Date of Award

8-2024

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Animal and Veterinary Sciences

Committee Chair/Advisor

Ahmed Ali

Committee Member

Mireille Arguelles-Ramos

Committee Member

Jeryl Jones

Abstract

This thesis aimed to evaluate the effects of interrupting the daily scotophase period on bone health and production in laying hens. Modern commercial laying hens are prone to high rates of bone demineralization due to the constant mobilization of calcium to withstand daily eggshell calcification mechanisms. The industry light standard for laying hens is 16 hours of continuous light (photophase) and 8 hours of continuous darkness (scotophase) daily. During scotophase, physical activity is reduced due to instinctive perching behaviors, and thus, feeding behaviors are halted. However, physiological processes, including digestion, excretion, and reproduction, remain active during scotophase.

Most eggshell formation occurs during scotophase during the nightly fasting period. During this time, dietary calcium available to the bird is limited to what was consumed immediately before scotophase. Since digestion continues during fasting, dietary calcium is depleted over time, leaving minimal calcium available to the bird for deposition to the eggshell. Adaptation over time has resulted in changes in bone biology, leading to mechanisms for calcium mobilization from skeletal sources to be recycled for deposition during eggshell formation. This biological mechanism consists of increased osteoclastic (cells responsible for bone tissue resorption) activity, specifically in the long bones and keel bones (prominent sternum bone and attachment point of wing muscles) of laying hens. The osteoclastic activity aims to resorb medullary (specialized, porous bone found in female avian species and utilized for calcium storage) bone as a critical source of calcium during times of high demand. However, these cells are not specific to only medullary bone. As a result, cortical (compact, structural outer layer of most long bones) bone is also resorbed, leading to increased bone fragility over time. Progressive resorption of bone calcium is considered to be the leading cause of osteoporosis and inferior eggshell quality in commercial laying hens, the two most prevalent problems facing the commercial laying hen industry.

Because the capacity of calcium absorption rates is met in standard commercial diets, in this study, we focused on the delivery of calcium with varying lighting schedules rather than varying calcium sources or dietary changes. Targeting the delivery of dietary calcium at a time of highest demand could decrease the rate of endogenous (bone) calcium from entering the blood-borne pool by increasing the rate of exogenous (dietary) calcium during eggshell formation.

This study investigated 3 various light schedules in Hy-line W36 laying hens from 20-70 weeks of age. Control hens received the industry standard of 16 hours of continuous light and 8 hours of continuous darkness. Two treatment groups received daily scotophase interruption. W1 (treatment group which received 1 hour of scotophase interruption) hens received one hour of daily scotophase interruption, while W2 (treatment group which received 2 hours of scotophase interruption) hens received 2 hours of daily scotophase interruption.

One of our objectives in this study was to investigate the interruption of scotophase interruption on bone health in Hy-line W36 laying hens over different stages of the lay phase. In doing so, we investigated serum calcium concentrations, bone demineralization markers, tibiotarsus area and bone mineral density, ash percentage, and biomechanical properties of laying hens under various light schedules (Chapter II). Our working hypotheses indicated that hens experiencing daily scotophase interruption would show significant improvements in each parameter when compared to the control group. The results of this study supported our working hypothesis.

Another objective of this study was to investigate the interruption of daily scotophase interruption on performance and production parameters in Hy-line W36 laying hens over different stages of the lay phase (Chapter III). We investigated the average daily feed intake and utilized these data to calculate a feed conversion ratio when analyzing the performance of the hens. We also investigated the calcium components of the egg with egg quality parameters and ash percentages. Our working hypotheses were that external parameters would be improved in treatment hens when compared to the control group due to the daily interruption of the scotophase period. The results of this study supported our working hypotheses in that external components of egg quality were improved in treatment hens when compared to the control group. In contrast, internal quality components were not affected. Production measures indicated a longitudinal increase for treatment hens in comparison to control hens, indicating higher rates of production sustainability for treatment hens. Overall, findings from this experimental study supported scotophase interruption as a technique for improving bone health and eggshell quality in laying hens. Future studies are needed to determine whether findings would be reproducible in a commercial setting.

Author ORCID Identifier

https://orcid.org/0009-0002-2010-6657

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