Unexpected results when developing a test to asses underlying aggressiveness in Japanese quail using a photocastrated stimulus bird

MARIN, R.H.; PELLEGRINI, S.; KEMBRO, J.M.; GUZMÁN, D. A.; CALIVA, J.M.

Orlando, Florida

Congreso; PSA Annual Meeting; 2017

Poultry Science Association

Aggressions are social interactions present in all animals. In the context of poultry, these behaviors can affect both animal welfare, performance and productivity. Behavioral tests used to asses aggressiveness usually evaluate direct or indirect interactions with an unfamiliar conspecific with similar characteristics or within a social group. Because the aggressions observed are dependent on the quality of the opponent, they reflect relative rather than absolute levels of underlying aggressiveness. Based on the assumption that photocastrated (6:18h light:dark photoperiod) birds will not actively provoke a confrontation, we propose their use as stimulus birds in a social interaction test to promote photostimulated (16:8h light:dark photoperiod) birds to express their underlying levels of aggressiveness. Birds were reared in male-female pairs. A first experiment evaluated at 16 wk of age 10 min social interactions between pair combinations of a photostimulated male or female with either a photocastrated male or female (photocastration begun when stimulus birds were 11 wk of age). In general, highly aggressive birds received little or no aggressions from their opponent. However, unexpectedly, we found that approximately 38% of both photocastrated males and females were aggressive, and photocastrated males even initiated the aggressive interactions in similar proportion than their photostimulated counterparts. Results were attributed to the their social experience prior to photocastration. Thus, a second experiment using naive photocastrated males (photocastration started when they were 4 wk of age; prior to sexual development) was performed. In this trial, no aggressions were found from photocastrated males toward their photostimulated counterparts. Bird´s differences in aggressiveness were not related to their weight or cloacal gland volume nor to their fearfulness during mechanical restraint or tonic immobility tests. Our findings suggest that naive photocastrated males can be used as a non-aggressive stimuli during a social interaction aimed to asses expression of aggressiveness in photostimulated birds. However, caution should be taken when applying the photocastration protocol considering that prior fighting and/or sexual experience during sexual maturation could interfere during subsequent aggressive testing.