Minimizing inter-pig aggression during mixing.
2005
Marchant-Forde, J. N. | Marchant-Forde, R. M.
Unacquainted pigs of all ages fight when mixed, resulting in body lesions, increased circulating stress hormones and increased heart rates. Aggression can therefore compromise pig welfare, and can also have an economic impact for the producer. Aggression in slaughter pigs can impact growth rates, increase veterinary costs, increase mortality rates and increase condemned meat at slaughter. Aggression in sows can also impact the number of returns to service and litter size. In commercial production, mixing is unavoidable but the aggressive consequences can be minimized. Mixing in the evening can reduce aggression by up to 55% in the 90-minute period post-mixing. Likewise, mixing after a period of pre-exposure can reduce aggression by up to 60% over the two-week period post-mixing. Pen design can reduce aggression - the incorporation of 'get-away' areas or provision of barriers can enable subordinate pigs to escape their aggressor and reduce aggressive interactions by 25% in the 12-hour post-mixing period. With sows, mixing in the presence of a boar can suppress inter-sow aggression by 43% and also access to ad libitum feed at mixing can have beneficial effects in terms of less severe skin lesions indicating less severe aggression. Again, the design of the system can provide advantages - dividing up the lying area can help the sows to retain an element of their sub-group structure formed prior to mixing into the large group. Other methods, which have proven unsuccessful over the long term, include adding fresh bedding, restricting space and chemical intervention - either tranquilizers or non-pheromonal olfactory masking agents. These methods may show a positive short-term effect, but usually this is just a postponement of aggression rather than an overall reduction.
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