1. Chapter 16: Egg Laying Chapter overview:
Chapter 16 reviews the reproductive anatomy of the bird and the physiology of egg laying, including:
structure and production of the egg
anatomy of male and female bird
factors affecting egg laying

2. Parts of the Egg: Shell - produced in the uterus
Shell membranes - produced in the isthmus
Albumen (white) - produced in the magnum
Yolk (ovum) - produced in the ovary
Germinal disk - chromosome container on the yolk

3. Egg Shell: Two main layers Composed of calcium carbonate Porous
Translucent when laid; becomes opaque when dry
Covered by a thin film called cuticle which tends to seal the pores

4. Shell Membranes:
Two membranes are located just inside the shell and surrounding the albumen
Membranes are bonded together except at the blunt end, or “air cell” end
With time and evaporation the air cell forms by the membranes pulling apart

5. The Egg White:
The egg white (albumen) is high in protein and water and has four principal layers:
Outer thin white
Thick white
Inner thin white
Thick white surrounding yolk; twisted into a rope-like structure called the chalaza on opposite sides of the yolk

6. The Egg Yolk:
The egg yolk (ovum) is suspended in the center of the egg by the chalaza and is:
High in fat and water
Arranged in alternating light and dark layers
Contained in a thin yolk sac called a vitelline membrane
The location of the chromosomes in a germ cell in a tiny area (“spot”) on its surface

7. Weight of Selected Bird Eggs, g:

8. Anatomy of the Avian Male:
Testes - paired; located in the abdominal cavity near the kidneys; sperm of the avian survive at internal body temperature
Vas deferens - paired; convey sperm outside the body during mating
Cloaca - terminus of the digestive and urinary tract, also receives the vas deferens
Vent - external opening of the cloaca

9. Anatomy of the Avian Female:
Ovary - single; in chickens the right ovary regresses in early life
Stigma line - nonvascular suture line on the developing follicle that ruptures to release the ovum
Infundibulum - funnel-like structure that receives the ovum and guides it to the remainder of the oviduct; site of fertilization

10. Anatomy of the Avian Female:
Oviduct - single; anatomically divided into several distinct areas:
Magnum: adds albumen
Isthmus: adds shell membranes
Uterus: adds shell; rotation creates chalaza
Vagina: prepares egg for laying (oviposition)
Cloaca - terminus of the digestive tract; egg passes through by inversion of the vagina

11. Hormones and Egg Laying:
Follicle stimulating hormone (FSH) - stimulates growth of ovarian follicles; source: anterior pituitary
Luteinizing hormone (LH) - causes ovulation; source: anterior pituitary
Parathyroid hormone - maintains blood calcium balance for egg shell formation; source: parathyroid glands

12. Hormones and Egg Laying:
Thyroid hormone - influences molting and seasonal changes in egg laying; source: thyroid gland
Oxytocin - causes oviposition and laying; source: posterior pituitary
Prolactin - causes manifestation of maternal instincts; source: anterior pituitary

13. Factors Affecting Egg Laying:
Age at sexual maturity - commercial egg laying is optimized by managing hens to begin production at about 20 weeks of age
Light pattern - optimize production with hours of (artificial) day length
Removal of eggs from the nest - removal increases rate of egg laying

14. Intensity of Egg Laying (Chickens):
Interval between ovulations is hours
“Clutch”- an uninterrupted series of laying days of days is desired; inheritable
Laying begins at 18 to 20 weeks of age
Peak production (90 percent laying per day) is reached at about 30 weeks of age
Laying period is typically 12 to 14 months

15. Molting and Recycling:
Molting - shedding and replacing of feathers
A rest period to rebuild hens that are to be recycled
Reduce light, feed, and water
Requires a period of 6 to 8 weeks to rebuild
Recycling - allowing hens a second laying cycle
Shorter production period, but larger eggs

16. Factors Affecting Egg Size:
Genetics - egg weight is highly heritable
Age of bird - older birds lay larger eggs, therefore recycling can be an advantage
Size of bird - larger hens usually lay larger eggs
Environment - heat stress reduces egg size
Nutrition - balanced diets maximize production and shell strength