Unexpected results when assessing underlying aggressiveness in Japanese quail using photocastrated stimulus birds

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

POULTRY SCIENCE

POULTRY SCIENCE ASSOC INC

Año: 2017 vol. 96 p. 4140 - 4150

0032-5791

Aggressive behaviors can affect both animalwelfare and productivity. Because the expression of aggressive behaviors isdependent on the quality of the opponent, they reflect relative rather thanabsolute levels of underlying aggressiveness. This study was aimed to characterize the aggressive responsiveness ofphotostimulated (14:10h light:dark photoperiod) adult Japanese quail wheninteracting with a photocastrated (6:18h light:dark photoperiod) counterpart ina novel test environment and to assesses interindividual variations. This was based on theassumption that photocastrated birds will not actively provoke an aggressiveconfrontation. Birds were reared in male-female pairs. Frequencies of behaviors(i.e., pecks, threats, chases, grabs, mounts) were determined during 10 minsocial interactions in a novel environment. A first experiment evaluated 78encounters between a photostimulated male or female with either aphotocastrated male or female (photocastration of sexually mature birds startedat 11 wk of age). High interindividual variability was observed and in general,highly aggressive birds (performing 20or more aggressive interactions) received little or no aggression from their testcounterpart. However, unexpectedly, we also found that 37 and 32% ofphotocastrated males and females, respectively, performed aggressions towardtheir photostimulated counterparts, and initiated the aggressive interactionsin a similar proportion than photostimulated males. Aggressive photocastratedmales did not perform reproductive-type behaviors (i.e. grabs, mounts). Aggressivenessin the photocastrated birds was attributed to their social experience prior tophotocastration. Therefore, a second experiment evaluated 106 encounters betweena photostimulated male or female and a naive photocastrated male(photocastration started at 4 wk of age, prior to sexual development). Photocastratedmales performed no aggressions toward their photostimulated counterparts.Consistently with previous studies, our findings show that naive photocastratedmales can be used as a non-aggressive stimulus during a social interactionaimed to assess expression of aggressiveness in photostimulated birds. However,caution should be taken when applying the photocastration protocol consideringthat prior fighting and sexual experience or other physiological changesrelated with maturation can interfere during subsequent aggressive testing.