Equine Dermatology Flashcards
Where is the equine skin thickest and thinnest? Why?
- THICKEST = dorsal head, neck, thorax, tail head
- THINNEST = ears, axillary, inguinal, perianal
prey species - predators are large carnivores that jump on their back to hunt
What glands are unique about the equine skin? What is their subcutaneous space like?
sebaceous and sweat glands are larger and more numerous compared to other LA species
more connected - SQ injections of fluids or medications are much more uncomfortable
What is an ergot?
vestige of digits 2 and 4, cornified tissue on the flexor surface of the fetlock
What is a chestnut?
vestige of digit 1, keratinized area of the medial aspect of the radius
- no vascularization or nervous tissue
What is the hoof?
keratinized covering of digit 3
What type of hair do horses have? What influences replacement?
simple primary
- photoperiod (Spring/Fall)
- ambient temperature
What parts of the horses’ hair do not shed? What 2 hormones affect their coats?
mane, tail, fetlock
- thyroid - increased growth
- glucocorticoids - hypertrichosis associated aith PPID (Cushing’s) in older horses
Horse medical history associated with dermatologic disease:
Herd medical history associated with dermatologic disease:
What are important aspects of the physical exam for diagnosing dermatologic disease?
- note the general condition of the horse, including hair coat and hooves
- assign a condition score
- assess all systems
- examine hair coat closely, including mane and tail
- evaluate all lesions
- record the distribution, description, and document (photos)
- palpate what you cannot see
- examine diet, teeth, housing, etc
- herd problem: examine all affected animals
What part of the physical exam is especially important for diagnosing pediculosis? What are the 2 main distributions of lesions?
lice - careful evaluation of tail and mane
- mane, tail, fetlock, pastern - sucking
- dorsolateral flank - biting
How does the type of lice affect treatment options?
sucking lice respond to oral/systemic Ivermectin
biting lice do not undergo prolonged injection of fluids from its host and eat dander, so they respond better to topicals and dusts
Pediculosis, mane:
sucking!
What is the most common use for fungal culture/ID? How is it done? What is also part of the examination?
identification of dermatophytes (ringworm)
- clean hair gently with alcohol
- let hair dry
- pluck out several strands
- place hair in Sabourands +/- Cycloheximide (slows down growth of non-pathogenic fungi) agar
examining hair directly under the microscope
What are 2 common fungi that cause dermatological disease in horses?
- Microsporum macroconidia
- Trichophyton macroconidia
What is the purpose of performing skin scraping? How is it performed?
identifying ascariasis - mange, mite infestation
- pick an edge of affected area
- use a dulled #10 blade held at an angle, squeeze skin, and scrape
- wipe on slide and add mineral oil
- examine for mites
What is the purpose of a sweat test? How is it performed? What is the normal response
test horse’s ability to sweat and diagnose anhidrosis
- create four, 10-fold dilutions of epinephrine or terbutaline (1 IU:1000, 1 IU:10000, 1 IU:100000, 1 IU:1000000
- clip and mark neck with dilutions
- inject o.5 cc
sweat at all dilutions in 15-30 mins
What is the purpose of intradermal skin testing? How is it performed?
identify causative irritants in the horse’s diet or environment
- select antigens, histamine as a positive control, and saline as a negative control
- clip and mark neck
- intradermal injection of 0.1-0.2 cc of antigen at each site
- injection blebs should be of equal size
How does the time of a reaction to an intradermal skin test show the cause of the reaction?
- 30 mins = acute
- 3-4 hrs = cell-mediated, delayed response
- 12-24 hrs = cell-mediated, delayed response
What is the purpose of skin biopsies? How are they performed?
tumor classification +/- removal
- pick the border of the lesion, clip, and scrub gently
- inject 1-2 cc of lidocaine SQ (won’t affect histopath!)
