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What is a photoperiod?

What does a photoperiod control?

Photoperiod= Peroid of time when a bird recieves illumination; daylength

Bird are seasonal, "long day" breeders

Srping- warmer climate and adequate food supply --> neonatal survival

Poultry- synchronize flock and improve and maintain reproduction

Use a photoperiod to control sexual maturity


How does light perception singal the photoreceptors?

Light perception:

Major photoreceptors in the pineal gland and eye. Photoreceptors transduce energy contained in photons into a biological singal

Endocrine effects of photostimulation


Melatonin is synthesized at night. Where is the source and what is the function?

What inhibits it?

Source: Pineal gland and eye

Function: Time signal to body. Regulates the circadian rythms of biological functions. Antioxidant. Immune system. 

Synthesis is inhibited by light


How are circadian rhythms affected by light perception?

Internal circadian rhythms occur on an aprox 24 hour time frame. Distinguish beween long and short day length.

Light is the primary zeitgeber (time giver)

Critical day length in chickens: 11-12 hrs

--> period of photosensativity starts, rapid stimulation of hormone release.

Commercial photoperiod: 14-16 hours (done to account for biological variation in species)


What is photorefractoriness?

Failure to maintain gonadotropin secretion during long days. Can occur after extended exposure to long days.

To be photosensitive again, hens must be exposed to short days for 10-12 weeks

Birds are photorefractory at hatch. Juvenile photorefractoriness (unable to respond sexually to a photoperiod until they have experienced short days)

In industry, looking at modern genotypes to find the best for breeding to ideal needs of industry.


The photoperiodic response. Photo


For commercial practices for layers:

Growing pullets require what duration of day length?

How can photoperiod control age of sexual maturity?

Duration of day length: Growing pullets (young unsexualized hens) are exposed to decreasing and short days (8L: 16D) short days. Increasing daylength is used for photostimulation

Using photoperiod to control age at sexual maturity 16-17wk (16L: 8D). Induction of sexual maturity- increase photoperiod beyond critical photoperiod.

Critical daylength- 12L :12D (in commercial use 16h of light so all the birds are stimulated at the same time)

Never decrease photoperiod length.


Which ovary is functional in hens?


Left ovary is function. Right ovary is rudimentary (non-funcation)

--> Ovotestis if the left ovary is destroyed.

At sexual maturity some of the ocytes (ova) begin to develop.


Discuss chicken oocyte growth and the SWF and SYF

Embryonic- quiescent primoridal follicles (60 μm diameter) develop in the funcional left ovary.

Around 500,000 oocytes at hatch. around 2000 viable in immature ovary.

As birds become sexually mature, incorperation of protein rick white yolk leads to fomation of small white follicles (SWF- 203mm diameter) --> FSH

Some SWF continue to develop and eventually start lipid-rich yellow yolk incorperation to form small yellow follicles (SYF 6-7mm diameter). 

Most SYF undergo atresia, an important apoptotic porcess that keeps the number of rapidly growing follicles fairly small

Selected SYF enter the follicular heirarchy, where follicles grow rapidly for 7 days.

Much of the yolk mass is imported as VLDL and vitellogenin that is synthesized and secreted by the liver. (large amount of material to be incorperated into the follicle).

Follicles are aprox 30-40mm in diameter at ovulation



In which case is defective follicular heirarchy common in hens?

Defective follicular heirarchy is common in overweight broiler breeder hens. 

Where multiple ova are released per day, matured at same time

Usually one in infertile, and if both are fertilized at least one will die, usually both cause there isn't enought nutrients for both to grow.


What are the endocrine effects of photostimulation


How is the deposition of Ca2+ in medullary bone affected by steriodogenesis?

Steroidogenesis by ovarian follicles: Deposition of Ca2+ in medullary bone. Secondary bone found only in laying hens. Egg shell formation when GI tract is empty. 

Not enough Ca2+ results in osteoporosis (the medullary bone Ca2+ stocked will get used then will start to use structural Ca for Ca supply. Which can lead to cage layer fatigue.


What does steriodogenesis by the ovarian follicles result in?

Production of yolk precursors by the liver (VLDL and vitellogenin).

Development of the reprod tract.

Development of other sex characteristics

As the follicles frow: Production of oestrogren declines. Androgen secretion --> Increases to F2 and is terminated within 16h of F1. (increases so that F2 can become a F1 follicle, then decreases once it has become an F1 follicle)

Progesterone secretion increases with follicle development.


