What are the two ways oxygen is transported in the body?
-freely dissolved
-bound to hemoglobin
Which plant is the cyanide-containing plant of interest?
Sorghum. spp
What is this plant and its characteristics?
Sorghum spp.
-coarse, drought-tolerant
-grows up to 6 feet tall
-flowering seed heads are yellow-purple
-johnson grass is roadside weed; sudan grass is cover crop
-young, wilted plants are most toxic
What is the mechanism of toxicity for Sorghum spp. and other cyanide-containing plants?
-affects ruminants
-cyanogenic glycoside is hydrolyzed to free hydrogen cyanide, which is absorbed from the GI tract
-free hydrogen cyanide combines with ferric iron to inhibit cytochrome oxidase in the mitochondria
-inhibition prevents dissociation of oxygen from hemoglobin
-aerobic cellular respiration cannot occur; causes cytotoxic anoxia in heart and brain
What are the clinical signs of Sorghum spp./cyanide-containing plant intoxication?
-dead cattle
-bright red/cherry red venous blood and mucus membranes***
-stress results in collapse and death
-tachypnea that progresses to dyspnea, open-mouth breathing, asphyxia, and death
-excitability/anxiety
-abortions/birth defects
-muscle tremors
-weakness
-convulsions
-coma
-excessive salivation
What smell is associated with Sorghum spp./cyanide-containing plant toxicity?
bitter almond smell of the ruminal contents
How is Sorghum spp. intoxication diagnosed?
-severe resp. difficulty with cherry red mucous membranes or sudden death + close proximity to cyanogenic plants
-testing of ruminal contents, other plant material, or liver for cyanide
-sodium picrate test; paper strip turns brick red
What is the treatment for Sorghum spp. intoxication?
-avoid stress
-sodium nitrite
-sodium thiosulfate
How is Sorghum spp. intoxication prevented?
-do not allow animals to graze near cyanogenic plants for 5-7 days after a frost
-do not allow animals to graze cyanide-containing forages until they are 18 to 24 inches tall or taller
-do not allow access to cyanide-containing shrubs or plants
What is this plant and its characteristics?
pigweed; Amaranthus spp.
-erect stem 30-150 cm tall with hairy stems
-ovate to lanceolate leaves
-densely crowded spikes of green flowers at tips of stem
What is this plant and its characteristics?
nightshade (Solanum spp.)
-herbs/shrubs with either simple or compound ovate to lanceolate leaves
-radially symmetrical flowers with 5 petals arranged in a 6 to 10 mm star
-smooth round fruits that turn black when ripe
-prefer disturbed soil
Which plants are nitrate-accumulating and of interest?
-pigweed
-nightshade
What is the mechanism of toxicity for nitrate-accumulating plants?
-affects ruminants
-nitrates are absorbed from the soil via plant roots and converted to nitrite
-nitrite oxidizes ferrous iron to ferric iron in hemoglobin, converting it to methemoglobin
-methemoglobin cannot accept oxygen, leading to systemic anoxia, clinical signs, and eventual death
What % of methemoglobin is need in the blood to cause clinical signs and death?
clinical signs: 20 to 40%
death: 80 to 90%
What are the clinical signs of nitrate-accumulating plant toxicity?
-dead cattle
-cyanotic/brown mucus membranes*
-dark/brown urine*
-chocolate-colored blood***
-tachycardia
-tachypnea/dyspnea
-weakness
-tremors
-ataxia
-convulsions
-abortions
How is nitrate-accumulating plant toxicity diagnosed?
-history of ingestion or proximity to nitrate-accumulating plants
-presence of cyanotic/brown mucus membranes with dark/brown urine and blood
-serum nitrate levels > 20 ppm
-aqueous humor nitrate levels > 30 ppm
-diphenylamine test to assess nitrate levels in forage
What is the treatment for nitrate-accumulating plant toxicity?
-avoid stress
-1% methylene blue
-oxygen therapy
-supportive care based on clinical signs
How is nitrate-accumulating plant toxicity prevented?
-test forage for nitrate accumulation
-do not feed forage if > 0.5% nitrate on a dry matter basis
What is the hemolytic plant of interest?
red maple
What is this plant and its characteristics?
red maple; Acer rubrum
-tree with characteristic 3-lobed leaves that turn red in fall
-helicopter seeds
-wilted and dry leaves are toxic
-bark is toxic
What is the mechanism of toxicity for red maple?
-affects horses
-toxins include pyrogallol, gallic acid, and tannins
-toxins cause oxidative damage to RBC membranes and hemoglobin
-damage results in methemoglobinemia, heinz body formation, intra- and extra-vascular hemolysis
-results are hypoxia and death
What are the clinical signs of red maple toxicity?
-acute hemolytic anemia***
-icterus
-cyanotic/brown mucous membranes
-chocolate-colored blood
-dark/brown urine
-weakness
-lethargy
-tachycardia
-tachypnea
-sudden death
-abortion
How is red maple toxicity diagnosed?
-presence of hemolytic anemia with heinz body formation
-horses that have access or proximity to wilted or dried red maple leaves
What is the treatment for red maple toxicity?
-blood transfusion
-intravenous fluid therapy
-methylene blue (NOT if Heinz bodies already present)
