Ante-mortem detection of PSE and DFD by infrared thermography of pigs before stunning.
Using water-holding capacity and colour measurements (L and b values) as objective quality parameters, we have observed an increasing incidence of meat quality defects with the increasing skin surface temperature of pigs by infrared thermography prior to stunning. Below 32·2°C, 50% of the 32 pigs measured had normal meat while the other half showed meat quality defects. Above 32·2°C, however, 71% of the 49 pigs showed meat quality problems classified as moderate PSE (6%), PSE (30%), moderate DFD (22%) and DFD (37%). At this temperature level, meat quality of the remaining pigs was normal and decreased to 29%. Although infrared thermography of live animals cannot predict whether the meat will be PSE or DFD, it seems to be a practical and rapid method to detect pigs who will yield a significant proportion of meat quality defects. An early post-mortem identification of meat quality could supply the missing information.
Plasma levels of norepinephrine and epinephrine during malignant hyperthermia in susceptible pigs.
Malignant hyperthermia (MH) is a genetic disease of man, swine, dogs, cats, and horses. The syndrome is normally triggered by inhalational anesthetics or the administration of depolarizing muscle relaxants such as succinylcholine or various environmental stress factors. We have used the MH-susceptible pig as an animal model to study the hormonal changes developing during this highly lethal syndrome. High-performance liquid chromatography with electrochemical detection was used for the quantitation of the plasma levels of norepinephrine and epinephrine during MH. This research presents evidence that the rapid release of massive quantities of norepinephrine (up to 108 ng/ml) into the blood stream occurs simultaneously with the initiation of tachycardia which is the herald signal of the onset of MH. Norepinephrine levels exceed epinephrine by a 4:1 ratio early in the syndrome. Even pigs with MH which do not develop the muscle rigor phase have high levels of circulating norepinephrine. Tachycardia, pulmonary hypertension, increased venous oxygen desaturation, and increasing core temperature develop as the syndrome progresses.
Role of Sympathetic Activity in Porcine Malignant Hyperthermia
Malignant hyperthermia (MH) is characterized in part by sympathetic hyperactivity associated with increased levels of circulating catecholamines. Controversy exists as to whether the sympathetic nervous system is in some way abnormal and primarily contributing to MH, or whether the sympathetic response is secondary to the stress of MH originating from skeletal muscle. Total spinal anesthesia with resulting sympathetic denervation was used in genetically susceptible Poland China swine to investigate this question. isobaric tetracaine, 1.2–2.2 mg/kg, was injected via the sacral hiatus into the cerebrospinal fluid to produce total spinal anesthesia (paralysis of all four limbs). Total spinal anesthesia failed to prevent the occurrence or attenuate the course of MH in swine given halothane, 1 per cent (five pigs) or halothane and succinylcholine, 3 mg/kg (one pig). Total spinal anesthesia did prevent the expected increases in norepinephrine and epinephrine during MH in all six swine. Since dantrolene is specifically therapeutic in MH, its effect on the sympathetic response to stress was measured in two other susceptible swine. Treatment with dantrolene, 10 mg/kg, intravenously, did not prevent increases in catecholamines due to stress caused by either respiratory and metabolic acidosis (Paco2 110 torr, base excess −20) combined or hemorrhagic hypotension (mean pressure 40 torr). The authors conclude that the sympathetic nervous system is involved in porcine MH only as a secondary response to stress; that conduction anesthesia will not protect pigs from MH; and that the efficacy of dantrolene in porcine MH is due to its effects on skeletal muscle rather than to depression of the sympathetic nervous system.