Maintaining Hatching Egg Quality
A large number of factors are involved in the production of a high quality chick which should not been seen as independent of each other but rather should be looked at holistically. For example, the conditions during incubation may interact with the quality of eggs set or the age of the breeder flock. The quality of the egg embraces its size, shape, colour, cleanliness, the integrity of the shell and the absence of shell malformations.
On the Farm:
At all times, hatching eggs should be handled carefully to reduce cracks. Try to limit the number of times eggs need to be handled. Each time an egg is handled one can expect at least 1% cracks (not always visible). Even before collection, many eggs are broken in the nest as the result of inadequate cushioning in the nesting material. It is important to keep the nesting material clean and dry. The ability to absorb moisture is an important quality to consider in selecting a good covering for the bottom of the nest. Keep in mind too that eggs cool much more quickly on bare, exposed nest floors than in a nest with litter and rapid cooling reduces hatchability.
Reduce the number of floor eggs. The following suggestions help induce hens to lay in nests rather than on the floor:
Normally, hatching eggs are picked up from the nests four times each day, however, during periods of extremes in temperature, either high or low, five or six collections may be necessary. Frequent collections decreases breakage in the nest and in hot weather prevents pre-incubation. Eggs laid late in the day should be collected the same day rather than left in the nests until the next morning.
The type of containers used for holding the eggs collected is important. Once laid, hatching eggs should cool gradually, not suddenly. They are best collected on egg flats. Plastic flats are better than fiber. Litter and dirt accumulate on fiber flats. When using corrugated cardboard egg cases, several holes about 5cm in diameter could be cut on the sides of the cases. These allow movement of air through the cases. A polythene egg case is also available for storing hatching eggs. Using plastic incubator trays reduces handling and they can be washed after incubation. Regardless of the type of container or tray used to hold eggs, the relative humidity of the air in the holding room should be 75 – 80%. This materially reduces egg evapouration and does not cause too much egg-case deterioration.
Reducing the bacterial contamination of eggs is very important. Formaldehyde gas has good disinfecting properties. It is a valuable disinfectant for breeding farms and hatcheries. It is both cheap and effective. From the operators point of view it is unpleasant to work with and toxic at even low concentrations. Research in 1953 showed that in order to kill Salmonella pullorum on the egg shell after 20 minutes exposure to the gas a minimum concentration of 600 mg/m3 at 21°C was necessary. This recommendation still stands today. How to achieve 600 mg/m3 of formaldehyde:
At the hatchery:
Once the eggs are laid they must be held for a day or two to fit the setting schedule of the incubator. On occasion hatching eggs may not be set for 1 – 2 weeks after they are laid. The requirements for storage are influenced by storage time. The conditions under which they are stored have a great bearing on helping to maintain as much of their original quality as possible.
Although the optimum temperature for embryonic development in the forced-draft incubator is in the region of 37.5°C, this does not mean that there is no embryonic growth when temperature is below this figure. There is a threshold temperature of 20°C above which embryonic growth commences and below which it ceases. One may alter the environmental temperature above or below this threshold area several times before an embryo is completely killed, however, each time the temperature goes above or below the threshold the embryo grows weaker and its chance for hatching decreases.
After hatching eggs are laid they should be cooled to a temperature well below the threshold and kept at this temperature until shortly before being placed in the incubators. Temperatures in the egg holding room should be 18.3°C, when eggs are set at intervals of less than 14 days. Hatchability will be reduced if the holding temperature is less than this. Some recent work shows that with short-term egg storage (1 – 3 days), hatchability will benefit from higher (20°C) storage temperatures. This is not beneficial for eggs stored for 5 – 7 days. These eggs do better when stored at 16°C. When eggs are held for longer than 14 days, holding at 10.5°C will produce better hatches.
Reduction from the hens body temperature of 40°C to this optimum holding temperature of 18.3°C should be gradual, taking several hours. Sometimes eggs may cool too rapidly, at other times the cooling process may be too slow. Some of this difference in cooling rate may be attributed to the container in which the eggs are stored during the holding period. If cases are stacked close together, without air movement between them, the time necessary to cool eggs will be much longer.
Time to cool eggs to 18.3°C
When hatching eggs are held at a temperature of 18.3°C, embryonic development is fully arrested. However, hatchability decreases for each day the eggs are held. Eggs held for less than 5 days show little perceptible reduction in their hatchability or in the quality of chicks hatched from them. When the period of holding is longer than 5 days, hatchability will drop materially with each additional day.
Effect of normal egg storage on hatchability and incubation period
Rule of thumb: Hatching time is delayed 30 minutes and hatchability reduced by 4% for each day eggs are stored after 5 days.
Eggs from a young breeder flock can be held longer than those from an old breeder flock. Eggs from older flocks should be set as soon after laying as possible.
When hatching eggs are held for less than 1 week before being set there seems to be no need for turning them during this period. However, in some operations (pedigree farms) it may be necessary to hold eggs for long periods. Rotating eggs from side to side over a 90° angle will improve hatchability. Place eggs in an egg case and place a 25cm block under one end. The next day remove the block and place it under the other end. It may also be beneficial to store eggs upside down and enclose in plastic bags.
When eggs are removed from a cold room to a room with a higher temperature, as moving eggs from egg holder room to egg traying room, moisture will often condense on the shell. This picks up additional bacterial organisms floating in the air and increases shell contamination. The table below shows the temperature and relative humidity at which eggs will “sweat” (temperature of eggs is 18.3°C):
If moisture is condensing on the shells when the eggs are moved from the egg holding room to the egg traying room there are 2 remedies:
Date published: 2006-03-23