8:30 am - 9:30 am
A graduate exam seminar is a presentation of the student’s final research project for their degree.
This is an ALES MSc Final Exam Seminar by Daniella Batres. This seminar is open to the general public to attend.
Thesis Topic: Evaluation of dietary calcium level effects on the productivity, eggshell quality, and bone traits in laying hens
MSc with Dr. Doug Korver.
Given the significance of calcium (Ca) in the metabolism of laying hens, this thesis aimed to contribute to existing knowledge regarding Ca metabolism and requirements. Phosvitin (PV) is an egg yolk phospholipid protein that increases Ca bioavailability, absorption, bone incorporation and reduces bone mobilization. Consequently, the effects of dietary PV as a strategy for protecting the shell and bone quality of end-of-cycle laying hens fed a Ca-reduced diet were studied. A total of eight experimental diets were used, including a positive control (PC), negative control (NC; 21% less Ca than the PC) and six NC-based diets that contained either PV (PV; 37.4% purity), dephosphorylated PV (DPV; 39.5% purity) or PV peptides (PVP; 39.8% purity), each fed at a 1% or 0.01% of the diet. It was hypothesized that dietary PV products would protect laying hen bone quality via increased Ca digestibility while maintaining productivity and shell quality in end-of-cycle laying hens. Overall, the NC diet did not affect egg production and mass throughout the experiment. Additionally, bone and shell quality remained unaffected by dietary treatment. This suggests that commercial end‐of‐cycle laying hens can maintain egg production, shell quality and bone quality under substantial reductions in dietary Ca, at least in the short term.
The impressive performance of the hens fed substantially reduced Ca in the first experiment prompted investigating Ca requirements in laying hens via a meta-analysis performed with publications using varying levels of dietary Ca. Dietary Ca level was defined as the independent variable of interest. Dependant variables included: egg production (%), Ca intake (g/hen/day), phosphorus intake (g/hen/day), egg mass (g), feed intake (g/hen/day), feed conversion (feed: eggs and feed: dozen eggs), egg weight (g), shell weight (%), eggshell thickness (mm), egg specific gravity, egg breaking strength (N), bone breaking strength (N), bone Ca (%), bone phosphorus (%) and bone ash (%). Ultimately a data set containing 791 observations were compiled from 57 published papers between 1981 and 2020. Eight moderator variables (Record No., Year, Strain, Phase of Production, Molted, Ca Particle Size, Ca Source and Heat Stress) were considered for inclusion in each regression model. Ca intake (1.04 g/hen/day per 1% unit increase in dietary Ca) and FI (1.54 g/hen/day per 1% unit increase in dietary Ca) were each significantly affected by dietary Ca levels. Additionally, each feed conversion parameter decreased with increasing levels of dietary Ca (-0.022 feed: egg ratio and -0.051 feed: dozen per 1% unit increase in dietary Ca), where Phase of Production was a significant random variable. Shell weight (0.24 % per 1% unit increase in dietary Ca), eggshell thickness (0.0075 mm per 1% unit increase in dietary Ca), specific gravity (0.0015 per 1% unit increase in dietary Ca), and egg breaking strength (1.23 N per 1% unit increase in dietary Ca) each increased with increasing dietary Ca, which agrees with others who suggest dietary Ca is essential in maintaining eggshell quality. Additionally, the significant effect of Phase of Production confirmed the well-documented effect of age on eggshell quality. The positive relationship between dietary Ca levels and bone ash (1.03 % per 1% unit increase in dietary Ca) was unexpected compared to existing literature. However, the significant effect of early Phase of Production reflects the intense bone metabolism that occurs early in the laying phase. Bone breaking strength significantly increased with increasing dietary Ca levels (12.92 N per 1% unit increase in Ca). This supports the idea that increasing dietary Ca levels prevents hens from depleting skeletal Ca when adequate dietary Ca is available. The presence of Year as a significant random variable in this relationship suggests that the relationship between dietary Ca and bone quality is changing over time. Using the National Research Council (1994) Ca requirements as a reference, there do not seem to be negative consequences associated with over-supplementation of Ca within the Ca ranges studied, as illustrated by the lack of plateaus or decreases in the response variables tested.