Module 9 unit 3

Question 1

What factors contribute to development of signs of toxicity

Answer 1

– Plant factors – Species factors
– Individual animal factors
•  Behaviour
•  Pharmacokinetics ( differences in absorption, metabolism or excretion)

Question 2

What causes phalaris poisoning

Answer 2

•  Causes sudden death in sheep when grazing young shoots

Question 3

Mechanism of Toxicity: Phalaris

Answer 3

•  Peracute ammonia toxicity •  Why does this happen?
Phalaris contains a toxin (unidentified) that inhibits a ruminant’s ability to metabolise nitrogen This leads to elevated ammonia levels in the blood and brain damage

Question 4

What plant factors contribute to development of signs of toxicity?

Answer 4

– Fresh shoots are most toxic because they contain higher nitrogen load
– Autumn, early winter is greatest risk period (and any period of higher grazing pressure)

Plants absorb soil nitrogen more efficiently after rain or when recovering from grazing pressure

Question 5

What animal factors contribute to development of signs of toxicity?

Answer 5

Livers of animals coming off pastures with low nitrogen load are less able to cope with high nitrogen pastures

Question 6

How does this understanding inform management of the risk of poisoning?

Answer 6

•  Avoid high grazing pressure at time of when phalaris is likely to be most toxic
– Fresh shoots are most toxic because they contain higher nitrogen load
– plants absorb soil nitrogen more efficiently after rain or when recovering from grazing pressure)

Question 7

How can you do with the management of phalaris pastures?

Answer 7

•   Increase nitrogen load in diet before introducing stock to phalaris pasture
•   Don’t overgraze when strip grazing (avoid grazing by hungry animals)
•   Don’t move nitrogen deprived animals onto spelled phalaris pasture