Eggshell Quality in Laying Hens D. R. Korver University of Alberta Edmonton, Alberta, Canada

Eggshell Formation First phase – First ~5 hours of calcification Ca crystals begin to form Second phase – Next 12 hours of calcification – 90% of Ca deposition – mg Ca/hour

Eggshell Formation ~5.5 g of eggshell per egg ~2.2 g of Ca Eggshell composition – 95% CaCO 3 – 0.3% P – 0.3% Mg

Eggshell Formation Egg size increases with hen age (body weight) Shell deposition remains constant

Issues in Shell Quality 250 eggs = ~20 times total bone Ca reserves After peak production, a consistent amount of shell material is put on each egg – Larger eggs, thinner shells

Calcium Metabolism Eggshell formation – demand for Ca from ~6-24 hrs of ovulation cycle enough skeletal calcium for ten eggshells enough medullary bone for one eggshell ANSC 463

Calcium Metabolism Eggshell formation – 60-80% of calcium required for eggshell formation derived directly from the diet on shell-forming days – the greater the proportion of eggshell calcium derived from bone stores, the poorer the shell quality ANSC 463

Implications Shell quality problems are often seen before bone problems

wks 20 wks 22 wks 24 wks 26 wks Experimental Design 1.00 % Ca (grower) 3.25 % Ca (breeder)

a ab bc c c cd c c de e P<0.01 Average Egg Weight to 31 Weeks

ab a b b bb ccc P< Shell Weight

P< Specific Gravity

Broiler Breeders vs Layers Time of switch to high Ca diet is important in broiler breeders – Especially at high temperatures Laying hens seem to be less sensitive to early switch – Effect of high temperature?

Soluciones

Nutrients & Eggshell Formation Ca level; Ca-P ratio – Change with age Vitamin D – Reduced metabolism with hen age NaCl – feed, water – High NaCl reduces shell quality Phytate – Binds Ca, P

Nutrients & Eggshell Formation Trace minerals – Copper – lysyl oxidase Cross-links in shell membrane fibers – Manganese Mucopolysaccharide formation – mammilary layer – Zinc Carbonic anhydrase – bicarbonate ion secretion

Management & Eggshell Formation Body weight at placement – Small pullets may lack sufficient medullary bone Pre-lay or not pre-lay? – Not before 10 days prior to first egg Switch to high Ca layer diet – ~5% production

Management & Eggshell Formation Environmental temperature – Minimize heat stress Electrolyte balance – Panting causes a loss of CO 2 – Blood pH increases from 7.2 to Loss of bicarbonate ions limits CaCO 3 – Limits shell formation

Feed Intake Feed particle size – large particle calcium sources 2/3 large particle (> 1mm) – Retained in gizzard 1/3 small particle (<1 mm) – Quickly available Top-dress feed (emergency)

Eggshell Formation Hendrix Genetics

Feed Intake Brown layers – Begin eggshell formation ~4 hours before lights out – Encourage feed intake during the last 6 hours of the day – Midnight feeding – Particle size 70% particles of 2-4 mm – slow release 30% particles of <1 mm – quick release

Feed Intake White layers – Begin eggshell formation just before lights out – Encourage feed intake during the last 4 hours of the day – Midnight feeding 50% particles of 2-4 mm – slow release 50% particles of <1 mm – quick release

ANSC 463 Possible solutions to low calcium status: – midnight feeding allow access to feed for 1 hour in the middle of the night dietary calcium available during peak eggshell formation short duration of lighting does not appear to affect photoresponsiveness Calcium Metabolism

ANSC 463 Egg Production in Layers response to 1 hr of 12 AM Supplemental Lighting begun

Feed Supplements Phytate Vitamin C Trace Minerals Vitamin D 3 – 25-OH Vitamin D 3

Strain Diet S x DNS Defective Shells W36-D W36-25-OH D 3 W98-DW98-25-OH D 3 Number of Eggs per Hen

Bone Density Strain NS Diet P= S x D NS W36-DW36-25-OH D 3 W98-D W98-25-OH D 3 Bone Mineral Density (mg/cm 3 ) W36-DW36-25-OH D 3 W98-DW98-25-OH D 3 Strain P= Diet NS S x D NS Cortical Medullary a bb a

Heat Stress Electrolyte balance – Panting causes a loss of CO 2 Replace 30-35% of NaCl with NaHCO 3

ANSC 463 Possible solutions to low calcium status: – water supplementation of calcium Calcium Metabolism

Conclusions Shell quality problems can be caused by many factors Shell quality problems often precede bone quality problems. Practical solutions can be used to prevent & correct problems

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