Field Tests for Toxicity in Animals

Field tests for toxicity are strychnine test, grunwald’s test (lead test), nitrate and nitrite test, cynide test, etc. done at field level for immediate diagnosis of toxicity.

Strychnine Test

• To 3 ml of filtered stomach contents in a test tube, add carefully 5 ml of concentrated sulfuric acid
• For a control, to 3ml of distilled water in another test tube add carefully 5ml concentrated sulfuring acid.
• To each tube drop a few crystals of potassium dichromate and thump gently
• Hold the tubes up in front of a light. Falling colored streams of tube; violet, red and orange from the falling crystals indicate strychnine.

Lead Test (Grunwald’s test)

• Take a small amount of scrapings from abomasum wall during postmortem examination.
• Add a few drops of concentrated nitric acid and heat very gently or air dry until dry, over heating causes blackness and makes it difficult to read.
• Add few drops of water. add couple of drops of 10% potassium iodide
• Positive for lead is indicated by a marked yellow colour.

Nitrate or Nitrite toxicity test

Reagent

• 0.5g of diphenylamine in 20ml of water. add sulfuric acid to make 100 ml. Cool and store in a brown colored bottle.
• For half strength add equal parts of the above mixture with 80% sulfuric acid.

Procedure

1. To test rumen fluid

• A drop of test solution is mixed with a drop of rumen fluid
• An intense blue colour with 10 seconds indicates a concentration of greater than 1% nitrate which is more than permissible level.

2. To test the fodder

• Put one drop of the test reagent on the freshly cut surface of a plant
• Green to blue colour reaction is a positive for nitrate.
• Green to blue colour with half strength solution indicates 2% of nitrate (Dangerous for animal al feed)

3. Nitrate test on silage and straw

• Use silage juice or put a small amount of water on the silage, stir, then squeeze the water out
• This juice should be filtered or centrifuged before using
• Add few drops of diphenylamine test solution
• Shades of green or blue colored are positive for nitrate
• Do not stir the mixture.

4. Nitrate in blood (The cooking field test)

• Take 2 samples of blood from the suspected animal (one sample of blood with anticoagulant and another without an anticoagulant). Usually blood containing a dangerous amount of nitrate will be a shade of chocolate colour – depending upon the concentration of nitrate.
• Draw a 3rd blood sample from healthy animla. These samples should be allows to clot. when this and sample (without the anticoagulant) from the suspected animal have clotted, these to two sample should be placed in bolling water bath for 45 minutes or longer or they should be autoclaved for 15 minutes at 15lb of pressure.
• After cooking and cooling, a nitrate blood clot should be a chocolate colour. It pulls away from the tube’s side. Its top surface should be convex (mounds up). Allow all tubes to cool before making final reading.

Cyanide Test

Reagent

• Sodium bicarbonate – 0.5gm
• Picric acid – 0.5gm
• Water – 100ml

Procedure

• Wet a strip of filter paper with the above mixture.
• Use dry or slightly damp filter paper for the test.
• The following will serve as test samples: fore stomach contents or ground plant material (suspected plants) or , on autopsy, finely diced pieces of the right half of the liver may be used mixed with enough water to make a slurry mixture.
• Place the material into a large tube or small bottle to 1/4 full. Add few drops of chloroform.
• Stopper the filter paper tightly in the top of the tube or bottle. incubate or keep in a warm place.
• Hydrocyanide gas causes violet colour on filter paper. Smaller amounts will cause pink to red colour.
• Observe frequently for any colour change, retain for 24 hrs before reporting negative.