Animal Welfare Information Center Bulletin, Spring 1999, Vol. 9 No. 3-4

Animal Welfare Issues: Swine

Palmer J. Holden
Department of Animal Sciences, Iowa State University, 109 Kildee Hall
Ames, Iowa  50011-3150
John McGlone
Department of Animal Science, Texas Tech University
Lubbock, Texas  79409-2141


Issues of animal welfare and animal rights are concerns now facing the pork industry. People who raise animals, whether for meat production, companionship, recreation, or other purposes, have a responsibility to sustain the basic welfare of their charges. Modern domesticated and confined animals depend completely upon their caretakers for their nutritional, environmental, and social needs. This is true whether the animals are raised in a pasture system (extensive production) or in an indoor unit without access to soil or grass (intensive production).

To: Contents | Introduction | Discussion | Assessment of Animal Welfare | Current Production Practices--Standard Procedures | Current Production Practices | Space | Alternative Practices | Glossary | References |

Swine in traditional indoor farrowing pen. Swine in outdoor environment.


Assessment of Welfare

Assessment of animal welfare is difficult. The British Farm Animal Welfare Committee, referenced by Muirhead (1), noted: “There are few positive methods of assessing the well-being and contentment of animals; we must not assume that animals’ feelings and reactions are the same as those of human beings. It is clear that a healthy and well-fed animal will not necessarily be a happy, stress-free animal and there are a few positive indicators to evaluate with any accuracy the degree of stress; there is also evidence that some stress is necessary for the animal’s well-being.” Productivity may not be the best measurement of well-being, but it must be considered as one measure in a battery of measures until more reliable indicators are found. Important measures of welfare include behavior and physiology.

Pork producers have a profound interest in the well-being of their charges. Pig performance and welfare have significant impacts on the success and profitability of the pork production operation. Swine kept in less than ideal conditions have impaired growth rates, reduced efficiency of feed utilization, and low reproductive performance. Stressed pigs show signs of immunosuppression and, therefore, greater disease incidence. They often show behavioral changes, which may differ from one stressful environment to another. Cold-stressed young pigs, for example, show poorer feed efficiency and greater likelihood of respiratory and enteric disease, and they shiver and huddle in a characteristic manner.

Each production practice adopted by producers is intended to optimize economics and to be suitable to the pig’s biological needs. Pork producers try to meet or exceed these biological requirements in the most cost-effective manner. Both facility design and management practices make the most of the available alternatives. When some discomfort must be imposed, the benefit is less overall pain or discomfort. Thus, one animal may have its movement restricted to save the lives of others (as in the farrowing crate where the sow’s movement is limited to prevent baby pigs from being crushed).

Extensive pork production cannot by definition be more pig friendly or less stressful. Some stressors, such as predators and parasites, affect pigs negatively when encountered during extensive production. Many scientists and pork industry leaders conclude that the stresses of even well-managed extensive pork production typically exceed the stresses of well-managed intensive production systems. Others have shown overall economic benefits to the use of extensive systems.

Animal welfare concerns about pork industry practices include two areas:

Several research laboratories in the United States are initiating projects in swine welfare and behavior. Currently, most projects deal with sow housing during gestation and lactation using newer housing or penning systems. Other projects seek to better understand how pigs perceive their environment through cognitive processes.

Current Production Practices—Standard Procedures

Several common practices that are considered to cause some pain are regularly performed on newborn pigs by pork producers. Examples include ear notching and tagging, teeth clipping, tail docking, and castration. Pork producers perform these standard practices because they believe each procedure will help the animals and prevent more pain and suffering later in their lives.

Ear notching is typically performed near the time of birth, and the pain is considered to be minimal. If each animal has an individual identification, it can be better treated when it becomes ill and its progress (in terms of growth and reproduction) can be tracked. Ear tags can also be used (much like piercing ears) to provide an identification number, but they have the potential disadvantage of falling off. New technology is being developed to implant (under the skin) an electronic identification device that can be read by a computer scanner.

Piglets are born with eight sharp “needle” teeth. Needle teeth are probably used by pigs in the wild to defend against predators. Piglets (domestic or wild) generally use their needle teeth to establish dominance. In so doing, they wound littermate piglets and may tear the sow’s udder during suckling. Pork producers use a clean clipper for individual piglets to take the sharp edge off the tip of the needle teeth. The procedure is performed shortly after birth, and the brief discomfort experienced by piglets is much less than might be experienced by sows with shredded udders.

Adult or immature pigs occasionally show an abnormal behavior called tail biting or cannibalism. When a tail biting episode begins, the vice usually spreads quickly in the affected pen and throughout the neighboring pens. The tail has a rich blood supply, and the bleeding tail of the bitten pig stimulates pen mates to further chew the wounded tail. Pigs sometimes bleed to death; in other cases, aggressive penmates chew the tail down to the spinal cord and cause infection, illness, and possibly death. Docking tails soon after birth substantially reduces the incidence of tail biting. Pigs may cannibalize whether they are housed inside or on dirt lots, and the practice occurs with widely different stocking densities. An outbreak of tail biting is expected to be very painful for the pigs with bitten tails. The small amount of discomfort caused by docking is much less overall than what would be experienced by pigs during an outbreak of tail biting.

