Osteological investigations of the incidence of cranial alterations in domestic ducks (Anas platyrhynchos f. dom.) with feather crests

The feather crest of the domestic duck (Anas platyrhynchos f. dom.) represents a peculiar mutation of the integument of the head, which has been known since the 17th century. In literature this is described as a variety with malformations in skull and brain anatomy in which various central nervous deficiencies in affected birds are possible. Our examinations demonstrated several conspicuous anatomical alterations in the skulls of domestic ducks with feather crests. Osteophytes of different size in the hypodermis of the crest integument were found as well as cranial perforations located in the parieto-occipital region. In morphometric studies, a significant increase in the capacity of the cranium was found in Crested ducks compared to other examined breeds (Abacot Ranger, German Pekin ducks). This increase in cranial capacity in Crested ducks results from the occurrence and enlargement of a tentorial fatty depot during craniogenesis. The formation and enlargement of the fat body can influence cranium growth as long as the cranial bones are not entirely fused. Thus, in comparison to other phenotypically similar domesticated birds like the crested chicken, the expression of feather crests in domestic ducks demonstrates symptomatologic differences. In conclusion, our examinations demonstrate that the skulls of Crested ducks show various peculiar morphological alterations whose genesis is up to now not known with satisfactory accuracy. Further investigations are continuing to assertain whether there are linkages between cranial alterations (malformations of the calvaria, osteophytes, increased capacity of the cranium) and the extremely high prenatal and postnatal mortalities and numerous abnormalities described in crested breeds of the domestic duck.