Management of Disease - Equine Flashcards
What is anaemia
Anaemia is the reduction of circulating red blood cells or reduced haemoglobin concentration. Functionally it is the reduced oxygen carrying capacity of the blood.
What is the normal PCV for:
a. hot blooded horses
b. cold blooded horses and ponies
Thoroughbred or hot blooded horse = 35-40%
Cold blooded horse or pony = 25-35%
what is so important about the equine spleen?
The spleen stores 1/3 of the horses’ entire blood volume which it can expel when excited, scared or during exercise to increase the PCV by up to 25%. Can compensate for blood loss for a significant while and is also a main store for platelets
what are the clinical signs of anaemia?
Tachypnoea, tachycardia, pale mucous membranes, exercise intolerance, collapse, weakness, lethargy. Can sometimes hear a flow murmur due to changes in blood flow upon auscultation
What are the clinical signs of hypovolaemic shock
Tachypnoea, tachycardia, hypothermia, cold extremities, weak pulses, muscle weakness, pale, tacky mucous membranes, increased capillary refill time
Why is melena so uncommon in horses?
the bacteria in the large intestine break down the blood
What is the normal blood volume of a horse?
8% of it’s body weight
how much blood can a horse lose before going into shock?
30% of it’s total blood volume
What compensatory mechanisms are there for coping with blood loss other than the spleen?
Catecholamines induce vasoconstriction and increase cardiac output
Plasma volume is expanded by increased renal absorption of fluid due to ADH release
what is polychromasia?
variation in cell colour
what is anisocytosis?
increase in cell size
Why is it difficult to determine if anaemia in a horse is regenerative and how can you tell?
Horses don’t have circulating reticulocytes so instead you must take a blood test then take another a week apart and compare the PCV
what colour is normal horse serum?
very yellow
What test would you use to check for equine infectious anaemia?
coggins test
name some causes of acute blood loss anaemia
Epistaxis, uterine artery rupture, guttural pouch mycosis, tumours, rib fracture in foals, thoracic vessel rupture in race horses, mesenteric artery rupture due to strongyle parasites, renal haemorrhage
name some causes of coagulopathies
Secondary to sepsis, SIRS (systemic inflammatory response syndrome) or severe liver failure
name some causes of haemolytic anaemia
Neonatal isoerythrolysis ( mare has antibodies against foal’s blood group), blood parasites, equine infectious anaemia, oxidant induced haemolytic anaemia due to toxicity (red maple leaf)
Name some causes of non-regenerative anaemia
Bone marrow disorders, anaemia of chronic disease – renal failure resulting in reduced levels of erythropoietin, iron deficiency (chronic blood loss), folic acid deficiency (medication)
what are the main three causes of anaemia?
Increased destruction, reduced production or blood loss
When carrying out a clinical exam what questions should you ask the owner as part of your subjective exam?
Taking a History, questions to ask in addition to the normal ones (has he been eating, drinking, coughing, sneezing, diarrhoea, urinating, defeacating, exercising ok etc):
• How long have you owned the horse
• Was a pre-purchase exam performed before buying the horse?
• Is the horse up to date with its worming and vaccinations?
• When was it last visited by the farrier?
• When was it last visited by the dentist?
• Is this a problem with an individual or with a group of animals?
• Has the horse recently travelled?
Signalment - some horses of a certain breed, age, gender, colour are more susceptible to certain diseases. e.g. grey horses are more susceptible to melonomas and Squamous cell carcinomas are more common in pink eyed animals.
Ponies can be more pre-disposed to hyperlipaemia (abnormally high conc of lipids in blood )and laminitis
Horses are more prone to atrial fibrillation (irregular heart rate due to chaotic beating of the atria causing poor blood flow to the rest of the body), cervical vertebral instability and idiopathic laryngeal neuropathy (dysfunction of the larynx) - roaring horses.
When examining the horse from a distance what should you look at?
demeanour, body condition, resp rate, any increased respiratory effort or unusual posture, any unusual behaviour, look at where it is housed, is it eating, what do it’s droppings look like
what is the normal rectal temperature of a horse
Temp 36.5 - 38.5 (exercised or hot day) degrees
When hospitalised how often should foals be weighed and how much weight should they gain?
