Egg Shell Mottling and Hatchability

Date of publication : 6/27/2008
Source : Univ. of Arkansas Cooperative Extension Service
Hatchability Problems

Hatching egg quality parameters have become increasingly important as commercial broiler breeder producers attempt to maximize hatchability. The egg pack can be easily monitored and growers held responsible for sending too many poor quality eggs to the hatchery. However, even good quality eggs can be mishandled. When care is not taken the incidence of otherwise good hatching eggs sent to the hatchery in the form of upside-down, or filth covered eggs, which may cause contamination, or even slab sided eggs, will also reduce hatchability.

When troubleshooting hatchability problems, traditionally producers have placed the blame in one of three areas, fertility, hatchery (incubation) conditions, or egg handling. Obviously most of the attention is usually turned to the males in the breeder house and overall flock fertility. This is normal considering that the majority of actual hatchability related problems are directly related to poor fertility. Additionally, poor fertility is correlated with increased early embryo mortality which results reduced hatchability. A second area often responsible for poor hatchability can be directly linked to actual hatchery or incubation conditions. Even with the modern technology available today, hatchery equipment can, and does, wear out and malfunction over time. Equipment maintenance is often more than a full time job when trying to manage a hatchery for optimum production. A third area often responsible for reductions in hatchability is egg handling conditions and procedures. While it is obvious that we have much to learn in this area and that our ‘tried and true’ methods for egg handling may not be the best, that will be the focus of future articles. The purpose of this article is to address another area that is sometimes blamed for poor hatchability, namely egg shell quality.

Egg Shell Mottling

Recently, there has been an apparent increase in the incidence of egg shell mottling. Egg shells that are mottled appear as a thinner, weaker portion of the egg shell. It has been postulated by many commercial hatchery personnel that eggs with mottled shells cause reduced hatchability and increased moisture loss. Many integrators have spent time and money on products in an attempt to reduce or eliminate shell mottling with the hopes of improving hatchability. Therefore, a study was conducted to identify if, and to what extent, shell mottling affects hatchability and potentially chick quality.

Setting up a Field Study on Egg Shell Mottling

Four flocks of broiler breeders were chosen ranging from 37 to 55 weeks of age, with a different flock selected for each of the four replicate trials. Hatching eggs from the egg storage room from two commercial hatcheries were candled and sorted into two groups; one group contained eggs with extreme cases of shell mottling, and another group contained eggs with no visible shell mottling. All eggs in each individual trial were laid on the same day and stored and handled as normally mandated by company protocol. Each replicate trial consisted of three trays of 154 eggs per tray for each of the mottled and non-mottled egg shell groups. In each trial, each tray of eggs was weighed prior to placement in the commercial setter and weighed again at transfer at 18 days of incubation to determine percent moisture loss. Following transfer to the egg hatching baskets, each of the three trays of eggs from each group was pulled from the hatchers following normal company procedures after 21 days of incubation to determine percent hatchability. These trials were spread out throughout the year to eliminate any potential seasonal effect.

Field Study Results

The results of this study were somewhat surprising. Moisture loss was 13.16 % for the mottled, or windowed eggs and 13.71% for the control eggs or eggs without any apparent shell mottling. The moisture loss data was very consistent in the four separate trials with no significant difference in any trial. Hatchability for the two groups of eggs was 78.79 % for the mottled eggs and 72.73 % for the non mottled eggs, respectively. In three of the trials hatchability was numerically higher for the mottled eggs and nearly identical in the fourth trial. Although these hatchability data were not significant due to the fact that we had a wide range in hatchability values with a low of 58.4 % (control) and 61.0 % (mottled) for set number one (oldest flock) and high percent hatch of 90.28 % (control) and 90.33 % (mottled) in set number four, the numerical results indicate that shell mottling did not cause losses in hatchability. Furthermore, specific gravity was used to estimate shell quality in a different group of mottled and non-mottled eggs with no correlation there either.


So, what is causing the appearance of some eggs shells to change resulting in these ‘windows’ or mottled looking eggs? Apparently the discoloration results from a slight separation of the underlying egg shell membrane from the shell itself. This occurs in pockets which then become discolored giving the appearance of a thinner portion of the shell often called ‘windows’. From this study and discussions with at least one other hatchery who conducted a similar type trial, egg shell mottling does not affect percent moisture loss or hatchability in commercial broilers. Although the appearance on the shell can be somewhat alarming, particularly if hatching eggs are sold on the open market, it does not negatively affect hatchability.

By R. Keith Bramwell, Extension Reproductive Specialist, Center of Excellence for Poultry Science - AVIAN Advice newsletter - University of Arkansas
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