Avian Reproduction

what is a photoperiod

length of time an animal is exposed to light (day length)

what type of breeders are birds

long-day breeders

Why do birds breed in spring

• warmer climate

• more food → better offspring survival

what structures detect light in birds

• eye

• pineal gland

• hypothalamus

what is melatonin

hormone regulating circadian rhythm; inhibited by light

is melatonin required for photoperiod response

no

what is critical day length in chickens

11-12 hours of light

what happens after critical day length is reached

rapid increase in reproductive hormone release

what is photorefractoriness

loss of reproductive response after prolonged long-day exposure

how is photorefractoriness reversed

exposure to short days (10-12 weeks)

which ovary is functional in birds

left ovary

what happens to the right ovary

regress (rudimentary)

is the oviduct functional

only left oviduct is functional

how many oocytes at hatch

500,000

what are SWF and SYF

SWF = small white follicles

SYF = small yellow follicles

what is follicular hierarchy

ordered sequence of follicles (F1-F3) with one ovulating per day

what hormone initially drives follicle growth

FSH

What receptor switch occurs

FSH → LH receptors

What do small follicles produce

Estrogens and Androgens

Effects of estrogen in birds

• medullary bone formation (calcium storage)

• Female plumage

• Reproductive tract development

What triggers ovulation

LH surge

Where does follicle rupture

Stigma

Is there a corpus luteum in birds

No

What are the main parts of the oviduct

Infundibulum → magnum → isthmus → shell gland → vagina

function of infundibulum

• captures ovum

• site of fertilization

• adds vitelline membrane

function of the magnum

• adds albumen (egg white)

• Egg stays (around 3 hours)

What is the function of the Isthmus

• Adds shell membrane

• Forms air cell

shell gland function

• shell gland formation (CaCO3)

• egg stays (around 19-20 hours)

function of the vagina

• egg transport

• sperm deposition and selection

what is egg shell made of

98% calcium carbonate

What are shell layers

• mammillary

• palisade (spongy)

What are pores for

gas exchange

what is the cuticle

Outer protective layer of egg

function of the cuticle

• blocks bacteria

• protects pores

what is medullary bone

• calcium storage bone unique to laying hens

• provides calcium for eggshell formation

where does egg spend most time

shell gland (20 hours)

what is oviposition

laying of egg

where are eggs usually laid

mornings or early afternoon