Taxonomy/Natural History

Suids consist of 13 species occurring naturally in Europe, Asia, the East Indies, and Africa. Some examples of wild suid species include the Eurasian wild boar (Europe, N Africa, Asia), the common warthog (Africa), babirusa (Sulawesi), bearded pigs (Borneo), and the red river hog (W Africa). Suids, most notably the Eurasian wild boar, have been introduced into the Americas, Australia, Tasmania, New Zealand, and New Guinea.^4,5

In the United States, introduced Eurasian wild boars have flourished, often hybridizing with domestic swine, to create large populations of feral pigs in areas of Florida, Texas, California, Hawaii, and other states.³ Many studies have documented the deleterious effects that these animals have on ecosystems and crops. For example, in regions of Hawaii inhabited by pigs, more than 80% of the soil is bare of vegetation. In the US, an estimated $800.5 million per year is spent on costs associated with feral pigs.⁷

Tayassuids, or peccaries, consist of 3 species endemic to North, Central, and South America: collared peccary, white-lipped peccary, and Chacoan peccary. Peccaries are easily distinguished from suids by their long, slender legs and short tails.^4,5

Many zoos and private owners house domesticated suids. Among the most common are Vietnamese pot-bellied pigs and domestic swine.

While many suid species are considered invasive pests, the Visayan warty pig (two islands in the central Philippines), and the Pygmy Hog (India) are critically endangered, mostly due to habitat loss and hunting, according to the IUCN Red List of Threatened Species.

Clinically Relevant Anatomy

GI Tract

Suids have a simple, glandular stomach and, except for the babirusa, are hindgut fermenters, with a spiral colon. The majority of their omnivorous diet consists of roots, tubers, bulbs, and other below-ground material. Additionally, such foods as fruit, fungi, reptiles, eggs, small rodents, and carrion are eaten opportunistically. The babirusa has an extra compartment to the stomach used for foregut fermentation of fruits and concentrates.^4,5

Tayassuids eat a similar diet to suids, but also eat more fruit, berries, cacti and grass, possibly the reason for having a more complex stomach. The stomach consists of a glandular portion, a large gastric pouch, and two blind pouches, or cecae.^4,5

Upper Airway

Suids and tayassuids have an elongated soft palate (4) and a pharyngeal diverticulum (13) dorsal to the entrance to the esophagus (16) (See Figure below).¹

Figure 34-10. Median section of the head of a 4-week-old pig; nasal septum removed (4) soft palate, (6) oropharynx, (7) nasopharynx, (11) laryngeal ventricle, (12) larynx, (17) trachea From 1Dyce et al. (1996)

Feet

Suids and tayassuids are even-toed, hoofed mammals. All limbs have accessory digits (#1, #4), which are non-weight-bearing, but do contain a full number of bones (not rudimentary).¹

Teeth⁴

Pigs and peccaries have brachydont teeth. Some examples of dental formulas are listed below.

Handling and Restraint

Wild suids are generally not amenable to physical restraint. The large canine teeth (tusks) can cause serious injury to handlers. Wire hog snares are not recommended, but a modified snare may be made with a nylon dog leash, looped just caudal to the canine teeth. Push boards may be used to move animals and as shields for persons giving injections. Commercial pig boxes or squeeze chutes may be used for medium to large suids.² Positive reinforcement training has been used to facilitate such minimally invasive procedures as abdominal ultrasound, blood sample collection, hoof trimming, and vaccinations.

