Lecture 8 - diseases Flashcards
Malnutrition causes?
immunosuppression
- increases risk of infection
What about horses magnifies problem feeding practices
small stomach capacity
tight sphincters
Factors that compound nutrition related diseases
Stall confinement
increased housing density
USA national health monitoring system report for 2000
- 13% of all horses (exlcuding racetracks) suffered from laminitis
- 4.7% had to be euthinized
Laminitis
- 2nd most lethal condition of horses following colic
- lamellae of hooves weaken and inflammation sets in with onset foot pain
- lamellae normally support suspensory apparatus, which attaches to coffin bone
- lamellae separate from coffin bone inside hoof and the weight forces it down into the hoof capsule, can even perforate the sole
- disturbance in blood flow can change growth rate of hoof wall
- heel grows fast than toe, growth rings of hooves
Hoof composition
distal phalanx (coffin or pedal bone)
lamellae
navicular bone
deep flexor tendon
Acute vs Chronic Laminitis
Acute
- 24-72hrs
- shifting of weight from toes to heels
Chronic
-4 or 5 days +
Determining whether chronic laminitis has occurred?
Growth rings on hooves
- the more space out the rings at the heal, more likely chronic
Major cause of laminitis
Carbohydrates
- high intake of soluble from overgrazing of lush pasture
- overload of grain and forages
- excess undigested in SI and fermented in cecum and LI
How laminitis develops - LI to stomach
Carbs fermented in cecum and LI
- large increase of lactic acid producing bacteria (anaerobic lactobacilli and streptococci)
- decreases intracecal pH from 7 to 4
- proliferation of starch fermenting organisms declines because of low pH
- lactic acid accumulation causes damage to intestinal mucosa
- increased permeability of intestinal epithelium to bacteria and endotoxins
How Laminitis develops - intestinal bacteria
Increased permeability of intestinal epithelium
- intestinal bacteria produce metabolites that activate metalloproteinases in the hoof wall
- weekens bond between hoof wall and coffin bone
How laminitis develops - endotoxins
endotoxemia - endotoxins from stomach reach blood
- reduces blood flow to the lamella of the hoof
How laminitis develops - biogenic amines
Increase lactic acid in intestinal tract
- causes microbial breakdown of amino acids
- have hormone like properties including vasoconstrictor effects
- cause constriction of digital arteries and veins via stimulation of serotonergic receptors or displacement of norepinephrine from perivascular nerves
Biogenic amines
serotonin epinephrine norepinephrine putrescine spermine spermidine histamine tryamine
Lactic acid producing bacteria
lactobacilli
streptococci
First signs of laminitis
lameness and awkward stature
- from decreased blood flow
- caused by endotoxemia and biogenic amines
Cool season grasses have high concentration of
fructan
- fructose rich polymers
- not degraded in small intestine
- higher risk of laminitis
Cool season grass examples
perennial rye timothy brome orchard grass small grains - oats, wheat, barely
warm season grass examples
bluestem
crabgrass
switchgrass
Bermuda grass
soluble carbohydrate content of plants is affected by
plant species
season
time of day
weather and soil fertility
Main risk factor of laminitis
- steps in preventing this
consumption of lush pasture
- monitor time on pasture
- fructan content in grass highest in spring and early summer
- fructan peaks during the day, so early morning and evening grazing is recommended
- stems are consumed with overgrazing, has highest fructan content
- laminitis complications minimized with mineral oil or activated charcoal
- early cut hay should not be avoided
- fall cold stress may cause premature hay, high fructan
Non structural carbohydrates (NSC)
simple sugars, starch and fructans
NSC recommendation
15% NSC to minimize laminitis risk
Exertional Rhabdomyolysis caused by
results from skeletal muscle injury
- cell membrane ruptures, cell contents leak into blood
Exertional Rhabdomyolysis characterized by
Elevated blood myoglobin, creatine kinase, aspertate aminotransferase and aspertate transaminase
myoglobinuria - dark discolouration to urine (black water)
Exertional Rhabdomyolysis other names
tying up
azoturia
black water
monday morning disease
Exertional Rhabdomyolysis first found
draft horses
- work 6 days a week, rest on sunday
- stiff hindquarters on monday morning after rest, difficulty rising
- Monday Morning Disease
Exertional Rhabdomyolysis symptoms
profuse sweating
increased pulse and respiration rates
discoloured urine (myoglobinuria)
Exertional Rhabdomyolysis two subcategories
- PSSM - Polysaccharide storage myopathy
- mainly quarter horses, warm bloods and draft breeds
- characterized by abnormal muscle glycogen metabolism - RER - Recurrent ER
- thoroughbreds in training, Arabs and standardbreds
- abnormal intercellular calcium metabolism in muscle and abnormal contraction of muscle fibers
Exertional Rhabdomyolysis diagnosing
Blood CK levels
- rise 2 - 12 hours following muscle injury
- peak 1-3 days following injury
- can reach 5x normal
Cause of muscle stiffness in Exertional Rhabdomyolysis
Rapid calcium influx into muscle cells cause necrosis and muscle stiffness
- theory
Susceptibility to ER dependent on
age sex temperate exercise levels lameness - nervous animals higher risk
Severe recurrent ER metabolite concentrations
low blood sodium, calcium and chloride
elevated potassium and phosphorus
- excess sweating and release of electrolytes from damages cells
Specific dietary problem with ER and performance horses
energy dense diets are required for performance - but also promote ER
- high fat low starch provide concentrated energy may benefit
Race horses typical diet
- how to change diet
sweet feed
- high starch feed
- contains corn, oats, wheat meddling and molasses
- most likely to cause ER
introduction to a new diet could take up to 3 months
- vegetable oil added to rice bran improve palatability
Current thought on ER cause
abnormal calcium homeostasis in skeletal muscle
- cramps caused because calcium not released to cells
- VitE and selenium no benefit