Consumers expect to find a perfect yolk and albumen each and every time they crack open an otherwise good-looking egg. Yet, eggs are imperfect, a natural, biological life form, produced by less-than-perfect creatures. Thus, a small number of eggs are prone to be laid with inherent, internal issues that make them unacceptable to the modern consumer.
The most important issue regarding internal egg quality is, of course, that of a lack of freshness, which can be avoided by judicious management and handling of eggs from the point of collection to the point of use. Other, less frequent problems, such as blood spots, discoloration, pale yolks, etc., cannot be resolved after the egg is laid. These issues are usually the outcome of a combination of factors, including genetics, flock age, nutrition, health, management and stress, and ambient temperature and humidity. Here, we will examine a short list of common issues of internal egg quality that can be influenced or even prevented by nutritional intervention.
The color of the yolk of a healthy egg is expected to be strong yellow-orange. This perception is based on experience from when hens were kept outdoors. Free range hens kept at each farm house consumed plants rich in xanthophylls (natural pigments) that gave to the yolk its strong orangey hue. Under those conditions, only sick hens produced pale eggs and, as such, these were not consumed.
Today, under modern commercial conditions, the color of the yolk can range from pale yellow (hens fed an all-wheat diet) to light orange (hens fed an all-maize diet). Of course, in both cases, such eggs have the same nutritive value and are perfectly safe. Nevertheless, most markets worldwide still prefer yolks that are deep orange in color.
This intense color can be achieved only by feeding such ingredients rich in xanthopylls as maize gluten and alfalfa meal, or concentrated forms of natural and synthetic pigments, such as canthaxanthines and apocarotenoic esters. The exact inclusion rate for each ingredient or pigment depends on the desired yolk color. For example, feeding about 10% maize gluten will produce a deeply orange yolk, while adding as much alfalfa meal in an all-wheat diet will give the equivalent of an all-maize diet in terms of egg yolk color. Today, achieving the desired yolk color is not difficult but it requires prior and careful design.
Apart from diseases, other factors can reduce egg yolk coloration. For example, a deficiency in vitamin A (due to a mixing error, or losses during premix storage) can reduce the intensity of yolk color. In contrast, a hyper dosage of vitamin A (usually through drinking water as part of a veterinary treatment) can lead to egg color variation that includes loss of color intensity. Also, the absence of synthetic or natural antioxidants (such as vitamin E) can affect the potency of carotenoids (natural and synthetic), and thus the degree of egg yolk coloration that is achieved.
Apart from an aesthetic point of view, blood (or even tissue or meat) spots have no real significance. But, they are, nevertheless, objectionable, especially when they are large or diffused. It is estimated that this problem can affect as much as 10% of all eggs, but this is usually less than 5%, and most blood spots are hardly noticeable.
Blood spots occur when blood vessels rupture in the hen’s reproductive system. From practical experience, ensuring diets (a) contain sufficient vitamin A and vitamin K, and (b) they are free from mycotoxins is all that can be done nutritionally. Here it should be added that vitamin K antagonists exist in alfalfa meal.
Normally, a watery albumen is an indication of an old egg or one that has been allowed to deteriorate due to improper storage and handling. To help strengthen the albumen, several nutritional strategies have been suggested over time. Of these, manipulation of protein and acid-base balance appear to be the least effective.
In contrast, adding magnesium and zinc appears to be rather more effective, but a high level of magnesium can impair the integrity of the shell. Vanadium, a metal contaminating most phosphates, reduces albumen quality severely even at low levels; this should be taken into account when purchasing phosphates for feeding to laying hens.
This refers to complete discoloration or the appearance of patches of different color throughout the yolk and even the albumen. Nutritionally, this can be related to low levels of vitamin A (a variation of pale egg syndrome), but evidence is rather empirical and limited. A greenish hue in the yolk can be due to feeding cottonseed meal high in free gossypol. This problem is usually resolved by adding about 0.5% ferrous sulfate in the final diet (the exact amount depends on total free gossypol).
Likewise, a pinkish hue can be seen in albumen, again due to high levels of cottonseed meal in the feed, due to the presence of cyclopropene fatty acids in this ingredient (and also in certain weeds that could possibly contaminate other feed ingredients).
Here we refer to eggs that have an undesirable odor due to certain feed ingredients. Naturally, the most offensive is that from feeding high levels of fish meal or fish oil. Fishy eggs are highly objectionable to consumers and this can be avoided by limiting total fish oil concentration in the final diet below 1%. When high levels of fish oil are required to produce designer eggs rich in omega-3 fatty acids, this can be achieved only by using deodorized fish oil.
Rapeseed meal can also produce a fishy smell in eggs, but only when fed to hens with the Rhode Island gene. In these hens, there is a genetic anomaly that prevents them from breaking down trimethylamine (a derivative of sinapine, a natural compound in rapeseed and other plants). Finally, it has been reported that eggs from hens fed high levels of flaxseed (also used to produce eggs rich in omega-3 fatty acids) can have the smell (and even taste) of paint!
Nutrition may not play the greatest role in most cases of egg internal quality problems. Yet, careful formulation design and certain intervention strategies can solve some rather unpleasant issues. Achieving 100% perfect eggs is rather impractical, or even impossible, but at least they don’t have to taste like wall paint!