Tox Exam 2 Feed & Water Related Toxicants Flashcards
What is the most commonly used non-protein nitrogen (NPN)?
urea
it is also the most toxic one
Explain MOA of urease.
urease breaks down urea into ammonia (NH3) and CO2
Urease is found in ______.
rumen microflora
What species are susceptible to NPN toxicity.
cattle and horses
Optimal temp and pH for urease activity?
temp optimum=49* C
pH optimum=7.7-8.0
peak ammonia levels are 1/2-2 hrs post ingestion
T/F Alkaline pH enhances hydrolysis of urea by urease.
TRUE–this is bc urea is a weak base
T/F Animals less than 1 yr are more sensitive.
TRUE–but very young animals–3-6 wks are tolerant
T/F Animals who are routinely exposed to NPN have a lower toxic dose.
FALSE–animals who are preconditioned to NPN are more tolerant
What factors increase NPN toxicity?
fasting, dehydration or low water intake, hepatic insufficiency, diet low in carb (E) and protein but high in fiber, feeds rich in urease (soybeans), stress, increased rumen temp and pH
ADME of NPN?
A=non-ionized ammonia is absorbed–ionized ammonia is NOT absorbed
D=non-ionized ammonia crosses the cell membranes, BBB and placenta
M=non-ionized ammonia converted by liver to urea; too much ammonia (> liver capacity)–>hyperammonemia
E=urea excreted in urine–or recycled in saliva of ruminants
pH around 5-6.5 ammonia will be in ______ form?
ionized
pH around 8-9 ammonia will be in _______ form?
non-ionized
Is it preferred for ammonia to be in non-ionized or ionized form in the rumen?
ionized! want it to stay in the rumen to allow microbes to convert it to protein–do not want it absorbed systemically–which leads to increased blood ammonia levels and toxicity
Describe how microbes in the rumen utilize urea.
Use urease to convert urea into ammonia. Ammonia aminates ketoacids (from soluble carbs) to amino acids. These amino acids form bacterial protein. Bacterial protein can then be converted into animal protein.
MOA of ammonia?
Inhibits citric acid cycle–lack of energy, decreased cellular respiration, tissue damage.
T/F Toxicity of urea is actually due to ammonia; urea is harmless.
TRUE!
What is the cause of death d/t urea poisoning?
respiratory or cardiac failure
Onset of clinical signs d/t urea poisoning?
rapid onset–30 mins to 3 hrs
convulsions and death w/in 1-2 hrs
Clinical signs of urea poisoning?
restlessness, aggression, muscle tremors, salivation, teeth grinding, colic, sternal recumbency while standing on hind limbs, bloat, rumen stasis, usually NO D+, saw horse stance, excitable, hallucinations
Changes seen in blood due to urea poisoning?
increased blood ammonia, anaerobic glycolysis, blood lactate, metabolic acidosis, blood glucose, BUN, serum K & P, transaminases, PCV
Pathology of urea poisoning?
no characteristic lesions
congestion and degeneration of liver/kidneys
dead animals extremely bloated
ammonia odor and rumen alkalotic
T/F Postmortem exam very helpful in diagnosing urea poisoning.
FALSE–not helpful–only see bloat and that rumen alkalotic (greater than 7.5 pH)
Specimens used for the diagnosis of urea poisoning?
feed for urea and blood, rumen fluid, vitreous for ammonia
Differential diagnosis for urea poisoning?
Agents which cause colic–> caustics, inorganic arsenic–generally cause D+ (often bloody) & no CNS signs
Lead, metaldehyde, CH pesticides–no abnormal posture, jumping, maniacal behavior in urea as in CH px
Organophosphates–cause parasympathomimetic signs & respond to atropine therapy
Grain engorgement, nitrate px, enterotoxemia, cyanide px–differentiate by necropsy & lab tests
Prognosis for urea poisoning?
Much better if animal is urinating, if animal ceases to urinate then bad prognosis bc unable to excrete urea.
Treatment of urea poisoning?
Relieve bloat first. Acetic acid 5% or vinegar to cattle, sheep, goats followed by large amounts of cold water.
Symptomatic–>normal saline for dehydration, Na bicarb IV for acidosis, rumenotomy