DSM Corporate | | Print | A A A

Vitamin E and egg quality and production

Any chance to market a more nutritious food while also increasing production is doubly welcome to the poultry industry, especially with the growth of "designer" eggs to improve consumer demand. Now, a growing body of research is reporting both benefits when laying hens receive diets with increased vitamin E fortification.

These studies show that the resulting increases in the yolk's vitamin E content provide table users of eggs with a significantly better source of this essential nutrient, while food manufacturers have access to an ingredient whose antioxidant properties can help retard oxidative damage, or rancidity, in their food products. Meanwhile, studies such as Whitehead (1998) have shown increases of 3 to 16 percent in the number of eggs produced per hen when higher levels of vitamin E are fed during periods of heat stress.

The effectiveness of increasing the vitamin E content of eggs through greater fortification of hens' diets has been demonstrated in numerous studies. For example, Cherian et al. (1996) reported that as vitamin E supplementation rose, the enhancement of total tocopherols in tissues was greatest for egg yolk, followed in descending order by liver, adipose tissue, dark meat and white meat.

Meluzzi et al. (2000) reported that yolk alpha-tocopherol content increased linearly (P < 0.01) as fortification of the hens' diet increased from 0 to 200 IU of vitamin E per kilogram of feed (Table 1). Eggs from the hens receiving the highest level of fortification provided 313.84 µg of vitamin E per gram of yolk, or more than three times as much vitamin E as eggs from hens with the control diet. Furthermore, after 28 days of storage at room temperature (20° to 25°C), yolk vitamin E levels with increased fortification were still very close to those observed in fresh eggs.

Similar results have appeared in other studies. Jiang et al. (1994) fed diets with vitamin E fortification ranging from 0 to 400 IU per kilogram. Yolk alpha-tocopherol levels rose from 144 µg per gram of yolk with the control diet to 477 mg with the 400 IU fortified diet. In an unpublished study on a commercial operation in the United States, hens received a diet fortified with either 6 or 45 IU of vitamin E per kilogram. Yolk vitamin E levels with the higher level of fortification were 54.02 mg per gram, or three times the 18.75 µg found with the lower vitamin E diet.

Meluzzi et al. (2000) noted that an egg with a vitamin E content of 300 mg per gram would provide roughly 50 to 100 percent of the recommended daily allowances published by various nations for this essential nutrient.

Surai (2000) reported that consumption of vitamin E-enriched eggs as part of normal diet for eight weeks effectively increased the blood levels of alpha-tocopherol in participants. In work with laboratory rats, Yoshizawa et al. (1991) reported higher serum and tissue tocopherol levels in animals receiving vitamin E-enriched egg yolk powder than in control animals. Lipid peroxide levels were inversely proportional to the tocopherol concentrations in the eggs.

Meluzzi et al. (2000) also noted that increased vitamin E content should help maintain egg quality by reducing peroxidation. Scheideler (1998) did indeed report improved egg quality (P < 0.01) following increased vitamin E fortification. In this study, eggs were assessed for oxidative damage by measuring yolk levels of TBARS (thiobarbituric acid- reactive substances), which indicate oxidized fats. Eggs from hens receiving 50 IU of vitamin E per kilogram had only one-eighth the TBARS levels of the hens receiving 10 IU per kilogram.

The egg-quality research by Scheideler was part of a study that also reported increased egg production in hens receiving the higher level of vitamin E fortification. Hen-day production was increased (P < 0.01) by an average of 3 percentage points, from 79 to 82 percent, in birds fed the higher level of supplemental vitamin E before and during exposure to heat stress.

Whitehead (1998) also reported two studies in which egg production increased as vitamin E intake levels rose. In the first, hens received 10, 125 or 500 IU of vitamin E per kilogram and underwent chronic heat stress of 89.6°F (32°C) for four weeks. Although heat stress depressed egg production in all the hens, there was 16.4 percent greater production (P < 0.05) with the highest levels of vitamin E supplementation than with the lowest. Egg production figures were 65.4 and 56.2 percent for 500 and 10 IU of vitamin E supplementation, respectively. The diet containing 125 IU of vitamin E gave intermediate results.

In follow-up work, the decrease in egg production during heat stress was again minimized with increased vitamin E supplementation (Table 2). Performance was optimized at 250 IU per kilogram (P < 0.02). Furthermore, significant differences in egg production by vitamin E treatment were still apparent four weeks after heat stress ended.

In discussing possible modes of action, Whitehead (1998) noted that the improvements with increased vitamin E levels could be linked to improved circulatory supply of yolk precursors, particularly vitellogenin, during heat stress. Indeed, this study showed that vitellogenin synthesis in the liver decreased during heat stress and also, more importantly, that vitellogenin accumulated in the liver—at the expense of plasma concentrations for uptake by the ovaries.

In the hens receiving only 10 IU of vitamin E per kilogram of feed, liver concentrations of vitellogenin during heat stress increased by 77 percent compared with unstressed birds receiving the same vitamin E regimen. Plasma concentrations decreased by 49.6 percent during heat stress for this group.

In hens receiving 300 IU of vitamin E, by contrast, the same trends occurred but were much less pronounced. Liver concentrations of vitellogenin increased by only 10 percent in these hens, while plasma concentrations fell by only 28.2 percent.

Whitehead (1998) suggested that because vitamin E is the principal antioxidant in cell membranes, it may protect transport mechanisms across membranes from oxidative damage induced by heat stress.

References:

Cherian, G., et al. 1996. Dietary oils with added tocopherols: effects on egg or tissue tocopherols, fatty acids and oxidative stability. Poult. Sci. 75(3):423-31.
Jiang, Y.H., et al. 1994. Alpha-tocopherol, beta-carotene, and retinol enrichment of chicken eggs. Poult. Sci. 73:1137.
Meluzzi, A., et al. 2000. Effects of dietary vitamin E on the quality of table eggs enriched with n-3 long-chain fatty acids. Poult. Sci. 79:539.
Scheideler, S. 1998. Vitamin E and heat stress in layers. Proc. 1998 Multi-State Poultry Meeting.
Surai P.F., et al. 2000. Designer egg evaluation in a controlled trial. Eur. J. Clin. Nutr. 54:298.
Whitehead, C.C. 1998. The influence of vitamins on the performance and health status of laying hens and turkeys. Proc. 1998 Multi-State Poultry Meeting.
Yoshizawa, Y, et al. 1991. Effects of vitamin E-enriched egg yolk on lipid peroxidation, hemolysis and serum lipid concentration in young and old rats. J. Nutr. Sci. Vitaminol. 37:213.