Recently, I received a note from an egg farmer that said “We sustain production well but start to run into issues around 45 weeks of age with egg shells that are rough, deformed, misshapen etc. I don’t think IBV is the cause as I vaccinate with Mildvac Ma5 (Merck) every 6 weeks over the production cycle. We are currently at 65 weeks and 7-8% seconds and some cracks.” This note encouraged me to write an article on the factors influencing egg shell quality.
There are many factors that influence egg shell quality such as bird age and strain, growth trajectory, stress, disease, mycotoxins, production system, and nutritional factors. That being said, we need to think of these together due to the interactions among them.
Let’s start with the age effect as this is more relevant to the above-mentioned farmer’s issue at first glance. A number of studies have shown that aging can impair egg shell quality. One potential explanation could be the depletion of calcium reserves from the medullary bones, which act as a calcium bank account. In addition, increase in egg size, and a reduction in the activity of 25-hydroxy-cholecalciferol-1-hydroxylase (an enzyme involved in calcium homeostasis) in older hens can also affect egg shell quality. Dietary supplementation of zinc, copper, and manganese (especially in the organic forms) might improve egg shell quality in aging hens. Certain dietary manipulations that aim at reducing egg size might increase egg shell quality in older hens. For instance, Keshavarz (2003) reduced dietary methionine, folic acid, and vitamin B12 to reduce egg weight in old laying hens from 54 to 72 weeks of age; dietary manipulation increased egg shell quality without any adverse effect on egg production.
Handling, environmental, climatic, and nutritional stresses can impair egg shell quality. High stocking density increases the production of body-checked eggs. Body checks are ridges or grooves that occur around an egg, usually at the pointed end. Stress can cause contraction of the shell gland (a segment of the reproductive system) through the activation of the sympathetic nervous system, which can result in misshapen eggs such as white-banded and slab-side eggs. Slab-side eggs are formed when two eggs enter the shell gland shortly after another, which interrupts normal calcification. The second egg will not be as complete as the first and may be flattened at the side where the eggs made contact. The white-banded eggs are formed when one egg is retained beyond the normal oviposition time; the first egg retained in the shell gland will have an extra layer of calcium seen as the white band marking. Managing optimal stocking density is an important consideration. Adequate levels of vitamin C and E may alleviate the adverse effects of stress. Vitamin C is closely associated with the production of corticosterone hormone in the body. Stress induces depletion of vitamin C in the adrenals, which is associated with corticosterone release. Dietary supplementation of vitamin C maintains the high adrenal concentrations of vitamin C, thereby limiting the rise in circulating corticosterone concentrations in chickens under stress. Whenever I talk about feed additives such as vitamin and mineral premixes, I like to emphasize the importance of the accuracy of adding these supplements to the poultry diets. Mixing errors can deteriorate mineral metabolism in poultry. This reminds me of a broiler breeder farm’s story where their egg production and egg shell quality dropped, and some birds were exhibiting a backward twisted neck due to a mixing error in the mineral supplements.
Water quality affects egg shell quality. Saline water (high amounts of dissolved salts) reduces egg shell quality and increases the incidence of egg shell defects. Providing saline water to broiler breeders reduces the production of day-old chicks due to reduced numbers of settable eggs and lower hatchability. The adverse effect of saline water appears to be related to the supply of bicarbonate rather than calcium to the shell gland for egg shell formation. Under this condition, drinking water desalination is necessary; dietary supplementation of vitamin C and zinc-methionine (an organic zinc source) might also accelerate the treatment procedure. Zinc is a mineral that is necessary for the function of carbonic anhydrase enzyme. This enzyme assists conversion of carbon dioxide and water into carbonic acid, protons, and bicarbonate ions during egg shell formation.
Measuring egg shell quality can help track the nutritional and environmental management in a poultry operation. Producers can choose a simple method such as egg specific gravity. Specific gravity is the ratio of the weight of an object to the weight of an equal volume of water. The specific gravity of the whole egg can be measured by immersing eggs in saline solutions of different specific gravity (typical concentrations are 1.070, 1.075, 1.080, 1.085, and 1.090) to see at what concentration of solution they float. The specific gravity of the solution in which the egg floats is the specific gravity of the egg. Managing for optimal egg shell quality is complex. For best results, changes to management strategies should be done in a stepwise manner in order to assess the impact of egg change without being confounded by other changes.
Picture from https://store.alltech.com/blogs/poultry/20-common-egg-shell-quality-problems-and-causes
Picture from https://store.alltech.com/blogs/poultry/20-common-egg-shell-quality-problems-and-causes
Picture from https://store.alltech.com/blogs/poultry/20-common-egg-shell-quality-problems-and-causes
Resource
Using Specific Gravity to Measure Eggshell Strength
References
Keshavarz, K. 2003. Effects of reducing dietary protein, methionine, choline, folic acid and vitamin B12 during the late stages of the egg production cycle on performance and eggshell quality. Poultry Science. 82:1407-1414.
Li L, Miao L, Zhu M, Wang L, Zou X. 2019. Dietary addition of zinc-methionine influenced eggshell quality by affecting calcium deposition in eggshell formation of laying hens. British Journal of Nutrition.
Mabe, I, Rapp, C, Bain, MM and Nys, Y. 2003. Supplementation of a corn-soybean meal diet with manganese, copper, and zinc from organic or inorganic sources improves eggshell quality in aged laying hens. Poultry Science. 82:1903-1913.
Roberts, J. R. 2004. Factors affecting egg internal quality and eggshell quality in laying hens. Journal of Poultry Science. 41:161-177.
Whitehead, C. C. and T. Keller. 2003. An update on ascorbic acid in poultry. World’s Poultry Science Journal. 59:161-184.
