FAC28: Farm Animal Toxicology (Mycotoxins and Metals)

Question 1

At what point does chronic copper poisoning occur?

Answer 1

Chronic copper poisoning occurs after the liver’s capacity for lysosomal copper storage has been exceeded, resulting in the release of copper into the peripheral circulation causing intravascular haemolysis and jaundice

Question 2

What are the common mycotoxins?

Answer 2

Aflatoxin (aspergillus)

Deoxynivalenol (Fusarium)

Zearalenon (Fusarium)

T-2 Toxin (Fusarium)

Fumonisin (Fusarium)

Ochratoxin (Penicillium)

PR Toxin (Penicilium)

Ergots (Claviceps)

Question 3

Which plants contain aflatoxin?

Answer 3

Peanuts, Soybean, and cereals

Question 4

How do aflatoxins cause toxicity?

Answer 4

They are metabolised in the liver into epoxide, which binds macromolecules

Question 5

Which plants are commonly contaminated by zearalenone?

Answer 5

Maize, wheat, barley, and soy

Question 6

How does zearalenone cause toxicity?

Answer 6

It is a potent nonsteroidal oestrogen that binds to estradiol receptors on DNA then RNA synthesis leads to sings of oestrogenism

Question 7

Which plants are associated with fumonisin?

Answer 7

Cereal crops

Question 8

How does fumonisin cause toxicity?

Answer 8

It is structurally similar to sphingosine (found in myelin) and blocks synthesis of sphingolipid.

Causes pulmonary oedema in swine

Question 9

Which plants are associated with ergots?

Answer 9

Rye and other forage plants (fescues and ryegrasses)

Question 10

How doe ergots cause toxicity?

Answer 10

Causes vasoconstriction

• direct action on muscles or arterioles; repeat doses injure vascular endothelium
• Initially reduce blood flow causing complete stasis and terminal necrosis of extremities

Can cause stimulation of CNS followed by depression

Inhibits pituitary release of prolactin

Question 11

How do you prevent mycotoxin poisoning?

Answer 11

• Avoid contaminated feeds
• Investigate mycotoxin content of feeds
• Dilution of feedstuffs with non-contaminated feed
• Remove lightweight or broken grain
• Regular topping of affected pasture
• Addition of mycotoxin binders

Question 12

What are the common causes of copper poisoning?

Answer 12

• Fungicide/algicides
• Anthelmintics
• Dietary supplementation
• Poultry litter
• Molybdenum deficiency

Question 13

What are the common causes of lead poisoning?

Answer 13

• Paint
• Car batteries
• Gunshot
• Fishing weights
• Industrial waste

Question 14

Which breeds of sheep are highly susceptible to copper toxicity?

Answer 14

Bluefaced Leicester

North Ronaldsay

Texel

Suffolk

Question 15

Which breeds of sheep are not highly susceptible to copper toxicity?

Answer 15

Cheviots

Scottish Blackface

Question 16

At what concentration of copper is it considered subclinical copper toxicity? What is the highest concentration of copper at which it is considered full capacity for storage?

Answer 16

Subclinical liver damage @ ~8,000 umol/Kg DM

Capacity for copper storage exceeded at: ~15,000 umol/Kg DM

Question 17

How do you treat copper toxicity?

Answer 17

Supportive treatment with fluids

Low morbidity/high mortality

Question 18

How do you control against copper toxicity?

Answer 18

Remove sources of copper

Administer molybdate in feed

Question 19

What are some sources of lead?

Answer 19

Lead-based paint

Car batteries

Lead gunshot/fishing weights

Question 20

How does lead cause toxicity?

Answer 20

Lead ingested and absorbed in SI by Ca transport system.

• Interferes with various enzymes
• Replaces zinc as cofactor in some metabolic pathways
• Can inhibit haemoglobin and erythrocyte synthesis

Question 21

How do you treat lead toxicity?

Answer 21

• Remove source of lead
• Cathartic agents to increase defaecation (oral magnesium sulphate)
• Chelation (calcium disodium edetate)
• Thiamine may reduce CNS signs

Question 22

How does copper cause toxicity?

Answer 22

Circulatory copper causes intravascular haemolysis through a series of biochemical interactions with RBC membranes components

• Debris may block renal tubules and cause renal failure with accumulation of metabolites which are toxic to other tissues including the brain

Question 23

What are some stereotypical signs of copper toxicity?

Answer 23

Head pressing

Jaundice

Haemoglobinuria

Question 24

What is usually the cause of acute copper poisoning?

Answer 24

Usually follows gross overdosage of injectable or oral copper preparations used for prevention of deficiency syndromes and occurs when high circulatory copper concentrations overwhelm the hepatic capacity for removal and storage

Question 25

From where is lead excreted?

Answer 25

Bile, Milk and urine

Question 26

How does lead cause toxicity?

Answer 26

Lead is deposited in the liver and kidneys and is then redistributed to bone (particularly growth plates) and can lead to osteoporosis

Circulating lead is strongly bound to RBCs, increasing their fragility and suppressing haematopoiesis

In nervous tissue, lead binds to the endothelial cells of the brain capillaries, increasing their permeability and resulting in brain oedema.

Question 28

How does lead toxicity affect the fetus?

Answer 28

Lead readily crosses the placenta, causing foetal damage, teratogenesis, and abortion