Check Your Ideas on Incubation

New Zealand Journal of Agriculture, Volume 63, Issue 2, 15 August 1941, Page 153

Check Your Ideas on Incubation

By

F. C. BOBBY,

Superintendent of Poultry Husbandry, Wellington;

IT is a matter of interest and vlaue to poultrymen to review from time to time, present-day knowledge of the various phases of poultrykeeping, and it is proposed to discuss some of the practices and theories i connected with, the iAcubation of hen eggs. Material of this kind may be referred to on more than one occasion, and in order that any one point on incubation may be referred to quickly, this article will be divided up under a number of headings of a practical nature. ’

A. Hatching Eggs Before They Reach the Incubator.

To obtain successful hatching results certain precautions must be taken with

eggs before they are actually placed in the incubator. • ' . ■ (1) How Long May Hatching Eggs Be Stored? It is a commonly accepted axiom, supported by scientific investigation, that hatching eggs' should be set as soon as possible after being laid. Investigations have indicated • that there is little loss in hatchability with eggs

stored for five to six days, but that with. eggs stored for more than six days there is a steady decrease in hatchability for every extra day of storage. Accordingly, poultrymen are strongly recommended not to hold hatching’eggs for longer than ten days unless exceptional circumstances force them to do so. Eggs older than ten days will hatch, but a definite loss in hatchability must be expected. (2) Conditions Affecting Eggs When Stored. Closely connected with the length of time that eggs may be held for incubation comes the question of the conditions under which,,, such eggs should be stored. The chief, factor affecting fertile eggs which are held for hatching is temperature. Contrary to common opinion, low temperatures are far less harmful than high or even medium temperature. In a fertile egg the germ may begin to develop at a temperature of 60 deg. F. —an ordinary comfortable room temperature. Thus, eggs subjected to this or higher temperatures during the day and . lower temperatures at night may easily show a decrease in hatchability as against eggs maintained at a lower temperature throughout the day and night. Unfortunately, no investigational work has been completed which fixes the danger point for low temperatures. It has been demonstrated that subjecting hatching eggs for three successive nights to a temperature just above freezing point did not reduce hatchability. If, however, eggs are allowed to freeze the result is usually a burst egg. :■... ' To sum up, poultrymen are advised to maintain a temperature of about 50 deg...to .55 . deg. F. in the room , used for holding hatching eggs, and to avoid allowing the temperature to rise above 60 deg. F. for any appreciable time. Such conditions appear to be the ideal. It is obvious from these suggestions that there is an advantage in collect-'' ing eggs from the laying shed as often as practicable, say, three times daily when possible. Apart from temperature, currents of air affect hatching eggs. A heavy current of dry, warm air, or even cool air (that is, a draught) passing over hatching eggs will remove moisture, more especially from any eggs with porous shells. This must be avoided if good hatchability and the best class, of chick is required. , ■ (3) The Position of a Stored Hatching Egg. .. ’Where eggs are stored for not more than ten days the position in which the egg is kept appears , to be immaterial; • If kept for longer than ten days, the practice should be to place the eggs on their side and to turn them daily. Turning hatching eggs when

they are held for only ten days has not been proved to be essential, but is a safeguard against damage being done to the germ. (4) Clean Eggs Wanted Not Cleaned Ones. Eggs for incubation purposes should not be washed, but any dirt on the shell should be scraped off. Washing makes a shell more porous, making the eggs liable to lose too much moisture both while being stored and during incubation in the machine. Eggs which lose too much moisture hatch out undersized chicks.

B. Eggs Which Should Not Be Placed in an Incubator.

Most - poultrymen are aware that double-yolked, misshapen, ridged, and rough-shelled eggs should not be used for incubation, but there are one or two other types of eggs to which less attention is paid. The internal quality and shell texture are two characteristics which must be considered. It may be noted that the authorities responsible for laying contest regulations had this in mind when they allocated a proportion of the scoring points for the external (condition of shell) and internal qualities of the eggs produced by the birds in these contests. It will be , interesting at this stage to trace what effect shell texture and internal quality have upon hatching results. (1) Porous-shelled Eggs. It. is well known that this type of egg gives poor results. Rapid evaporaton occurs, resulting in an undersized chick or. no chick; at all. . Shells of this type can usually be noted by. their rough surface and metallc ring if tapped with a finger-nail. The soundest method of detection, , when ,in doubt, is to place the egg in front of a candling lamp, when the mottled appearance of the shell is easy to observe. This type of shell is also liable to what are usually termed “hair cracks.” Ordinary cracks are easy to see or easily detected by gently tapping two eggs together. Hair cracks are often more difficult to detect, and here again the safe method is the use of the candling lamp. It might be thought that such small shell cracks are of small importance from a hatching, point of view, but the figures quoted below and taken from experiments conducted in England reveal the true position with regard to these hair cracks.

