Heavy metals: Selenium Dr. Shokry

Question 1

Most common source of selenium toxicosis

Answer 1

Cattle, sheep & horses may graze Seleniferous plants

Swine & poultry may eat grains grown on selenium rich soil

Question 2

Selenium deficiency dz

Answer 2

White muscle dz (WMD) or nutritional muscle dystrophy (NMD)
in lambs but also seen in calves & foals

Hepatosis dietetica in young pigs

exudative diathesis in chicks

nutritional pancreatic atrophy in chickens

porcine stress syndrome in pigs

Question 4

requirements for selenium

Answer 4

0.1 mg/kg depends on Vit E

Question 5

what are Se indicator plants (obligate accumulators)

Answer 5

• Astragalus* (locoweed, milk vetch)
• Stanleya* (prince’s plume)
• Oonopsis* (golden wood)
• Xylorrhiza* (woody aster)

Question 6

which of the 3 types of accumulator plants are most commonly seen in selenium toxicosis

Obligate

Facultative

Passive

Examples?

Answer 6

Passive - they can accumulate enough to be toxic but not enough to be really unpalatable

crop plants such as corn, wheat, oats, barley, grass & hay and others

Question 7

Properties of selenium

Answer 7

essential trace element

3 oxidation states: selenate (+6), selenite (+4) & selenide (-2)

chemical & physical propeties similar to sulfur & arsenic

antioxidant - is a component of glutathione peroxidase

Question 8

why is the fact that selenium has properties similar to sulfer & arsenic important

Answer 8

because it explains how Se can replace -Sh groups in proteins like hair creating changes in hair coat seen in toxicosis

Organic arsenic can be used to enhance elimination of selenium in tx of toxicosis

Question 9

toxicity of selenium

Answer 9

organic selenium in plants > selenate or selenite > selenide > synthetic organoselenium compounds

toxicity reduced by high protein diet & incr Cu (binds to Se)

Question 10

MoA of selenium toxicosis

Answer 10

Acute: respiratory signs due to pulmonary hemorrhage/pulmonary edema due to damage to pulmonary capillaries

Oral: GI signs

Subacute: combo of acute & chronic signs has been called “blind staggers” in cattle by ranchers

+ in swine can get posterior paralysis

Chronic: hair & hoof changes seen, “alkali disease” in cattle, “bobtail disease” in horses due to loss of tail/mane hair

Question 11

Best sample (antemortem) to dx selenium toxicosis

(postmortem)

Answer 11

Blood levels of Se or glutathione peroxidase activity

hoof (wash hoof to remove soil) & hair

Question 12

Tx for Se toxicosis

Px

Answer 12

no specific antidote/chelator

supportive/symptomatic tx

Acute toxicosis: Poor because animals die quickly