CattleII- Toxicology

Cattle A, B, C, D; soil and forage

hay cubes (horses), contaminated wheat, oatlage (baled wet in plastic bags), feed contaminated with "animal parts"

phosphorous deficient soils/ pica (South Africa, South America)

blocks the release of acetylcholine, inhibiting muscle contraction--> flaccid paralysis

• consumption of pre-formed toxin: toxin elaborated in feed prior to ingestion (protoxin converted to toxin in the GI tract)
• toxicoinfectious botulism: ingestion of BACTERIA (elaboration of toxin in gut)
• wound associated botulism: wound infected w/ bacteria then toxin production and absorbed systemically

progressive muscle weakness, drooping head carriage, tongue paralysis, dysphagia, increasing respiratory difficulty--> death

confinement, limit organism growth, antitoxin, supportive (ventilation)

• common to add urea to feed to increase nitrogen content--> rumen microflora use N to synthesize protein, controls feed spoilage
• poisoning occurs when animals gain access to large amounts/fed too much too rapidly

protein production from urea--> microbe assimilate NH3 and release amino acids-->rumen urease hydrolyzes urea to free NH3-->  rapidity of NH3 released and rumen pH determines toxicity (gradually increasing urea may be tolerated)

normally urea converted to AA by microbes; release of NH3 and NH4+, rapid breakdown of urea--> rumen becomes alkaline--> animal not acclimated, leads to high levels of free NH3--> readily absorbed from alkaline rumen--> NH in liver re-converted to urea (usually urinated, saliva,etc); when overwhelmed, inc blood NH3, systemic lactic acidosis

pH where 50% is ionized

NH3; NH4+

lactic acidosis, hyperkalemia

bloating, odontoprisis/ bruxism (grinding teeth), weakness/ recumbency, salivation, hypersensitivity, aggression, labored respiration, convulsions/ tetany, death

indigestion, diarrhea, splashy rumen

• hx of NPN (nonprotein nitrogen) feed supplement, rumen pH > 8 suggestive, compatible history/ signs, systemic metabolic acidosis, blood ammonia >2mg/dL
• save sample of offending feed for analysis

• lower rumen pH- VINEGAR
• cool rumen- COLD WATER
• rumen lavage +/- rumenotomy
• treat metabolic acidosis- SODIUM BICARB

ammoniated feed toxicity

trembling, muscle twitching, wild stampeding, salivation, convulsions, death

in cattle fed ammoniated high-quality hay, silage, molasses, and protein blocks is thought to be caused by formation of 4-methylimidazole (4-MI) through the action of NH3 on soluble carbohydrates (reducing sugars) in these feedstuffs. Cattle fed dietary components containing 4-MI develop a syndrome known as the “bovine bonkers syndrome". Because nursing calves are affected, the toxic principle apparently is excreted in milk

urease is normally present in the functional rumen after 50 days of age

remove ammoniated feed, add grain/molasses, laxatives, anti-seizure drugs

high sodium diet (feed or water)--> sodium accumulation intracellularly in brain--> decreased Na+ transport and glycolysis--> CNS depression, encephalopathy

hypernatremia--> intracellular Na+ accumulation in brain--> thirst--> unlimited access to fresh water--> intracellular water accumulation--> CNS edema, increased intracellular pressure--> acute encephalopathy

Na+ion not rapidly equilibrated b/w blood and CSF, increases over time (days), but when re-exposed to H2O, CNS gradient rapidly draws water into the cells

muco-hemorrhagic diarrhea, colic, grinding teeth (bruxism), nystagmus, aggression, blindness, star gazing, seizures, head pressing, death

eosinophilic meningoencephalitis, cerebrocortical necrosis, polioencephalomalacia

• CSF and Serum Na+ >160mEq/L
• CSF: Serum Na+ > 1
• hemolysis, hemoglbinuria

restrict water intake to 50% or less of normal for several days, slow IV infusion of normal or hypertonic saline (oral rehydration is possible, but it is slow and labor intensive)

improved feed efficiency, control coccidiosis, growth promotion, Johne's dz treatment/ prevention

horses

• acute: diarrhea, depression, anorexia, apprehensiveness, dyspnea, rear limb ataxia, death
• sublethal or chronic: decreased appetite, heart failure, jugular pulses, murmurs, tachycardia, elevated cTnI

cause altered balance of Na+, K+, and Ca2+, in cells, leading to death of myofibers

edematous lungs, pleural effusion, cardiac and skeletal muscle necrosis (white areas), skeletal muscle may appear normal acutely

• vacuolar degeneration of myocardium
• focal areas of skeletal muscle degeneration and fibrosis

calcium phosphate; blood flow; anaerobic infection

monensin toxicity, nutritional myopathy (selenium), Cassia occidentalis (senna), white snakeroot, Vetch

remove incriminating feed, administer activated charcoal, laxatives, supplemental vit E and selenium

conditions that stress the plant, esp drought [most nitrate accumulation is in the stem or lower parts of plant]

[30min-4hr post-ingestion] anxiety, polypnea, dyspnea, rapid weak pulse, exercise intolerance, cyanotic MMs, death in <24hr

• appearance of "chocolate blood"- methemoglobinuria
• clinical signs

methylene blue- reduces Fe3+ to Fe2+

sorghum, sudan grass, birdfoot trefoil [leaves and stems!] [more with high nitrogen fertilizers!]

cyanide interferes with cellular cytochrome oxidase, shutting down electron transport--> oxygen use by cell is inhibited--> cells become anoxic (even tho blood has oxygen)--> cells with great conc of cytochrome oxidase (cardiac muscles and brain) are rapidly affected

found dead, excitement/ muscle tremors, bright red MMs, polypnea, dyspnea, lacrimation, salivation, defecation, urination, convulsions

smell of bitter almond in rumen+ Hx of sudden death and exposure to CN containing plants

usually they're dead BUT supply thiosulfate (body forms thiocyanate, which is excreted by kidney)

lead poisoning; batteries, caulking, solder, linoleum, bird shot, oil

chronic- lead is accumulated over time, animals need not ingest a toxic dose to develop clinical signs

RBCs, muscle, bone; food safety

lead inhibits delta-aminolevulinic acid dehydrase, causing increased levels of trans-ALA--> interferes with many enzyme systems---> increased RBC fragility--> decreased energy metabolism by brain--> encephalopathy

DORSOMEDIAL STRABISMUS, anorexia, depression, rumen stasis, grinding teeth, head pressing, central blindness, spastic eyelids, convulsions

cerebral edema, polioencephalomalacia, damage to cerebral microvasculature

• calcium EDTA "Versenate"- lead chelator
• DMSA
• thiamine
• +/- rumenotomy

lead poisoning, Vit A deficiency, polioencephalomalacia/ cerebrocortical necrosis, Na+ toxicity/ water intox

Cu: Molybdenum

sheep

anemia, lethargy, anorexia, weakness, trembling, icterus, hemoglobinuria, death

• blood fails to clot, hemolytic plasma, yellow friable liver, dark kidneys, enlarged spleen, icterus, dark urine in bladder
• rhodamine, Rubeanic acid + stains of liver

ammonium molybdate, sodium thiosulfate, ammonium tetrathiol molybdate, new methylene blue, D-penacillamine, supportive care

copper poisoning, salt poisoning/water intoxication