Modeling collisions in laying hens as a tool to identify causative factors for keel bone fractures and means to reduce their occurrence and severity

Abstract

Keel fractures represent a major productivity and welfare issue for the laying hen industry with greater than 50% of birds in recent surveys across various commercial operations and nations exhibiting some form of damage by end of lay. While the causes are likely multifactorial and influenced by age, diet, genetic line, and other factors, high energy collisions with house furnishings and conspecifics in the barn are believed to be a major contribution to the frequency and severity of factures. The current study applies a previously described ex vivo impact testing protocol to quantify susceptibility to keel bone damage across an extensive range of collision energies and ages. We also link fracture susceptibility with bone and physiological measures likely to influence skeletal resilience. Further, we applied the impact testing protocol to evaluate the benefit of an omega-3 enriched diet to improve bone health and reduce fracture susceptibility. Our results indicated that fracture susceptibility increased rapidly from 23 weeks of age, peaking at 49.5 weeks of age and thereafter decreasing. Fracture susceptibility also varied with multiple natural characteristics of bone, including mineral density, though the nature of that relationship was dependent on whether an old fracture was present. Severity of the experimental fracture demonstrated considerable variation with collision energy and biomechanical properties. An omega-3 enhanced diet provided a protective effect against fractures, though only in terms of collision energies that were relatively low. In conclusion, the impact testing protocol provided a unique means to assess fracture susceptibility and quantify the role of likely influencing bird-level biological factors, both those that vary naturally as well as when altered through specific interventions.

Fig 1. Modeled probability (% Y-axis) of experimental fracture in relation to hen age (weeks; X-axis) and collision energy (J).

Fig 2. Modeled probability of an experimental fracture (%; Y-axis, left side) in relation to the mineral density of the keel’s base (mg/cm²; X-axis) and the presence of an old break.

Superimposed on the graph is a histogram of the number of keels (#; Y-axis, right side) assessed.

Fig 3. Modeled probability of an experimental fracture (%; Y-axis) in relation to impact collision energy (J; X-axis) and bird mass (Kg).

Fig 4. Modeled probability of experimental fracture (%; Y-axis,) type (Minor (top), Major (middle), and Severe (bottom)) in relation to collision energy (J; x-axis) and hen age (#; weeks represented by different line colors as show in the legend of the bottom panel).

Superimposed on the graph is a histogram of the number of experimental impacts (#, Y-axis, rightside) across all ages that resulted within each respective severity grouping.

Fig 5. Modeled probability of experimental fracture (%; Y-axis,) type (Minor (top), Major (middle), and Severe (bottom)) in relation to collision energy (J; x-axis) and bone mineral density (mg/cm2) in the keel base.

Fig 6. Probability of experimental fractures classified as Minor, Major, and Severe (%; Y-axis) in relation to toughness of the humerus (N; X-axis).

Fig 7. Probability of experimental fractures classified as Minor, Major, and Severe (%; Y-axis) in relation to Young’s Modulus of the humerus (mm/N; X-axis).

Fig 8. Probability of experimental fractures classified as Minor, Major, and Severe (%; Y-axis) in relation to humerus strength (J, X-axis).

Fig 9. Probability of experimental fractures classified as Minor, Major, and Severe (%; Y-axis) in relation to breast mass (g, X-axis).

Fig 10. Probability of a Major experimental fracture occurring (%; Y-axis) across collision energy (J; X-axis) in relation to a minor fracture across treatment diet.

The Figure represents both Major and Minor fractures, i.e. the proportion of Minor factures is the value of the line subtracted from one or the space above the line.