4/30/2018 Monday, 30 April 2018 1 Monday, 30 April 2018 2 Programme Avian Eggs The law Biology and reproduction in the chicken Embryo development Incubation of chicken eggs Minor techniques Welfare and “Humane End Points” Chris Trower Euthanasia Monday, 30 April 2018 3 Monday, 30 April 2018 4 The Law Biology of Avian Eggs The 2010 EU Directive (2010/63/EU) does not protect bird or reptile eggs. But some stages of embryonated eggs remain protected in the UK, under the revised ASPA of 2012. However, the point of protection has changed from ½ way through incubation to 2/3 rds way through incubation. An embryo is protected if you manipulate it during the first two-thirds of the incubation period and then allow it to survive into the final third of the incubation period. Monday, 30 April 2018 5 Monday, 30 April 2018 6 What is an egg? Fish and Amphibian eggs Common usage Fish and Amphibians lay unfertilised eggs (ova) The oval or round reproductive cell laid by a female bird, reptile, amphibian, fish or invertebrate. in water Biological definition Fertilisation and subsequent development takes A mature, female, haploid, germ cell (ovum), which may divide to give rise place outside the female. to an embryo, usually after fertilisation by a haploid male cell (spermatozoa) Most amphibians respire through gills as aquatic larvae, although the majority subsequently develop lungs. However, they also use their skin as a secondary respiratory surface, which must be kept moist to function efficiently . 1
4/30/2018 Monday, 30 April 2018 7 Monday, 30 April 2018 8 Reptiles and Bird eggs Mammal eggs The eggs of birds are enclosed in a chalky shell. Only 2 species of mammals lay eggs. The eggs of reptiles are enclosed in a leathery membrane. Both can survive in dry conditions on land Development of the embryo takes place within the shell/membrane. This occurs partly inside the female, before the egg is laid and partly outside, during incubation Echidna Duck-billed platypus Commercial importance of poultry eggs Research importance How many embryonated chicken eggs are Over 30 million egg laying chickens in UK used in research every year in the UK? Each hen lays approximately 300 eggs/year Nobody knows UK produces 10 billion eggs/year (approx 30 million The numbers are not reported to the Home Office. eggs /day) However, 1.2 billion eggs are used worldwide annually, to produce Average person consumes 170 eggs/head/year 3 billion doses of human influenza vaccine. 10 Reproduction in Chickens Chicken Embryos in Research Male anatomy First described by Aristotle around 350 BCE Abdominal testes Able to view developing chick without needing a microscope Deferent ducts (vas deferens) widen as 16 th century – able to differentiate different developmental tissues they approach cloaca – act as main 17 th century – development of microscope storage organ for spermatozoa Open into papillae in cloaca 18 th Century – embryology as a science Papillae are mating organs Immunology - host-graft response (1914) Sperm can remain viable in oviduct Propagation of pox virus (1931) of female for up to 3 weeks Chicken genome sequenced (2004) 2
4/30/2018 Reproduction in Chickens Formation of the egg The Follicle Female anatomy Each ovary contains about 500,000 oocytes (immature ova) at hatching. Only one functioning ovary and oviduct (the left) Each oocyte is enclosed in a cell membrane, which is covered by an extra- cellular protein coat – the vitelline membrane The right ovary develops until about day 7, and then regresses Vitelline membrane The vitelline membrane is surrounded by a layer of Nucleus follicular cells - the zona radiata Mature ovaries contain numerous follicles of various sizes The follicular cells of the zona radiata pass nutrients from capillaries of the ovary to the growing egg Oviduct produces albumen and shell to surround the egg as it passes This structure is called a follicle down from ovary to cloaca Cytoplasm Zona radiata Monday, 30 April 2018 15 Formation of the egg Formation of the egg The Follicle Yolk The ovary of a mature hen contains follicles of different sizes and Yolk is produced by the hens liver and transported to the follicular cells developmental stages. in the blood stream, whence it passes to the ooctyte. Most follicles degenerate, but about 2,000 will continue develop to The yolk contains lipids, proteins and polysaccharides. reach approximately 6mm in diameter (white follicles) The colour of an egg yolk is from xanthophyll Under the influence of gonadotrophin and steroid hormones, white carotenoids - lutein and zeaxanthin Component % follicles are periodically initiated to accumulate yolk protein and grow in Water 48 size to become yellow follicles. Yolk makes up about 33% of the liquid weight Protein 17.5 of a newly laid hen’s egg and contains Fat 32.5 As they grow larger, the yellow oocytes are pushed toward the outer approximately 60 calories, three times the edge of the ovary, until remain connected by only a stalk. Carbohydrates 1 calorific content of the egg white. Other 1 16 Formation of the egg Formation of the egg Yolk Ovulation Over a period of about 10 days, the oocyte accumulates so much yolk The follicle ruptures along a line with few, if any, blood vessels (the that the nucleus of the cell and most of the cytoplasmic contents are stigma). pushed to one side of the cell at the equator. If by chance any blood vessels are ruptured at ovulation, a small drop This side of the egg is referred to as the animal pole. The opposite side, of blood (blood spot) may be deposited on the yolk. where the yolk is stored, is referred to as the vegetal pole. Once released from the follicle, the oocyte, surrounded by the vitelline When the oocyte has reached a suitable size (40mm), by accumulation membrane, passes into the thin, funnel-like lips of the infundibulum of of yolk, the follicle will rupture and release the oocyte into the hen’s the oviduct. oviduct (ovulation). Ovulation in chickens will first occur between 18-24 weeks, depending Ovulation in chickens occurs approximately every 24-27 hours on breed, feeding, light intensity and other management factors. 18 3
4/30/2018 Monday, 30 April 2018 20 Formation of the egg Formation of the egg Meiosis Fertilisation The released oocyte (egg) is a single cell. Inside the lower portion of the oviduct are special crypts (sperm storage tubules) Shortly after release from the follicle, the nucleus of this where sperm from a rooster can be stored cell will undergo meiosis to produce a haploid gamete. and remain viable for up to three weeks. If fertilisation occurs, the fused male and female gametes Ovulation causes the walls of the oviduct to contract and cilia lining the will become a zygote and thence a chick embryo. walls to move, causing an upward current in the oviduct. Whether the oocyte is fertilized or not, it will continue down If sperm are present in the storage tubules of the lower oviduct, some the oviduct to be covered by layers of albumen (egg white), of these will be swept up the oviduct toward the oocyte, and fertilization and enclosed in a shell. will take place in the infundibulum. Formation of the egg Formation of the egg The Isthmus The Magnum The magnum is separated from the uterus by the isthmus, a narrow ring without glands. Whether or not the oocyte has been fertilised, it will leave the infundibulum and enter the magnum section of the oviduct within about The egg remains in the isthmus for approximately 1 hour, where a 30 minutes. further 10% of the total albumen is secreted The dense portion of the albumen is The 2 shell membranes are also added in the magnum formed here 50% of the total albumen is added here. The shape of the egg is largely determined in this section. The egg remains in the magnum for approximately 3 hours Formation of the egg The egg at time of laying Uterus (Shell gland) The egg remains in the uterus for 20 hours Final 40% of (thin) albumen is secreted here Shell formed of crystalline calcium carbonate Pigmentation occurs at a late stage Shell is finally covered in a muco- protein layer which protects the egg from micro-organisms 23 4
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