NAVLE (North American Veterinary Licensing Examination) · USA / Canada · International Council for Veterinary Assessment (ICVA); scored by NBME, delivered by Prometric
Original practice questions written to the published syllabus · not past papersWater and air hygiene, waste and carcass disposal, disinfection, pollution and climate change as they affect animal and human health.
In the exams: NAVLE environmental health and safety 5%
NAVLE and BCSE (North America)
Environmental health and safety (about 5% of NAVLE): occupational hazards such as hydrogen sulphide in manure pits, zoonoses from laboratory and farm animals, needlestick and sharps handling, disinfectant selection for parvovirus and other resistant agents, carcass disposal for anthrax and reportable disease, rodenticide exposure, and heat stress in cattle and horses.
How our questions for NAVLE spread across the units of Environment & Environmental Hygiene. Difficulty: 8 easy, 24 medium, 4 hard.
| Air hygiene | 9 | |
| Disinfection | 8 | |
| Water hygiene | 5 | |
| Carcass disposal | 4 | |
| Experimental animal medicine | 3 | |
| Waste management on livestock farms | 2 | |
| Biomedical waste | 2 | |
| Environmental pollution | 2 | |
| Climate change and livestock | 1 |
Choose an answer, then open the working. Each explanation says why the right answer is right and why the others are not.
Feedlot steers develop blindness, head pressing and recumbency in a hot spell. The diet is standard, but a new well supplies drinking water. Which water analysis is most relevant?
C. Sulphate concentration, for sulphur-associated polioencephalomalacia
High-sulphate water adds to dietary sulphur; rumen reduction to hydrogen sulphide causes polioencephalomalacia, with blindness and head pressing, and intake (and risk) rises in hot weather. Fluorosis is chronic and affects teeth and bone, not acute neurology. Hardness mainly scales pipes; turbidity does not measure algal toxins.
Further reading: Merck Veterinary Manual, Polioencephalomalacia; NRC water quality guidance
Why does the smell of hydrogen sulphide give a poor warning of danger in a slurry building?
D. High concentrations paralyse the sense of smell
H2S smells of rotten eggs at low concentration, but higher concentrations cause olfactory paralysis, so the odour disappears as the danger rises. It is heavier than air and collects low down, in pits and at animal level.
Further reading: Occupational safety guidance on slurry gases
Why does high atmospheric ammonia increase respiratory disease in housed pigs and poultry?
A. It damages the mucociliary escalator, so inhaled pathogens are cleared less well
Ammonia irritates and damages the respiratory epithelium and slows ciliary clearance, so organisms such as Mycoplasma and Pasteurella establish more easily. It is a chemical irritant, not an infectious agent, and does not neutralise antibodies.
Further reading: Wathes & Charles, Livestock Housing
Which practice is the commonest cause of needlestick injuries in veterinary clinics and should be avoided?
C. Recapping used needles by hand
Recapping by hand is a major cause of needlestick injury; the used needle should go straight into a sharps container placed at the point of use. The other practices reduce injuries.
Further reading: Occupational safety guidance for veterinary practice
How many mL of 5% sodium hypochlorite solution are needed to make 10 L of a solution containing 200 ppm available chlorine?
D. 40 mL
5% = 50,000 ppm. C1V1 = C2V2: 50,000 × V1 = 200 × 10,000 mL, so V1 = 40 mL. 4 mL treats 5% as 500,000 ppm; 400 mL treats 5% as 5,000 ppm (a factor-of-ten slip); 20 mL halves the target.
Further reading: Standard dilution arithmetic
Culicoides midges, vectors of bluetongue virus, are best reduced on a farm by:
D. Housing animals at dusk and dawn in the vector season and reducing wet breeding sites
Culicoides breed in wet, organic-rich mud and dung and are most active at dusk and dawn; housing at those times and managing breeding sites reduces biting. Formaldehyde fumigation or water additives do not affect outdoor midge populations.
Further reading: Bluetongue control guidance
Excretion of macrocyclic lactone parasiticides in dung is an environmental concern mainly because:
D. Residues harm dung beetles and other dung fauna, slowing dung breakdown
Macrocyclic lactone residues in dung are toxic to dung-breeding insects, especially some beetles and flies, which slows dung degradation on pasture. They do not produce toxic gas or raise nitrate.
Further reading: Veterinary parasitology and ecotoxicology literature
Which laboratory species, like primates, requires dietary vitamin C because it cannot synthesise it?
D. Guinea pig
Guinea pigs lack L-gulonolactone oxidase and develop scurvy without dietary vitamin C. Rats, mice and rabbits synthesise their own.
Further reading: Laboratory animal medicine texts
Ten here, 36 in the app. The Laisha app has every practice question we have written to NAVLE in this subject, marked as you go, with timed papers, a jump-to-unanswered list and a certificate when you pass at 70 per cent.
Free for ten days, then one subscription of US$10 a month. We would rather say so here than have you find it later.
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