Equine Physiology Flashcards
Old dental naming system
Inscisors: - corner - intermediate - central Wolf tooth: vestigial - then number 1-6 - or: PM1 (wolf tooth) - PM4 and M1, M2, M3
Triadan numbering system
*start with central inscisor* Upper right: 100s (101-111) Upper left: 200s (201-211) Lower left: 300s (301-311) Lower right: 400s (401-411)
What tooth number is the wolf tooth on the upper right side?
105
What tooth number is the canine tooth on the lower left side?
304
Herbivores vs carnivores
Grinding vs shearing
- even inscisors are flat in the horse
- grinding high silica content feed wears away teeth
Hypsodont dentition
Teeth which have a limited growth period, but prolonged eruption
- seen in horses
Elodont teeth
Permanent growth and eruption throughout life
- seen in rabbits
Brachydont teeth
Limited growth and limited eruption time
- seen in dogs/cats
Equine teeth go thru contstant wearing away of _______
Occlusal surface
- pulp cavity constantly retracting
- secondary dentin constantly being laid down to seal pulp cavity
- any malocclusion leads to dental overgrowths –> can impede mastication
What cell type lays down secondary dentin?
Odontoblasts
- reside in periphery of pulp cavity, but have processes that extend through the dental tubules (3-5 mm)
What are the 3 types of dentin?
Primary: laid down as the tooth forms before it erupts and is in wear
Secondary: continues to form as the occlusal surface is worn away and pulp cavity retracts –> seals off pulp cavity
Tertiary: forms in response to local insults
What is dentin composed of?
- 70% minerals (hydroxyapatite crystals)
- 30% organic components
When do permanent premolars erupt?
- 06s: 2.5 yrs
- 07s: 3 yrs
- 08s: 4 yrs
- all are preceded by a deciduous tooth*
When do molars erupt?
- 09s: 1 yr
- 10s: 2 yr
- 11s: 3.5 yrs
When do the incisors erupt?
- 01s: 2.5 yrs
- 02s: 3.5 yrs
- 03s: 4.5 yrs
- are in wear against the opposite member within 6 months and are preceded by a decidious tooth*
When should all caps be gone?
By 5 years, all teeth should be fully in wear against opposite member
When does root development slow down?
By 7 years, overall length of teeth begins to become shorter
- by 12-15 yrs all development has stopped
Anisognathic
Upper arcade is 25-30% wider than the lower
- naturally leads to sloped occlusal surface which increases feed efficiency
- incisors meet, cheek teeth do not!
Points
Where teeth do not meet
- teeth won’t wear and will overgrow
- most horses develop points to some degree, leading to poor feed utilization and loss of body condition
Points create _____
Ulcers
- prevented by rasping the sharp edges
- typically occurs in the outer edges of the uppers and inner edge of lowers
Hooks
Upper arcade is set rostral relative to lower arcade, resulting in rostral aspect of upper first cheeck tooth getting overly long and caudal aspect of last lower cheek tooth doing the same
want to be careful to not cut off at the pulp cavity!
Formation of hooks will stretch the jaw out of alignment and create stress on the _____
TMJ = unequal wear on the incisors
- pushes upper arcade even more forward
Esophagus
- rostral 2/3 is striated
- caudal 1/3 is smooth with thicker muscle and a smaller lumen = well developed lower esophageal sphincter
- enters stomach obilquely
Do horses vomit?
No, many horses will rupture their stomach before they regurgitate or vomit
- passing a stomach tube on a colic is life saving
GIT of the horse
Small stomach, long small intestine with a fast transit rate
- fermentation occurs in the colon
- GIT has more nerves than the spinal cord (local enteric nervous system) and lacks a blood barrier
Equine GI volumes
- stomach: 8-15 L (8%)
- SI: 40-60 L (30%) = 70 ft
- cecum: 28-36 L (15%) = 4 ft
- large colon: 80-90 L (38%) = 10-12 ft
- small colon: 16 L (9%) = 10-12 ft
Do horses have a gallbladder?
