Equine Physiology Flashcards
Heart Sounds
S1 - S4 = all heard in horse & normal
Split S1 may be heard = normal
- indicative of venrtricles emptying at different rates d/t athletic hypertrophy (especially of LV)
Measuring HR
- indirect ausc. w/ steth
- arterial palpation = submandibular a./facial a.
- on-board HR monitor
- ECG = holter recorder mounted on horse, telemetry
Normal HR
Foal = 60-80/min if relaxed *(~2x the adults’)
*
Adult at rest: 24/min < HR < 40/min
- have high vagal tone that leads to low resting HR
- ↓ rate is physiologic by ↑HR with excitation/excercise
HRrest
↑ with:
- excitation
- fatigue
- pain
- cardiac abnormalities
- other illiness +/- fever
HRrest is NOT affected by level of fitness
HRexercise
Walk = 60-100/min
Trot/Pace = 100-140/min
Canter = 140-160/min
Gallop = 160-220/min
Anaerobic treshold ~160-180/min
HRmax ~ 220-240/min
↑ with:
- exercise intensity
- ↓ degree of fitness/conditioning
- excitation
- fatigue
- pain
- cardiac abnormality or other illness
HRrecovery
should decline by at least 50% in first 30s recovery after exercise
↑ with:
- excercise intensity
- ↓ degree of fitness/conditioning
- excitation
- fatigue
- pain
- cardiac abnormality or other illness
Stroke Volume (SV)
amount of blood pumped by heart in single beat
resting SV in adult = 900-1300 ml
does not change measurable with onset of exercise
Larger heart → ↑SV → ↑CO (if HR constant)
Measuring Heart Size
1) Heart Score = sum of QRS durations at an ECG paper speed of 50/mm/sec
2) Echocardiography
Cardiac Output (Q)
Q (L/min) = HR (bpm) x SV (L)
exercise → ↑ Q
- if SV remains constant then ↑ Q ← ↑ HR
Maximal Oxygen Consumption (VO2max)
best indicator of aerobic capacity in any athlete
measured with facemask system
Fick Principle → Vo2 = Q x (a-v O2 difference)
Packed Cell Volume (PCV)
indicator of red cell mass + oxygen-carrying capacity
↑ with:
- dehydration (along with TP, USG)
- training
- altitude
- blood transfusion
- eyrthropoietin (r-EPO/darbopoeitin)
Splenic Reserve
PCVrest = 30-45%
with onset of exercise, spleen contracts & releases stored RBC mass into circulation
PCVexercise = 55-65%
Cobalt
Inhibits enzyme which breakdown of Hypoxia Inducible Factor (HIF-Ia) →
- ↑ HIF-1a → ↑ activity of EPO gene → ↑ production of endogenous EPO → ↑ circulating red cell mass → ↑ oxygen-carrying capacity
stage racing regulators are now setting thresholds for [Co] in urine &/or plasma
Exercise → ↑ Q
blood diverted to excercising tissues
- muscles
- heart + lungs
blood is diverted away from non-excercising tissues
- GI tract blood flow ↓
- skin blood flow ↓
BP
BP = Q x TPR
excercise → ↑ Q → ↑ BP unless TPR ↓
exercise → ↓ TPR in exercising muscles
- ↑ blood flow to exercising muscle
- ↑ delivery of O2 + other nutrients (glu, FFA) to exercising muscles
Mucous Membranes
oral, scleral, nasal, vaginal
capillary refill time = CRT
- blanch oral mm with thumb pressure
- normal = 1-2s
- delayed CRT implies circulatory compromise
↑ Training/Conditioning
CV Effect
↓ HRexercise at given WL
↓ HRrecovery
↑ VO2max
↑ PV
↑ RBCmass
↑ blood HB content
↑ capillary density in muscle
Tissue Oxygenation for Exercise
- movement of ambient O2 to alveolus = ventilation
- movement of alveolar O2 across alveolar + capillary membranes = diffusion
- movement of diffused O2 thru blood = transport via Hb
- discharge of O2 to exercising tissues
Horses are obligate:
obligate nose-breathers
- dilate nostrils
- abduct laryngeal arytenoid cartilages
- bronchodilate
can breathe in so hard the nostrils collapse
horse mouth breathing = bad
Respiratory Rate
Foal = 20-30/min
Adult at rest = 12-20/min
adult w/ exercise:
- RR linked 1:1 with stride rate at canter/gallop (1 breath per cycle)
- RR approaches 180-200/min w/ exercise
should decline rapidly after exercise
- inversion = RR > HR during recovery
↑ RRrecovery indicates:
- unfitness
