Intraobserver repeatability for a standardized protocol to quantify keel bone damage in laying hens using discrete and continuous radiographic measures

Cerano Harrison, Jeryl Jones, William Bridges, Ahmed Ali

Background: This study describes a standardized protocol for quantifying keel bone damage (KBD) in laying hens using radiographic measures.

Study: The study was a retrospective, secondary analysis of 470 keel bone radiographs that had been previously acquired for a prospective laying hen study. The study aimed to develop and assess intraobserver repeatability of the protocol using open-source image analysis software and discrete and continuous variables.

Methods: The protocol involved dividing the keel bone into equal cranial and caudal segments, counting the number of fractures and calluses in each segment, measuring the area of ventral margin deviation and total keel bone area, calculating the proportion of deviation (POD), and measuring the angle of displacement (AOD) of the dorsal margin. All measurements were performed in triplicate by a graduate student using Horos software. Intraobserver repeatability was assessed using intraclass correlation coefficient (ICC) and control chart methods.

Results: The control chart analyses showed that most of the measurements were within the acceptable range of variation, indicating moderate to high intraobserver repeatability. The highest percentages of acceptable measurements were for the numbers of cranial calluses, caudal calluses, and incomplete caudal fractures. The lowest percentages were for the numbers of complete cranial fractures, incomplete cranial fractures, complete caudal fractures, POD, and AOD. The ICC values were low for some of the measures due to a few outliers causing widely ranging values.

Limitations: The study did not assess interobserver repeatability, the effect of additional observer training, or the repeatability of the protocol for hens older than 36 weeks of age. The study also did not evaluate the clinical significance of different types of KBD or the pain associated with them. The time required to complete the measurements using the protocol was long and may limit its applicability for large-scale studies.

Conclusions: The study introduced a standardized protocol for quantifying three types of radiographic KBD using open-source software and discrete and continuous variables. The protocol had moderate to high intraobserver repeatability based on control chart analyses. The protocol may be useful for experimental studies on the causes and effects of KBD in laying hens. Future studies are needed to determine the interobserver reliability and the clinical relevance of the protocol.

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