Deep Straw in Hoops: Managing Manure in Concert
with the Natural, Social and Economic Environments

Mark and Nancy Moulton
Farmers, Rush City, MN

Mark and Nancy Moulton and their three sons farm 200 acres of corn, 80 acres beans, 30 of oats and alfalfa, and 75 acres of pasture. Along with other family members, they rent another 400 acres for a total of 800 acres. They manage a 40-cow beef operation, as well as the 120 sow farrow-to-finish operation, marketing 2000-3000 hogs a year. They have a standard slatted floor, 24 crate, confinement farrowing unit with a liquid pit below, a 400 pig nursery and a conventional confinement grower unit that can house 200 pigs. They have used a Cargill open front finishing system for several years. In 1997, the Moulton's were named Chisago County (MN) Farm Family of the Year.

Located on the north edge of the rapidly growing town of Rush City, Minnesota, the Moulton's began to personally experience the town vs. farmer conflict about odor. Although well managed and in compliance with Minnesota Pollution Control rules, Moulton's began to hear complaints about odor from their farm, coming both from neighbors and a new school that was built nearby. These voices added to their existing concerns about surface and ground water pollution potential from their farm. The pit beneath the confinement units is only 4 feet deep due to a high water table, and they worried about runoff from the Cargill units causing surface pollution.

These concerns resulted in them looking into new ways of housing pigs, and in the fall of 1995, they erected a 30 by 72 hoop house. To see if it would reduce odor as touted, they located it on Mark's brother's farmstead, about a mile from their confinement buildings that utilize liquid manure systems. With the help of a demonstration grant from the Energy and Sustainable Agriculture Program of the Minnesota Department of Agriculture, Mark committed to a three year project to evaluate the risk of nutrient leaching into and through the bedding and into the subsoil. Randomized grid soil core samples were taken and analyzed before filling the structure with animals, and will be compared to samples taken at the end of the three year period.

Mark's brother, the local vet, was highly skeptical about the chances for success with the fabric covered building, concerned, both about durability of the structure and performance of the pigs. Two years later, the buildings have proven so successful that the Moulton's have erected a total of four hoop buildings, three for finishing pigs and one for machinery storage. Neighbors from both town and farm have visited to evaluate the structures with their own eyes and noses.

The results have been favorable, according to Mark. "At our Sustainable Agriculture Field Day (August 1997) we had 60-70 people here for the program. We had pork burgers, beans and potato salad, and we had this 10 feet away from the hoop house. Now I don't know any other system of raising hogs where you could have people enjoy a meal right next to a hog barn. Plus I had 6 months worth of manure being stored in a compost pile nearby. I don't think I would really want to eat next to a lagoon or a typical confinement barn. I think here everybody ate well and enjoyed themselves even thought they were next to a hog barn." As Nancy says, "It really reduces odor."

The Moulton's hoop houses are 30 feet by 72 feet and house 160-170 pigs per group. They are built on a clay base slightly above grade with the floor slightly sloped away from the raised concrete platform at one end of the structure that supports the feeding and watering units. The walls are constructed by setting treated wood posts six feet apart into the ground and filling the holes in with crushed lime. Weather-treated tongue-and-grove lumber is nailed to the posts to create a wall approximately 4 feet high. Galvanized tubular steel hoops are anchored to the tops of the wooden posts. A multi-layer polyethylene fabric cover is stretched over the hoops and secured to the wall with rope lashing or adjustable straps and buckles. The structures are erected in a north-south orientation to improve airflow. Tarp ends on rollers can be lowered during the winter. The south end is opened when the temperature is above 0 F. Natural ventilation is provided by an air intake at the junction of the walls and cover with air exhausted in the open spaces at the top on both ends.