- overheating = panting
- overuse = exhaustion
Ventilation
Ve = f (breaths/min) x Vt (L/breath)
f = RR
At rest = 50-60 L/min
at full gallop = >1800 L/min
at nares → max airflow ~40 L/s thru each nostril
- total max flow → ~70-80 L/s
Respiratory-Locomotory Coupling
fixed ratio between RR (f) + stride freq. (SF)
fast canter + gallop = 1:1
- inhale when forelimbs extended in stride
- exhale when standing one forelimb + hindlimbs flexed underneath in stride
- abdominal piston/pendulum explanation
trot/pace usually = 2:1
- horse is on same diagonal or same pace side when it inhales
- horse is on opposite diagonal or pace side when it exhales
Hypoxemia Mechanisms
assuming normal red cell mass, normal heart:
1) ↓ ventilation (hypercapnea a hallmark)
2) diffusion limitation
3) V/Q mismatch
4) shunt (failure to respond to O2 therapy is hallmark)
5) transport limitation (anemia, cardiac pump failure)
Excercised-Induced Arterial Hypoxemia
normal horses undergoing max intensity exercise →
- ↓ paO2 (hypoxemia)
- ↑ paCO2 (hypercapnia) → indicative of hypoventilation
horse literally cannot breathe fast & deep enough
- should ↑ ventilatory drive but does not
- probably d/t resp-locomotory coupling
RBC time in capillaries
at rest = ~1s in cap
w/ exercise = 0.38-0.40s in cap
Upper Airway Obstructions w/ Exercise in Horses
- Left laryngeal hemiplegia (LLH)
- dorsally-displaced soft-palate (DDSP)
- epiglottic entrapment
- dynamic pharyngeal collapse
Dorsal pharyngeal collapse
when placed on bit
with ↑ poll flexion, repeatable DDSP + coughing but no other noise was ever apparent
Lung Sounds
Lung Borders:
- rib 6 ccjxn
- rib 11 mid-thorax
- rib 16 at tuber coxae level
normal sounds = slight air movement
re-breathing bag
- bag over nostrils →→→ ↑ RR +/- depth → ↑ ability to auscult abnormal lung sounds
cannot hear lung sounds through back musculature of horses
Abnormal Lung Sounds
Wheezes
- indicative of ↓ airway d/t bronchoconstriction or exudate
- high-pitched musical sounds similar to pipe organ
Crackles
- indicative of rapid alveolar opening, alveoli prev. collapsed d/t exudate
- indicatived of exudate which moves around w/ resp resulting in rattling/popping/crackling sound
- harsh sound similar to cellophane
Lower Airway Obstructions with Exercise in Horses
- poor mucociliary clearance 2nd to viral infxn
- pneumonia
- COPD (or RAO)
- exercise-induced pulmonary hemorrhage (EIPH)
↑ Training/Conditioning →
Resp Effect
1) resp system thought to not be trainable
- VE does not change with ↑ fitness (only mild increase in respiratory muscle)
2) ↓ RR w/ ↑ fitness thought to be more of a function of:
- ↑ CV fitness
- ↑ IM fitness, ↑ aerobic enzyme capacities
- ↑ thermoregulatory capacity
3) same VO2 at given WL
4) ↑VO2max by 15-20%
Horse Dietary Energy Sources
CHO > fat > protein
-CHO from :
- grains (starch) eaten as concentrates
- minor CHO source = hindgut use of fiber
Dietary VFA from hindgut ferm. of fiber
protein should not be considered a good source of energy in horses
Energy for exercise/work comes from:
high energy phosphate bonds (ATP, CP)
Anaerobic Threshold
- point of “onset of blood lactate accumulation” (OBLA)
- point at which IM lactate production + accumulation overwhelms liver’s ability to catabolize lactate → ↑ plasma [LA]
typically ~ 60-80% of max effort (% HRmax + %VO2max)
Standard [LA] Measurement
Commonly agreed that 5-10 min post-exercise = peak plasma [LA] for most exercise bouts
- ↑ active warm-down → ↓ IM + plasma [LA]
post-exercise [LA] can be used to assess:
- innate ability
- severity of exercise bout
- fitness
- response to training (should ↓ with ↑ fitness)
Mechanisms of Fatigue
Peripheral Fatigue:
- ↑ [LA]
- ↓ substrate availability (↓ blood + muscle GLC or FFA)
Central Fatigue:
- ↓ blood + brain GLC
- ↑ blood + brain NH3
- ↑ blood + brain tryptophan
Does ↑ [LA] → ↑ fatigue?
