© 2006 Japanese Society of Animal Science Animal Science Journal (2006) 77, 447–453 doi: 10.1111/j.1740-0929.2006.00371.x Blackwell Publishing AsiaMelbourne, AustraliaASJAnimal Science Journal1344-3941© 2006 Japanese Society of Animal ScienceAugust 2006774447453Original Article BEAK TRIMMING AND AGGRESSION IN HENST. SHINMURA et al . Correspondence: Tsuyoshi Shinmura, School of Veterinary Medicine, Azabu, University, Sagamihara-shi, 229-8501, Japan. (Email: slow-but-steady@j04.itscom.net) Received 30 September 2005; accepted for publication 26 December 2005. ORIGINAL ARTICLE Effects of light intensity and beak trimming on preventing aggression in laying hens Tsuyoshi SHINMURA, Yusuke EGUCHI, Katsuji UETAKE and Toshio TANAKA Graduate School of Veterinary Medicine, Azabu University, Sagamihara-shi, Japan ABSTRACT This study aimed to investigate the effects of decreased light intensity and beak trimming on aggression prevention in lay- ing hens. In total, 181 White Leghorns were used. At 17 weeks of age, 36 birds were allocated to battery cages (three birds/cage), 36 birds to furnished cages (four birds/cage), and 109 birds were transferred to an aviary. Since aggression increased in the birds from 23 weeks of age (from 0.3% to 6.0%) especially in the furnished cages, , the light intensity dur- ing the daytime was decreased to about one-tenth (from 680 lux to 70 lux) at 28 weeks of age. The birds in the furnished cages then had their beaks re-trimmed lightly by using a debeaker at 29 weeks of age. Behavioral observations using scan- ning techniques at 10 min intervals were conducted. Feed intake, bodyweight and feather score were also measured. There was no significant difference in aggression before and after decreasing the light in all three housing systems. On the other hand, the proportion of birds showing aggression decreased significantly just after trimming and four weeks after beak trimming in the furnished cages (P < 0.05 and P < 0.01, respectively). The aggression also became similar to the propor- tions observed in the battery cages and in the aviary. In proportion to the decreased aggression, the proportion of birds eating significantly decreased (P < 0.05). However, their feed intake and bodyweight did not decrease significantly. Against this decreased aggression, the proportion of birds preening significantly increased (P < 0.05). Aggression was observed more frequently at the dust bath in the furnished cages and at the litter floor in the aviary (both P < 0.001). The total feather score for all body parts in the birds in furnished cages increased significantly (P < 0.01) from 25 to 29 weeks of age (at beak trimming), but did not increase significantly from 29 to 33 weeks of age. The increments of neck, breast and tail feather scores in the furnished cages were smaller. In conclusion, there was no significant difference in aggression between just before and after decreasing the light in any housing system. However, aggression in the furnished cages was reduced not only by decreasing the light intensity, but by additional beak trimming. Aggravation of feather conditions – especially at the neck, breast and back – was prevented by the treatment. Key words: aggression, beak trimming, housing system, laying hen, light intensity. INTRODUCTION In our previous study, it was indicated that adjustment of aviary birds to the system just after introduction had been delayed in comparison with caged birds because of their pre-rearing conditions and the environmental complexity of the aviary (Shinmura et al. 2006). How- ever, the observation period in the study was only two weeks just after their introduction. To evaluate the welfare level of each housing system more thor- oughly, long-term experiments were required. Hence, the comparative experiment of three housing systems (aviary, furnished cages, and battery cages) had been continued. In the long-term experiment, aggression in the birdswas frequently observed from about 23 weeks of age, especially in furnished cages. During the first two weeks after being introduced into these cages, the average proportion of birds displaying