Behavioural reactions, semen quality and testosterone levels in cocks: Genetic implications

Intense selection for productivity may have indirectly affected some behavi oural traits in poultry. Intensive husbandry systems change rapidly, and th e animals may have difficulties in coping with their environment and manage ment. The aims of this study are to examine the fear reactions of two strai ns of chicken (Gallus gallus domesticus) and to test the relationship betwe en these fear reactivity levels and the chickens' semen characteristics. Se men characteristics may indicate the Effect of genetic selection both on th e productivity and fitness of the animals. Forty cocks of two genetics stra ins (an egg-type strain and a meat-type strain), housed in single cages, we re used in the study. During the breeding period, semen was collected twice a week from each animal. Each cock was submitted to an open-field test and a tonic immobility test. The results show that strong genetic selection, c arried out over a long period on domestic chickens in order to improve egg and meat production, seems to affect some aspects of behaviour. The reactio ns to the fear tests show many differences between the two strains in the o pen-field test, the egg-type cocks show higher levels of exploratory behavi our and lower general fearfulness (eg lower frequency of vocalisations and head movements). On the other hand, the meat-type cocks show a significantl y lower duration of tonic immobility, indicating a lower level of fear spec ifically towards humans. Moreover, a key nearest neighbours analysis carrie d out using the behavioural data allows us to discriminate between the two strains with an error rate of 0%. These results suggest the potential for g enetic selection aimed at reducing fear reactions, both towards novel envir onments and towards human beings, which may significantly improve the welfa re of cocks.