from: why do clocks run clockwise & other impoderables - david feldman - Harper & Row - 1987
What Kind of Hen Lays Extra-Large Eggs?
What Determines the Size Categories of Chicken Eggs?

Although there are six official sizes of eggs, the smallest size a grocery store consumer is likely to encounter is the medium egg. Sizes are determined strictly by weight, as the chart below indicates:

Size Minimum Weight Per Dozen Eggs

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Small- and peewee-sized eggs are generally sold to bakers and food processors at a lower price per pound than larger eggs, so the prudent egg producer wants to encourage hens to lay big eggs. The Single-Comb White Leghorn, the most popular laying hen in the United States, eats approximately a quarter-pound of feed per day. It takes about four pounds of feed to produce a dozen eggs, so larger eggs are not without cost to the farmer. The biggest variable in egg size is the age of the chicken. Generally speaking, the older the chicken, the larger the egg. Hens that start laying eggs prematurely tend to lay more but smaller eggs. Different breeds also tend to vary in size of eggs produced. Leghorns, for example, tend to lay larger than average eggs.

The weight of the bird is another factor in egg size. A pullet (a hen less than one year old) significantly underweight at sexual maturity will tend to produce small eggs. For this reason, farmers must pay attention not only to the quantity but the quality of feed given to hens. Feed without sufficient protein and fatty acids, while cheaper to supply, will yield smaller eggs. Hard evidence suggests that hatching environment also affects egg size. Heat, stress, and overcrowding all lower the size of eggs. Consumers are often confused about the relative value of different sizes of eggs. Some feel that larger sizes have disproportionately more shell than smaller eggs (not true: shells constitute approximately 10 percent of the weight of all eggs). Which size will constitute the best buy is likely to vary from week to week and can be determined by a formula devised by the American Egg Board. Let's say large eggs cost 96 cents a dozen and a dozen extra-large eggs cost $1.05. Which is the better buy? First, find the price difference by subtracting the price of the smaller size from that of the larger. In this case, the price difference is $1.05 minus 96 cents, or 9 cents. Then divide the price of the smaller eggs by 8 to find the "magic number." In this case, 96 cents divided by 8 is exactly 12 (round off the number if it isn't even).

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If the magic number is lower than the price difference, the smaller eggs are a better buy.

Leyden note:
this rule of economics must be adjust for inflation between the date of the book - 1987 -- and today. Have students do research and construct their own economic rule.
If the magic number is higher than the price difference, the larger eggs are a better buy. Because in the example 9 (the price difference) is less than 12 (the magic number), the extra-large eggs would be cheaper per weight than the large eggs. You divide the price difference by 8 to find the magic number because egg sizes vary in increments of exactly 3 ounces. Large eggs (the one size that is always available in stores) are 24 ounces per dozen, so 24 divided by 3 equals 8, the price of 3 ounces of eggs. All of this makes perfect sense, even though we sense eyes glazing over as you read it.

Submitted by Helen M. Tvorik, of Ma yfield Heights, Ohio.

Why Do Some Chickens Lay Brown Eggs and Others Lay White Eggs?

The color of eggs comes exclusively from the pigment in the outer layer of the shell and may range from an almost pure white to a deep brown, with many shades in between. The only determinant of egg color is the breed of the chicken. Because white eggs are preferred in almost every region of the country, the Single-Comb White Leghorn has become by far the favorite egg-layer in the United States. The Leghorn is prized for many reasons: it reaches maturity earlier than most pullets; it uhlizes its feed efficiently; it is relatively small (an important consideration when most chickens are kept in cages even smaller than New York City studio apartments); it is hardy, adapting well to different climates; and most important, it produces a large number of eggs. If more consumers went along with New England's preference for brown eggs, more breeds

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such as the Rhode Island Red, New Hampshire, and Plymouth Rock would be provided to produce them. A simple test to determine the color of a hen's eggs is to look at her earlobes. If the earlobes are white, the hen will lay white eggs. If the earlobes are red, she will produce brown eggs. Although many people are literally afraid to try brown eggs, they are no more or less nutritious or healthy than white ones. In fact, brown eggs have some cachet among health-food aficionados, which guarantees their higher cost, if not greater benefits. Egg yolks also range dramatically in color, but yolk variations are caused by dietary differences rather than genetic ones. Yolk color is influenced primarily by the pigments in the chicken feed. If the hen gets plenty of yellow-orange plant pigments known as xanthophylls, the pigments will be deposited in the yolk. Hens receiving mash with yellow corn and alfalfa meal will lay eggs with medium yellow yolks. Those fed on wheat or barley produce lighter yolks. A totally colorless diet, such as white corn, will yield a colorless yolk. For cosmetic reasons alone, farmers avoid giving chickens a colorless diet, because consumers prefer a yellowish hue to their yolks.

submitted by jo ellen flynn of canyon county,. CA