Abstract
The objective of this study was to assess beak shape variation in domestic turkeys (Meleagris gallopavo) and determine the effects of age, sex, and beak size on beak shape variation using geometric morphometrics. Dorsal and right lateral images were taken of 2442 turkeys at 6 and 18.5 weeks of age. Landmarks were digitized in tpsDig in three analyses of the dorsal upper mandible, lateral upper mandible, and lateral lower mandible shape of each turkey at both ages. The coordinate data were then subjected to a principal components analysis (PCA), multivariate regression, and a canonical variates analysis (CVA) with a Procrustes ANOVA in MorphoJ. For the dorsal images, three principal components (PCs) showed beak shape variation ranged from long, narrow, and pointed to short, wide, and blunt upper mandibles at both ages (6 weeks: 95.36%, 18.5 weeks: 92.21%). Three PCs showed the lateral upper mandible shape variation ranged from long, wide beaks with long, curved beak tips to short, narrow beaks with short, pointed beak tips at both ages (6 weeks: 94.91%, 18.5 weeks: 94.33%). Three PCs also explained 97.80% (6 weeks) and 97.11% (18.5 weeks) of the lateral lower mandible shape variation ranging from wide and round to narrow and thin lower mandibles with superior/inferior beak tip shifts. Beak size accounted for varying proportions of the beak shape variation (0.96–54.76%; P < 0.0001) in the three analyses of each age group. For all the analyses, the CVA showed sexual dimorphism in beak shape (P < 0.0001) with female upper mandibles appearing wider and blunter dorsally with long, curved beak tips laterally. Whereas male turkey upper mandibles had a narrow, pointed dorsal appearance and short, pointed beak tips laterally. Future applications of beak shape variability could have a genetic and welfare value by incorporating beak shape variation to select for specific turkey beak phenotypes as an alternative to beak treatment.
Highlights
A significant proportion of mortalities and culls in domestic turkeys show signs of injurious pecking, which suggests that this damaging behaviour contributes to decreased productivity and economic losses in commercial production
The objective of this study was to evaluate the phenotypic variation in turkey beak shape using landmark-based geometric morphometrics, and to determine if age, sex, and beak size had an effect on the beak shape variation in domestic turkeys
Along the axis of centroid size, centroid size explained the variation from long, narrow beaks with pointed tips to short, wide beaks with blunt beak tips for the dorsal upper mandible shape of both male and female turkeys
Summary
A significant proportion of mortalities and culls in domestic turkeys show signs of injurious pecking, which suggests that this damaging behaviour contributes to decreased productivity and economic losses in commercial production. Injurious pecking represents a serious welfare concern for domestic turkeys [1,2,3]. The existing research into the development and causation of injurious pecking in turkeys suggests a complex relationship among multiple factors, but there is little literature on environmental and genetic approaches to reduce this damaging behaviour in modern flocks [2,4]. Infrared beak treatment is standard practice to reduce injurious pecking damage in commercial turkey flocks. With beak treatment potentially being phased out of commercial practice, there is concern within the industry that environmental approaches alone will not prevent pecking damage from increasing in modern turkey flocks. One potential alternative solution is to examine the phenotypic variation in beak shape to explore the possibility of genetic selection to produce morphological results similar to beak treatment
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