Maintaining egg shell quality is important for maximizing production of broiler chicks from breeders as shell quality and hatchability go hand in hand. Thin shells allow for higher water vapor loss during incubation resulting in dehydrated chicks and higher late embryonic mortality.
For the salt bath method, eggs are placed in the lowest solution and those eggs that do not float are removed and placed into the next high-er salt solution, and so forth until the egg floats.The specific gravity of the solution in which the egg floats is the specific gravity of the egg. This method allows for rapid measurement of large numbers of egg, with minimal affect on the eggs.The best time to measure specific gravity is in the hatchery after the eggs have had a chance to reach the same temperature as the prepared salt solutions
Also, egg shells that are thin crack easily during collection and transportation, resulting in poor hatches and higher losses of chicks, from both contamination and excessive moisture loss. The major factors that influence egg shell quality are genetics, diet, climate, housing and age of the hens. Therefore, current knowledge of a flock’s shell quality allows for better management of that flock by changing management practices to improve poor quality egg shells and subsequent hatchability and chick quality.Of the different measures of egg shell quality, egg specific gravity is the easiest and most widely utilized method. Specific gravity is used to measure shell thickness and, indirectly, the percentage of shell deposited on the egg. There are two methods to obtain egg specific gravity, the Archimedes method and the salt solution method. The Archimedes method involves weighing eggs individually, then weighing them in water and then using the formula; [dry weight/(dry weight-wet weight)]. The salt bath method utilizes several tubs of salt water containing graduated levels of salt solution
Specific gravity and hatch
To investigate the relationship between hatch-ability and specific gravity in modern broiler breeders 1,944 eggs were measured for col-or and specific gravity, with each egg labeled so that every egg could be followed through to hatch. Eggs came from five different flocks of hens in prime production with flock ages be-tween 33 and 45 weeks of age. Salt solutions were maintained in the egg storage room at a local commercial hatchery and measured after they had time to adjust to the temperature of the room. The salt solutions were check regularly for accuracy with a hydrometer and specific gravity ranged from a low of 1.065 to a high of 1.090 in increments of 0.005. Once eggs were measured they were placed with the rest of the eggs from that flock and hatched at the hatchery using industry standards. After hatch, a residue breakout was preformed on all unhatched eggs to deter-mine fertility and time of embryonic mortality. These results indicate that eggs with a specific gravity of 1.070 hatch as well as those with higher specific gravities and that hatch was not negatively affected until specific gravity was 1.065 or lower.These results are different than those published by McDanielet al., 1981 and Bennett, 1992, who report that eggs with specific gravities less than 1.080 had poor hatch and increased embryo mortality. The difference in results may be the result of genetic progress and changes made during the last 20 years, or in experimental methodology
Shell color and hatch
Over the years it has often be assumed the light colored eggs in broiler breeders do not hatch as well as darker eggs. There forein the previously mentioned experiment we also recorded the egg shell color for each egg using a color imeter that gave a numeric measurement of the shell color. By using a color imeter we were able to remove humane error from trying to determine the shell color. The color imeter produced high numbers for whiter eggs while darker eggs had lower numeric values.
"The major factors that influence egg shell quality are genetics, diet, climate, housing and age of the hens. Therefore, current knowledge of a flock’s shell quality allows for better management of that flock by changing management practices to improve poor quality eggshells and subsequent hatchability and chick quality"
Summary
Specific gravity can be effectively used to rapidly evaluate the shell quality in broiler breeders, however, it is a procedure that can be time consuming. Eggs with specific gravity values high-er than 1.070 will have similar hatchability while those with low-er values will result in reduced hatchability. And lighter colored eggs (color scores above 87) hatched at a lower rate than did darker eggs. However, other than the excessively light eggs,eggs shell variation within a group of was not necessarily a negative factor towards hatchability
