We literally watched them from 7:30 a.m. to 5 p.m. and drew little scale maps to estimate how far gestating sows will move within a day,” she says. Their level of movement was equivalent to or less than the high-exercised sows tested. Around 80 to 85% of their movements took place within an hour or two around feeding time.

Schenck concludes that today's modern sows are a sedentary lot, and producers who currently house or are planning to house sows in groups should take special care to separate feed and water stations to encourage more exercise.