| Summary: | The effect of mixing unfamiliar finishing pigs (Sus scrofa) on agonistic behaviour and productivity over a 3 week period was investigated. Nine groups of six pigs were allocated to one of three treatments and eight groups of six pigs to the fourth treatment. In the first treatment (unmixed) littermate groups were moved into a new pen and in the second treatment (3:3 mixed) 3 pigs from one littermate group were mixed with 3 pigs from a second littermate group. The third treatment (Stresnil-treated) was similar to the second treatment but pigs were injected with the tranquilizer Stresnil (azaperone) prior to mixing. In the fourth treatment (5:1 mixed) groups of five pigs were introduced into a pen already occupied by either a single relatively light weight pig or a relatively heavy weight pig. Intense fighting was displayed by the regrouped pigs immediately following mixing, while unmixed and Stresnil-treated pigs generally went to sleep.
During feeding periods, initiated aggression was the most common agonistic behaviour exceeding aggressive responses and submissive responses by a factor of up to 14. In mixed groups initiated aggression was significantly higher than in unmixed groups. Administration of Stresnil appeared to disrupt the animals' behavioural repetoire by delaying aggression, retarding social hierarchy establishment and depressing productivity. Prior occupancy of pen space also appeared to influence aggressive behaviour. Over the entire three week sample period, average daily weight gains (ADG) of all three mixed treatments were significantly less than unmixed groups. The differences were significant during the first week but not in the second or third weeks. The mixed groups were also poorer converters of feed during the first week and over the three week period. Stresnil-treated pigs, on average, exhibited the poorest productivity of the mixed treatments. The economic costs of raising mixed groups from an initial weight of 76 kg to a standard final weight of 95 kg as a result of their reduced weight gain and feed efficiency, was substantial: $2.92 per pig for Stresnil-treated groups; $1.43 per pig for 3:3 mixed groups; and $1.13 per pig for 5:1 mixed groups. Assuming that growth rates remain the same, extrapolation of the data to a market weight of 102 kg resulted in overall costs of $3.50 per pig for Stresnil-treated groups, $1.94 per pig for 3:3 mixed groups and $1.54 per pig for 5:1 mixed groups. === Land and Food Systems, Faculty of === Graduate
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