Management in Swedish Deep-Bedded Swine Housing Systems: Background and Behaviorial Considerations
Interest in alternative manure handling systems is growing, as evidenced by the Minnesota legislature's decision last year to allocate $125,000 of swine odor research funds to the University of Minnesota's Minnesota Institute for Sustainable Agriculture (MISA), for demonstration and promotion of low-emission, low-energy swine production methods. A model mentioned in the legislation is Swedish deep-bedded group nursing systems. This paper describes evolution of and experiences with the Swedish systems.
Development of Deep-Bedded Swine Housing Systems in Sweden
In the 1950's and 60's, breeding herd housing in Sweden was becoming very much like that typical of large-scale facilities in the U.S. today -- individual stall or crate housing under factory-like conditions. Indeed, according to Miller (1968), gestation stall housing first appeared in Scandinavia and spread initially to Great Britain. The idea behind individual feeding stalls is to create a situation where individual sow feed intake can be more readily regulated. In Europe, use of feeding stalls for the breeding herd had been common "even in the better types of sow yard" (Miller 1968). But, once they were conceived of as "permanent" housing, it became obvious that individual stalls or crates could make it possible to contain large numbers of breeding animals in a small space, saving on building costs. Development of slatted floors, which allowed passive collection of manure beneath the floors of pens, made such housing labor saving as well. Together with the introduction of subtherapeutic antibiotic use for disease prevention and growth promotion, these developments made intensive confinement possible.
Tethers for restraining dry and farrowing sows were banned in Sweden in 1971, when it was shown that tethered sows were "afflicted with an extremely high incidence of traumatic injuries" (Ekesbo 1973; Högsved 1991). Research by Bäckström (1973) showed a higher incidence of morbidity among dry sows housed in crates than in dry sows loosely housed in groups (Ekesbo 1995). Although Bäckström_s research did not lead to a ban on gestation crates in Sweden at the time, it may have influenced farmers. The transition in Sweden to deep-bedded loose housing systems for the breeding herd began around 1973, with one farmer in east central Sweden. He built a bank of individual feeding stalls with a spacious bedded area in an uninsulated barn. Once a few of his neighbors saw his design, they adopted it and soon the system spread. By 1985, deep-bedded housing systems with individual feeding stalls had become, and are today, the conventional method of dry sow housing in Sweden. The 1988 Farm Animal Protection Act required phase-out of the few remaining gestation crate systems in 1994.
Farmer preference caused widespread conversion to deep-bedded group housing for the breeding herd. Swedish farmers still cite its efficiency, aesthetics, friendliness to neighbors and the environment, and its contribution to sow well-being, fitness and health. To return to the old days of individual sow and boar housing in crates without bedding would be seen as a step backward by the majority of Swedish swine producers.
Conventional Swedish gestation housing today includes a feeding stall for each sow in the group. The stalls have rear gates, with a mechanism whereby several at a time can be locked by the farmer, and individual front gates. The stalls are raised off the main floor about 16 inches to accommodate the growing bedding pack. When the bedding pack reaches the level of the stalls, the room is cleaned out. With a feeding stall for each sow it is possible to keep feed intake even; eliminate competition for feed; administer medical or other individual treatments efficiently; lock all sows in while the room is being cleaned and rebedded; and easily transfer selected sows from the main group through the front stall gates to breeding or farrowing. Behind the stalls is the bedded area for activity and lying. Several stable subgroups of sows, maintained for batch mating and farrowing, share a single room. Sows are generally marked on the back with colored chalk by subgroup so it is easy to see who belongs to which subgroup. New sows are added only in subgroups of five or six or more, never smaller, and never singly. Boars are housed in bedded pens. The law requires straw and a minimum boar pen size of 64 square feet.
It is quite important to have enough clean straw for sows to keep busy and to keep the tops of the beds dry and fresh by adding bedding to wet spots. Sows need about six and a half feet between them when they are meeting to allow a lower-ranked sow to show her submissiveness by turning aside when she meets a higher-ranked sow (Algers 1992). Thus, she can avoid a fight. No less than 27 square feet of space per sow is provided in the bedded area for this reason. With less space stress can be great on lower-ranked sows.
It is also important not to keep too small groups of sows. Ten sows in a group with 27 square feet of space per sow is not enough to prevent fighting, perhaps because of the reduced total area available to an individual sow. Groups of 30 to 40 seem to result in a good "total space" for peaceful relations (Högsved 1991). If groups are smaller than that, floor space should be increased to between 30 and 40 square feet per sow.
About 1,800 pounds per animal per year of straw is required for deep-bedded gestation and breeding. Important principles of straw and manure handling include beginning with three to four 750-pound bales or equivalent to a room, depending on room size. Farmers usually spread three and take the twine off a fourth for the animals to spread. After animals enter and begin soiling the bed, fresh straw must be added to wet spots daily. This helps to keep the bed surface clean and free of pathogens and sustain aerobic decomposition. A large round bale of straw is added every week. The straw to manure balance provides a high carbon/nitrogen ratio, which binds nitrogen. When correctly managed, and not allowed to get too wet or uneven, the beds do not give off ammonia; hydrogen sulfide, a product of anaerobic decomposition, is not created. Two major manure emission sources are thus controlled. Composting also destroys pathogens.