Anesthesia

Chemical immobilization is usually necessary for physical examination. Intramuscular (i.m.) injection is best achieved in the semimembranosus and/or semitendinosus muscles, using 1.5- to 3-inch long needles to minimize the possibility of injection into the fat layer. Alternatively, the biceps or triceps muscles may be used in less aggressive suids. The neck is not a suggested i.m. injection site due to the likelihood of injection into fat. Remote delivery of anesthetics via darting may be necessary in large adults and/or aggressive animals. Multiple anesthesia protocols have been described.^2,6

B - butorphanol; M - medetomidine; TZ - tiletamine-zolazepam; D - detomidine; Mz - midazolam; X - xylazine; K - ketamine; P - propofol

Intubation

This is challenging due to suids' unique oropharyngeal anatomy, long snout and minimal ability to open the jaws. The animal may be placed in dorsal or ventral recumbency. Soft gauze caudal to the canine teeth is used to hold the mouth open. A long-bladed laryngoscope is useful to visualize the epiglottis, and may be used to dorsally displace the elongated soft palate to relieve an entrapped epiglottis. Laryngospasm may be reduced with the topical application of 2% lidocaine to the laryngeal folds. The endotracheal (ET) tube may be easier to advance if threaded over a preplaced stylet in the larynx. The ET tube tends to travel dorsally into the pharyngeal diverticulum; this situation may be prevented by initially directing the tube ventrally and gently twisting the tube upon entry into the trachea. Isoflurane and sevoflurane have been used successfully for anesthetic maintenance.

At the Oakland Zoo, a fabricated, extended, straight laryngoscope blade met with only mildly increased success. Additionally, ET tubes have been extended by 10–14 cm at the adapter end with extra silicone tubing due to the need for longer (but not larger diameter) ET tubes for larger suids. Endoscopic-guided intubation has also proven successful. A flexible gastroscope is placed into the ET tube and the tube is visually guided through the laryngeal opening. This procedure is limited by the size of the animal and ET tube required.

Laryngeal edema has been reported as a consequence of even atraumatic intubation, resulting in dyspnea and severe apprehension. Treatment of this condition typically requires additional sedation to relax any laryngospasm present, systemic steroids, and supplemental oxygen. In severe cases, re-intubation may be necessary.

All species of suids are at risk for hyperthermia, due to their low body surface area to volume ratio and abundant SQ fat stores. A rectal thermometer will enable the clinician to accurately monitor body temperature. Treatment of hyperthermia includes cooling the skin with alcohol and/or ice packs, cool intravenous (i.v.) fluids, and cold water enemas. Pigs suspected of suffering from malignant hyperthermia (elevated body temperature, muscle rigidity, tachycardia, hypoxemia, elevations in serum potassium, ionized calcium, and creatinine phosphokinase) need immediate supportive care including removal of inhalant anesthetics, muscle relaxants, i.v. fluid support, antiinflammatories, and/or systemic steroids.⁶

Vascular Access

Jugular Vein

The suid is placed in ventral recumbency, with the snout positioned dorsally to reveal the jugular furrow. Use a 1.5-inch (or longer in larger species) needle placed perpendicularly to the spine. Direct the needle cranially and slightly medially to advance into the vessel. Long-term i.v. catheter placement in the jugular vein is possible, but requires surgical cut-down for access.

Cranial Vena Cava

Venipuncture is per the technique described for domestic swine.

Cephalic and Lateral Saphenous Veins

These vessels are easily accessible in pot-bellied pigs, warthogs and red river hogs. They are useful for short-term catheterization but may be difficult to maintain in conscious animals.

Auricular Veins

Of variable size per species, present on the dorsolateral aspect of the ears, these vessels generally provide rapid access for small volume injections and/or small blood sample collection. A butterfly or regular catheter may be secured to the ear, but care must be taken not to damage the sensitive ear tissue.

Coccygeal (Tail) Vein

This vein is approached on the ventral aspect of the base of the tail, using a 21–23-gauge needle. It may be prone to collapse with excessive application of negative pressure.

