Crossed beaks in a local Swiss chicken breed

Abstract

BackgroundCrossed beaks have been reported to occur in Appenzeller Barthuhn, a local Swiss chicken breed. The assumed causes for this beak deformity which are also seen in other bird species including domestic chickens, range from environmental influences to genetic factors. The aim of this project was to characterize the prevalence, the phenotype, and the underlying genetics of crossed beaks in Appenzeller Barthuhn chickens.ResultsThe estimated prevalence of 7% crossed beaks in Appenzeller Barthuhn was significantly higher compared to two other local Swiss chicken breeds. A breeding trial showed significantly higher prevalence of offspring with deformed beaks from mating of affected parents compared to mating of non-affected parents.Examination of 77 Appenzeller Barthuhn chickens with crossed beaks showed a variable phenotype presentation. The deviation of the beak from the median plane through the head ranged from 1° to 61°. In more than 60% of the cases, the upper and lower beak were bent in the same direction, whereas the remaining cases showed different forms of crossed beaks. Computed tomographic scans and bone maceration of the head of two chickens with crossed beaks revealed that the maxilla and the mandibula were affected, while other parts of the skull appeared to be normal.The gene LOC426217, a member of the keratin family, was postulated as a candidate gene for beak deformity in domestic chickens. Sequencing of the coding region revealed two significantly associated synonymous variants for crossed beaks in Appenzeller Barthuhn chickens. A genome-wide association study and a comparative analysis of runs of homozygosity based on high-density SNP array genotyping data of 53 cases and 102 controls showed no evidence of association.ConclusionsThe findings suggest a hereditary cause of crossed beaks in Appenzeller Barthuhn chickens. However, the observed variation in the phenotype, together with the inconclusive molecular genetic results indicates the need for additional research to unravel the genetic architecture of this beak deformity.Electronic supplementary materialThe online version of this article (10.1186/s12917-018-1398-z) contains supplementary material, which is available to authorized users.

The Morphology of Cross-Beaks and BMP4 Gene Expression in Huiyang Bearded Chickens

“…The upper and lower jaw bones are part of the craniofacial bone tissue, and any changes to them may shape the development of a beak. In this study, we observed significant deflections of the maxilla and mandible, which were consistent with previous studies [3,5]. In Appenzeller Barthuhn chickens, cross-beaks were more likely to deflect to the right side [3].…”

“…In this study, we observed significant deflections of the maxilla and mandible, which were consistent with previous studies [3,5]. In Appenzeller Barthuhn chickens, cross-beaks were more likely to deflect to the right side [3]. Even though no different occurrence was observed between the left and right cross-beaks in this study, lower cross-beaks were found to be more likely to deflect to the right side.…”

“…These findings indicate that the lower beak is more prone to deformities, which may be supported by a previous study describing that changes to the mandible are underneath changes to the facial bones, and the mandible moves more easily than other facial bones [21,22]. Additionally, the deviation of angles (more than half of chickens with cross-beaks) were mainly concentrated at 1 • -10 • , which is similar with the above study that had 50% of all deviation angles between 1 • and 9 • for the upper beak and 2 • to 9 • for the lower beak [3].…”

“…All chickens that were characterized as having a cross-beak, by one or both beaks deviating laterally from the longitudinal axis of the head along with the backbone, were selected according to a previous study [3]. The main manifestation is that the upper and lower beaks are dislocated and cannot be properly closed.…”

“…A cross-beak is a dysmorphology relating to deformed beaks and has been suggested as a threat to animal welfare breeding. There are 1%-3% of Chinese native chickens that have beak deformities, leading to great economic loss and animal welfare issues in the poultry industry [1][2][3]. Typically, cross-beaks refer to the misalignment of upper and lower beaks.…”