Male pigs are usually castrated within the first 3 to 14 days after birth. New pork industry swine care recommendations (2) suggest that boars be castrated at 2 weeks of age or younger. If males more than 8 weeks old must be castrated, the industry recommends use of anesthetics to reduce the pain. Most adult male pigs develop a characteristic off-flavor and odor that has been termed “boar odor,” which consumers find highly objectionable. Castration substantially eliminates the occurrence of this odor. At market time, pork producers receive much less compensation for boars than for castrated males (barrows). In a recent demonstration project, boars had only two-thirds the market value of barrows (3).

To: Contents | Introduction | Discussion | Assessment of Animal Welfare | Current Production Practices--Standard Procedures | Current Production Practices | Space | Alternative Practices | Glossary | References |

Current Production Practices


Pigs in modern pork production systems are more likely to be found inside buildings than in the more extensive pastoral setting. The move towards indoor systems has probably enhanced pig welfare. Pigs housed inside buildings are generally exposed to a more constant and comfortable temperature, drier, and freer from parasites. Overall animal care is often better when animals are more easily handled. However, well-designed and managed extensive systems also promote acceptable animal welfare.

Much research has been conducted on the subject of crowding. Crowding leads to reduced feed intake, slower weight gain, and increased disease incidence. More basic studies have shown that crowding causes elevated stress hormones and increases aggressive behavior. Therefore, there are both economic and animal welfare reasons for maintaining lower population density.

Space needs for adult sows and boars are less well understood. Adult pigs are typically fed a limited amount of feed, since overfeeding leads to fat animals with lower reproductive success. To maintain normal, lean body weights, sows and boars are fed about one-third of the calories they would eat if given free access to feed.

Adult pigs have very strong social relationships, with one animal having clear dominance over subordinate pigs. Dominant sows that are hungry will steal feed from sows of lower social rank. Sows housed in groups have a greater chance of injuries caused by various aggressive behaviors (for example, vulva biting (4)). To prevent problems associated with group housing, sows are provided individual feeding stalls or are penned in individual gestation stalls. Individual housing of sows in gestation stalls eliminates the pressures of social stress that group-housed sows experience. Record-keeping services (with records on tens of thousands of sows) and controlled studies generally support the idea that penning sows in gestation stalls increases their reproductive performance. Clearly, some genetic strains of swine are more adaptable to indoor housing.

Since stress has dramatic negative effects on reproduction, it is possible that the stress of individual penning is less than the stress of being a submissive sow in a social group. Further study is needed to understand fully the physiology and behavior of sows in individual and group housing systems. An abrupt industry move to certain types of group housing systems for sows could lead to reduced sow welfare.

Alternative Practices

Extensive swine production is an economical component of production in the United States. Land and labor requirements are greater, but this is a viable system for producers with low capital resources. On a per-head basis, extensive systems are as profitable as indoor production, but the net profit of the unit will be less because of smaller volume and less consistent production.

Sows farrowing on pasture in portable houses weaned 0.8 fewer pigs per litter (5) than confined sows and have higher death losses in wet, cold weather. Sows farrowing in pens and turned out to feed and water wean as many or more pigs than sows maintained in a stall for the lactation period. They get more exercise and eat more feed. More time is required to turn sows in and out and to remove soiled bedding.

Research studies must determine which practices are stressful and if those stressors are detrimental. For example, data suggest that individually stalled sows are more productive than group-housed sows, based on productivity and longevity in the herd. Stockmanship also affects stress and performance. Researchers observed a positive relationship between pigs/sow/year and sows that were “at ease” with human caretakers (6). In mild seasons, pigs raised outdoors grow as well as or better than confined pigs. In hot and cold seasons, pigs grow faster indoors.

New housing, penning, and management practices are being developed. Before these new systems are introduced into pork production units, we must be sure they provide animal well-being that is equal to or better than the systems they replace.

To: Contents | Introduction | Discussion | Assessment of Animal Welfare | Current Production Practices--Standard Procedures | Current Production Practices | Space | Alternative Practices | Glossary | References |


Barrow — Male pig castrated before sexual maturity.
Boar — Intact (not castrated) male pig.
Gilt — Female pig of any age prior to second pregnancy.
Pig — Young swine of either sex.
Piglet — Baby pig.
Sow — Female swine having produced one or more litters.
Castration — Removal of testes.
Farrow — To give birth to a litter of pigs.

To: Contents | Introduction | Discussion | Assessment of Animal Welfare | Current Production Practices--Standard Procedures | Current Production Practices | Space | Alternative Practices | Glossary | References |


  1. Muirhead (1991). International Pigletter 11:21.
  2. National Pork Producers Council (1996). Swine care handbook. Available at NPPC, P.O. Box 10383, Des Moines, IA 50306.
  3. Demonstration study conducted at Texas Tech University and reported in Successful Farming, October, 1991.
  4. Den Hartog, L. A., G.B.C. Backus, and H.M. Vermeer (1993). Evaluation of housing systems for sows. Journal of Animal Science 71:1339-1344.
  5. Stevermer, E. J. (1992) 1991 Swine Survey. Swine Enterprise Record, ASB1991:EJS-269, Iowa State University.
  6. Hemsworth, P.H., G.J. Coleman, and J.L. Barnett (1994) Improving the attitude and behavior of stockpersons toward pigs and the consequences on the behavior and reproductive performance of commercial pigs. Applied Animal Behaviour Science 39:349-362.

To: Contents | Introduction | Discussion | Assessment of Animal Welfare | Current Production Practices--Standard Procedures | Current Production Practices | Space | Alternative Practices | Glossary | References |

This article appeared in the Animal Welfare Information Center Bulletin, Volume 9, Numbers 3-4, Spring 1999

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