Most of the emphasis on odor problems in hog operations focuses on manure storage systems.

Now there is evidence from a survey that more odor complaints were received during a year from building sources than from manure storage units.

Airborne dust particles are a major cause of poor quality environments in hog buildings. And those particles also carry toxic and odorous gases.

Removing dust can therefore improve air quality in confinement and reduce the amount of odors and gases being exhausted from these buildings into the atmosphere.

At the University of Minnesota, agricultural engineer Larry Jacobson developed a study for the '97/'98 winter to evaluate the odor and gas reduction potential of sprinkling soybean oil for dust control.

This study was performed at the West Central Experiment Station of the University of Minnesota in Morris. It was performed at two, side-by-side, off-site, modular nursery buildings.

Fill time was one week. The six-week trial ran from pigs weighing 15 lb. to about 50 lb. One barn was used for the oil treatment, the second as the control group. Although the soybean oil spraying began as soon as the first pigs were placed in the treatment barn, data collection didn't start until four to seven days after the spraying, or when the treatment rooms were filled to 180-head capacity.

Spraying was done with a handheld, commercial paint sprayer during morning chores. Spray was distributed as evenly as possible throughout the room, including pens and alleys. A "daily maintenance level" equal to about one cup of oil was applied to the treatment room each day. Before that, during the first four days that weaned pigs were added to the treatment barn, a somewhat heavier dose of the oil spray was applied.

Also, one day every two weeks a "surge" amount equal to the first spray application level replaced the maintenance level.

Since the trials were conducted during winter, only a variable-speed exhaust fan was run continuously to provide ventilation. Room temperatures began at 85 degrees F, were lowered 2 degrees for every week of the trial.

Weekly measurements were taken of odor, gas and dust levels in treatment and control barns.

Air was measured for odor with an olfactometer (by a trained odor panel). Hydrogen sulfide, ammonia and carbon dioxide were measured from the same air samples with either an electronic (Jerome) meter or colorimetric tubes. Dust concentrations were measured with gravimetric (weighing filters) methods. All samples were collected during a six-hour time span (10 a.m. to 4 p.m.).

There was an overall reduction in odor levels of the nursery pigs housed in the treated rooms. There was a consistently lower odor level as measured by the odor panel and expressed as odor units (o.u.).

In trial 1, average odor level of only 150 o.u. was recorded for the oil treatment and an average of 400 o.u. for the air in the rooms housing the control pigs.

Trial 2 revealed lower odor units in the air collected in the treatment room, compared to the control group, for the first three sampling times.

But that was not the case for the last two weeks. Odor units were fairly high during week 4 in the second trial and fairly low for the last week of collection.

According to Jacobson it is unknown why the odor levels changed so much during the last two weeks of trial 2 and why the oil treatment did not seem to be effective. He suggests there may have been some weather effect, since the winter trials coincided with a warming trend. See Figure 1 and Figure 2.

Hydrogen sulfide gas levels were reduced across the board as shown in Figure 3 and Figure 4. Average gas concentrations in the oil treatment rooms were 100 and 350 ppb for trials 1 and 2, respectively. Hydrogen sulfide levels in the control rooms were 250 ppb in trial 1 and 550 ppb in trial 2.

The oil treatment program had no impact upon ammonia levels. Treated rooms recorded 10 ppm, untreated 9 ppm in trial 1. Similar levels were seen in trial 2 as the treated room had concentrations of 11 ppm and 10 ppm in the control rooms.

Growth performance was also monitored during the trials. Results indicated that pigs in both the treatment and the control groups performed well. Average daily gain and feed efficiency were both lower in the treated group in the first trial, but during the second trial, performance was almost identical in the treatment and control groups. Mortality averaged 1% for both nursery barns in trial 1, 3% and 0% for the control and treatment rooms, respectively, in the second trial.

The first trial ran December 1997 to January 1998. The second trial ran February to March 1998.

Researcher: Larry Jacobson, University of Minnesota, St. Paul, MN. Phone: (612) 625-8288.