10 - Avian Female Reproduction Flashcards
Describe egg formation broadly
Egg formed inside out
Yolk is released from the ovary into the oviduct at ovulation. Travels through the oviduct then other components like egg white, egg shell and membranes are deposited around the yolk
What is the germinal disk
Where fertilization happens if there is sperm in the oviduct
Why does the egg yolk have dark and light layers
Yolk deposited when the gut is empty is lighter, when feed was in the gut is darker
What is the chalaza
“Bungee cord”
Part of egg white/albumen
Twisted around yolk to hold it in the middle of the egg (if yolk hits egg shell, fertilized germinal disk may be compromised = embryonic mortality)
What are the shell membranes
Attached everywhere except on the larger side of the egg (air cell)
What is the point of the air cell
Allows gas exchange
When embryo is big enough it cracks the shell with its beak there
Parts of the avian oviduct
- Infundibulum
- Magnum
- Isthmus
- Shell gland
- Vagina
- Cloaca
Slide 6
Important
When do follicles appear in birds
All the follicles (ova/yolks) ever required are present as very tiny follicles at the time she hatches
How many ovaries in chickens and turkeys? What happens to mature follicles
Only one (left)
They are released from the ovary (ovulated)
What is the POF
Post-ovulatory follicle (called CL in mammals)
No role in avian species, remains inactive after ovulation
When/what produces progesterone in avian species
F1 (mature) follicle produces progesterone BEFORE ovulation
In mammals, CL produces it after ovulation
What is the stigma
Clear part of the yolk (no blood vessels) where ovulation occurs
It ruptures and the yolk is released into the oviduct (no bleeding during ovulation)
Four different kind of follicles in birds, ranked from largest to smallest
- Large yellow follicles (largest)
- Small yellow follicles
- Large white follicles
- Small white follicles (smallest)
Slide 10*
What matters most with regards to what follicle ovulates?
Follicle maturation, not size
If it is producing enough P4 it is mature enough to ovulate
Slide 12
Yolk deposition pattern
What is the structure of the follicle (cells present, their roles)
Granulosa cells around yolk: produce progesterone
Theca cells on outside: produce estradiol and androstenedione hormones
What do androgen hormones do
Involved in feather patterns and comb growth in females
Yolk color depends on… Different colours and why they are like that
On nutrition! (not health, housing)
- Orange colour = fed pepper, alfalfa meal
- Pale yellow = wheat-based diets
- Dark yellow: corn-based diets
Function of the infundibulum, and how long the ova spends there
Funnel shaped entry point for an egg yolk to be picked up as it ovulates from the ovary
Location for fertilization
Duration 15 mins
Function of the magnum, how long the yolk spends there
Addition of albumen (egg white) around yolk
Duration 3 to 4 hours
Function of the isthmus, how long the ova spends there
Inner and outer shell membranes are added around the egg yolk and white
Duration 1 hour
Function of the shell gland, how long the yolk spends there
Addition of shell material (mainly calcium carbonate) + pigments (e.g. brown, blue)
Duration 21 hours
Function of the vagina, how long the ova spends there
Passage way for the egg from the shell gland to the cloaca.
Waxy cuticle film (bloom) is applied to seal egg pores and to prevent the egg from dehydrating
Duration <1 min
Why do we get eggs in the fridge in NA
We wash eggs bc of salmonella risk, which removes the bloom and exposes the egg to contamination through the egg shell pores
In Europe, they do not wash and can keep the eggs outside
Where does the chalaza form
In the magnum as the developing egg rotates traveling down it
Air cell is important in… When does it grow
Hatching process for chicks
Increases in size as egg loses moisture, either through storage or incubation
Egg shell colour depends on…
Genetics (not nutrition or bird health)
Look at slide 19
What are SSTs? Where are they located?
Sperm storage tubules, in
Primary storage site at utero-vaginal junction
Secondary sperm storage site in the infundibulum
How long can sperm survive in female domestic birds?
