Behavioral and adrenal responses to various stressors in mule ducks from different commercial genetic selection schemes and their respective parental genotypes.

The mule duck, a hybrid produced by crossing a Muscovy drake and a Pekin female, is reported to express inappropriate behavior such as collective avoidance of people, the resulting distress and physical consequences potentially compromising their welfare. The present study was carried out to characterize the responses of mule duck strains from different commercial selection schemes to various stressful conditions and to confirm previous data on the genetic cross effects observed in a specific genotype. Three independent experiments were conducted with ducks from 3 French breeding companies (A, B, and C). Each experiment compared 2 mule genotypes sharing one common parental origin (paternal for ducks from company A or maternal for ducks from companies B and C). Mule duck males from the 2 genotypes and their respective parental genotypes (Pekin and Muscovy) were subjected to a set of social and stressful physiological and behavioral tests. Previously reported differences in genetic cross effects on fear responses between the parental genotypes and the corresponding hybrid were confirmed in these commercial crosses. Both mule duck and Pekin genotypes showed more active physiological and behavioral responses to stress than Muscovy genotypes. The new finding of this study is that mule genotypes appear to be more sensitive to the social environment than both respective parental genotypes. Few differences were observed between the 2 mule genotypes from A and C. On the other hand, several traits of the 2 mule genotypes from B differed. In addition, A and C mule genotypes were characterized by the same adrenal and behavioral traits but contrasting responses. The B mule genotypes were characterized by a different set of behavioral traits, and only 1 of the 2 B mule ducks was characterized by a group of adrenal traits.