Incubator Capacity Required. The aim on commercial duck farms is to hatch all of the eggs produced which are suitable for the purpose. Practically no eggs are sold except the cracked eggs or those which would not give good results in the incubator such as too large or too small eggs. Occasionally, of course, there will be sales of duck eggs in comparatively large lots for incubation purposes where someone is starting a duck farm. Occasionally also duck farmers buy from each other a few eggs for incubation in order to secure new blood. On the whole, however, practically all of the eggs laid are incubated and it is necessary to have an incubator capacity sufficient to take care of the eggs as they are produced during the flush season.
Since the egg production at this time will run around about 80% and since the period of incubation is 28 days and a couple more days must be allowed to take the ducklings out of the machines and to clean up the machines, it is necessary to figure on 30 days between hatches. To take care of the flush production at this time there would be required an incubator capacity of from 20 to 25 eggs per head of breeding ducks. The latter figure is a safer estimate than the former. Of course, eggs sufficient to fill the entire incubator capacity are not put in the machines at any one time but different lots are put in as soon as a sufficient number is obtained to make it worth while. There will be, therefore, eggs in various stages of incubation in different sections of the machines at the same time. While Pekin duck eggs will run about ½ heavier in weight than hens' eggs they do not take up a proportionately greater amount of space in the incubator. An incubator tray will accommodate about 5/6 as many Pekin duck eggs as it will hens' eggs.
Age of Hatching Eggs. Duck eggs should be set as often as enough are secured to fill one or more trays in the incubator or enough to produce a sufficient number of ducklings to utilize brooding space to advantage. Since duck eggs deteriorate more rapidly than hens' eggs they cannot be kept so long before they are set. It is best not to save them for longer than one week. During the season of flush production it is not, of course, necessary to save them that long since enough eggs will be secured to set each day if desired. The usual practice at this time is to set twice a week. During the early part of the season when the production of eggs is low and the temperature cool the eggs are often saved for as long a period as two weeks without noticeably bad results.
Care of Hatching Eggs. Eggs for hatching should be kept in a cool place. Any place suitable for keeping hens' eggs for hatching is a suitable place for duck eggs. The temperature should be from 50° to 70° Fahrenheit. Where the eggs are not kept longer than one week, it is not necessary to turn them, especially if they are kept on end. If kept longer than this it is safer to turn them once a day or once in two days, handling them carefully so as not to crack any or to injure their hatching qualities.
Selecting the Eggs for Hatching. Medium sized eggs are preferred for this purpose. Therefore, the extremely large eggs and the very small ones are thrown out. Rough shelled eggs or eggs with crooked or deformed shells are likewise thrown out since they are not likely to hatch well. Eggs that are badly soiled so that they cannot be tested easily are washed but the clean eggs are not. All the eggs intended for incubation purposes are sounded by striking them gently against one another in order to detect and remove the cracked eggs. No selection is made on the basis of color. The eggs may be white, creamy white or a blue, or bluish green in color. At the present time a considerably less proportion of the eggs show a blue tint than formerly. As the egg laying season advances the eggs laid by the ducks tend to get a little larger.
Temperature. Up to the time of testing, that is, about the fifth day, the incubator is run at a temperature of from 101 to 102 degrees. After the fifth day the temperature is kept as near 103 as possible. The most sensitive period for a duck egg is during the first 3 or 4 days of incubation. If they are allowed to get too warm during this time the germ may be killed while if the temperature is too low, development will be retarded.
Position of the Thermometer. In figuring on the proper temperature at which to run the incubator, the thermometer should be so placed that the bulb is on a level with the top of the eggs, preferably touching a fertile egg. If the thermometer bulb rests on an infertile egg the temperature recorded will be lower than the actual temperature of fertile eggs in the later stages of incubation, due to the animal heat of the developing embryos, with the result that the machine would be operated at too high a temperature.
Testing. It is common practice to make only one complete test. This is done on the evening of the fifth day. Testing may be done by means of an ordinary candling device such as is used with hens' eggs, each egg being examined separately. To save time a piece of apparatus may be used which is simple in construction and which simplifies the process of candling considerably. This may be termed a testing table. It consists of a table the same width as an incubator tray and longer than the tray. In the table there is an opening the size of a row of eggs and beneath this are placed several electric light bulbs with reflectors back of them so as to throw the light up through the eggs. By sliding the tray along the table each row of eggs is brought over the lights and their condition can be quickly noted. At this test all the infertile eggs are taken out as well as any eggs in which the germs have died. The infertile eggs after a careful retest are then packed in cases and sent to market where they are usually sold to bakers as tested eggs. While no second test is made of the eggs left in the machines the experienced incubator operator is constantly on the watch for and is constantly removing any eggs which die at a later time. To the experienced eye the color of the egg indicates that it has died as it takes on a sort of pinkish or darkish tint. Duck eggs after they die will spoil very quickly and must be removed promptly as the odor which they throw off is very strong and will prove harmful to the other eggs. The inexperienced operator can readily locate dead eggs by smelling over the tray.
