A STUDY OF THE RELATIVE AVERSIVENESS OF A NEW DAILY INJECTION PROCEDURE FOR PIGS

This experiment examined the aversiveness of a new injection procedure (''Injection treatment''), developed for the daily administration of porcine somatotropin to pigs, which was imposed on pigs over a 3 week period late in the growing phase. The injection was via a 13mm, 16 gau ge needle and utilized a low penetration gas injection gun. Observatio ns were conducted on the escape-avoidance responses of treated pigs to this injection procedure and to humans. In addition, the cortisol res ponse to treatment and the cortisol response of pigs to an ACTH challe nge were determined and the adrenal glands were weighed. To gauge a re lative measure of the magnitude of these behavioural and physiological responses, a positive control (''Positive treatment'', a treatment wi th rewarding components such as a human patting and stroking approachi ng pigs), a negative control (''Negative treatment'', a treatment that is clearly aversive involving regular electric shocks) and a neutral control (''Control treatment'', a treatment with minimal human contact , similar to the amount of contact which occurs during routine husband ry) were included in the evaluation. Based on the relative behavioural and cortisol responses to treatment, the Injection treatment was judg ed to be moderately aversive. This relative assessment is based on thr ee findings. Firstly, the escape-avoidance responses of pigs to the In jection treatment were intermediate between those of pigs to the Negat ive treatment and to the Control and Positive treatments. Secondly, th e cortisol response of pig to the Injection treatment was similar to t hat of pigs to the Control and Positive treatments but was lower (P le ss than or equal to 0.05) than that of pigs to the Negative treatment. Thirdly, in response to humans in a standardized test, pigs in the In jection treatment behaved similarly to those in the Control treatment for three of the four variables measured and significantly (P less tha n or equal to 0.05) different than those in the Negative treatment for three of the four variables. Although there was evidence that the pig s in the Negative treatment may have experienced a chronic physiologic al stress response with a significant (P less than or equal to 0.05) d epression in growth rate, there was neither physiological nor producti on evidence to indicate that the Injection treatment adversely affecte d the long-term stress physiology of the pigs. In conclusion, the dail y imposition of tills new injection procedure over a 3-week period is moderately aversive to pigs and the welfare of these pigs is similar t o that of pigs receiving minimal human contact as occurs in the routin e husbandry of growing pigs.