EFFECTS OF GROUPING UNFAMILIAR ADULT-PIGS AFTER DARK, AFTER TREATMENTWITH AMPEROZIDE AND BY USING PENS WITH STALLS, ON AGGRESSION, SKIN-LESIONS AND PLASMA-CORTISOL CONCENTRATIONS

The effects of methods, previously shown to reduce aggression, were de termined on the number of aggressive interactions, skin lesions and pl asma cortisol concentrations following grouping of four unfamiliar, ad ult ovariectomised pigs, There were four treatments involving 24 pigs in six replicates: (i) Control; (ii) Stall, in which there were four p artial stalls used for feeding; (iii) Amperozide, an anti-aggression d rug; (iv) Dark in which the pigs were grouped 30 min after sunset, All treatments were in rectangular pens providing a space allowance of 1. 4 m(2) per pig, Aggressive interactions were observed for 90 min follo wing grouping and for 40-min periods around feeding on the day followi ng grouping and 9 days later, Skin lesions were assessed 3 days after grouping, The spatial use of the pens was determined during a 60 min p eriod between 14:00 and 16:00 h on the day following grouping and 9 da ys later, Total cortisol concentrations were determined from samples c ollected during a 75 min period commencing 90 min and 24 h after the s tart of grouping and total and free cortisol concentrations were deter mined from nine blood samples collected at hourly intervals on days 8 and 10. Fewer aggressive interactions (P < 0.05) occurred 15-90 min af ter grouping in the Amperozide and Dark than the Control treatment, Th e Stall treatment reduced aggressive interactions (P < 0.05) around fe eding on day 10, There were no effects of treatment on the number or l ength of lesions or the use of the pen during a rest period (P > 0.05) , However, there were significant positive regressions between aggress ive interactions and the number and length of lesions (P < 0.05). Ther e was an acute stress response in the Amperozide treatment 90-165 min after grouping compared with all other treatments (0.001 < P < 0.01) a nd the magnitude of this stress response raises some welfare concerns on the use of amperozide. animals in the Stall treatment showed a lowe r (P < 0.01) total cortisol concentration on day 10 than animals in th e other treatments and this indicates a welfare benefit from the provi sion of stalls.