Behavioural Reactions, Semen Quality and Testosterone Levels in Cocks: Genetic Implications
Intense selection for productivity may have indirectly affected some behavioural traits in poultry. Intensive husbandry systems change rapidly, and the animals may have difficulties in coping with their environment and management. The aims of this study are to examine the fear reactions of two strains of chicken (Gallus gallus domesticus) and to test the relationship between these fear reactivity levels and the chickens' semen characteristics. Semen characteristics may indicate the effect of genetic selection both on the productivity and fitness of the animals. Forty cocks of two genetics strains (an egg-type strain and a meat-type strain), housed in single cages, were 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, carried out over a long period on domestic chickens in order to improve egg and meat production, seems to affect some aspects of behaviour. The reactions to the fear tests show many differences between the two strains: in the open-field test, the egg-type cocks show higher levels of exploratory behaviour and lower general fearfulness (eg lower frequency of vocalisations and head movements). On the other hand, the meat-type cocks show a significantly lower duration of tonic immobility, indicating a lower level of fear specifically towards humans. Moreover, a key nearest neighbours analysis carried 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 genetic selection aimed at reducing fear reactions, both towards novel environments and towards human beings, which may significantly improve the welfare of cocks.
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