When vitamin E deficiency is accompanied by a sulfur amino acid deficiency, chicks show a severe nutritional muscular dystrophy, especially of breast muscle, at about four weeks of age. Cystine is likewise effective in preventing nutritional muscular dystrophy in vitamin E-deficient chicks. Cystine, however, is apparently ineffective in preventing the dystrophic condition in other animals. Although vitamin E and selenium are generally both highly effective in preventing exudative diathesis, selenium is only partially effective in protecting against muscular dystrophy in chicks when added in the presence of a low level of dietary vitamin E. Much larger quantities of selenium are required to reduce the incidence of dystrophy in chicks receiving a vitamin E-deficient diet low in methionine and cystine (Scott et al., 1982).
Prolonged vitamin E deficiency can result in reproductive failure and permanent sterility. Vitamin E has been shown to be essential for normal hatchability (Wilson, 1997). Hatchability of eggs from vitamin E-deficient hens is reduced (NRC, 1994), and embryonic mortality may be high during the first four days of incubation and during later stages as a result of circulatory failure. A vitamin E inadequacy caused an increase in embryo mortality during the last week of incubation in White Leghorns and during the second and third weeks of incubation in Rhode Island Reds (Leeson et al., 1979). Vitamin E showed a protective effect against a decrease in hatchability, and dietary vitamin E concentration was positively correlated with the hatching percentage (r = 0.74) in the first week of an experiment (Tobias et al., 1992).
The effect of vitamin E supplementation on egg production in physiologic conditions is often negligible (Hossain et al., 1998). Nevertheless, in some stress conditions, vitamin E is considered to have a protective effect against an egg production decline. The depression in egg production in laying hens brought about by heat stress was partially prevented by dietary supplementation with vitamin E (Utomo et al., 1994). Evidence was also obtained that the mechanism might involve a restoration of the supply in the circulation of egg yolk precursors, particularly vitellogenin. A larger-scale experiment was carried out in which hens were housed in two climatically controlled houses and exposed to chronic heat stress of 32†C (90†F) from 24 to 28 or 32 to 36 weeks. They were fed diets containing 10, 125 or 500 mg vitamin E per kg (4.5, 56.8 or 227.3 mg per lb) from point of lay and egg production characteristics and feed intake were measured up to 40 weeks. Egg production was severely depressed by the stress but over both periods the diet containing 500 mg per kg (227.3 mg per lb) gave 7% better production than the diet with 10 mg per kg (4.5 mg per lb). The diet containing 125 mg per kg (56.8 mg per lb) gave immediate results (Bollengier-Lee et al., 1998). When flaxseed was fed to laying hens, vitamin E at 50 IU per kg (22.7 IU per lb) significantly improved egg production compared to 27 IU per kg (12.3 IU per lb) (Scheideler and Froning, 1996).
The association between vitamin E deficiency and decreased fertilizing capacity of cockerel's spermatozoa was established more than 30 years ago (Surai, 1999). Vitamin E, by acting as a lipid-soluble antioxidant within membranes and hence preventing chain reactive oxidation (Niki, 1993), plays a key role in the protection of spermatozoan lipids against peroxidation.
B. Turkeys and Other Poultry Species
The combined deficiency of selenium and vitamin E in poults was found to produce a mild type of exudative diathesis (Creech et al., 1957). This condition was characterized by hemorrhaging on the inner margins of the thighs and caudal breast muscles; in contrast to the exudative diathesis of the selenium- and vitamin E-deficient chick, it involved only a mild edema. For ducklings exudative diathesis would appear to be more similar to that of the chick, i.e., green-colored edema of the subcutaneous tissues can be seen most frequently on the thigh with associated petechial hemorrhages of the thigh musculature (Combs and Combs, 1986). The appearance of exudative diathesis is infrequent and occurs in association with only the more severe cases of nutritional muscular dystrophy in deficient ducklings (Jager, 1977). For Japanese quail the combined deficiency of selenium and vitamin E has only produced exudative diathesis in some animals.
Degeneration of the smooth muscle of the gizzard is the most characteristic sign of selenium deficiency in the young turkey poult. In marked contrast to the skeletal myopathy of the vitamin E-deficient chick, gizzard myopathy in the selenium- and vitamin E-deficient poult is not prevented by dietary sulfur-containing amino acids but is completely prevented by supplements of selenium (Walter and Jensen, 1963). However, the dietary level of vitamin E affects the amount of selenium required for the prevention of the disorder. It was necessary to use a basal diet low in methionine and vitamin E, as well as selenium, to produce gizzard myopathy experimentally. Muscular dystrophy in ducklings is characterized by degeneration of the sarcoplasmic reticulum and mitochondria of the smooth muscle of the duodenum and gizzard, and is prevented with either vitamin E or selenium (Illus. 6).