Foals should gain 0.5-1kg every day - should be weighed every day when hospitalised.
when examining the respiratory tract what should you look for?
Clinical Examination
• Noises — Coughing, Grunting, Stridor
• Nasal Discharge — Serous, Mucopurulent or Sanguinous
• Rate — Influenced by temperature, stress, metabolic
state
• Depth — Increased depth provides better alveolar
ventilation
Pattern — biphasic (both inspirator,’ and expiratory)
• Heave Line — external abdominal oblique muscle
• Nasal airflow — feel for equal airflow
• AUSCULTATION -with rebreathingbag
Scant, moderate or marked to describe quantities
Heave line is also a classic presentation for animals trying to take weight off their feet e.g. laminitis
upon auscultation:
Remember to check the trachea and larynx
Locate point of most intensity if you hear an abnormal noise
Larynx palpable in most horses - feel arytenoid cartilages
• Breath Sounds
— Loud
— Quiet
Wheezes — long sounds
• Crackles — short, sharp popping sounds
Area over which sounds can be heard
• Pleural friction rubs
Constriction of bronchioles - wheezes
Moisture or effusion in the lungs - crackles
Calves with pneumonia - friction rubs
Effusion can cause absence of lung sounds
Nostrils - symmetry, flexible, no mucous , air coming through both, look at nasal mucosa, smell air that comes out of each nostril
Palpate and percuss paranasal sinuses - should be filled with air so sound hollow and check facial symmetry
Larynx - obvious solid structure felt high up in the throat, above this can feel the muscular processes of the arytenoids - should be symmetrical
Palpate traches - rings can be palpated in the upper neck
Auscultate trachea for fluid accumulation
Re-breathing bag - Should increase resp rate significantly - can make it easier to auscultate lungs
When examining the cardiovascular system what should you look for?
Rate — Influenced by temperature, stress,
metabolic state
Rhythm — Regular, regularly irregular, irregularly
irregular
• Pulse —Quality, deficits
Venous engorgement — Jugular pulse, jugular
distension
Oedema — Limb oedema, ascites
Murmurs — Point of Maximal Intensity, Grade 1-6
Regularly irregular rhythm can be quite normal in the horse
Increased preload can cause venous engorgement
Many horses have functional heart murmurs
Check mucous membranes
Transverse facial artery, over the heart ( fit horse can feel heart beat) and under mandible can be used to check pulse
Heart located quite cranially - straight up behind elbow P on left and T on right
when examining the gut what would you look for
Normal to hear background gut noises
4 quadrants - should hear gut sounds in all
Right dorsal - caecum - caecal flush - one every minute
Auscultate the abdomen - gut sounds should not be high pitched
Left:
Dorsal - small intestinal movement,
Ventral quadrant - colonic movement
Right:
Dorsal - caecum
Vetral - Right ventral and right dorsal colon - soft sounds
look for urine and diarrhoea staining around the anus and check muscle tone and integrity
when doing a musculoskeletal exam what would you look for?
Forelimb:
Palpate limb for swelling, heat pain or deformity - pay particular attention to soft tissue areas
Lift the foot - palpate, test movement of major joints
The foot - always clean it out thoroughly first, look for evidence of a foreign body, next apply a hoof tester across the entire foot including the heel and across the frog. Also tap the foot to assess for a focus of pain
Palpate the leg once more before allowing the foot to fall.
Hindlimb:
Palpate as for the forelimb, look for digital pulses - exaggerated with some conditions
Lift the foot, check range of movement and palpate
Clean the hoof, check for foreign bodies, use hoof testers as for the forelimb and tap in all areas
Palpate once more before allowing foot to fall
Examine horse during movement - At walk - At trot - Turning in a circle - Sometimes on different elevations and ground types Sometimes with a rider
What are your list of differentials upon an equine clinical exam?
