Page 507 - Veterinary Toxicology, Basic and Clinical Principles, 3rd Edition

474 SECTION | V Metals and Micronutrients

VetBooks.ir and viability in rodent models (Kaur and Bansal, 2005; understand. The small difference between deficiency and
toxicity in terms of dietary intake makes the risk of acci-
Shalini and Bansal, 2007, 2005; Boitani and Puglisi,
dental selenium poisoning high. Many areas of the world
2008). If other species have similar effects, this could
negatively affect herd reproductive performance. In addi- have seleniferous soils that can cause poisoning via
tion, it must be noted that Se accumulates in the fetus at ingestion of natural forages grown on them. As there is
the expense of the dam (Puls, 1994). Thus, higher accu- no specific treatment for selenium toxicosis, it is critical
mulation of selenium in the fetus may result in abortions, that appropriate education be utilized in order to mini-
stillbirths or weak/lethargic calves. Yeager et al. (1998) mize the risks to the livestock industry.
reported a 7% abortion rate in a beef herd where cows Future research needs to address the mechanisms of
had selenium concentrations suggestive of chronic seleno- physiologic damage caused by both acute and chronic
sis and fetal hepatic selenium concentrations suggestive selenium poisoning with differing chemical forms of sele-
of toxicosis, but in a dosing study they only had one weak nium. With an understanding of the cellular mechanisms
calf born that died shortly after birth. Although terato- of selenium poisoning, more specific means of treatment
genic effects of selenium poisoning are well documented might be developed. In addition, a clearer understanding
in avian species, historical reports are all that are avail- of thresholds for chronic selenium poisoning is needed.
able for horses and sheep (Smith et al., 1936; Beath et al., With the knowledge that certain ruminal microbes can
1939). However, toxic plants in the environment may reduce various forms of selenium to nonabsorbable forms,
have also played roles. At least some of the adverse preventive use of these microbes in seleniferous areas to
effects on reproduction caused by excess selenium in prevent systemic accumulation and poisonings should be
ruminants are caused by interference with absorption and investigated.
retention of copper that results in copper deficiency.
Selenosis in poultry and other avian species has major REFERENCES
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