More Precision in Control of Intramuscular Injectable Anesthetics in Swine by D. Bruce Lawhorn

In swine destined for human consumption, veterinarians correctly stress that the ham muscles are not to be used for injection because any lesions in this area will reduce the value of a major portion of the pork carcass. The neck muscles and subcutaneous areas behind the ears and the lose skin in the axillary spaces of the front or hind limbs are excellent sites for antibiotic and deworming injections and vaccinations (always follow product label instructions for injection site). However, intramuscular injection of tranquilizers such as xylazine and anesthetics such as TelazolR and ketamine have the most predictable onset of action, duration of anesthesia and recovery time when injected into the ham muscles. Tranquilizer and/or anesthetic injection using the neck muscles in obese potbellied pigs or even lean show swine seem to be more poorly absorbed and often necessitate repeat administration to achieve an acceptable plane of anesthesia or restraint, and makes the recovery time prolonged. The worst scenario is lack of anesthetic control when previously injected drugs suddenly exert their action and cause the plane of anesthesia to become too deep. At this point, resuscitation may be required.

In addition, every possible advantage should be sought before anesthetizing Sus scrofa. Fast the animal for 12 to 24 hours and withhold water 4 hours prior to the procedure. Aspiration pneumonia in non-intubated pigs (intubation is difficult in pigs) is a real risk Preanesthetic injection of atropine (0.05 mg/kg IM) has been recommended to reduce salivation induced by inhalant anesthetics such as halothane. It has been reported that xylazine prevents salivation induced by TelazolR or ketamine. Clinical experience with xylazine and TelazolR anesthesia in swine substantiates this reported claim.

Perform a physical exam to rule out obvious problems such as pneumonia, that significantly increase the odds for anesthetic death. Also obtain a history that includes tolerance to exercise and on the pig’s arrival to the clinic walk it around to observe for signs of respiratory distress or muscle tremoring. Pigs with pneumonia will usually cough after light exercise. Heavily muscled show pigs may display signs of Porcine Stress Syndrome (PSS) such as stiffness, muscle tremors, extremely rapid elevation of body temperature (PSS also called malignant hyperthermia), vasodilation and red blotching of entire skin surface (seen in white pigs), and mouth breathing when exercise stressed. The smaller the size of the pig, the better the chance for recovery from a PSS episode. This is why the history is so important. Smaller pigs may have had non-fatal episodes of PSS that can be described or “hinted at” by the owner in a thorough history. One probable nonfatal case of PSS in a potbellied pig (PBP) under isoflurane gas anesthesia has been documented, and another PBP case with a fatal outcome during a routine spay was recently diagnosed PSS positive and confirmed by a DNA blood test at Marshfield Laboratory. PSS genes are inherited in association with heavy muscling, therefore light muscled breeds, such as the PBP, are expected to have a low prevalence of this genetic defect. However, if PSS cases continue to be reported in PBPs, extensive inbreeding could be the cause.

Care must be exercised in blood sampling a suspected PSS pig since any stress such as restraint may trigger the syndrome and cause death. Alternatively, the sire and dam may be blood sampled and tested. If both parents are carriers (have one PSS gene [heterozygous] ), 25 percent of a litter will carry two mutant genes and be PSS animals (homozygous recessive), likely to express PSS signs after stress and die; 50 percent will be carriers and 25 percent will be normal. If one parent is a carrier and one is normal, 50 percent of offspring will be carriers and 50 percent will be normal. Carrier swine do not express malignant hyperthermia of PSS when stressed.

Two labs currently offering the PSS test are Marshfield Laboratory, 1000 North Oak Avenue, Marshfield Wisconsin, 54449 (800-222-5835) and GeneScreen, 2600 Stemmons Freeway, Suite 133, Dallas, Texas 75207 (800-752-2774). Marshfield requires at least a 2 ml EDTA blood sample that is refrigerated and sent overnight with coolent, but Genescreen uses a testing procedure requiring only several drops of blood on a card that may be sent unrefrigerated in an envelope (also will accept whole blood EDTA samples). Obviously it is much easier and less stressful to obtain several drops of blood from a needle prick of ear vein or other area than to collect larger quantities. However, remember that any amount of stress on a PSS pig may cause expression of the syndrome and possible death. Both test are expensive but registration (registration instructions available from either lab) slightly decreases the cost.

Swine recovering from anesthesia seem to take at least 6 hours to regain adequate thermoregulatory ability. This means they are susceptible to hypo- or hyperthermia depending on their recovery environment. Show swine are commonly anesthetized in a trailer and transported before completely recovering from anesthesia. PBPs may be anesthetized at the client’s home with recovery observation assigned to the owner. On days with temperature extremes, swine recovering from anesthesia are at risk for complications and death. Animals recovering from anesthesia should be observed, temperatured and turned at least once an hour until they are walking around and alert. This usually takes 2 to 6 hours with IM anesthetics. Monitoring recovery is best performed by veterinarians or professional staff that can recognize hypo- or hyperthermia and other complications and take appropriate actions.

Injectable anesthetics in swine can be safely and effectively utilized if the previously discussed practices are considered and implemented to fit into each practitioners routine of swine practice..

From Bruce Lawhorn, DVM, MS, Associate Professor and Extension Veterinarian, Texas Agricultural Extension Service and Dept. of Large Animal Medicine and Surgery, College of Veterinary Medicine, The Texas A&M University System; Swindle MM. “Anesthetic and Perioperative Techniques in Swine: An Update,” Charles River Laboratories , Spring 1994; Ko JCH, Thurmon JC, Benson GJ, et al. “Using Telazol-ketamine-xylazine anesthesia for castration of cryptorchid pigs,” Veterinary Medicine, October 1994, 999-1002; Claxton-Gill MS, Cornick-Seahorn JL, Gamboa JC, et al. “Suspected Malignant Hyperthermia Syndrome in a Miniature Pot-Bellied Pig Anesthetized with Isoflurane,” Journal American Veterinary Medical Association, Vol. 203, No. 10, November 15, 1993, 1434-1436; and personal communications with Barbara Baker and Jenny Blaney