LA productin allows anaerobic exercise to continue longer than if not produced
↑ [LA] → altered Ca2+ activity @ muscular SR
- ↓ myofibrillar contractility
- ↑ muscular fatigue
glucose infusions can help delay onset of fatigue
CNS Balance w/ Exercise
- perfusion of CNS = hydration, BP, oxygenation
- A-B/electrolyte balance
- thermoregulation
- energy balance (blood glucose)
- neurotoxins from exercise
- peripheral v central fatigue
Central Fatigue
↑ blood [NH3] associated with intracranial neuro signs in horses w/ hepatoencephalopathy
- possible central mediator of fatigue
- tested infusions = no treatment effect on time to fatigue
another proposed mediator = tryptophan
- used ilegally in USA show hunters to calm them down for horse shows
- tryptophan overrides glucose
Ergogenics Mechanisms
- supp. fuel for energy production
- affect flux of fuels in energy pathways
- delay or minimize affects of end-product accumulation (heat,lactate)
- affect NS by affecting coordination, recruitment of muscle fibers or psychological effects
Nutritional Mechanisms Used Frequently for “Improving” Performance in Horses
- dietary manipulations
- B vitamins
- antioxidants
- hemantinics
- alkalinizers
Dietary Manipulations for Exercising Horses
Type of feed before exercise:
- ↑ CHO
- ↑ fat
- ↑ sugar beet pulp (SBP)
- ↑ protein
Debate: composition of meal
- forage v grain
- amount of forage
- timing of forage
Forage v Grain Before Exercise
Forage:
- meals consumend 2-3 hrs pre-exercise have minimal effects on substrate availabilty + oxidation during sustained exercise
- hay ad libitum for 12-24 hrs pre-exercise may ↑ gut fill → ↑ BW → ↓ performance
Grain:
- corn, oats, or mix
- feed < 3hrs prior to exercise
- at onset of exercise → ↑ blood [GLC + insulin] + ↓ plasma [NEFA]
- during initial exercise → ↓ blood [GLC] (glycemic effect)
Dietary Manipulation:
↑ CHO
↑ muscle glycogen content
no demonstrable positive effect on performance
↑ HR + ↑ blood LA accumulation in high intensity exercise
**
danger of CHO overload = laminitis**
Dietary Manipulation:
↑ Fat
- inclusion of vegetbale oil fat common in diets for athletic horses
- up to 20% total daily DE may be fed as fat
- several weeks necessary for fat adaptation
-may commercial diets now ↑ fat & ↓ CHO
↑ plasma phospholipids + cholesterol
↓ plasma triglycerides
↑muscle activity of lipoprotein lipase + b-oxidation enzymes
- adult horses eventually tolerate 1 cup corn oil 2x daily top-dressed on regular grain ration
- fat spoils easily in summertime if ration not fully consumed
Dietary Manipulations:
↓ SBP
Non-starch high-CHO feeds have become common additive for atheletes
- ↑ fiber intake in concentrate diet = SBP or soya hulls
- ↓ glycemic + insulinemic responses to concetrate meal
molasses SBP → no change in responses
Dietary Manipulations:
↑ Proteins
protein is an unimportant substrate during exercise
dietary protein > 2g/kg b wt in endurance
adverse effects on:
- water intake
- urea metabolism
- ammonia metabolism
- ↑ urinary N*
*adverse effects on resp health d/t ↑ ammonia content of urine in stalls
B Vitamins
most equine diets contain sufficient B vitamin conc. except B12 since its gut-synthesized
B1 = thiamine
- coenzyme in coversion of pyruvate to acetylCoA
- given in high enough doses, it would lower blood [LA]
-
Carnitine
produced from dietary precursors
commerical carnitine supplements produced/marketed for horses
- poorly absorbed from equine GI tract
- no measurable ↑ in muscle/plasma [carnitine]
Antioxidants
protect tissues from oxidant damage
- oxidants produced at ↑ rate duringe exercise