2-15 weeks
After oviposition, stored sperm travel through oviduct to infundibulum to fertilize the next ovulated follicle/yolk
What is the vent
Common external opening: urine feces and egg all excreted from cloaca
Hen can invert her cloaca during mating and laying, so the egg exits directly from the shell gland
Primary control center of reproduction in hens
HPG axis
Hypothalamus Pituitary Gonad
Role of the hypothalamus in hen reproduction
- receives and sends signals via neurotransmission
- releases Gonadotropin-releasing hormone and/or gonadotropin-inhibiting hormone
Role of the anterior pituitary in hen reproduction
- receives signal from hypothalamus, feedback from ovary
- releases gonadotrophins (LH and FSH)
Role of ovary in hen reproduction
- follicle pool
- produces estradiol and progesterone
The hypothalamus must be…
mature to respond to photostimulation
Factors affected GnRH and GnIH release from the hypothalamus
Environmental: light, nutrition, temperature, stress
Intrinsic: metabolic status (body composition, growth trajectory)
Function of GnRH in hens
Travels via portal bloodstream to anterior pituitary to stimulate production and release of FSH and LH
Function of LH in hens
Baseline: pre-hierarchical follicle E2 production
Peak: progesterone production in F1 granulosa cells, causing ovulation
Function of FSH in hens
Follicle growth and steroid hormone production
Role of estradiol in hens
Released by small white follicles
In ovary: sexual maturation process (maturation of follicles)
In liver: production of yolk lipis
Role of progesterone in hens
Released by pre-ovulatory follicle (F1)
Positive feedback to the hypothalamus: causes LH surge, ovulation
Organs associated with yolk forming tissues, albumen forming tissues and shell forming tissues
yolk: liver
Albumen: oviduct
Shell: skeletal system, oviduct (shell gland)
Difference in calcium use in rearing vs laying phase. What is cage fatigue?
Rearing (0 to 16 weeks) = calcium deposition into bones
Laying = calcium released to blood to synthesize egg shell
When calcium needs to be taken from structural bones = cage fatigue
What is oviposition
Laying down of an egg. Follows ovulation by 24-28 hours and occurs in sequences
What is a laying sequence
Period of several days of continuous laying of one egg per day
What is the open period for LH release
6 to 8 hour period of the day in which LH level is high and a hen can ovulate
LH “office time”
Beyond this time, if follicle becomes mature, does not ovulate until LH releases next morning
What is the scotophase
Dark period of the photoperiod
What is pause
Each laying sequence separated by non-laying day known as pause
What is photoperiod
Number of hours of daylight and darkness that birds are exposed to in a day
Photophase vs scotophase
Determinate vs indeterminate layers
Determinate:
- avians that ovulate a defined number of follicles (1-4 usually) in a clutch
- clutches separated by period of incubation and rearing of young
- typically 1 (maybe 2) clutches a year
Indeterminate:
- avians that continue to ovulate if eggs are removed
- laying occurs in sequences
- eventually production ceases and birds become photo-refractory
Slide 29***
Laying sequence or clutch
What is a prime sequence in hens? Usually occurs when? Typical prime sequence length
Longest laying sequence of a hen (chicken PB)
Usually occurs about the time of peak production (32 weeks)
Egg type hen: 60 days
Broiler breed: 20 days
What makes prime sequences longer
Faster follicle maturation rate
What is lag
Different (in hours) between the laying of eggs in a laying sequence
E.g. an egg laid at 9am one day followed by 11am the next day = 2 hour lag
Long lag times are related to…
Slow rates of follicular maturation and result in short sequences
What is different about the first egg in a sequence? Why?
Always heavier
Not due to yolk mass, but egg white mass
What is ovulation? Governed by
Process which occurs when a ‘mature’ follicle is released from the ovary
Governed by circadian cycle (LH surge) and follicle maturation rate
Mature follicle is…
capable of producing progesterone
When does ovulation occur during the day
Defined period known as the ‘open period for LH release’
What is a ‘mature’ follicle? What is ovulation governed by?