Infectious: Virus Bacterial Fungal Protozoa Parasitic
Non-infectious: GIN 'N' THONIC Genetic/ developmental Immunological/ allergic Nutritional/ toxic Neurological Traumatic Hormonal Neoplastic Idiopathic/ iatrogenic
What to look for on diagnostic imaging of the equine leg
soft tissue:
- swelling
- abnormal presence of air and gas
- mineralisation
- foreign bodies
Bone:
- margins
- medulary cavity and the cortex
- look at the trabecular pattern
- look at the bone density
- look for areas of bone re-modelling
Articulation:
- symmetry
- joint space
- orientation
What is Sclerosis
increased bone density
can be to wall off infection
due to joint stress
to protect a weakened area
what is osteolysis
decreased bone density
can be due to fracture, blunt trauma, infection or excessive pressure on a joint
How can you tell the difference between active and in-active lesions
active lesions have irregular, poorly demarcated, sharp edges
in-active lesions have smooth, well defined, rounded edges
what are osteophytes
bony projections associated with cartilage degeneration
What are enthesiophytes
focal areas of new bone production at the origin or insertion of soft tissue, often caused by stress at the point of soft tissue attachment
Name the indigenous poisonous plants
v Ragwort - associated with weight loss due to severe liver failure v Giant hogweed v Water hemlock v Foxglove v Bracken v Deadly nightshade v Oak tree and acorns – severe gastrointestinal problems rhododendron
Name the plants that act as neurotoxins
v deadly nightshade v yew v hemlock v oleander v sorghum v flatweed v ryegrass lathyrus sativus (singletary pea)
Name plants that act as hepatotoxins
v senecio (ragwort)
v lantana camara
echium lycopsis
Name plant that act as cardio-respiratory poisons
fox glove
Name the plants that act as dermo toxins
mimosa
leucena
Name the plants that act as enterotoxins
oak/acorns
rhododendron
What problems does ragwort poisoning cause?
· Hepatotoxins
· Un-palatable when fresh but when dried it becomes less distinguishable – beware of it getting into hay
· Spring is a time to be vigilant as the small growing plant can often be ingested by the horse. In full bloom when the plant is easily seen it is mostly left alone
· Clinical signs are secondary due to hepatotoxicity and include:
- Dullness
- Depression
- muscle tremors and weakness
- frequent yawning
- blindness
- Incoordination
- Jaundice
- photosensitisation ( agents causing this are usually detoxified by the liver)
- head pressing
- nasal regurgitation of food and water
- inappetence, weight loss and difficulty swallowing
- Can also see ventral oedema and coagulopathies.
- Laryngeal paralysis is also seen and the horse is generally unresponsive
· Very difficult to reverse hepatotoxicity
· Pathology often develops gradually – often see damage to the liver parenchyma causing megalocytosis
· Treatment of little value if chronic liver damage present and tend to treat symptomatically
Control includes uprooting and burning, cutting off the tops to prevent flowering and seeding and spraying herbicide
What problems does St Johns wort cause?
· Common in hedgerows and gardens
· Causes primary photosensitisation due to a chemical called hypericin
· Found in immune booster tablets for people
Photoactivated pastern and cannon leukocytoclastic vasculitis is associated with yellow flowers and is increasing in prevalence. Occurs on the shaded areas and goes away when the animals are kept out of sunlight
What problem does giant hogweed cause
· Noxious weed
· No specific signs but causes oral irritation and mouth ulcers
What problems does Sorgium cause?
· Not very common in this country – grown in tropical countries, crop is harvested and horses are left to graze stalks
Causes chronic cyanide poisoning - cystitis and bladder paralysis
what problems does oleander cause?
· Common in warmer countries · Extremely toxic – affects humans too, contains cardiac glycosides · Clinical signs include: - Diarrhoea - Melaena - Disruptive cardiac arrhythmias - Death often within minutes Limited necropsy findings except possibly the plant in the ingesta
what problems does false dandelion cause?
- Common plant in stable yards and poorly maintained pasture
- Widespread
- Normally ingested in low amounts without causing a problem
- neurotoxin
- Can induce stringhalt in horses – hyperflexion of hindlimb, form of neuropathy, seems to be a breed susceptibility
what problems does belladonna cause?
· Causes atropine related signs, blocking muscarinic parasympathetic receptors (mydriasis, tachycardia, dry mucous membranes, colic, shivering and muscle spasm.
