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

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

POULTRY SCIENCE

POULTRY SCIENCE ASSOC INC

Año: 2017

0032-5791

ABSTRACT Aggressive behaviors can affect both animal welfare and productivity. Because the 18 expression of aggressive behaviors is dependent on the quality of the opponent, they reflect 19 relative rather than absolute levels of underlying aggressiveness. This study was aimed to 20 characterize the aggressive responsiveness of photostimulated (14:10h light:dark photoperiod) 21 adult Japanese quail when interacting with a photocastrated (6:18h light:dark photoperiod) 22 counterpart in a novel test environment and to assesses interindividual variations. This was based 23 on the assumption that photocastrated birds will not actively provoke an aggressive 24 confrontation. Birds were reared in male-female pairs. Frequencies of behaviors (i.e., pecks, 25 threats, chases, grabs, mounts) were determined during 10 min social interactions in a novel 26 environment. A first experiment evaluated 78 encounters between a photostimulated male or 27 female with either a photocastrated male or female (photocastration of sexually mature birds 28 started at 11 wk of age). High interindividual variability was observed and in general, highly 29 aggressive birds (performing 20 or more aggressive interactions) received little or no aggression 30 from their test counterpart. However, unexpectedly, we also found that 37 and 32% of 31 photocastrated males and females, respectively, performed aggressions toward their 32 photostimulated counterparts, and initiated the aggressive interactions in a similar proportion 33 than photostimulated males. Aggressive photocastrated males did not perform reproductive-type 34 behaviors (i.e. grabs, mounts). Aggressiveness in the photocastrated birds was attributed to their 35 social experience prior to photocastration. Therefore, a second experiment evaluated 106 36 encounters between a photostimulated male or female and a naive photocastrated male 37 (photocastration started at 4 wk of age, prior to sexual development). Photocastrated males 38 performed no aggressions toward their photostimulated counterparts. Consistently with previous 39 studies, our findings show that naive photocastrated males can be used as a non-aggressive 40 stimulus during a social interaction aimed to assess expression of aggressiveness in Page 2 of 36 https://mc04.manuscriptcentral.com/ps Poultry Science For Peer Review 41 photostimulated birds. However, caution should be taken when applying the photocastration 42 protocol considering that prior fighting and sexual experience or other physiological changes 43 related with maturation can interfere during subsequent aggressive testing.