Response of stress-susceptible and stress-resistant Hampshire pigs to electrical stress. I. Physiological and biochemical effects.

Abstract

Stress susceptible (SS) and stress resistant (SR) purebred Hampshire swine, weighing approximately 100 kg, were utilized to study the effects of electrical stress on plasma creatine phosphokinase (CPK), blood pH, plasma lactic dehydrogenase (LDH), plasma glucocorticoids, rectal temperature, heart rate and respiration rate. Blood samples were obtained from jugular cannulas 15 min and 5 min pre-stress, and subsequently at 0, 5, 10, 15, 30, 60 and 120 min post-stress. The electrical stress (.05 amperes and 30 volts) was administered intermittantly (2 sec on and 1 sec off) directly on the skin at the point of the poll between the ears and on the medial side of the fore leg above the point of the elbow for a total stress time of 4 min over a 6-min period. Each pig was stressed three times with 3 days rest between stimulations. Post-stress responses (P<.01) were obtained over time for all the variables measured except respiration rate. Plasma CPK levels were greater (P<.01) for SS pigs at all the pre-stress and post-stress bleeding times. Thus, CPK may have value in differentiating between SS and SR pigs under standardized environmental (stress) conditions. The SS pigs had marked post-stress decrease (P<.01) in blood pH compared to SR pigs, although pre-stress blood pH was similar for both groups of pigs. Pre-stress plasma LDH levels were similar for the SS and SR pigs while several post-stress levels were greater for the SS pigs. Plasma glucocorticoid levels were similar for the SS and SR pigs at all the pre-and post-stress bleeding times. The SS pigs had a higher (P<.05) overall mean rectal temperature compared to the SR pigs. Both the SS and the SR pigs had elevated post-stress rectal temperatures. The heart rate of the SS pigs was higher at 0 min post-stress compared to the SR pigs while both groups were similar at the other times. Respiration rates were similar for both groups.