(2) Internal Quality of Hatching Eggs. Internal quality is more difficult to observe, but with the use of a candling lamp two types of faulty , eggs can be detected, namely, “watery whites” and “blood spots.” Both these types of faulty eggs give poor hatching results, as can be seen by noting the figures given below. These figures were obtained in the same experiment in England quoted for “hair cracks”:

Further comment upon these figures is unnecessary. Porous shells and eggs with watery whites or blood spots should be avoided whenever possible. Fortunately, the last two named are present in very small numbers among eggs produced on a well-managed farm with good stock. - > In the experiment referred to ■ above all the chicks which were obtained from faulty eggs were toe-punched and the deaths and culls killed during the first month of rearing were recorded. The results were of considerable interest: — Chicks from— Normal eggs 5.9% loss Blood spots ... .: 7.6% loss Hair cracks 10.5% loss Watery whites ;. 22.8% loss

C. Incubation Routine.

Incubators .in use today may be divided roughly ,for type into two •groups'—the table-top and cabinet machines. The incubation'practices to be discussed will x 'be largely limited to management applicable to both types, unless otherwise stated. (1) Placing Eggs in an Incubator Once in a while broken yolks, as detected with the candling lamp at testing time, become troublesome. Ths is caused by eggs heating up too rapidly when first put into an incubator. The sudden heating-up causes the yolk to expand too rapidly and to burst the delicate -membrane which surrounds this yolk material. Speaking generally, this occurs only when eggs are very cold when placed in the incubator, so that when eggs are thought to be unusually cold they should be preheated by being placed in a warm room for some hours before being placed in the incubator. A practical method of testing the temperature. of an egg is to place it against one’s closed eyelid. An. eyelid is very sensitive to temperature, and is therefore a useful guide. '

The position of eggs on an incubator tray is not considered important provided the small end of the egg is not uppermost. (2) Turning Eggs During Incubation. Eggs must be turned regularly in an incubator if satisfactory results, are to be obtained. If this simple operation is not carried out the yolk rises towards the top side of the egg, bringing the germ towards the shell, where it will stick and' die. To avoid this, poultrymen turn their eggs at least twice daily, although quite often tabletop machines are not turned for the first 24 hours after being set. This period allows the eggs to warm up completely, and the temperature in the machine to become stable. A point which is not always realised is that, within reasonable limits, the more often eggs are turned the more chance there is of increased hatchability. This statement is supported by both the results of scientific investigation and results obtained in practice at the large hatcheries in the U.S.A., . where it is not uncommon for eggs to be turned four times daily. Thus, where it is at all practicable, poultrymen are advised to turn eggs in incubators three times daily—early morning, noon, and evening. (3) Cooling Eggs. There is no evidence in support of the old-established theory that cooling eggs during incubation increases the number of chicks hatched, always provided the incubator concerned is efficiently ventilated. No attempt to cool eggs in a modern cabinet machine is necessary, as ventilation is efficient. On the other hand, it should be noted that during, hot weather there is a possibility of insufficient ventilation in some table-top machines, and in this case the cooling of eggs will have a beneficial effect. Cooling, in these circumstances, supplies additional fresh air (oxygen) to the eggs, which is essental for the developing chick, while it also gives the machine an opportunity for changing its air-content. When cooling is practised it should be progressively increased from about five minutes in the first week up to, say, 20 minutes in the third week until the sixteenth or seventeenth day.

D. Temperature, Humidity and Ventilation of an Incubator.

Upon the correct adjustment of these three factors in an incubator largely depends the success or otherwise of the hatching. Incubators, climatic conditions, and the room in which'the incubator is < operated vary so extensively that it is unwise to lay down any hard-and-fast rules for-' governing these all-important factors. Each poultryman must in the first place act upon

the manufacturer’s instructions when first running an incubator, and then later adjust those instructions to meet local conditions, according to the results obtained. Temperature is usually a comparatively simple problem, but humidity and the adjustment of ventilation must be . watched and controlled according to the manner in which the eggs dry off as hatching progresses. At hatching time' the size and condition of the chicks should be noted, special attention being paid to the healing-off of the navel, which should be, clean and not inflamed. A diagram is included showing the size of the air space at the fifth, tenth, fifteenth, and nineteenth day of incubation, and may

i be used as a guide. -Table-top machines • are not normally fitted with humidity gauges, but they are supplied with ■ cabinet machines.

When using machines fitted with wet bulb thermometers ' for measuring humidity, care must be taken that only distilled water or rain water, collected in a clean vessel, is used for the gauge. If ordinary water is used the wick attached to the thermometer will become covered with mineral salts as the water on this wick evaporates in the incubator. In time, these salts will cover the bulb of the thermometer, until finally the . water in the wick ceases to be drawn up satisfactorily on to the bulb. At. this stage the reading on the thermometer becomes unreliable as a humidity gauge, as it is higher than actually should be the case.

Normal Eggs. Hair Cracks. Set .... 25,799 289 Infertile ■ 11% ■ 21% ' Dead Germs .. • ' 6% . 11% Dead in Shell '' 12% 18% Hatch of All Eggs Set .. 70% 49%

Normal Eggs. . Blood Spots. Watery ' Whites. Set .. .. | , 25,799 • 170 63 Infertile .. 11% 22% 44% - Dead Germs • 6% 9% 11% Dead in Shell 12% 15% 16% Hatch of All - • ■ •: Eggs Set .. 70% ' 53% -127% '