Pregnant sows (including gilts) are kept in a variety of production systems. The industry has moved toward gestation stall (crate) housing, because gestation stalls increase caregiver productivity, require lower capital investment, and are easier to manage than some indoor group housing systems.
The AVMA recognizes that veterinarians approach the issue of pregnant sow housing from different viewpoints based on personal and societal values. Some veterinarians are opposed in principle to close confinement of animals, some are opposed in principle to the use of animals for food, and some work with the swine industry to maintain animal health and productivity. This position statement is based on consideration of animal welfare as assessed through the scientific literature and professional judgment and experience.
Concerns that commonly arise regarding animal welfare are that:
- Animals should function well in the sense of being healthy and thriving,
- Animals should feel well, especially by prevention of serious pain, hunger, fear, and other forms of suffering, and
- Animals can live in a manner consistent with the nature of their species.
Each of these elements needs to be considered when drawing conclusions about animal welfare.
The science of animal welfare includes assessments of physiology, behavior, production and health. A review of the literature indicated the following:
- PhysiologyGestation stalls do not induce a physiologic stress response compared to group housing for pregnant sows.
- BehaviorSows show different behavior when housed in gestation stalls as compared to some group pens because of restricted movement, reduced caloric consumption, reduced opportunities to forage, absence of bedding, and restricted social interaction.
- ProductionSows kept in gestation stalls have production performance not different than sows kept in groups.
- HealthThe rate of sow injury is reduced in gestation stall housing compared with group housing. Industry experience indicates that other aspects of health are predominantly affected by factors other than the housing system.
The science and professional judgment indicate that we cannot consider housing systems in isolation from other important factors that influence animal welfare. These include:
- ManagementThis by itself is a major determinant of animal welfare. Some housing systems can be expected to work well at one level of management, but not at another.
- Feeding systemWith concentrated diets, there is a need to limit feeding to avoid health problems, but this can result in chronic hunger, restlessness, motivation to forage, and competition for food. Systems that might work well with one feeding system may not work well with another.
- Environmental featuresCertain environmental features allow sows to occupy their time and escape from aggressive group mates. How well a housing system functions may depend on whether such features are present.
- Type of sowThere are important genetic differences in temperament that affect how well sows function in different housing systems. There are also individual differences; a housing system that is good for more dominant animals may not be favorable for less dominant ones.
- Given the number of variables and large variation in performance within both group and stall systems for pregnant sows, no one system is clearly better than others under all conditions and according to all criteria of animal welfare.
- Sow housing systems should:
- Minimize aggression and competition among sows;
- Protect sows from detrimental effects associated with environmental extremes, particularly temperature extremes;
- Reduce exposure to hazards that result in injuries, pain, or disease;
- Provide every animal with daily access to appropriate food and water;
- Facilitate observation of individual sow appetite, respiratory rate, urination and defecation, and reproductive status by caregivers; and
- Allow sows to express most normal patterns of behavior.
- All systems have advantages and disadvantages for welfare. Current group systems allow freedom of movement and social interaction. However, these same systems, when they fail to work well, lead to problems, especially in the areas of aggression, injury, and uneven body condition. When they lack manipulable material, sows in group systems are also unable to forage. Current stall systems minimize aggression and injury, reduce competition, allow individual feeding, and assist in control of body condition. Stalls, however, also restrict movement, exercise, foraging behavior and social interaction. Because the advantages and disadvantages of housing systems are qualitatively different, there is no simple or objective way to rank systems for "overall" welfare.
- To address animal welfare in the long term, advantages of current housing systems should be retained while making improvements to overcome problems identified. Improvements should be adopted as soon as:
- The technology is sound enough that producers can adopt it with confidence,
- The skills needed to operate the systems are understood and available, and
- Systems are economically viable.