Hatchability linked to eggshell translucency
Eggshell quality plays a key role in hatchability, influencing embryo protection, respiration and nourishment.
In the modern poultry industry, the importance of hatchery operations is critical for the success of subsequent portions of the broiler production chain. Broiler producers carefully monitor several egg parameters in the hatchery that are known to affect hatchability and chick quality, such as egg weight changes, eggshell features, and consistency of egg contents.
Of these, eggshell quality plays a key role in hatchability, influencing embryo protection, respiration, and nourishment. While there are several methods for assessing eggshell quality, nondestructive methods — including egg specific gravity (flotation method) and eggshell color — are preferred.
While egg specific gravity is a frequently employed approach due to its low cost, practicality and significant correlation with shell thickness, it comes short of detecting some eggshell abnormalities that can be observed during candling such as hairline cracks and translucent spots (eggshell mottling).
These translucent spots, caused by “ultrastructural disorganization” in the eggshell layers during formation, allows moisture from the egg contents to accumulate in the eggshell, which leads to increased light transmission through the shell. Translucent spots have also been associated with potential risks of bacterial penetration and crack development.
A newer method for eggshell quality measurement has been developed to score eggs based on the amount of translucency of the eggshell, and a new study investigated possible interactions among eggshell translucency, egg specific gravity, and egg color relative to egg weight loss, hatchability, and embryonic mortality. Results of the study were recently published online at https://www.sciencedirect.com/science/article/pii/S003257912400107X?via%3Dihub.
The researchers evaluated eggs from the same flock for specific gravity (five categorizations) and color (light, intermediate and dark). Subsequently, only light and dark eggs within each specific gravity category were numbered, weighed, and analyzed for shell translucency. Eggs from the same specific gravity category and eggshell color groupings were then incubated and hatched in the same tray to enable monitoring of hatching parameters. Translucency scoring uses light to determine eggshell quality and consistency. Translucency score 1 eggs show few and small translucent spots; score 2 eggs have more translucent spots widely distributed throughout the eggshell, and score 3 eggs have several spots and larger translucent windows all over the eggshell.
According to the researchers, no correlation was found between eggshell translucency and specific gravity, nor between translucency and eggshell color. Additionally, no interactions between translucency and specific gravity or between translucency and eggshell color were found for the analyzed variables.
In the study, eggshell translucency influenced egg weight loss, hatchability, and embryonic mortality on days 11-18 of incubation, with score 3 eggs differing from score 2 eggs in weight loss and hatchability and from score 1 eggs in embryonic mortality. Egg weight loss and hatchability were also found to be equally affected by specific gravity.
The researchers noted that while both translucency and specific gravity affected egg weight loss and hatchability separately, it is likely that they are not interconnected because translucency derives from the way eggshells are formed while specific gravity is related to eggshell thickness.
This study determined that despite its individual effect, translucency had no relationship or interaction with specific gravity or shell color over incubation parameters. High translucency eggs (score 3) were found to have lost more weight and hatched less, but these differences were only significant relative to medium translucency eggs (score 2).
