this presentation is brought to you by auburn university department of poultry science with funding provided by poultry products safety and quality peaks of excellence program and the u.s department of agriculture in a hen an ovary and an oviduct make up the reproductive system that creates an egg the yolk grows in the ovary and the rest of the egg forms around the yolk as it passes through the oviduct most females have two ovaries but birds are unusual and have only one a hen's ovary rests against the back body wall just to the left of the spinal column the oviduct begins at the ovary folds back and forth upon itself and leaves the hen's body through the vent just below the tail the ovary and the oviduct occupy a surprisingly small space within the body of the hen only a few cubic inches but when the oviduct is stretched out it's nearly two feet long and has five distinct sections the infandibulum the magnum the isthmus the shell gland and the vagina when a hen is actively laying nutrients from the food she eats are converted into the building blocks of egg yolk these building blocks one-third protein one-third fat and one-third water are then carried by the bloodstream from the liver to the ovary in the ovary tiny tissue bags called follicles fill with yolk and grow the largest follicle on the ovary will release the yolk of the egg the hen will lay tomorrow while the next largest will produce the next day's yolk and the next largest will yield the next day's yolk and so on in one to two weeks a follicle grows from less than one millimeter in diameter to the mature size of 25 millimeters when a yoke matures the follicle ruptures along a line relatively free from blood vessels the stigma [Music] and the yolk is released [Music] if any blood vessels cross the stigma a drop of blood may spot the yolk as it is released from the follicle [Music] called the infundibulum the funnel shaped upper end of the oviduct envelops the ovary and catches the most mature follicle as it reaches maturation and ovulates then the yolk embarks on a 24-hour journey down the oviduct when the yoke emerges from the follicle and moves into the upper part of the infantibulum it's the only time in its progress when it is not covered by a layer of albumin fertilization if it is to occur will take place here some bacterial pathogens such as salmonella and terridus are able to colonize the reproductive tracts of infected hens if these bacteria become associated with a developing egg as it passes along the tract and before it is surrounded by a shell they can cause disease in a human consumer of the contaminated yolk or albumin the yoke spends about 15 minutes in the infundibulum before it passes into the magnum in the magnum over a period of about three hours it will be covered by a dense shock-absorbing layer of albumin or egg white as the albumin forms around the yoke spiral ridges which run the length of the magnum cause the yoke to spin like a bullet in a rifle barrel this spinning twists the protein fibers in the albumen just in front of and just behind the yoke and makes two pigtail-like structures called the shellesa the scheleza keep the yolk suspended in the center of the albumin and ultimately prevent it from moving around inside the egg the magnum gives way to the next section of the oviduct the isthmus here the shell membranes are deposited these thin layers of protein wrap loosely around the albumin covering the yoke it is as though the yoke and its layer of albumin are a blob of jello wrapped with two sheets of cellophane the process does not result in a smooth egg-shaped structure in fact an egg leaving the isthmus probably looks more like a prune than a plum the partially formed egg then enters the shell gland here over the next 20 hours the shell will form first a thin albumin is secreted this thin albumin is mostly water and it moves by osmosis through the two shell membranes into the highly concentrated thick albumin surrounding the yolk this plumps the egg into a normal shape and stretches the shell membranes tight around it next a highly concentrated solution of calcium carbonate is secreted by the shell gland and crystals of calcite form and grow on the outer shell membrane as the crystals expand they grow into one another to form a solid shell very tiny spaces left in between the crystals leave pores in the shell lastly a special protein solution called the cuticle is deposited onto the eggshell gas can pass through the proteinaceous cuticle and through the pores in the shell but the two layers protect the egg from harmful bacteria finally in a process called ova position the egg flips end over end this occurs through contractions of the uterus synchronized with relaxation of the muscular vagina and pushes the egg out of the hen's body [Music] an important part of the egg does not form until after it is laid when an egg is laid it fills the shell however a hen's body temperature is 106 degrees fahrenheit and eggs are generally laid into environments that are 20 to 40 degrees cooler as the egg cools the inner portion contracts and forms an air cell between the two shell membranes a chick would puncture and breathe through the air in this cell before hatching the fully formed egg now begins another journey if it has been fertilized it will go to a hatchery if not it will go to one of two places an egg processing and packaging plant for distribution to grocery stores or to an egg breaking plant where once processed the egg will be included in one of countless food products such as mayonnaise cake mixes or salad dressing [Laughter] you