The absence of emerging disease threats, except, perhaps, for avian influenza in Mexico and China, and the positive impact of falling grain prices resulted in a program for the 2013 Iowa Egg Industry Symposium that got back to some basics: egg quality and egg processing, with some additional information about on-farm welfare assessments.
Primer on egg quality
Dr. Douglas Grieve, global technical services director, Hy-Line International, presented a summary titled "The Science of Egg Quality," starting with the process of egg formation in the oviduct. The yolk is formed over time in the ovary and is greatly affected by the hen's age and diet. Yolk size will increase as the hen ages, and color is largely affected by dietary pigments. Yolk content can also be affected greatly by dietary fat soluble vitamins and fatty acid content, allowing designer egg processors to enhance important vitamins, such as Vitamin E, in the egg yolk and to dramatically change lipid composition of egg yolk to increase good fatty acids like omega-3.
Albumen, which contains 40 different proteins, is produced in the magnum. Enzymes, such as lysozyme, are present in egg albumen, which can break down egg albumen proteins over time. Several diseases, such as Infectious Bronchitis, affect the oviduct and production of quality albumen. Grieve noted that genetic selection can affect the amount of thick albumen in the egg. The shell membranes are deposited onto the albumen in the isthmus of the oviduct.
The uterus, also known as the shell gland, is the site of eggshell formation and also the part of the oviduct in which the egg spends the most time for formation (18-20 hours per egg). The shell membranes are made tight as the egg enters the uterus by a process called "pumping," in which water is pumped through the eggshell membranes into the albumen and the albumen volume is doubled in size due to this uptake of water. The shell membrane becomes tight and the process of calcification begins.
Eggshell deposition
Calcification starts with the production of a matrix of protein fibers and thin layer of calcium salts to form the mammillary bodies of the eggshell upon which the organic and crystalline palisade layers of eggshell can build upon. The protein fibers are important in that they give the eggshell its elasticity in the base allowing the shell to be shock resistant.
The crystalline palisade layer is where the calcium carbonate crystals are formed and eventually fused into a proteo-ceramic eggshell complex that makes up the majority of the eggshell. Normally, the hen produces a fairly constant amount of eggshell per day, so unfortunately, as egg size increases, the amount of eggshell does not. This leads to overall thinner shells on larger eggs as the hen ages.
Eggshell pigments are deposited onto the eggshell at the end of eggshell formation. Pigments are protoporphyrin and biliverdin proteins produced during hemoglobin metabolism and are transported from the liver through blood to the uterus. They can also be produced from red blood cells in the uterus. Shell color is strongest in young hens and fades as the hen ages, restoring after a molt.
The outermost layer of shell is the cuticle, which is a non-calcified protein layer added prior to oviposition. The cuticle helps to protect the egg from bacterial invasion. At the same time, it is also porous to allow for air exchange during incubation. A typical egg has approximately 6,000 pores.
Selecting for egg quality
Blood and meat spots are interior egg qualities that are undesirable and negatively affect the egg's grade. Blood spots are a result of a hemorrhage during ovulation, which is carried with the yolk and becomes a part of the egg's contents. They are usually easily detected during egg candling. Meat spots are more likely deposited during albumen production and come from cellular debris in the oviduct.
Grieve noted that Hy-Line's egg quality laboratory scores all of their genetic lines for internal egg quality and includes such data in their selection process. The lab also takes measurements of a number of exterior eggshell quality factors to include breaking strength by a texture analyzer type of apparatus and acoustic resonance that measures the "dynamic stiffness" of the egg. Dynamic stiffness measurements have also become important criteria in efforts to select hens for improved eggshell quality.
Improving shell egg safety
Dr. Kevin Keener, food process engineer, Purdue University, presented egg processing technologies that can reduce bacterial contamination of eggs through improved cooling and internal pasteurization techniques. Keener showed some interesting data about how a dirty egg packaging plant can increase eggshell bacterial contamination, especially with dirty wash water.
The Food and Drug Administration Egg Safety Rule requires a reduction of Salmonella enteritidis in eggs during production, storage and transportation. Keener said that there is still a need to cool eggs more quickly during storage and transportation to limit multiplication of bacteria on the egg.
It takes time to cool an egg from over 100F to 45F. Field testing of several technologies to cool eggs more quickly has been done, such as cryogenic cooling, cooling tunnels and rapid egg cooling. All could be important future practices to help reduce egg bacterial growth during storage and transportation.
Pasteurization techniques
Egg pasteurization techniques were reviewed by Keener. There are a number of treatments that can pasteurize the whole egg without overcooking it that are already being used by egg processors, including hot water immersion, water vapor/condensation and others that have potential, such as microwave heating, atmospheric cold plasma treatment, egg irradiation, pulsed UV and electrolyzed oxidized water treatment.
At this time, the majority of consumers are not willing to pay the price for pasteurized eggs, and to quote Keener, "It will take an Act of Congress to change egg safety from a numbers game [more tests, more inspections] to a risk based [HACCP-like] preventative system and only under a risk based system will new technologies receive timely regulatory review and widespread acceptance."
Welfare assessments
Dr. Suzanne Millman, associate professor, College of Veterinary Medicine, Iowa State University, discussed the practical considerations for putting together on-farm welfare assessment criteria and protocols. In the age of audits, many companies and producers are putting together animal welfare data and internal programs. This is not an easy task, but, at the same time, it need not be completely daunting.
Millman reviewed four principles of good animal welfare and presented 12 criteria to measure. The four principles included good feeding, good housing, good health and appropriate behavior. The first three are all obvious good husbandry practices that our industry has been practicing for years. Appropriate behavior is a bit more difficult for some to measure in a concrete way. Appropriate behavior measures demonstrate expressions of social behavior, emotional state and human-animal relationship. Millman didn't present assessment tools for appropriate behavior.
