This dissertation is an investigation into the effect of different zinc sources and levels on eggshell quality and microstructure, as well as keel bone damage. Eggshell function is two-fold; eggshells function to protect the developing embryo, as well as act as a barrier against bacterial penetration, optimizing food safety of the egg for human consumption (Mabe et. Al., 2003). Two small trials were conducted in order to determine differences in eggshell microstructure of eggs produced from hens at peak lay (26 weeks of age) and at the end of lay (88 weeks of age). Two groups of hens were fed a calcium sufficient or a calcium deficient diet. From this it was determined that eggs with higher breaking strengths had some differences in eggshell microstructure. Eggs with greater breaking strengths had a greater density of ‘normal’ structures, compared to ‘abnormal’ structures. Additionally, eggs requiring a greater breaking force, had a thicker micro-structure, compared to shells requiring less breaking force. With this knowledge on microstructure, a larger, 36-week study was conducted using different zinc sources. Every four weeks, eggs were collected and standard egg quality measurements were taken and keel bones were scored. At the end of the study, keel bones were collected from randomly selected hens representing each treatment. Picture of these keel bones were taken and measurements were taken to determine type and degree of deformation, in comparison to scores taken on the live bird. Pens selected for keel bone analysis, were the same pens that eggs were taken for imaging by the scanning electron microscope, to determine eggshell microstructure. From this data, it was determined that egg quality differences were detected, as well as differences in eggshell microstructure. Additionally, keel bone scores progressively worsened throughout the 36-week long study, with type and degree of deformation differing depending on zinc source.

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