Ionophores

Question 1

What are ionophores used for?

Answer 1

Anticoccidial in cattle, poultry, and goats

*also have an antibacterial effect that can be beneficial for the rumen –> growth promoter

Question 2

What is monensin approved for in the US?

Answer 2

to improve efficiency of milk production in dairy cattle

also approved for poultry

Question 3

T/F: Ionophores have a high lipid solubility

Answer 3

TRUE

They will form lipid soluble complexes with polar cations (Na, K, Ca, Mg) and then have the ability to transport across cellular membranes

Question 4

How are cattle and poultry exposed to ionophore toxicosis?

Answer 4

They would have to be overdosed in their additives - which is not very common

Question 5

What species is most susceptible to ionophore toxicosis?

Answer 5

Horses

accidental and malicious exposure

**MONENSIN

sheep and dogs have the potentially to be accidentally exposed as well

Question 6

What is the order of ionophore toxicosis susceptibility of poultry, horses, and cattle?

Answer 6

Most to least:

Horses
cattle
poultry

Question 7

T/F: Horses that ingest recommended levels of ionophores for cattle are not poisoned

Answer 7

TRUE

Question 8

Concurrent administration of what drugs will increase ionophore toxicosis?

Answer 8

Tiamulin - antimicrobial
Chloramphenicol- AB
Erthromycin- AB
Sulfonamides - AB
**these are all microsomal enzyme inhibitors

Cardiac glycosides - have a synergistic effect - ionophores are cardio toxic

Question 9

What is the difference in monensin absorption in ruminants vs monograstric animals?

Answer 9

Ruminants absorb only about 50%

Monogastric animals absorb 100%
slow elimination in horses - since it is excreted in bile and they lack a gallbladder slower metabolism

Question 10

T/F: Monensin will accumulate in tissues when animals receive high doses

Answer 10

FALSE

no tissue accumulation

Question 11

What metabolism process do ionophores undergo?

Answer 11

P-450 oxidative demethylation in the liver

**fast in ruminents

**slow in equine –> lowest oxidative demethylases

Question 12

What is the MOA of ionophores?

Answer 12

Disrupt transmembrane electrochemical gradients

1. attach to ions - increase intracellular Na
2. intracellular Ca increase (sequestered in the mitochondria)
3. Lack of energy all over peripheral tissues (skeletal muscle, cardiac muscle, kidneys)

Cell death due to homeostatic disruption
*catecholamine release - results in oxidation products and free radicals –> membrane damage

Question 13

What clinical signs are associated with monensin toxicosis in horses?

Answer 13

Acute onset and acute death

Anorexia, profuse sweating, colic, depression, incoordination, hyperventilation, tachycardia/arrythmias, prostration, death

Question 14

What clinical signs will be seen in cattle with ionophore toxicosis?

Answer 14

Anorexia, dhr, depression, labored breathing, ataxia, prostration, death

Question 15

What clinical signs will be seen in poulty with inonophore toxicosis?

Answer 15

Anorexia, dhr, ataxia on the knees and wings - leg directed outward, decreased egg production

Question 16

What clinical signs are associated with ionohore toxicosis in dogs?

Answer 16

Ataxia, muscle weakness in hind limbs, respiratory paralysis, dysuria, constipation, depression

Question 17

What lesions are associated with ionophore toxicosis?

Answer 17

Mainly cardiac muscle lesions in horses: pale cardiac muscles, white streaks of necrosis in the myocardium, and skeletal muscle lesions

Mainly skeletal muscle lesions in sheep, swine, and dogs

Both skeletal and cardiac muscle lesions in cattle and poultry

Question 18

What is the best sample to test if you suspect ionophore toxicosis?

Answer 18

FEED

other - GI contents, liver, feces

Question 19

What clin path abnormalities are expected with inonophore toxicity?

Answer 19

Increased: CK, AST, LDH, ALP

Decreased Ca and K during first 12 hours

Increased PCV

Question 20

What consequence will animals who survive ionophore toxicosis be faced with?

Answer 20

Sudden death due to scarring and fibrosis in the myocardium –> cardiac arrest

Question 21

What toxic plants may mimic skeletal damage seen from ionophore toxicosis?

Answer 21

Coffee senna (Senna occidentalis)
Coyotillo (karwinskia humboldtiana)
White snakeroot (Euratorium rugosum)

Question 22

What toxic plants can mimic the cardiotoxicity seen from ionophore toxicosis?

Answer 22

Oleander
Taxus spps
Milk weed
Vetch

Question 23

What is the treatment for ionophore toxicosis?

Answer 23

No specific antidote

remove medicated feed, activated charcoal/mineral oil/saline cathartics

Symptomatic tx: IVF, correct lytes, monitor cardiac function, vitamin E and Se (cattle and swine)

*horses should not be ridden or stressed for months after a toxic event

Question 24

What is the prognosis for ionophore toxicosis?

Answer 24

Depends on severity of damage

Horses that survive may suffer myocardial scaring and necrosis

Horses may not reach previous performance