What is ovulation induced by?

Discuss the post-ovulatory follicle.

Ovulation is induced by LH surge (LH surge is produced at night). Coordination of open period (LH peak) and follicle maturation.

LH and progesterone interact to cause peak LH sufficient to promote ovulation. Follicle ruptures at the stigma (in pic).

Post-ovulatory follicle:

Most recent ovulation: P1, P2....

No CL, there is secretion of prostoglandins which promote SYF into follicular heirarchy, oviposition (egg laying) and nesting behaviour (brooding in hens)


Hen oviduct (diagram)


Discuss what happens in the hen oviduct: Infindubulum.

Infindibulum will catch anything at the time of laying, including blood specks and meat spots. 

Actively recieves ovum from ovary pocket within 15 min of ovulation (in there for 15-30 min)

Internal laying (yolk not taken up by ovuduct instead deposited into abdomin of the bird)

Site of fertilization and sperm storange tubules. Secretes outer layer of the yolk (vitelline) membrane --> seperates the yolk from the albumin

Ovum spends 15-30 min in the infundubulum 

10cm in length.


Discuss the role of the magnum in egg formation (in the hens oviduct)


The Magnum is where the egg white is depoisted over a 3hr period.

37.5 cm in length. Most of the egg albumen (egg white) is deposited

--> Chalaziferous or inner thick (form chalazae cord)

-->Inner thin albumen

--> Outer thick of firm layer (cushins the yolk in the centre of the egg, ovomucin fibers produced by epithelial cells)

-->Outer thin- derived from shell gland


Hen oviduct: What is the role of the Isthmus?


Egg spends 1.5 hours in this region. 10cm in length

Deposition of the two shell membranes (inner and outer membranes)

Air cell forms at large end of egg (from change in temp after laying)

Older the egg the bigger the air pocket.


Hen oviduct: What happens in the shell gland?

Shell gland (NOT called UTERUS)

Egg spends 19-20 hours in this region

10cm in length

Outer thin albumen then Shell deposition


Discuss the egg shell structure:

The two main structures and the site for gas exhange


Shell gland there is shell deposition

Shell (12% of egg weight): 98% calcium carbonate

Two layers:

Mammillary layer (Knob like structures)

Pallisade or spongy layer (Column like formation)

Pores are the site for gas exchange



How is shell pigment determined?

What is the name of the brown pigment and the blue pigment?

Shell pigment is a heritable trait (breed specific)

Brown pigment= Porphyrin (porphyrins) derived from haemoglobin metabolism.

Blue/green eggs = Oocyanin. Which is a product of bile formation, responsible for the colour. (Araucana chicken breed)


What is teh role of the cuticle on the shell and when is it added?

Cuticle or bloom is added just before oviposition. 

The cuticles dries and seals the pores to prevent bacterial invasion and evaporation

Partially blocks shell pores.


Overall egg structure pic


What the major area of sperm storage tubules?

The shell gland-vagina (utero-vaginal area) is the major area of sperm storage tubules. Other site is infindubulum, but this it the main site.

Sphincter like muscle that resembles the cervix of mammals.

Aprox 25,000 sperm storage tubules and each will contain an avg of 400 sperm per tubules. (after insemination)



What is the role of the vagina?

Vagina --> transport of egg through cloaca. Site of semen deposition. 

Inverted during natural copulation. Important for selection of healthy sperm (only 1-2% of the sperm deposited actually passes the urinal vaginal junction)

5cm in length


What is oviposition?


Oviposition time is linked to ovulation (as LH peaks at night)

Eggs are laid in the morning or early afternoon 24 hours later.


Where are the testis located in a male chicken?

Despite being internal there is no issue with sperm production. Internal body temp of 41 degrees and sperm is produced.


Testes sturcture (pic) chicken


Breify discuss the male chicken reproductive parts fucntion:

Rete testis, epididymis and vas deferens


What is the male chicken's copulatory organ? 

Chicken semen characteristics, LOL


Copulatory organ is the cloacal floor. Erectile fluid is lympth, not an intromittent organ.

There is no accessory sex organs. Not seminal vesicles, prostante glub or bulbourethral (Cowper) glands

True seminal plasma (small amount) -Transparent fluid (clear, watery).