An initial layer of straw, marsh grass or cornstalk bedding is put down 6-8" deep. One or two big round bales of bedding weighing about 1200 pounds are added each week. Providing enough bedding material and cover wet spots as soon as they occur is critical. The deep straw bed provides sufficient heat to maintain composting activity, which is essential to neutralizing pathogens, protecting animal health, and minimizing ammonia volatilization. The mix of straw, manure, and urine composts throughout the year, providing heat and comfortable bedding for the pigs. Mark says the deep bedding composting process has two advantages. First it binds the otherwise odor producing urine and fecal material to the straw, which composts and converts the bedding into a solid fertilizer, which has little odor. Second, says Mark, this process produces the heat, which warms the bodies of the pigs, reducing stress and promoting faster weight gain.

Large amounts of bedding are required for the hoop house system. Cycling three continuous groups of 170 pigs through this system requires approximately 60-80 large bales per year per hoop house. Approximately 200 pounds of bedding per pig is required in the summer and 350 pounds in the winter. When the buildings are properly managed with sufficient amounts of bedding, Mark has found that the clay base under the bedding is dry when the bedding pack is removed.

Mark bales his own corn stalks and oat straw, and figures it takes 25-30 acres of corn stalks to provide bedding for three groups in each building each year. Running his own equipment, Mark figures his costs for bedding are $3.60 per pig, which would go up to $6.00 per pig if he had to buy all his bedding.

Moulton's cost of these buildings, including cement, waterers, feeders and gates range have averaged about $10,000 depending on how much of the work he hired out. At an average of $58.80 per pig space, Mark figured he saved about $120 per pig space compared a confinement facility cost of $180-$200 per pig space. Depreciated over 10 years and with three groups of pigs per year, Mark figures the hoop house saves him $4 per pig based solely on the difference in initial purchase cost compared to a conventional building.

Mark puts his pigs in the hoop buildings at 40 to 50 pounds, and markets at 240 pounds. He buys soymeal and mineral and grinds his own corn for feed. He does not add antibiotics to the feed for the finishing pigs in the hoop buildings. Feed conversion averages 3.2 pounds of feed per pound of gain over the year. In the Minnesota winter the pigs in the hoop house will eat more than pigs in a temperature controlled environment, but in milder times of the year there is no difference. Mark figures that it takes him 38 more pounds of feed, at $0.07 per pound, an average of $3.00 per pig more to finish in the hoop building.

The hoop buildings save Mark money in other ways. He figures he would have a $500 bill for electricity, and $1000 for propane with a conventional building. And with a 10-year amortization, he has only a $1,000 per year depreciation on a hoop building to finish pigs compared to $20,000 in depreciation on a conventional building.

It takes Mark and Nancy 30-60 minutes, 2 to 3 times a week, to bed the three hoop buildings. It takes an additional 3 hours per week to fill the feeders and observe the pigs in all three buildings. Mark uses a medium sized skid steer with a bucket and grapple to remove bedding after each group of hogs are shipped. It takes him two hours with this equipment to clean out a building. He piles the solid bedding and manure adjacent to the hoop buildings, to further compost, until he has an opening in the weather or between crops, when he can spread the manure. Fresh bedding is spread in the hoop, and it is ready for the next group.

Having the right equipment is critical to efficient removal of the bedding pack. While it only takes the Mouton's about two hours, other farmers have reported up to eight hours to clean out these types of buildings, when they have a loader without a grapple. The fact that the Moulton's can use the same equipment to handle solid bedding for their pig and cattle operations is an advantage in keeping equipment investment costs down. Nancy Moulton also noted that no pressure washer work is required to clean out between groups, reducing or eliminating labor intensive and unpleasant hand work.

Table 1.

3 groups per year,
both systems

6 Hoop Buildings, 170/lot (3060 pigs per year)

1,000 Head Confinement
(3,000 pigs per year)

Initial Cost



Cost, Pig Space per Year (10 year amortization)



Cost, Pig Space / Pig
(3 groups per year)



Pig cost, 40 lbs.



Feed Cost, per Pig



Utilities (Elect. & Heat)


$1,500 ($0.50/pig)

Cost per pig



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