final exam Flashcards
short pastern bone
P2-middle phalanx
coffin bone
P3-distal phalanx or pedal bone
gives shape, porous, light weight
navicular bone
distal sesamoid bone, non-weight bearing, acts as a fulcrum for the deep digital flexor tendon, source of lameness
hoof wall
keritinized tubular structure that has sensitive and insensitive laminae, grows from coronary band, weight bearing structure
coffin bone
connected to hoof wall via the sensitive/insensitive laminae and the white line
hoof sole
concave in shape, expands and contracts, bears weight on solid ground, 3/8-1/4 inches thick.
white line
junction of laminae from sole and wall
frog
tubular, keritinized, higher moisture content, absorbs shock, supports structure.
digital cushion
flexible tissue, interacts with frog, shock absorber, lateral spread, expansion, contraction
blood flow in hoof
hoof pumps venous blood to the heart, venous plexus, compression (lateral cartilage, coffin bone) forces blood up, blood enters the hoof when the foot is raised
hoof growth
occurs from coronary band down, growth rate correlated with age, nutrition, season, avg. growth rate is 1/4-3/8 inches per month
under-run heels
crushed heels, poor digital cushion, greater risk of tendon injury
contracted heels
frog cannot make contact with the ground, poor shock absorption, heel cannot expand
cracks
due to unbalanced hoof , environment or hot quality, may be superficial or deep
bruises
on the sole or wall of hoof, can lead to abscessing, may result from over-trimming, may be prevented with shoes or pads
abscesses
painful infection in hoof, may lead to acute lameness, many causes, remedied by pressure relief
thrush
bacterial infection of the frog, foul odor, thick black discharge, results from poor hoof care, diseased tissue may be cut away, killed by chemical agents
white line disease
fungal and/or bacterial infection of the white line, associated in wall separation that may lead to coffin bone rotation, must expose infected area to air
navicular disease
chronic degenerative disorder of navicular bursa and navicular bone, apparent on radiographs, can be managed but not cured
laminitis
painful inflammation of the sensitive laminae, , blood clots, edema in closed space, trauma to hoof, abscesses, may lead to shock
founder
separation of laminae that leads to rotation or sinking of the coffin bone-PAINFUL
ectoparasites
outside parasites, “bugs”
endoparasites
inside parasites, “worms”
black flies
small size, gray/black/brown, breeds in running water, worst in spring, cuts skin then laps blood, bleeding/crusts in bitten areas, use repellent to protect horses
stable flies
Medium size • Similar to housefly – Grayish brown – Feed on any warm-blooded animal • On horses, legs and belly – Worst in mid-late summer – Breed in manure/decaying plant material – Prevent with sanitation, covering compost piles (also silage bunks), insecticides
face fly
Adults: 1/4 inch long - Dull gray color, similar to a house fly - Feeds on mucus and the watery
secretions around the eyes, nose and mouth
- Host for Thelazia lacrymalis (eyeworm)
- Common in areas with cattle - Prevent with fly mask
deerflies
Medium size
• Slightly bigger than housefly • Black markings on wings
– Worst during summer – Breeds near water – Feeds on mammals, reptiles and birds – Painful bite, cuts skin then laps blood – Prevent with repellent, control difficult
horseflies
Large size
• Up to hummingbird size • Dark, color varies
– Breeds near water – Feeds on mammals, reptiles and birds – Painful bite, cuts skin then laps blood – Very disturbing to horses – Vector for equine infectious anemia (EIA) – Prevent with repellent, control difficult
Mosquitoes
– Sucks blood
– Feeds on many species
• Can cause allergic reactions in horses
– Vector for EEE, WEE, VEE, WNV – Breeds in water – Control by draining standing water, using
insecticides
– Prevent with repellent, don’t leave lights on near horses unless necessary