One that is capable of producing progesterone
Governed by circadian cycle (LH surge) and follicle maturation rate
Slide 37, 38
Too much info
Three mechanisms of light stimulation
- Pineal stimulation
- Hypothalamic stimulation
- Retinal stimulation
Two important phases that cause photostimulation in birds
- dawn
- photosensitive phase (11 to 13 hours after dawn): dictates whether birds perceive day as being long or short
Slides 47, 48
Functions of photostimulation
- cue sexual maturity in all birds
- limit broodiness
- create conditions for longer sequences
Rearing photoperiod, critical day length and laying photoperiod
RP: short days, limits sexual maturation, 8 hours, constant or decreasing, NOT increasing
CDL: minimum photoperiod needed to stimulate sexual maturation
LP: day length that meets critical day length, 14-16 hours, constant or increasing, NOT decreasing
Hemeral day, ahemeral day, short ahemeral day, long ahemeral day
HD: normal 24 hour day
AD: day in which photoperiod and scotoperiod do not add up to 24h
SAD: adds up to less than 24h, used in genetic selection of birds with faster follicle maturation
LAD: add up to more than 24h, match day length and ovulation rate
How is black out housing achieved
Dark-out shields/light traps on air intakes and exhaust fans
What is photorefractoriness
Condition in which the existing photoperiod does not provide adequate stimulation to sustain repro fxn
Advantages of photorefractoriness, outcomes
Prevents animals from becoming sexually active when environmental conditions are unfavourable
Birds cease laying
What is juvenile photorefractoriness
Chicks hatch with photorefractor
Males and females will not respond to light stimulation unless they have been exposed to period of short days then long days
What is adult photorefractoriness
Loss of response to long day length
Gonadal regression due to env stress
Important factors for initiation of puberty
- day length
- age (hypothalamic maturity)
- body weight
- body composition
- metabolic status
Changes in hen during puberty
Comb grows large and bright red
Pubic bones widen to allow egg
Oviduct enlarges and becomes active
Liver starts making egg yolk type fat
Slide 64
Condition at sexual maturation
Why is broiler breeder growth management difficult? Solution
High potential for growth, but need to lay eggs which can be contradictory
Solution is feed restriction program to control excessive growth
What is erratic oviposition defective egg syndrome in broilers breeders
Random ovulation
Random oviposition
High incidence of multiple yolked eggs, or multiple eggs per day
Shell defects
Follicular atresia
Symptoms of not enough follicles, presumed causes
Normal peak production but poor persistency (short sequences)
Inadequate light stim, high incidence of atresia, normal decline in follicle # w age
Symptoms of too many follicles, presumed causes
Excellent peak production, poor persistency, poor shell quality, double-yolked eggs
Birds fed aggressively coming into production
Principle for breeder feeding management
Make feed increases as small and as frequent as possible
Avoid sudden large increases
Examples of reproductive disorders in hens (10)
- two eggs in an oviduct
- double yolk egg n broiler breeders
- two eggs close to each other in an oviduct
- two eggs attached
- large follicle atresia
- internal ovulation
- internal oviposition
- two oviducts
- phantom follicles
- cystic ovaries
- multiple layers of shell membrane
Why do internal ovulation and oviposition occur
Ovulation: ovulated follicle into abdominal cavity (infundibulum did not catch)
Oviposition: lay egg inside abdominal cavity (moved backward, tear in shell gland)
What are phantom follicles
Unreconciled post-ovulatory follicles
Thought to represent internal ovulation
What are cystic ovaries
Fluid accumulates around it due to:
- anatomic abnormalities on ovary
- chronic inflammation
- pathological condition of ovary
What is broodiness
Beh exhbitied when they want to incubate egg
Prolactin hormone
Ceases egg production (follicle atresia)