ex) vit. E, C, B-carotene, coenzyme Q10
above-optimal levels not ergogenic
Vitamin E
deficiency not common in horses
- degenerative myelopathy
- equine LMN disease (LMND)
deficiency → ↓ time to fatigue in horses
negative correlation between plasma [antioxidants] & [CK/AST] after endurance exercises
Hematinics
“blood-builders”
widely used in horse industry
limited research to support use
spleen = huge red cell reserve for horse
examples involved in Hb/RBC synthesis:
- iron, copper, zin
- B6, B12, folic acid
iron deficiency does not occur in horses under normal NRC feeding conditions
normal horses’ red cell parameters do not respond to hematinics
Alkalinizers
exercise of sufficient intensity results in accumulation of lactic acid → acidosis may adversely affect contractile properties of exercising muscle
oral bicarb supp. produces metabolic alkalosis which may help to buffer lactic acidosis & allow continued intense exercise
illegal under nearly all racing rules (test close to race time)
manipulate race outcome by:
- improving performance when used
- adversely affecting performance when withdrawn
furosemide ↑ plasma bicarb
oral sodium acetate produced metabolic alkalosis similar to that produced by sodium bicard but with later peaks in pH, pCO2, tCO2, HCO3- + BE
Muscle Fiber Types
distribution based primarily on myosin ATPase staining activity (depends on pH of stain)
- Type I = endurance fibers
- Type II = sprinting fibers
Type I
Muscle Fibers
endurance
“red”
↑ myosin ATPase activity after acid-preincubation
↓ in area (not as powerful)
↑ aerobic capacity (endurance)
- ↑ TCA cycle activity
- ↑ mitochondrial enzyme activites → ↑ oxidative phosphorylation
Type II
Muscle Fibers
sprinting
“white”
↓ myosin ATPase activity after acid pre-incubation
↑ in area (more powerful)
↓ aerobic capacity
Training of Fiber Types
- can’t convert between types I + II
- can improve oxidative characteristics of Type II fibers w/ endurance training
- training can result in measurable ↑ in oxidative enzymes characteristic of endurance/aerobic fitness
Myostatin
myokine protein normally responsible for inhibition of myogenesis = musce cell growth + differentiation
animals lacking myostatin have more mucle mass
those with mutations in both copies of gene = signifcantly more muscle mass
Absence:
- double-muscled cattle = belgian blue, piedmontese
- whippets
- TB “speed gene”
↑ Training/Conditioning →
Muscular Response
change fiber type distribution ← ↑ oxidative fiber types
↑ muscle enzyme conc. →
- ↑ muscle oxi. capacity
- ↑ muslce aerobic enzyme conc.
- NC in muscle anaerobic enzyme conc.
- ↑ fat catabolism for energy source
↑ muscle glycogen conc.
↑ muscle fiber hypertrophy
↑ muscle capillary density
↑ muscle capillary transit time
↑ a-v O2 difference
↑ myoglobin conc. → ↑ O2 transport
↑ NM coordination/motor skill
Wolff’s law
bone remodels according to stress/loads placed upon it
normal bone requires certain daily loads/stresses to maintain normal homeostasis
strain = derformation as result of load
stress = force applied/cross sectional area
exercise stresses/loads:
- training/conditioning excercises
- velocity of training + performing
- event specific strains/loads + stresses
Bone Remodeling + Assessment
- exercise induces remodeling of bone
- changes take weeks-months
- less malleable than CV or muscular responses to exercise
- failure in bone adaptation can result in injury or failure or bone +/- soft tissue
Assessment:
- radiography
- scintigraphy
- U/S velocity
- markers of bone metabolism
- CT, MRI, PET
- etc.