- apply biopsy to skin, rotate, and lift sample
- cut away fibrous cord of SQ tissue
- suture with 2-0 dermalon
- use for culture and histopathology
Where on a lesion is a biopsy taken?
on the border —> get to compare abnormal and normal
What is the purpose of debulking and removing masses? How is it performed? When is it commonly rechecked?
ID border of abnormal tissue
- clip, wash, and block SQ
- incise 1/4-1/2 inch beyond border
- place removed tissue in formalin for histopathology
- close wound if tension permits - if not, keep it covered, clean, and have insect repellent
10-14 days, can remove sutures
What are common causes of itchiness in horses?
- Culicoides hypersensitivities
- ventral midline dermatitis
- pediculosis (lice)
- mite infestation (mange)
What is culicoides hypersensitivity? When is it most commonly seen?
type I hypersensitivity caused by biting midges
warm months, progressively gets worse as summer goes on
How do horses present with Culicoides hypersensitivity? How is it diagnosed?
scales, crusting, and excoriations affecting the tail, mane, chest, rump, and belly +/- rump, submandibular space, ears
clinical signs, seasonality
What is likely occurring in these horses?
- broken off manes
- rubbing causes thickened skin
- rubbed skin off tailhead
- dryness
Culicoides hypersensitivity
How can Culioides hypersensitivity be treated? What do severe cases require?
- limit development of wet areas and manure buildup
- apply fly spray (Absorbine Ultra Shield) or repellent cream (pyrethrin)
- use fans in barns and keep horses inside at dusk and dawn
- specialized turnout fly sheets
- prophylactic anti-histamines (must be given before the emergence of insects)
corticosteroids (Dexamethasone, Prednisolone) + clean/treat secondary skin infections/inflammation (Staph)
What causes ventral midline dermatitis? How do horses present?
hypersensitivity reaction to insect bite or parasite migration (rare Onchocerca)
scales, crusting, and excoriations limited to the ventral midline
How is ventral midline dermatitis treated?
- deworm with Moxidectin/Ivermectin to eliminate Onchocerca
- wash +/- antibiotic therapy
- apply fly spray (Absorbine Ultra Shield) or repellent cream (pyrethrin)
- specialized turnout fly sheets
- prophylactic anti-histamines
(the sooner the better)
What is pediculosis associated with? How do horses present?
lice infestation most common in the winter or early spring in horses with poor, dirty housing conditions
- extremely itchy - alopecia, scales, thickened skin, patchy coat
- usually multiple horses affected, especially young, old, and sick
What are the 2 major groups of lice affecting horses?
- SUCKING - Haematopinus asini in the mane, tail, fetlock, or pastern
- BITING - Damalinia equi on the dorsolateral trunk or neck
How are sucking and biting lice treated? What else is done to prevent more infections?
SUCKING - Ivermectin every 2 weeks for 3-4 treatments or Moxidectin every 4 weeks for 2 treatments
BITING - powders (Sevin) containing malathion, rotenone, or coumaphos dust applied weekly for 3-4 weeks
clean up the environment, grooming tools, and pads
What are 4 most common causes of ascariasis in horses?
MANGE MITES
- Sarcoptes equi
- Chorioptes equi
- Demodex
- rarely Psoroptes equi
What lesions are most commonly seen with ascariasis? What are the 3 distributions?
itchy papules, crusts, and scales
- SARCOPTIC - body mange = head, neck, shoulders
- PSOROPTES - mane mange = mane base, ears, fetlock, tail base
- CHORIOPTIC - leg mange = pastern, feathering
How is ascariasis diagnosed? 4 treatments?
mange = skin scrape
- organophosphate sprays - Lindane
- lime sulfur shampoo
- Frontline spray on
- Ivermectin - 2-3 doses
(ALL HORSES IN CONTACT)
Chorioptic mange:
What are some other causes of itching in horses?
- habronemiasis (summer sores)
- phycomycosis
- cutaneous onchocerciasis
- oxyuriasis
- Staph folliculitis