horn flies
1/2 to 1/3 the size of a house fly – Pierce the skin and suck blood – Scabs on midline area
• Horn fly biology
– Female lays eggs on fresh manure – Eggs hatch, pupate and emerge as flies – Adults stay close to host
• Becoming resistant to sprays
– Manure removal helpful
Lice
Small (2-3 mm long) – No wings, flat – Biting or sucking (different species)
• Suck blood • Chew on skin and secretions of host
– Lay eggs on hair close to skin
– Horse will look poorly groomed
• Infestation starts around head, neck, mane and tail, will spread over entire body
• Treat with topical insecticides
– Ivermectin for sucking lice
mites
Several species in horses – Sarcoptic, chorioptic and psoroptic – Very small – Extremely irritating
• Cause mange
– Spread by grooming implements and tack – Leads to hair loss – Identified under microscope from skin
scrapings
bots
Gastrophilus species
• G. nasalis, G. intestinalis, G. haemorrhoidalis
– Eggs laid on hair by botfly
• Flies do not bite
– Larvae emerge when horse’s mouth contacts the eggs
• Warmth • Moisture
– Larvae invade mouth tissues
• Migrate, molt and are swallowed • Larvae spend ~1 month in mouth Larvae attach to dorsal part of stomach
• Above the fluid line • Spend winter in the stomach
– Larvae release their hold and are passed in manure in late winter/early spring
– Pupate and mature to adult flies
bots clinical signs
Usually none, unless heavy burden – Can cause inflammation of staomach – Can cause colic when dewormed while
heavily infested
tapeworms
noplocephala species
• A. perfoliata, A. magna
• Small for tapeworms
– Adult worms attach near ileocecal junction – Not normally pathogenic – Heavy infestations can cause inflammation
of gut, overactive peristalsis and sometimes intussusception of ileum into cecum
tapeworm life cycle
Eggs shed in feces by infected horse – Eggs taken up by mites in soil – Eggs develop to infective cysticercoid
stage inside the mite – Horses ingest infected mites while grazing – New tapeworm develops – Species specific
• Only infects horses
– Life cycle requires mite
Ascarids (roundworms)
Parascaris equorum
– Large, white worm (6-8 inches or more) – Affects young horses up to 1 ½ years old – Causes pot-belly, anorexia, coughing
• Pneumonia
– Large masses can obstruct bile duct and
intestines
Ascarid life cycle
10-12, weeks, Infective larvae ingested in egg in soil – Larvae emerge, penetrate gut wall – Larvae migrate to liver – Larvae migrate to the lungs – Larvae develop and are coughed up – Larvae are swallowed and return to
intestinal tract
– Larvae develop into adult worms and begin producing eggs
threAscarid eggs remain viable in soil for years
• Although young horses are susceptible, immunity develops during yearling year
• Some horses that are not exposed to ascarids when young will get infections as adults
threadworms
Strongyloides westeri
– Passed from mare to foal in milk
• After colostrum
• Stimulated to move from mare’s tissue by parturition
– Free-living larvae can also penetrate skin
• Migrate through lungs, get coughed up and swallowed
– Adult stages live in small intestinean cause diarrhea, poor growth
• No longer believed to be the cause of “foal heat diarrhea
– Life cycle takes
pinworms
Pinworms
– Oxyuris species
• 0.8-1.3 cm in length
– Direct life cycle
• Fecal-oral transmission
• Spends most of its life in large intestine and anus
• 5-month life cycle
– Female worms migrate out of the anus and lay eggs on perianal skin
• In sticky fluid
Cause intense itching, tail-rubbing
• Rat tailed appearance
– Not usually harmful – Worst in late summer – Spread by grooming sponges, eggs on
pasture, eggs rubbed on objects
– Species-specific
• Children get pinworms from other children
large strongyles (bloodworms)
trongylus vulgaris, S. edentatus. S.
equinus– Once the leading cause of colic – Destructive worms that migrate to various
organs and damage tissues as they go
• Plug feeders – with teeth!
