Module 9 unit 2

Question 1

Why do you suspect a toxicological problem

Answer 1

ü The calves are from different sources ie different genetics and rearing ü Signs developed within two weeks of arrival in new environment
ü Multiple animals displaying similar signs
ü Evidence of exposure to a known toxic agent

Question 2

What is acute exposure

Answer 2

happened in a short period of time

Question 3

What symptoms does acute haemorrhagic syndrome

Answer 3

•   Pale mucous membranes
•   Evidence of bleeding (into skin, faeces & urine)
•   Jaundice
•   Increased susceptibility to infection
•   Weakness and failure to thrive

Question 4

What happens when the bone marrow die

Answer 4

•   Death of bone marrow precursors (shortlived cell lines most affected) ->
•   White cell depletion –> increased susceptibility to infection
•   Platelet depletion –> bleeding and anaemia
•   Red blood cell depletion –> anaemia

Question 5

What may the cause of the bone marrow toxin

Answer 5

ptaquiloside

Question 6

What does the chronic exposure of the bracken fern?

Answer 6

•   Intermittent blood in urine

*   Anaemia and ultimately death

Question 7

What are the effect of ptaquiloside

Answer 7

carcinogenic(potential to cause cancer) to bladder cells
• Presumed mechanism of action: long term low level exposure to ptaquiloside leads to alteration to DNA
•  Bladder cancer with ulceration and bleeding (because it affect the lining of the cell in the bladder)

Question 8

What are the factors that contribute to the acute form toxicity

Answer 8

• increased exposure leads to increased risk:
  •  Usually requires grazing of pasture containing bracken fern for at least 10 days.
  •  Increased palatability in Spring (young, tender fronds).
  •  Increased risk when pasture is scarce eg during drought
  •  Newly introduced and young animals likely to consume more bracken hence have greater exposure
  •  Slashing, ploughing or burning increase regrowth and increases palatability and hence exposure

Question 9

What causes a chronic form of the symptoms from ptaquiloside

Answer 9

long term, low level exposure leads to development of bladder lesions

Question 10

Why are other species not affected

Answer 10

•  Rare because other herbivores are unlikely to eat bracken (ie reduced exposure, due to grazing behaviour)

Question 11

What effect it might have on horses?

Answer 11

•   Horses - signs of thiamine deficiency (Vitamin B1) “bracken staggers” due to nerve damage
•   Bracken fern also contains a thiaminase, that destroys ingested thiamine

•  Horses require a dietary source of thiamine

Question 12

Why does vitamin B(thiamine deficiency) not seen on cattle

Answer 12

•   Thiamine is not required in the ruminant diet, as it is synthesised by ruminal bacteria
•   ( ie ingested thiaminase cannot produce a deficiency state)

Question 13

what differences in toxic effects of bracken fern depend on

Answer 13

•  Exposure 
–  Time: acute vs chronic 
–  Dose: affected by 
•  Palatability  
•  Alternative fodder 
•  Pasture management 
•  Behaviour of animals 
•  Individual preference 
•  Species –  Differences in physiology and  metabolism

Question 14

Differences in toxic effects of bracken fern depend on an interplay of multiple determinants of health, namely:

Answer 14

• Toxicology • Welfare/management • Environment • Nutrition • Genetics