· More commonly due to atropine drug poisoning so should monitor carefully if giving and use as lower dose and least frequency possible and remember it can cause gut stasis
Treat with supportive care e.g. fluids
What problems does bracken fern cause?
· Usually has a restricted distribution
· Carcinogenic
· Has thiaminase activity so clinical signs similar to that of a vitamin B1 deficiency
· Clinical signs (bracken staggers):
- Anorexia
- Cardiac dysrhythmia (cardiac enlargement over time)
- Convulsions
- Incoordination
- Crouched stance, arched neck, feet wide apart
- Poor body condition
- Clonic spasms
· Diagnosis via bracken on the pasture, known ingestion or can be identified due to low blood thiamine
· Treatment usually highly effective if caught early enough and given IV thiamine slowly over 7 days, IM also acceptable
what problems does mares tails cause?
· Common garden plants in UK
· Causes CNS signs
Also contains thiaminase so treat with thiamine
what problems does acorns and oak cause
· Contains tannins which cause the toxicity, present in the leaves and the acorns
· Clinical signs include sudden death, colic, tenesmus and haemorrhagic diarrhoea
· Mainly affects the GI tract causes gastroenteritis, haemorrhages in the abdominal cavity and oedema over the pelvic limbs and ventral body wall
· Poisoning is rare and some horses don’t appear to be affected
· Diagnosis: acorn traces in gut and faeces, can also look at urinary phenolic content to differentiate from other colics
· Treatment same as for colic, supportive fluid therapy, analgesia, laxatives, diuresis
· Control: fence off oak trees in the autumn or pick up acorns from pasture
what problems does hemlock cause?
· Flowers and leaves similar to cows parsley
· Flowers are the most toxic – the alkaloid has a nicotine like action – it stimulates then depresses the autonomic ganglia. End result is it paralyses skeletal muscle motor nerve endings
· No signs on post mortem
· Clinical signs if only ingested small quantities:
- Laboured irregular breathing
- Abdominal pain
- Inappetance
- Mouse like odour
- Possible cardiac arrest
- Depression
· Treatment – try to lavage the stomach to remove the plant
Prevention by removing plant from pasture is most important
what problems does yew cause?
· Evergreen with red berries in autumn – berries not poisonous but seeds within them are. Leaves are also poisonous
· Contains alkaloid taxines
· Damage cardiac myocytes
· Clinical signs:
- Trembling
- Ataxia
- Bradycardia
- Hypothermia
- Weakness
- Dyspnoea
- Rapid death
· Upon necropsy will see liver, spleen and lungs engorged with dark blood, a distended stomach and inflammation occurring after death for several hours
· Diagnosis via clinical signs, history or finding the plant in the ingest upon PM
· Prevention – avoid contact with the tree, remove it or fence it off
Treatment – try a gastric lavage and give glucose and hydroxycobalamin but may not be in time to treat
what are the problems caused by ergot infested grass
· Not as common in this country
· Infected grasses with ergot - fungus affecting plant seed
· Causes poor vascular function
· Clinical signs:
- Trembling, unsteadiness and poor muscle coordination
- Erratic and anxious behaviour
- Trembling around head and neck region
Clinical signs worsen if exposure increases
What is the difference between a mare and a filly?
a mare is a female over 4
What type of breeder are horses?
long day, seasonally poly-oestrus = breed only once a year in warmer months naturally but during this time come into oestrus many times
when does puberty occur in the horse?
12-24 months old
How many days is the oestrus cycle in a mare?
21 days in total
dioestrus lasts around 17 days
oestrus lasts 4-6 days
within 24 hours of ovulation the mare will no longer be receptive
what role does the dominant follicle have in ovulation?
induces ovulation by secreting oestrogen
What hormone does the corpus luteum produce
progesterone
At what point does the corpus luteum break down if the mare is not pregnant?
after 15 days due to the endometrium releasing prostaglandins
What signs will you see during the transitional period from anoestrus to oestrus ?
lasts up o 6 weeks
will see multiple small follicles on the ovaries which look like a bunch of grapes
the mare may show no signs or show eratic oestrus behaviour
What drugs can be used to manipulate oestrus?
