Sheep infertility

In 1956 selenium was identified (123) as an essential micronutrient iu nutrition. In conjunction with vitamin E, selenium is effective iu the prevention of muscular dystrophy iu animals. Sodium selenite is adrninistered to prevent exudative diathesis iu chicks, a condition iu which fluid leaks out of the tissues white muscle disease iu sheep and infertility iu ewes (see Eeed ADDITIVES). Selenium lessens the iacidence of pneumonia iu lambs and of premature, weak, and stillborn calves controls hepatosis dietetica iu pigs and decreases muscular inflammation iu horses. White muscle disease, widespread iu sheep and cattle of the selenium-deficient areas of New Zealand and the United States, is insignificant iu high selenium soil areas. The supplementation of animal feeds with selenium was approved by the U.S. EDA iu 1974 (see Eeed additives). Much of selenium s metaboHc activity results from its involvement iu the selenoproteia enzyme, glutathione peroxidase. 

Data on safety have been obtained from in vitro as well as in vivo animal and human studies (see also Section 10.4). About 50 years ago, Australian farmers observed an infertility syndrome in sheep associated with the consumption of clover species (Bennets et al., 1946). The clover compounds shown to cause the infertility (genistein, daidzein, equol, biochanin A, formononetin) were members of the isoflavone family (Bradbury and White, 1951 Shutt and Braden, 1968), raising the question of whether soy might cause infertility in humans (see also Section 10.4.9). A variety of reports further supported adverse effects of isoflavones on animal reproductive systems (Santell et al., 1997 Flynn et al., 2000a,b). 

Isofavonoids have a substituent at C-3. Examples are genistein and for-mononetin (see Fig. 11.11, below). Isoflavones exert estrogenic activity in mammals, interfere with reproduction in birds, and may render farm animals infertile. For example, sheep feeding on isoflavonoid-containing Trifolium suh-terraneum suffer reduced lambing (Harborne, 1993). 

Daily oral administrations of 2 or 5 mg kg body weight heptachlor for 78-86 days to pigs, sheep, and rats induced hepatic necrosis. Results of animal tests show that chronic exposure to heptachlor or its epoxide metabolite adversely affects the liver, kidney, and red blood cells. There is evidence that heptachlor and heptachlor epoxide are associated with infertility and improper development of offspring. Animal studies have shown that females were less likely to become pregnant when both males and females were fed heptachlor. The incidence of liver carcinomas increased in rats receiving doses of approximately 1.2 mg kg day of either heptachlor or heptachlor epoxide. 

For example, the infertility syndrome called clover disease of sheep, occurring in the 1940s in Western Austraha, was caused by equol. The disease was manifested by a decrease of sheep gestation, frequent abortions and postnatal complications. Similar syndromes have been found in other animals. 

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