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 Title: Factors influencing aggression in newly mixed pigs Author(s): Stookey, Joseph Mitchell Doctoral Committee Chair(s): Gonyou, Harold W. Department / Program: Animal Sciences Discipline: Animal Sciences Degree Granting Institution: University of Illinois at Urbana-Champaign Degree: Ph.D. Genre: Dissertation Subject(s): Biology, Zoology Agriculture, Animal Culture and Nutrition 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.) Issue Date: 1991 Type: Text Language: English URI: http://hdl.handle.net/2142/20551 Rights Information: Copyright 1991 Stookey, Joseph Mitchell Date Available in IDEALS: 2011-05-07 Identifier in Online Catalog: AAI9136745 OCLC Identifier: (UMI)AAI9136745
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