Eggshell translucency is linked to several hatching-egg quality parameters but not egg specific gravity or eggshell color, according to a recent study published in Poultry Science.
Study results suggest that eggshell-translucency scoring offers an additional method for estimating eggshell quality and hatchability in broiler chickens.
Broiler producers carefully monitor several egg parameters in the hatchery that affect hatchability and chick quality, such as weight changes, eggshell features and egg content consistency.
Eggshell quality plays a particularly pivotal role in hatchability, influencing embryo protection, respiration and nourishment. Nondestructive assessment methods, such as egg specific gravity (flotation method) and eggshell color, are the preferred approaches for evaluating eggshell quality.
Egg specific gravity is popular because of its low cost, practicality and significant correlation with shell thickness. However, it does not detect some eggshell abnormalities that can be observed during candling, such as hairline cracks and translucent spots (eggshell mottling).
These translucent spots, caused by microscopic disorganization in the eggshell layers during formation, allow moisture from the egg contents to accumulate in the eggshell, leading 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 to measure eggshell quality uses a scoring system based on the amount of eggshell translucency.
Evaluating eggshell translucency
A Brazilian research team evaluated eggs from the same flock for specific gravity (five categorizations) and color (light, intermediate, dark). Only light and dark eggs within each specific-gravity category were numbered, weighed and analyzed for eggshell translucency.
Next, the researchers incubated and hatched eggs from the same specific-gravity category and eggshell color groupings in the same tray to monitor hatching parameters.
They used a translucency scoring system that uses light to determine eggshell quality and consistency:
- Score 1: few and small translucent spots
- Score 2: more translucent spots widely distributed throughout the eggshell
- Score 3: several spots and larger translucent windows all over the eggshell
Translucency affects some parameters, not others
The researchers observed no correlation between eggshell translucency and specific gravity, nor between translucency and eggshell color. Additionally, there were no interactions between translucency and specific gravity or between translucency and eggshell color for the analyzed variables.
Eggshell translucency influenced egg weight loss, hatchability and embryonic mortality on days 11 to 18 of incubation, with highly translucent eggs having the lowest results. Score 3 eggs differed from score 2 eggs in weight loss and hatchability and from score 1 eggs in embryonic mortality.
Specific gravity affected egg weight loss and hatchability equally.
Although both translucency and specific gravity affected egg weight loss and hatchability separately, the researchers noted that they are likely not interconnected because translucency derives from the way eggshells are formed, and specific gravity is related to eggshell thickness.
“Our data indicate that despite its individual effects, translucency had no relationship or interaction with specific gravity or shell color over incubation parameters,” the researchers concluded.
The full paper, “Eggshell translucency: Its relationship with specific gravity and eggshell color and its influence on broiler egg weight loss, hatchability, and embryonic mortalities,” can be found in Poultry Science and online here.
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