| | Why store hatching eggs?
Cold storage of hatching eggs is a common practice in the poultry industry. Hatching eggs are not incubated immediately after laying for several reasons. Since eggs are not incubated on the farms on which they are produced, they must be transported to commercial hatcheries. Eggs must be stored on-farm since daily delivery of hatching eggs to the hatchery is not practical. Eggs may also be stored at the hatchery for several reasons. When hatching eggs are plentiful, incubator space may be limited; surplus eggs are stored until incubator space is available. Egg storage will also occur if the fewer chicks or poults are required for placement on grow-out farms. During the hot summer months in the southern United States hatching egg production declines. In this case, hatchery managers anticipate a reduction in egg production due to high temperatures, and accumulate eggs to maintain enough eggs for setting and subsequent poult placement on grow-out farms.
There are some negative effects of storing hatching eggs. Storing eggs for more than 1 week is known to increase embryonic abnormalities and mortality. Eggs stored longer than 1 week also show reduced hatchability and an increase in the amount of incubation time required to hatch. Post-hatch growth and quality of chicks and poults from eggs stored for long periods also suffers.
Five egg storage experiments
Five separate experiments were conducted to further define the effects of long term egg storage on embryo and poult viability and growth. In all but one study, eggs that were stored for 4 days (control group) were compared with eggs that were stored for 14 days (experimental group). In the second study, 1 day stored eggs served as the control group.
Study 1
The objective of the first study was to determine if there is an optimal stage of embryonic development at which to store turkey eggs to obtain maximum embryo survival and hatchability. Freshly laid turkey eggs were prewarmed (at incubation temperatures) prior to storage for 0, 7, 12, or 14 hours. Hatchability of fertile eggs was reduced in 14 day stored eggs (70%) compared with eggs stored for 4 days (77%). Prewarming the eggs prior to storage produced a numerical, but not statistically significant, increase in hatchability of fertile eggs (Table 1).
Bottom line
Embryos in prewarmed eggs were more developed prior to storage, but they did not withstand long term cold storage better.
Study 2
In the second study, transmission electron microscopy (TEM) was used to determine if the structure of the perivitelline complex (structure surrounding the yolk, frequently called the "yolk membrane") varies between 1 and 14 day stored eggs. It has been previously noted that the perivitelline complex becomes weaker as eggs are stored. Since the early avian embryo is in direct contact with the perivitelline complex, variation in this structure may influence embryonic growth and development. Examination of the perivitelline complex showed that the thickness of the two main layers of the perivitelline complex does not vary between 1 and 14 day stored eggs. However, the density, or amount of material making up the perivitelline complex layers in eggs stored for 14 days is reduced when compared with eggs stored for 1 day.
Bottom line
Reduced yolk membrane strength after storage may be the result of its reduced density.
Table 1. Prestorage warming affects on hatchability of fertile eggs
Number of hours eggs were warmed
prior to cold storage | Hatchability of fertile eggs
(%) |
0 | 73 |
7 | 73 |
12 | 76 |
14 | 75 |
Studies 3 and 4
The third and fourth studies looked at how 4 versus 14 days of storage affects carbohydrate metabolism in embryos and poults. During hatching the avian embryo relies solely on carbohydrate stores (glycogen) as its energy source to pip (break) through the shell and eventually hatch. In the third study, when glycogen concentrations of key glycogen storing organs (heart and liver) were measured, poults from eggs stored for 14 days had much lower heart glycogen concentrations. This indicates that poults from eggs stored for 14 days use more glycogen during hatching than poults from eggs stored for 4 days. This may be because the poults from 14 day stored eggs appear to take longer to hatch out from the time of internal pipping (poult breaks through the shell membrane and into the air cell at the large end of the egg) to the time of actual hatching. The reduction in heart glycogen concentrations was further depleted in the fourth study by holding the poults in the hatcher for extended periods (up to 24 hours) after hatching (Figure 1.) This shows that holding poults in the hatcher for long periods of time after hatching is a stressor. If there is a critical heart glycogen threshold below which the poult can not survive, it is the poults from the stored eggs which were held longer in the hatcher longer which will reach that threshold sooner.
Bottom line
The poults from stored eggs which are held in the hatcher post-hatching for 24 hours would be the poults first to die.
Study 5
The objective of experiment 5 was to determine how much more time was required to hatch poults from eggs stored for 14 days versus poults from eggs stored for 4 days. This experiment also focused on metabolic products and the activity of various enzymes of carbohydrate metabolism in an effort to provide further evidence that carbohydrate metabolism of poults is altered due to long-term storage of eggs. A few terms must be defined. Internal pipping is defined as the point at which the poult breaks through the shell membrane into the air cell. External pipping is defined at the point at which the poult breaks through the shell. Poults from 14 day stored eggs took significantly longer to reach internal pipping (15 hours longer), and external pipping (17 hours longer) than poults from 4 day stored eggs. The time interval from internal to external pipping was also longer in poults from 14 day stored eggs (7 hours longer). The overall time to hatch was extended by 18 hours in poults from eggs stored for 14 days. Poults from 14 day stored eggs also showed higher levels of protein breakdown as indicated by a high concentration of plasma uric acid and higher activity of the enzyme glucose 6-phosphatase in the liver. The results of this study indicate that poults from 14 day stored eggs deplete their carbohydrate reserves during the hatching process and must dip into protein reserves to make the needed carbohydrate required to complete the hatching process.
Bottom line
Poults from eggs stored for 14 days hatched 18 hours later, and burned up more protein reserves in the hatching
process.
Gaylene Fasenko, University of Alberta
Poultry Research Centre News - Vol. 6 No. 1, April 1997 |
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