prostaglandins progestagens oestrogen chorionic gonadotrophin deslorelin
How does oestrogen manipulate oestrus?
used in teaser mares for AI collection, induces the behavioural signs of oestrus but not true oestrus
How do progestagens manipulate oestrus ?
suppress oestrus, used to shorten the length of the transitional period as withdrawal of the drug increases ovarian activity
How do prostaglandins manipulate oestrus?
induces luteolysis of the corpus luteum. Oestrus will then commence 3-5 days post injection
side efects quite common - colic, sweating, diarrhoea
how does deslorelin manipulate oestrus ?
it’s a GnRH analogue
hormone implant given when follicle is over 30mm
induces ovulation within 48 hours in most mares
how does chorionic gonadotrophin
given during oestrus to induce recruitment of a dominant follicle, will induce ovulation within 24 hours if follicle is over 35 mm
How can oestrus be manipulated using photoperiod?
the breeding season an be brought forward using artificail light
need to provide 16 hours of day light, mares will begin ovulating 8-10 weeks later
how long is the unfertilised oocyte viable for post ovulation?
12 hours
when is the best time to mate to get the best chance of conception?
24-48 hours post ovulation
How long is sperm viable for within the mare’s reproductive tract?
48 hours
Signs a mare is in oestrus
dominant follicle in one ovary
uterine oedema - decreases 24 hours before ovulation
a soft oedematous cervix
behavioural signs
Name some common ovarian problems associated with the mare
persistent corpus luteum - prevents oestrus, give prostaglandins to induce ovulation
anovulatory follicle - results in prolonged oestrus, follicles increase in size but don’t ovulate. Usually regress in 4-6 weeks
granulosa cell tumour - nymphomania or stallion like behaviour, or persistent anoestrus. Diagnose via scan or blood test for anti-mullerian hormone. requires surgery
What pathogens can cause chronic infectious endometritis
strep zooepidemicus e.coli pseudomonas klebsiella yeast / fungi
What is the treatment for endometritis
uterine lavage
oxytocin - repeat dose every few hours
intra-uterine antibiotics
What is chronic degenerative endometrial disease (endometrosis)
progressive degeneration of the endometrium with replacement by fibrotic tissue
major cause of age related infertility
pregnancy lessens the progression of this condition
What is the length of an equine pregnancy?
336 days average but very variable
where does fertilisation of the oocyst occur?
in the ampulla of the oviduct
How long does the embryo remain in the oviduct
5-6 days
When does the embryo implant
day 15-16, this is also where endometrial cups develop
Describe the endocrinology of pregnancy
the CL continues to produce progesterone to maintain the pregnancy
at day 35 the endometrial cups start secreting ECG which encourages the formaion of a second CL
these maintain the pregnancy for the first 5 months
After day 7 the cups start to degenerate and dissapear by day 150
the pregnancy is then maintained from day 200 onwards (CLs regress) by placental progesterone
What lab tests can be done to diagnose pregnancy
blood test for ECG from dy 45-90 and to look for oestrone sulphate from day 120 onwards
urine sample from day 150 to identify oestrone sulphate
At what stage can a pregnancy be detected via manual palpation
and via ultrasound
from day 40
from 10 days with ultrasound
Causes of pregnancy failure
Early embryonic death - up to day 40 Viral - EHV - EVA - Bacterial - Fungal Twins Maternal illness/stress Foetal abnormalities Umbilical torsion Idiopathic
Describe the features of equine herpes virus 1
most common cause of infectious abortion, usually late term - 5 months plus
spread via respiratory route or via contact with infected discharge and foetal membranes
vaccine available to be given at 5,7 and 9 months of each pregnancy
Describe the features of equine viral arteritis
notifiabe
infected stallions become persistently infected shedders as it resides in the testes
mares abort and recover
vaccine available
Name the pathogens responsible for bacterial abortion
strep species e.coli staph species salmonella leptospirosis
How can abortions be induced
before 3 months an injection of prostaglandins should bring about abortion in 5-8 days
after 3 months need repeated prostaglandin injections
How can labour be induced in the mare?
inject oxytocin every 15-20 minutes until labour is induced