Swedish Farrowing Systems
A conventional Swedish farrowing system includes individual pens that are about 7 by 10 feet including dunging and feeding areas and a creep area for piglets. Some straw is required. Pigs are weaned at four to five weeks by removing both sows and piglets to make room for the next group. Pigs are taken to the growing facility and sows are returned to the breeding area.
Although the majority of Swedish swine producers still farrow conventionally, three innovations are of interest. In 1984 a new kind of lactation system got started. A farmer in southern Sweden modified his conventional system after reading about studies of maternal behaviors of sows that were being undertaken by researchers in a park outside Stockholm (Jensen 1986; Johansson 1992). He continued to farrow in conventional pens, but when the pigs were a week old he moved sows and litters to a large room where they lived in a group for the rest of the lactation. Because the pigs were quite small when moved, he kept his subgroup size smallfive to six sows.
In 1987, a farmer in west central Sweden discovered while he was disinfecting his farrowing rooms, that his sows did quite well farrowing as a group out in a straw-bedded shed. He also noticed that when sows were taken from the shed after five weeks, weaned pigs, who remained behind, did not contract weaning diarrhea (Ljungström 1992). Scours had been a problem in his herd, for which antibiotic therapy was required, ever since subtherapeutic antibiotic feed additives had been banned in Sweden in 1986. Something about weaning on a deep-straw bed had prevented or not caused the anticipated scouring.
This farmer started his own version of a deep-bedded group lactation system, farrowing subgroups of 16 sows in conventional pens and moving sows and their litters to deep-bedded group rooms when the youngest litter was 10 to 14 days old. Sows were removed from the rooms and returned to breeding when pigs were five weeks old. The pigs stayed behind in the room which then became a nursery. His system became more widely adopted when it was seen that it provided a natural way to avoid scours at weaning and allowed farmers to use farrowing pens more efficiently. Group lactation requires about 2,200 pounds of straw per sow/litter per year. It is all in-all out, with each room cleaned out and rebedded when the growers are transferred to finishing at 11 weeks of age. At least 81 square feet of space per sow and litter is needed in the bedded area for behavioral relations and, possibly, "ecological" reasons -- i.e., this space may be needed to create the proper mixture of dung, urine, air, and bedding for beds to compost. As in gestation, a skid steer loader can be driven through large outside doors to remove soiled bedding between groups. A solid gate across these doorways allows the doors to be opened during hot weather, or when bedding is added, but keeps the animals in. A new variation on this system takes pigs directly from conventional farrowing pens at five weeks of age and weans them on deep straw beds.
In 1989, a third farmer started another version of the group nursing system (Thorstensson 1992). Working with scientists at Swedish University of Agricultural Sciences, he modeled his system more closely on ethological research on sows maternal behaviors (Algers, et al. 1991). With his method, sows farrow directly in group rooms in temporary boxes that are put up along the sidewalls of the room and bedded eight inches deep with straw before pregnant sows enter. Doorways into the boxes are a little larger than the width of a large sow's shoulders with a 16-inch high, "roller-topped" threshold. The roller protects the sow's udder when she enters and leaves the box and keeps pigs in the boxes for a week and a half before they are able to follow their mothers out into the communal area. When pigs are able to jump out of the boxes, all boxes are taken away and all sows and litters mingle. The "innovation" of this group farrowing and nursing system made Thorstensson's entire feeder pig operation a deep-bedded system.
Regardless of which deep-bedded lactation system is used, ventilation is important. A maximum ventilation rate of +400 c.f.m. (+681 m3/hour) per sow/litter is recommended for summer; a minimum or continuous rate of 25 c.f.m. (68.16 m3/hour) per sow/litter is recommended for winter ventilation, adjusted with supplemental heat to keep relative humidity between 70 and 80 percent; and an intermediate rate of +60 c.f.m. (+102 m3/hour) per sow and litter for spring and fall (Karlsson 1996). A common Swedish method of ventilating insulated barns is called a "breathing ceiling". The entire ceiling serves as the air inlet, creating an even inflow of tempered, fresh air throughout the room, eliminating air pockets and drafts. Composting appears to occur more evenly throughout the beds in lactation rooms in insulated barns with breathing ceilings (personal observation of the author). Perhaps, in the absence of drafts, sows may not always select specific dunging sites. In structures with uneven air flow, sows do seem to pick out specific, often the draftier, places to dung, and composting may occur more unevenly in the beds, requiring more attentive management.
For composting, Swedish farmers have found it is important to use "cut" rather than "chopped" straw. The slightly longer length of the stems allows more air to get into the beds and begin the heating process. Straw must be of very high quality and mold-free. Moldy and dusty straw can cause illnesses and stillbirths. Coarser bedding such as corn stover and hay can be substituted for straw in growing and gestation/mating, but is not recommended for use in the farrowing boxes or the lactation room while sows are still in it, as small pigs find it harder to get around or away from the sows.
Society can be expected to succeed in pressing its concerns on hog producers to take stronger measures to improve the safety of their manure handling practices. Farmers who have mastered the techniques for operating alternative swine production and manure handling systems are likely to be a giant step ahead when that time comes.
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