Using naturally-occurring variation in beak morphology to reduce feather pecking damage in laying hens
Outbreaks of severe feather pecking continue to be a serious welfare and economic concern for the poultry industry, particularly within the egg sector. Increasing consumer awareness of how poultry is raised and managed has led to a shift from cage systems to loose-housed ‘alternative’ systems, increasing the risk of outbreaks. Severe feather pecking, a form of injurious pecking, is commonly observed in laying hen flocks and can lead to cannibalism and high mortality. As a result, research has increasingly focused on how best to prevent and control severe feather pecking without needing beak treatment (an effective method of reducing physical damage caused by severe feather pecking and is commonly performed at day-old using infrared energy). Alternative practices to beak treatment include genetic selection against the behaviour itself, using enrichment materials to encourage appropriate foraging behaviour, and genetic selection of traits related to the behaviour (i.e., feather cover, liveability, and beak shape). This project examined the possibility of using genetic selection of beak shape to reduce damage inflicted by severe feather pecking. Significant beak shape variation exists within and between breeding laying hen lines, and research has shown that aspects of beak shape are heritable. This suggests incorporating beak shape data into selection indices is possible; however, characterisation of beak phenotypes and the amount of physical damage different beak shapes can cause is first needed. The shapes of the premaxillary and dentary bones within the beak have also never been characterised before in laying hens. Examining the bone shape is important as it has been suggested that it may influence the external beak shape to a certain extent. A pilot study was performed to determine if the analysis of the beak and its underlying bone shape defined and quantified by geometric morphometrics (GMM) of radiographic images was repeatable. Twenty-four hens were radiographed four times. Repeatability ranged from 0.52 to 0.81, demonstrating that imaging live hens over time and landmarking those images was repeatable. Using radiography and GMM, a study was conducted to characterise the variation in premaxillary and dentary bone shape within two pure lines of White Leghorn laying hens. Premaxillary bone shapes ranged from long and narrow with pointed bone tips to short and wide with more curved bone tips. Dentary bone shapes ranged from long and wide to short and narrow. For both bones, the shape differed between the two lines, and the size of the bone significantly affected its shape. The results showed that a range of shape phenotypes exist for both the premaxillary and dentary bone, which may influence beak shape. Photographs of the two pure lines were also taken to analyse the beak shape using GMM and examine the relationship between beak shape, the underlying bone shape, feather cover, and mortality. Maxillary beak shapes ranged from long and narrow with pointed beak tips to short and wide with more curved beak tips. The maxillary beak was moderately correlated to the premaxillary bone in shape and size. The shape data suggest distinct beak and bone phenotypes within each line for the beak and its underlying bones. In addition, feather cover and mortality differed between the two lines, with one line having better feather cover and lower mortality over the 100-week production cycle. Therefore, beak shape may be one factor contributing to the differences seen in feather cover and mortality. These distinct phenotypes could be selected to help reduce damage inflicted by severe feather pecking and improve laying hen welfare. Two studies were conducted to understand and quantify the physical damage different beak shapes can cause. The first study used live hens with either a sharp or blunt beak that pecked at “chicken” models (foam blocks covered with feathered chicken skin). The change in block and skin weight, the number of feathers removed from the skin, and the number of successful (resulting in feather or tissue removal) versus non-successful (no removal) pecks at the model were recorded. The change in block weight did not differ between the two groups; however, the sharp beak group had a larger change in skin weight and removed significantly more feathers than the blunt group. The mean number of pecks made at the model also did not differ between the beak shape groups; however, sharp beak hens had a greater percentage of successful pecks, while blunt beak hens had a greater percentage of non-successful pecks. The results of this study show that sharp beak hens were more capable of removing feathers and, by extension, tissue, thus resulting in damage. The second study used a robotic device to mimic a hen’s natural pecking motion ex vivo. Using this device, chicken heads pecked into agarose gel, which mimics muscle, at three pecking forces. The depth and volume of the indentations into the gel were assessed to quantify damage. No differences in indentation depth or volume were found between the different beak shape groups. Pecking force did affect depth and volume; however, the results were inconsistent. The results of this study suggest that the beak shapes tested were perhaps too similar to discern differences. These two studies also suggest other factors beyond beak sharpness (i.e., the curvature of the maxillary beak over the mandibular beak), such as other beak shape characteristics or the motivation to perform the behaviour, contribute to feather removal and tissue damage. This project’s results show that specific beak phenotypes within laying hen breeding lines could be incorporated into selection indices. This project provides a foundation for future genetic and behavioural research investigating the effect of beak shape on other beak-related behaviours like feeding and preening and identifying quantitative trait loci that underlie beak shape. More research is needed to examine the relationship between beak shape and its capacity to cause damage.
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