In an article published in the October, 1995 issue of Industria Avicola the authors, Butcher and Miles, discussed all of the factors, up to that time, which were known to have a negative influence on pigmentation of brown-shelled eggs. The element, vanadium, was not listed as one of the factors because no research had ever been conducted which showed vanadium as being detrimental to eggshell pigmentation. In the past, the majority of research with laying hens concerning vanadium has been concerned with its negative influence on egg albumen quality.
In the December, 2002 issue of Industria Avicola, Miles and his coworkers reported that dietary vanadium was detrimental to brown eggshell pigmentation. In this present article, the authors briefly discuss their research which describes how the brown color of eggshells can be completely restored when vanadium is present in the diet of a laying hen. (Note: This research was published in 2006 in the Journal of Applied Poultry Research, 15:425-432).
Vanadium in poultry diets
The major source of vanadium (V) in poultry diets is usually poor quality feed-grade phosphate sources. The maximum tolerable level of V established for poultry diets is 10 ppm. Vanadium in the diet of chickens has been shown to be detrimental to egg production, interior quality of eggs (less albumen height), body weight, feed consumption, and pigmentation of brown eggshells.
Normally, laying hen diets contain concentrations of V that are of no concern to nutritionists and egg producers. There are times, however, when the diets of laying hens and other poultry may contain a poor quality phosphate source that contributes a high concentration of V to the diet. When V is consumed orally by laying hens it is usually retained in bone, kidney, liver and oviduct (magnum). Since V is a mineral with a high oxidation potential it is thought by several researchers that the detrimental mechanism of action that V exerts in animal cells, especially cells of the reproductive tract, is partly through inhibition of cellular enzymes and cell damage from lysis.
Overcoming the detrimental effects
In their studies, the researchers at the University of Florida supplemented a corn-soybean meal basal diet with 0, 15 and 30 ppm V as the compound, “ammonium meta-vanadate”. These dietary concentrations of V were used because the researchers felt that when balancing the diet for phosphorus with a poor quality feed-grade phosphate source, the phosphate source would not be supplying more than 30 ppm V to the diet. On days 3, 6 and 9 of a nine day period in which the three experimental diets were fed, each of the shells of the eggs collected from Hy-Line Brown egg-type laying hens was analyzed for their pigmentation by a computer color vision system. This established the base-line eggshell pigmentation value for eggs laid by hens fed each dietary treatment.
A significant decrease in eggshell pigmentation occurred by day 3 and continued until day 9 when the diets were changed and the hens began consuming a diet containing antioxidants. Assisted by a computer-based color vision analysis system the researchers were able to determine the actual cause of the “bleaching” effect which occurred in the eggshells. Vanadium caused a reduction in the “red” component of the eggshell rather than the “yellow” component. Also, these researchers were able to determine the influence that V had on eggs with different “shades” of shell coloration (i.e., dark brown vs. light brown). When V was added to the diets of hens laying eggs with dark or light brown shells, the magnitude of the decline in pigmentation in these eggshells was essentially the same. On day 9, the diets were changed so that the hens receiving the V supplemented diets received a diet also supplemented with one of the following antioxidants: none, 100 ppm vitamin C, 100 IU of vitamin E, or 100 ppm beta-carotene. Eggs collected on day 3, 6, 9, 12, and 15 following the diet change were used for shell color analyses.
Results of the above experiment indicated that when beta-carotene, vitamin C and vitamin E were supplemented to the diets containing either 15 or 30 ppm V, only vitamin C totally restored egg shell pigmentation. Vitamin E and beta-carotene had no influence on restoring pigmentation to the eggshells.
Further analysis of the data indicated that vitamin C restored the “red” component of the eggshell.
Supplementing the antioxidants alone or in combination to the control diet containing no V had no effect on eggshell pigmentation. The mechanism responsible for the complete restoration of eggshell pigmentation by vitamin C is not known. This can also be said for the mechanism involved in restoration of albumen quality (higher albumen height) when vitamin C is supplemented to laying hen diets at a concentration of 100 ppm and containing 30 ppm V or less. However, in this present pigmentation study, vitamin C was the only supplemental antioxidant that was water soluble. This may have been a contributing factor because, being water soluble, it was more available during the enzyme-catalyzed pigmentation reactions occurring in the water phase of the uterine (shell gland) cells.
If a crisis situation occurs and a poor quality phosphate source containing a high concentration of V must be used in the diet of commercial egg-type laying hens that lay either white or brown eggs, producers should expect to see a deterioration of egg albumen quality in eggs from both types of hens and a “bleaching” of the eggshell in hens laying brown eggs. Research data in the scientific literature clearly show that vitamin C will restore egg albumen quality in situations where hens are consuming diets containing 30 ppm V or less.
Also, in a practical field situation, the bleaching effect on eggshells which occurs when brown egg-type laying hens consume a diet containing 30 ppm V or less can be overcome. In this case, a complete restoration of normal eggshell pigmentation would be expected to occur when vitamin C is supplemented to the laying hen diet at 100 ppm.