NO, continuously forage throughout the day so no need for storage
Horses are _______
Non-ruminant herbivores (hind-gut fermenters)
- digest simple carbs and also utilize fibrous sources
Enzymatic digestion occurs in the ___
Foregut ahead of the cecum
- accounts for 52-58% of crude protein digestion, all protein absorption, long chain lipid absorption, and all soluble carb digestion/absorption
Is there enzymatic digestion in the large intestine?
NO
- all products of microbial proliferation are lost to the horse
Regions of the equine stomach
- stratified squamous: does not contain any glands
- cardiac: contains mucus and bicarb glands
- fundic: produce some mucus, mostly acid and protease production
- pyloric: rich in mucus glands, some bicarb, some protease production
Pepsin
Breakdown of proteins into amino acid chains
- occurs in the stomach
Does the stomach absorb water?
Yes, also ions and lipid soluble compounds
What is the end product of stomach digestion?
Chyme
- partially digested food as it moves through the GIT
Rate of food as it moves thru the stomach
- fluid: 20-30 min
- grain, pellets, short fresh grass: 0.5-5 hrs
- long stem dry hay: 16 hr
- stomach will empty when 2/3 full, regardless whether full digestion has occurred or not*
Horses are _____ grazers
Continuous
- produce acid 24 hr/d
- no gallbladder
- often fed once or twice daily by owners
Gastric ulcers
Caused by acid production
- horses eat continuously
- empty stomach is at pH 1.5, so forage is needed to act as a buffer
- feeding EOD results in ulcers and increased rate of cell destruction (also accomplished by NSAIDS)
NSAIDS
Inhibits production of PGE, limiting blood flow
- replication rate cannot keep up with destruction rate
Liver
- no gallbladder due to continuous feeding, so liver produces bile
- anorexia = hyperbilirubinemia (unconjugated form)
- converts VFAs into glucose or FAs
- proprionate = glucose (up to 50%)
- acetate = long chain FAs
Pancreas
- HCO3
- amylase (alpha bonds)
- chymotrypsin
- lipase (horses produce as much as a carnivore)
What is the predominant energy source for horses?
Carbohydrates
- reason why horses tolerate large amounts of fat added to their diet
Small intestine
- secretory H2O
- nutrient absorption
- rapid transit
The proximal half of the SI is more ____
Secretory than absorptive (when looking at volumes of water)
Grain overload
When significant levels of CHO pass thru SI without being absorbed and end up in the cecum = significant changes in microbial population
Amount of fluid secretion in the upper GI
- salivary: 10-12 L
- pancreatic: 10-12 L
- biliary: 4 L
= 120-140 L for a 500 kg horse
half of animal’s body water is circulated thru GIT
Large intestine microbial action
- carbs: cellulose, hemicellulose, lignin
- cellulase: beta bonds (glucose breakdown)
Glucose under anaerobic conditions produces ____
VFAs
- acetic acid: used directly by mammalian cells and liver
- proprionic acid: liver
- butyric acid: used by colonic cells
- pH slightly acidic
Proteases
Breakdown plant protein into peptides
- take in and converted into microbial protein
Cecum and colon
Anaerobic fermentation vat
- VFAs = 50-80% of energy needs –> 30% from cecum, 50% from colon
- some water soluble vitamins
Cecum: inlet and outlet near the top
MIcrobial fauna
Needs time to adapt to change
- grain overload leads to lactic acid buildup
- damage colon wall
- microbes die off
- endotoxin release
For every 24 hrs off feed
Microbial populations drops by 50%
- refeeding must be gradual
Colon
100-140 L
- water reservoir (beet pulp)
- effect on respiratory rate during exercise –> 200-300 lbs slams into diaphragm with each stride
- stride and respiratory rate are synchonized
