THE MERCK VETERINARY MANUAL
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Behavioral Problems of Swine

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Many behavioral problems in swine are related to confinement or stress. The treatment is usually directed toward managing social groups, establishing normal conditions when possible, and maintaining welfare.

Aggression

Piglets show aggression to other piglets within the first week of life while forming a teat order. Later, introducing new pigs into a group may lead to aggression as the pigs establish social ranks. Pigs may spend 1–2 min nosing each other, vocalizing, and then biting until one of the pigs retreats. It may take several days to establish a hierarchy in older pigs. Once the hierarchy is established, fights are rare and ranks are preserved mostly by threats from the dominant pig and submissive gestures from subordinates (eg, twisting the head away). During estrous cycles, sows may show severe aggression toward newly added sows. Submissive sows show the least estrous behavior, have small litters, and lose weight (most likely due to low nourishment). Most aggression in pigs seems to be related to resources such as food. Crowding and limited amounts of food increase aggression. During breeding, boars may fight and become very vocal; boars will strut shoulder to shoulder, champ their jaws (producing pheromone-rich saliva), then finally face each other and attack. Serious injuries may result, especially among boars that still have their tusks. Breed likely plays a role; Large Whites are more aggressive than Hampshires, which are more aggressive than Durocs. Body fat percentage may also be a factor; breeds with lower body fat are more aggressive when handled.

Management includes slow introduction of new pigs into existing groups, provision of shelters where subordinate pigs can hide, provision of sufficient resources and toys, and application of boar pheromones. Most producers keep lights dim in the pen to reduce aggression. Using tranquilizers such as azaperone (2.2 mg/kg) or amperozide (1 mg/kg) can help reduce aggression but may not be economical. Lithium (an antipsychotic) has been used successfully.

Tail biting is seen mostly in confined pigs. Overcrowding and boredom seem to be the main causes. Free-ranging pigs spend 5–10 hr daily looking for food and rooting, whereas pigs kept in pens consume meals in a short time. Slatted floors without bedding, low-salt diets, and low-iron soil seem to predispose pigs to tail biting. Once the problem starts, the taste of blood from the injured tail seems to arouse the other pigs and can even lead to death of the victim but rarely advances to pure cannibalism. Most losses are due to secondary infections that result in culling. Management includes removing the biting pigs (if there are only a few of them) and providing stimulation such as straw bedding to root, toys, and corn on the cob to chew. Most commercial producers dock piglets' tails; however, this does not reduce the motivation for tail biting, and pigs may bite the stump or ears instead.

Mostly seen in primiparous gilts, cannibalism accounts for 4% of piglet deaths and is estimated to affect ~18% of litters. It is most common immediately after parturition when the sow is stressed. Usually, the sow will bark to warn piglets walking by her head and then later attack them, biting them to death. Farrowing crates have been used successfully to reduce the incidence of cannibalism. Azaperone (2.2 mg/kg) has been used for treatment as well.

Heavy sows may lie on their piglets, killing them. This normally occurs when there are weak, underdeveloped, or sick piglets that cannot move fast enough to avoid the sow. However, it is also a breeding and management problem—sows are naturally intensely protective mothers that will prevent the handler from attending to the piglets; selective breeding for less-protective sows has resulted in sows less devoted maternally. Management includes providing appropriate farrowing crates with slopes and bars on the sides that allow the piglets to move away from the sow and prevent the sow from rolling over on the piglets. In addition, heat lamps provide the piglets with an alternative heat source and motivation to rest away from the sow.

Breeding-Related Problems

Reproductive problems are usually associated with management of boars and sows and estrus synchronization. These problems are fairly unusual in pigs because of rigid genetic control of sexual behaviors. Mating preferences are an important factor in breeding management of pigs.

Poor libido in boars can be caused by nutritional problems (deficiencies or overfeeding) and behavioral causes such as stress or fear. Exposing a boar to an aggressive female can result in low sex drive. Socialization, visual social contact with affiliative sows for a few days (in pens across from each other, not next to each other), and appropriate nutrition are the keys to successful management.

This is seen mainly in confined gilts, and stress seems to play an important role. Regrouping or overcrowding increases stress levels as well. These two factors (confinement and crowding) lead to chronic stress, delayed puberty, and failure to reproduce. On the other hand, acute and mild stress such as transport and gentle handling accelerate estrous cycles.

Normally, the sow lies in lateral recumbency and grunts to attract the piglets to nurse. Mastitis is the most common reason sows refuse to nurse piglets. A physical examination is necessary to exclude this and other medical conditions. The sow lies sternally, preventing the piglets from accessing the teats. Mastitis is typically seen during late phases of lactation when the farrowing crates are removed. Sows with postpartum dysgalactia syndrome and mastitis (see Postpartum Dysgalactia Syndrome and Mastitis in Sows) are usually too weak to move and prevent the piglets from nursing. However, these sows usually do not eat, and their piglets do not gain weight. Piglets of such sows should be transitioned to milk replacers and solid food. This can be encouraged by mixing sow's milk with the food or sweetening the food.

Stereotypic Behaviors

Stereotypic behaviors are not common in pigs and mostly relate to management, boredom, and nutrition. The most common stereotypic behaviors include rubbing nasal secretions on the floor or another pig, bar biting by confined sows, and polydipsia. Environmental enrichment in early stages is usually successful. Feeding smaller quantities more frequently and providing toys, bedding to root, corn on the cob, and clean tires can be enriching and mentally stimulating for pigs.

Last full review/revision May 2014 by Gary M. Landsberg, BSc, DVM, MRCVS, DACVB, DECAWBM; Sagi Denenberg, DVM, DACVB, Dip. ECAWBM (Behaviour), MACVSc (Behaviour)

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