• 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

•
Shel l - 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

• 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

• 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

• 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

• 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

Species: Weight, g: Incubation,
Ostrich 1,400 days:
42
Goose
Turkey
Duck
Chicken
Pheasant
200
85
80
58
32
28
28
30
21
24

•
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

•
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

•
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

•
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

•
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

•
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
14-18 hours of (artificial) day length
•
Removal of eggs from the nest - removal increases rate of egg laying

• Interval between ovulations is 24-26 hours
• “Clutch”- an uninterrupted series of laying days of 10-14 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

•
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

•
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