Skeletal Scintigraphy
- areas of ↑ bone activity have ↑ uptake of phosphorus/phosphate
- uptake of radiolabeled MDP is also ↑ in areas of ↑ bone activity
- after administration of MDP, gamma camera detects ↑ gamma emmission from areas of ↑ bone activity
Repeated training loads may result in:
Skeletal Response
- asymptomatic appropriate changes in bone
- asymptomatic inappropriate changes in bone - diffcult to diagnose
- symptomatic inappropriate changes in bone
Detraining
period of time after training/conditioning program has been discontinued
undergoing stepwise treadmill exercise test after 5 weeks of rest - previously fit SB horses had no measurable changes in:
- VO2max
- Q
- blood gas tensions
- pH
- plasma [LA]
- less rapid ↓ in aerobic capacity than humans
- minimal ↓ in agility flexibility, skill, NM coordination
- NC in muscle strenght (anaerobic capacity)
- sprinters especially can maintain fitness during brief periods of enforced rest
Long Slow Distance Training (LSD)
- all atheltic horses + sprinters can benefit from ↑ CV fitness
- long slow trotting work → ↑ CV fitness
- only trains horse to go slowly
- eventually speed workouts must be introduced for sprinters
response specific to sprint training:
- NC in muscle anaerobic enzyme conc.
- ↑ muscle hypertrophy
- ↑ NM coordination
- ↑ muscle capillary destiny
- ↑ mnuscle capillary transit time
- ↑ a-v O2 difference
- ↑ myoglobin conc. → ↑ O2 transport
Interval Training
- adopted in humans
- effective means of training SB racehorses
- commonly do 2-3 sprinting exercises with considerable jogging between bouts
- ~ fewer reps than humans
5 wks of combined interval + endurance training → metabolic adaptations comparable to those seen with 12 mo of conventional SB race training
most agree:
- not a panacea
- harder on horses’ legs + minds
- requires more attention + time + patience
Hill Training
- event horses + endurance horses must compete over varied terrain
- trail riding for fitness training inevitably leads to terrain changes
- commonly used in England for TB racehorse training
Racing Disciplines
true sprinters
training (sprinting) →
- ↑ muscular strenght → ↑ power
- ↑ CV conditioning
FEI Disciplines
- dressage + para-dressage
- driving + para-driving
- jumping
- eventing
- vaulting
- endurance
Olympic Equestrian Sports
- dressage
- jumping
- eventing (3 days) = dressage + cross country + jumping tests
Dressage
each horse in class performs same test
test designed to elicit horse + rider pair’s ability + preparadness to demonstrate:
- willingness/behavior
- movement/gait
- balance
- suppleness
welfare issue in europe regarding poll hyperflexion
- can lead to dorsal pharyngeal collapse when on bit
- repeatable DDSP + coughing may occur
Reining
“western seat dressage”
all competitors ride a single published pattern
ground jury members score the ride
high score wins
prone to hind limb injuries d/t sliding stops:
- stifle
- hock
- high suspensory
might wear special shoes
Hunter/Jumpers
Hunters:
- judged by manners, freedom of movement + gait, temperament
Jumpers:
- not judged
- scored on ability to clear jumps without knockdowns within time allowed
Eventing
Long Format (Classic)
- Day 1 = dressage test
- Day 2 = cross country (4 phases)
- Day 3 = jumping test
Short Format
- only phase D - cross country of cross country test
- seperate team + individual competitions
- need seperate horses for one trainer
D Box
rectal temp may increase to ~107F
inital HR ~180-200/min
initial RR ~180/min
indicators of a need for ↑ cooling efforts:
- T ↑ while recovering
- inversion of HR + RR while recovering
aggressive cooling may be required
Rotational Fall
when jumping over hurdles
horses prone to injure shoulder, neck or head
rider prone to injury
different hurdles made to help prevent injury
- frangible pins = has soft spot that break upon contact
- MIMs chlips = keeps pole from falling + rolling away