– Clinical signs
• Diarrhea • Depression • Gastrointestinal disturbances
damage done
– Cutting tissue and sucking blood – Poor overall condition – nutrient losses – Liver damage – Arterioles damaged
• Leads to reduced blood flow to the bowel • Blood clots in bowel
– Colic due to
• Decreased gut motility
– (Impaction)
• Blood clot episodes
large strongyle lifecycle
Direct life cycle – only horses involved – Infective larvae ingested by horse – Larvae penetrate intestinal wall – Larvae migrate to liver, molts (9 weeks) – Larvae encyst in right flank – Larvae excyst and migrate to colon – Mature to adult stage – Begin producing eggs
small strongyles
Cyathostomes – many species (> 50)
– Less harmful than large strongyles
• Smaller, takes smaller bites • No tissue migration beyond gut
– The focus of most adult equine parasite control programs today
– Very common in horses on pasture
– Clinical signs
• Colic, diarrhea, emaciation • Most horses have subclinical infections
small strongyle life cycle
Direct life cycle (similar to large strongyles)
• Without the tissue migration • Larvae on pasture
– Horse ingests infective larvae – Larvae develop in large colon – Encyst to emerge later – Excyst to develop into adult worms – Mass excystation causes damage to gut
wall
• Diarrhea, colic, anorexia, emaciationSmall strongyle excystation
– Survival strategy for overwintering – Triggered by
• Favorable season • Reduced worm burden in gut • Deworming
– Some dewormers target the encysted stage to prevent this
• Effectiveness of these drugs in doubt
parasite risk factors associated with housing
Pastures
– Nature’s most perfect home for horses and parasites
• Stalls
– Not a good environment for small strongyles
– Ascarid eggs can stick to floors, walls and buckets
Dirt paddocks
– Not a good environment for small strongyles
– Ascarid eggs can persist in soil for years
• Traveling horses bring their parasites with them
– Mares with foals at side – Shared paddocks – Trail camp sites
parasite risk by age
Foals – ascarids, threadworms, small strongyles, bots
• Yearlings to 3-year-olds - small strongyles, bots tapeworms
• 4+ years – as horses mature, they usually become more resistant to small strongyles
– A few will not – High egg shedders
anthelmintics (dewormers)
Most modern dewormers are considered to be “broad spectrum”
– Control multiple species of parasites
• One is specialized
– Praziquantel for tapeworms – Sold in combination with other drugs
• Ivermectin moxidectin (Quest) for bots, but are also broad spectrum
Most modern dewormers have been on the market for 15-40+ years
• Drug resistance has been reported for many species of parasite
– Small strongyles– Ascarids
• Labels do not reflect current state of drug resistance trends
fenbendazole (panacur, safeguard)
Broad-spectrum (including ascarids)
• Not effective against bots or tapeworms
– Active against parasites in gut (not tissues) – Wide margin of safety – Fenbendazole Powerpac (2x dose for 5
days)
• All of the above, plus encysted small strongyles - according to label
• Expensive
pyrantel (strongid)
Broad-spectrum (not bots)
• Kills tapeworms at 2x dose
– Active against parasites in gut (not tissues)
– Sold in paste (P) and pelleted form (C)
• Strongid C daily dewormer
– Wide margin of safety
macrocyclic lactones
Ivermectin
• Broad-spectrum, including bots, but not tapes • Wide margin of safety
Moxidectin (Quest)
Broad-spectrum, including bots, but not tapes • Effective against encysted small strongyles (?) • Narrower margin of safety • Can cause massive die-off, colic • Originally kept horses from shedding eggs for
up to 12 weeks – could be used less often
praziquantel
Used for tapeworms
– Combined with other drugs for broad-spectrum control
• Ivermectin (Zimectrin Gold) • Moxidectin (Quest Plus)
– No know resistance problems
ascarid drug resistance
Ivermectin/moxidectin
– No longer effective on many farms – Not recommended for this parasite
• Fenbendazole at 2x dose
– Some resistance reported – Oxibendazole may work better
• Pyrantel pamoate
– Some resistance reported
drug resistance in small strongyles
Fenbendazole
• Resistance reported in multiple studies conducted all over the world
• No longer recommended for strongyles
