Factors influencing aggression in newly mixed pigs
Stookey, Joseph Mitchell
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https://hdl.handle.net/2142/20551
Description
Title
Factors influencing aggression in newly mixed pigs
Author(s)
Stookey, Joseph Mitchell
Issue Date
1991
Doctoral Committee Chair(s)
Gonyou, Harold W.
Department of Study
Animal Sciences
Discipline
Animal Sciences
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Biology, Zoology
Agriculture, Animal Culture and Nutrition
Language
eng
Abstract
996 pigs were used to understand the effects of aggression on growth in swine, the role of previous experience on the level of aggression, and the basis on which a pig accesses recognition and familiarity when mixed with an unfamiliar pig. The hypothesis that fighting in newly mixed pigs is proximately triggered by an innate response to fight unfamiliar pigs as opposed to an alternative hypothesis that fighting is triggered by unknown dominance status was also addressed. Growth over a 2 week period was negatively effected when mixing near market weight pigs (average wt. 85.1 kg). Time spent eating, lying and standing were similar across all treatment groups by day 8 (P $>$.05), however time spent fighting for Mixed pigs continued to be higher than other treatments (P $>$.01). In a trial using 6 and 10 week old pigs, time spent fighting (TF), total number of fights and the winner loser of an encounter among unfamiliar dyads in a neutral pen during a 2 h period was not influenced by their previous dominance ranks (P $<$.10). Six week old pigs differed from 10 week pigs in TF (raw means 758 and 421 sec/2 h period respectively; P $<$.01). TF was positively correlated with the difference in weight between the paired pigs (maximum difference 6.2 kg; P $<$.05). Newly mixed pigs access strangeness based on familiarity gained through previous association as opposed to recognition based on phenotypic kin recognition. Pigs fought more if reared apart than separately (252 $\sp{\rm \ a}$ 33 sec vs 67 $\sp{\rm \ a}$ 45 sec respectively; P $<$.0001), but time spent fighting was not different between related or unrelated dyads. An attempt to exchange familiarity (FX) between two unfamiliar pigs prior to mixing was unsuccessful in eliminating aggression during a 2 h mixing period. FX pigs were pre-exposed to each other while one of the pair was under the influence of anesthesia. FX pigs were no different from Negative Control pigs (NC) or Sham Controls (SC) in time spent investigating each other or for any of the fighting parameters measured. FX pigs may have gained some familiarity during pre-exposure periods since they had a higher frequency of mounting during the 2 h mixing period then the NC and SC pigs (P $<$.01). (Abstract shortened with permission of author.)
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