Driving
retain “long format”
- Phase A = trotting
- Phase D = walking to recover from A
- Phase E = obstacles
Endurance Racing
races = 25-100 miles < 24 hrs
arabians most successful
- ↑ type I fibers
- ↑ plasma [FFA]
- ↓ RER
lose ~5% of BW in 100 miles → takes ~48hrs to put weight back on
Competitive Trail Rides
- distance event similar to endurance racing
- distance = 12-100 miles
- shorter segments split 1-3 days
Ride is judged, not based on fastest finisher:
- fitness : HR recovery
- soundess/way of going
- horses’ trail manners/behavior
Draft Horses
~1400-2200 lbs
true weight-lifters
large muscles masses →
- ↑ power for pulling loads
- ↓ endurance for long trips
- poor innate CV abilities
- thermoregulation is more difficult
smaller heart + spleen size relative to size compared to other breeds
Racing v Non-Racing Governing Bodies
Racing:
- international = by ind. country
- canada = provincial
- USA = by individual states
Non-racing
- FEI
- Equine canada
- USEF (USA)
Drug Testing Philosophies
1) Zero Tolerance = FEI
2) allowable limits
3) performance day use allowed (have thresholds)
General Medication Categories
- To win = stimulant, ergogenics
- To lose = depressants
- to restore “normal performance” = NSAIDS, intra-articular corticosteroids
- to mask/dilute = diuretics
Performance-Enhancing Drugs
- stimulants = opioids, cocaine, amphetamines
- ergogenics = bicarb + other alkalinizers
- blood-doping = EPO
- anabolics = anabolic steroids, GH, B adrenergic agonists
Stimulants
- primarily a problem in racing jurisdictions
- cocain + opioids
- suspected in horses with quick improvement of racing form
- non-racing horses which must be fast/animated = barrel racing + gaited horses
- tail (ginger)
- visual
- auditory
Performance Enhancers
difficult to prove given drug enahnces performance but still used/prohibited
- stimulants
- ergogenics = bicard, alkalinizing agents
- anabolic steroids = testosterone, etc.
- clenbuterol - bronchodilator, anabolic effects (prohibited in food animals)
Performance-Impairing Drugs
- sedatives = a2 adrenergic agonists (xylazine)
- tranquilizers = acepromazine, reserpine
- CV depressants = b-blockers
- withold water for several hours (drawing) then letting them drink ecessively before racing
Depressants
For:
- makes racehorse fail to race fast
- non-racing quiet performance
How?
- tranquilizers
- cocaine night before → excessive fatigue next day → quiet performance
Performance-Restoration Drugs
- bronchodilators
- NSAIDS
- corticosteroids
Maintenance drugs that may alter performance?
- vaccines, anthelminthics
- feed additives = vitamins, minerals
Analgesics
- opioids = prohibited under all rules
- NSAIDS = rules vary widely for use during competition
Masking Agents
diuretics
- enhance urine production
- furosemide
not as critical in horses when relying on blood/plasma test as opposed to urine tests only
RCI Uniform Classification Guidelines
1992
- No accepted therapeutic value
- therapeutics + high abuse potential
- therapeutics + lower abuse potential
- therapeutics + lowest abuse potential
- misc. therapeutics with no abuse potential but conc. limits
FEI MCP
medication control programme
Zero Tolerance:
- for many meds especially analgesics on performance day
- all NSAIDS prohibited since ‘92
Allowed Substances (2012)
- most abx
- anthelminthics
- vitamins
- fluids + electrolytes
- anti-ulcer meds
positives in the 90s mostly d/t show jumpers
USEF General Drug Rule Categories
- stimulants
- depressants
- performance enhancers
- analgesics
- masking agents
prohitied NSAID used in 2011
- may not use more than 1 NSAID at any time in comp
- plasma restrictions set in place
Positives
- NSAIDs > allowable limits
- tranquilizers = short v long acting
Drug Regulations Summary
FEI has zero tolerance for detection of drugs during performance
EC + USEF allows one NSAID during performance