• Powerpac dose is no more effective than regular dose
• Double dose for 5 days • Cost: ~$65
Pyrantel
– Paste was ineffective on 40% of 44 farms in Southeast US in a study that included Kentucky
• Effective on 45% of farms • Greater efficacy in Europe and the UK
– Daily pyrantel showing resistance problems, too
• Some blame this product for the rapid decline in this drug’s efficacy
drugs that still work on small strongyles
Macrocyclic lactones
– Effective on 100% of 44 farms in Southeast US in a study that included Kentucky (ivermectin)
– Using a 2-week time period for evaluation
• Egg reappearance times are getting shorter for ivermectin and moxidectin
– 4 weeks ivermectin, 5 weeks moxidectin – Resistance is developing
multiple drug resistance
Multiple drug resistance is possible
– Parasites combine genes when they mate – Triple resistence reported in Brazil
• No selection against drug-resistant parasites
– Resistance is forever – 40 years made no difference (Lyons, et al)
• You are selecting for resistance every time you deworm
fecal egg count
Can identify the parasites that are present
– Can identify which horses require treatment
– Only way to know which drugs work on your farm
– New deworming strategies require knowledge of fecal egg counts
targeted treatment for small strongyles
Test for eggs in manure
– Treat only horses with moderate to high egg counts and above
• 200- 500 EPG
– By targeting moderate to high shedders you can reduce total contamination of pastures by 95%
rationale for strategic deworming
Rationale for this approach
– Reduces selection pressure for resistance
– Buys time as new drugs are brought to market
• Nothing in the near future
– Resistance to the best drugs is developing in small strongyles – we must slow this progression if possible
– Untreated horses dilute the effects of the selection pressure through ‘refugia
refugia
Refugia is the proportion of a population of parasites that escapes the selection by the anthelmintic
• Encysted stages in horses not receiving a drug that kills them
• Migrating stages in horses treated with a drug that only acts in the gut
• Parasite larvae on pasture • Parasites in untreated horses
strategic deworming pros and cons
Pros:
– Horses aren’t being treated unnecessarily – Problem horses are being identified – Reduced larval load on pasture – Cost savings over time
• Cons:
– Fecal egg counts may cost more than dewormer
– Testing lab or equipment required – Sample handling is critical
adult horse parasite treatment
Start with fecal egg counts (FECs) on all adults to identify high strongyle egg shedders
• Only deworm horses with FECs above approximately 500 eggs per gram (EPG)
– Your vet may use a different cutoff
– Recheck after 4-6 weeks to see if high FEC has returned
Deworm all adult horses twice per year with ivermectin or moxidectin with praziquantel
– Fall, early spring (Zimectrin Gold, Quest Plus, etc.)
• Occasionally check a portion of your low egg shedders for changes in status
– Late spring, early fall, winter
– After the effects of previous dewormer have passed
foal and weanling parasite control
Ascarid control
– Start deworming at 60 days, then every 60 days thereafter
– Fenbendazole (Panacur, SafeGuard) – Pyrantel (Strongid paste or Rotectin) – Oxibendazole (Anthelcide EQ).
• These drugs should be given at double the dose
• Use fecal testing to check drug efficacy
Small strongyle control
– Start deworming at 90 days, then every 45-60 days thereafter, depending on egg reappearance time
– Ivermectin (Eqvalan, Zimectrin) – Moxidectin (Quest)
• If foal is at least 6 months of age
yearling to 3 yr old parasite control
Expect this group to have more high strongyle egg shedders
– Ascarid egg shedding should end
• Will require more frequent treatment than older horses
• Follow suggestions for adult horses
parasite management in pastures
Rotate with
non-equids
– Parasites are species-specific
• Put your youngest horses on your cleanest pasture Remove manure from pasture
– Labor intensive! – Effective!
• Dragging and mowing
– Timing critical - summer – Roughs have higher larvae counts
Rest pastures or use for hay one year
• Avoid putting foals in the same pastures year after year
