Which Came First, the Chicken or the Egg?

I'm not the only one who is glad to see the thaw occurring in the yard and on the streets today. With all the recent snow, my flock of 26 chickens (and "Viggo", the token rooster) haven't ventured out of their coop for two weeks. No way were they going to walk in that cold white stuff. They have all been squeezed onto the perches that they usually use only at night, huddled together trying to keep warm. They have tons of food-and it keeps disappearing, so I know someone is coming down to munch during the day. And some brave or confused girls are still laying eggs-I'm getting 3 or 4 a day despite the short day length. Chickens thrive on long days, just like me. On big egg production farms, hens are kept under lights to artificially stimulate the pituitary gland through the eye. This causes the secretion of a hormone to stimulate the ovary to produce eggs. 15 to 16 hours is an ideal "day" length for laying hens, although in some big production barns, lights are kept on even longer (and is why chickens there tend to "burn out" very quickly.) No way are we getting that kind of day length right now, but we just passed winter solstice so things are looking up. T-shirt weather is just around the corner.

Chickens are biologically a lot like mammals, but it is fun to note the little differences. They don't have teeth, of course, so use a muscular gland called the ventriculus (gizzard) to grind their food. They don't have sweat glands, and on hot days I often see them panting like dogs to dissipate excess body heat. Their normal body temperatures run extremely high, 105 to 107 degrees. Normal resting heart rates can range from 280 to 340 beats per minute.

The process of "making an egg" is pretty cool. After a rooster mates with a hen, sperm can remain viable in the oviduct for up to 20 days, fertilizing eggs the entire time. Roosters aren't "required" for hens to lay eggs, only to fertilize them. I have had chickens (and plenty of those marvelous, fresh eggs) for 10 years and this is the first year I have ever had a rooster. Viggo is a handsome son of a gun-and he sure knows it! Only the left ovaries are functional in chickens, and they consist of about 2,000 small ova in the immature bird. As they mature, follicles form-these will be the yolks. There are usually 4 - 6 yolks forming at a time, the largest one will be the next egg. The follicle is covered by a highly vascularized membrane except for one area, the stigma. At ovulation, the follicular membrane ruptures at the stigma, but if it ruptures anywhere else (any place where there is a lot of vessels) we will see that tiny spot of blood in the egg. The blood spot doesn't have anything to do with being fertilized or not.

After ovulation, the yolk moves through the first part of the oviduct, the infundibulum, just like the start of an assembly line. If fertilization is to take place, this is where it happens, as well as the production of the first layer of albumen. It takes about 15 minutes for the yolk to pass through the infundibulum. It next passes through the longest part of the oviduct, the magnum, where most of the albumen is formed and deposited around the yolk. The egg is in the magnum for 2 to 3 hours. The egg now goes to the isthmus where the inner and outer shell membranes are formed, taking about 1 1/2 hours. Then the egg enters the shell gland or uterus. Here the egg will take up salts and water in a process called "plumping" and the hard shell is added. This, along with the final calcification of the shell, takes about 18 to 21 hours. Mature female chickens have specialized bone called medullary bone which forms 10 days prior to the formation of their first eggs. This is where they will store the needed calcium for egg production-roosters and immature females do not have this kind of bone. Finally, the egg passes into the vagina, where the cuticle layer is added over the shell and the egg turns 180 degrees (so that the large end is delivered first.) Wow. A pretty amazing process, huh?

Another thing I found interesting is that the natural skin pigmentation of a hen (called xanthophyll) is gradually lost during the laying season as that pigment is diverted to the yolks, giving them their characteristic yellow color. Corn is the major component of laying birds' diets and is a principal source of the pigment. Hens that are thoroughly bleached out are usually the highest producers. Her pigment will return as she stops production-one of the ways you can determine which hens have stopped laying if you will be culling or removing older birds from your flock. I'm not very practical at all-my old girls don't have to worry about "earning their keep." They will have a home for life, eggs or not.

I don't get the opportunity to do much chicken veterinary care on birds other than my own-most people probably don't want to spend the money. Chickens are a lot like other birds and "exotic" pets-they tend to hide their illnesses from us, sometimes until it is too late to much about it. They think if they show they are vulnerable, they will get eaten by a predator. Care must be taken to really know your individual bird's habits, if not personalities, so you can recognize when things change. Even subtle changes could be the indicator of an illness. Good nutrition and proper housing go a long way to keeping your flock healthy. Mine enjoy the popcorn from when I go to the movies and LOVE left over spaghetti noodles-maybe they think they are really long worms!

Like I said, Viggo and his ladies certainly will be celebrating the thaw, finally getting out and stretching their wings a bit. I sure enjoy my little farm.

Peace,
DrReneigh