L7: Musculoskeletal Toxicity (Martyniuk)

Question 1

Common toxins affecting the MS system

Answer 1

Myopathy: gossypol
Lameness: 
Ergot/fescue
Selenium
Sorghum
Vitamin D overdose

Question 2

Phenoxyacetic acid herbicides chars.

Answer 2

• Ex: Scott’s Weed and Feed
• low toxicity in most animals (exception: Silvex, which is very toxic in dogs)
• affected animals usually exposed to concentrate or predisposed through kidney damage or genetics
• plant growth regulator

Question 3

Phenoxyacetic acid herbicides MOA

Answer 3

• involves uncoupling of oxidative phosphorylation
• may directly act on dog muscle
• may increase nitrate and cyanogenic glycoside concentrations in some toxic plants

Question 4

Symptoms of Phenoxyacetic acid herbicides

Answer 4

• GI effects: v/d, oral/GI ulcers
• Muscle effects: rigid skeletal m, ataxia, weakness, seizures, rumen atony
• Renal tubular degeneration
• Hepatic necrosis

Question 5

Dx of Phenoxyacetic acid herbicides

Answer 5

oral and GI ulcers
Enteritis, rumen stasis
Congestion of kidney/liver
Hyperemia of lymph nodes
Clin path (liver damage)
Serum, urine analysis

Question 6

Tx of Phenoxyacetic acid herbicides

Answer 6

• GI (emesis, lavage) or dermal (bath) decon
• activated charcoal/cathartic
• ion-trapping to enhance excretion (sodium bicarb if kidneys normal)
• prognosis good for treated animals

Question 7

Ergot alkaloids chars.

Answer 7

• produced in small grains by Claviceps purpurea; replaces seeds with sclerotia that look like mouse droppings
• fescue infection not detectable by naked ey
• develop in cool, wet spring followed by hot summer

Question 8

Ergot alkaloids MOA

Answer 8

• alkaloids are DA agonists and serotonin agonists which produce hallucinations
• activity at DA receptors in pituitary lead to dec. prolactin secretion
• smooth m. contraction –> alpha-adrenergic antagonist activity –> abortion, ischemia

Question 9

symptoms of ergotism in cattle

Answer 9

• “Summer Slump”: reduced feed intake, weight gain, heat tolerance, retain winter coat (due to vasoconstriction and not being able to regulate body temp.)
• Necrotizing ergotism –> lameness**, gangrene
• Fat necrosis
• poor repro performance

Question 10

Symptoms of ergotism in horses

Answer 10

abortion (due to DA effect on prolactin)
weak foals
prolonged gestation

Question 11

Symptoms of ergotism in pigs

Answer 11

infertility
early parturition
dec. milk production (due to DA effect on prolactin)

Question 12

Dx/Tx of ergotism

Answer 12

Dx: evidence of sclerotia in feed, fescue in forage, chem. analysis of feed/forage
Tx: remove source, prevent 2ary infections. Metoclopromide and Domperidone (DA antagonists) increase prolactin secretion and normalize gestation in mares

Question 13

Ionophores chars.

Answer 13

compounds that form lipid soluble complexes with cations

• facilitate specific ionic transport across membranes
• used as antibiotic or to improve efficiency of milk production
• monogastrics and horses most susceptible to toxicity

Question 14

MOA of ionophores

Answer 14

• increase intracellular Na and Ca –> mitochondrial swelling + cell death, esp. in muscle
• usually result of feed-mixing errors

Question 15

what animal is LEAST susceptible to ionophore toxicity?

Answer 15

poultry

Question 16

Symptoms of Ionophore toxicity

Answer 16

• anorexia common symptom**
• Horses: colic, profuse sweating on flanks, tachycardia
• Cattle: diarrhea, resp. difficulty, colic, tachycardia
• Poultry: down with limbs stretched out
• Dog: posterior paresis and paralysis with laslocid
• Cats: polyneuropathy

Question 17

Dx of Ionophore toxicity

Answer 17

• increased m. enzymes and myoglobinuria
• elevated AST, CK, LDH, Alkaline phosphatase, BUN, bilirubin
• dec. K and Ca
• chem. analysis of feeds, liver
• rule out other causes of colic
• necropsy: very pale m. tissue

Question 18

Tx of ionophore toxicity

Answer 18

• No antidote
• feed change, supportive therapy
• recovered animals may die later due to exercise intolerance