Common Clinical Conditions and Procedures

Hoof Care⁴

Without proper substrate or periodic hoof trimming, suid toes are prone to overgrowth, which may lead to foot infections and other chronic orthopedic abnormalities. Wild suids and peccaries appear to have more sensitive hooves than domestic swine, which can cause multiple clinical problems. Toe-tip erosions leading to osteomyelitis may be consequences of digging at hard surfaces such as concrete. Improperly moist substrate may lead to excessive sole growth, while hard or rocky surfaces can create sole bruises. Treatment consists of curing infections with systemic and/or topical antimicrobials, application of protective topical restoratives, and analgesic therapy. Additionally, it is extremely important to provide appropriate substrate and enrichment to prevent re-injury.

Dental Care

Periodic dental cleaning, including removal of dental calculus, and filing of tusks and dental points may be necessary, especially in geriatric animals, as periodontal disease has been observed in both captive and wild suids.⁴ Endodontic treatment and extractions have been performed in cases of tusk fractures and infections. Osteomyelitis as a result of periodontal disease has been seen and is treated with systemic antimicrobials and extraction of the affected teeth. Good quality skull and dental radiographs are essential in diagnosing dental disease.

Diet/GI Problems

In captivity, obesity is a major concern. Restricted calorie pelleted diets, limited treat foods, and increased exercise help prevent excessive weight gain. Suids may be prone to gastric ulceration. Nonsteroidal antiinflammatories should be used with caution. Constipation appears to be a significant cause of morbidity, and may be due to these animals' unique GI anatomy. It is important to provide sufficient fiber in suid and tayassuid diets. Additionally, some practitioners routinely employ mineral oil enemas during anesthesia in attempt to promote GI mobility and prevent postanesthetic constipation.

Musculoskeletal

Degenerative joint disease is common in aged suids in captivity, especially affecting elbow and stifle joints in overweight animals. Variable treatment success has been achieved with dietary supplements such as glucosamine and chondroitin sulfates, and methylsulfonylmethane (MSM). Doses are typically extrapolated from canine and human protocols. The author has used the following pharmaceuticals for short-term treatments without significant untoward effects.

Vaccinations

Vaccination of suids and tayassuids is based on assessed risk of disease exposure and is extrapolated from domestic swine recommendations. One suggested pot-bellied pig vaccination protocol is outlined below.⁴ Note that local laws may govern additional vaccines required for pet pigs, such as rabies vaccination.

 Erysipelothrix rhusiopathiae: initial dose 8–12 weeks, booster at 12–16 weeks; annual booster

 Clostridium tetani: initial dose 8–10 weeks, booster at 12–16 weeks, 2nd booster 24–32 weeks. Annual booster until 3–5 years of age.

 Leptospirosis: infection is common, but mostly asymptomatic except abortifacient in pregnant sows

 Parvovirus: use in breeding females only

References

1.  Dyce KM, Sack WO, Wensing CJG, eds. Pig Textbook of Veterinary Anatomy. 2nd ed. St. Louis, MS: Saunders; 1996:769–812.

2.  George L. The New Pot-Bellied Pig Manual. Veterinary Information Network. www.vin.com. 2012

3.  Kotanen PM. Responses of vegetation to a changing regime of disturbance: effects of feral pigs in a Californian costal prairie. Ecography. 1995;18:190–199.

4.  Morris PJ, Shima AL. Suidae and tayassuidae (wild pigs, peccaries). In: Fowler ME, Miller RE, eds. Zoo and Wild Animal Medicine. 5th ed. St. Louis, MS: Saunders; 2003:586–602.

5.  Nowack RM. Suidae: pigs, or hogs. Tayassuidae: peccaries. In: Walker's Mammals of the World. Baltimore, MD: John Hopkins University Press; 1999:1053–1066.

6.  Padilla LR, Ko JCH. Non-domestic suids. In: West GW, Heard DH, Caulkett N, eds. Zoo Animal and Wildlife Immobilization and Anesthesia. Ames, IA: Blackwell; 2007:567–577.

7.  Pimentel D, Zuniga R, Morrison D. Update on the environmental and economic costs associated with alien-invasive species in the United States. Ecol Econ. 2005;52:273–288.