-
Horses are grazing animals
- evolved from plains
- graze in cycles throughout the day as a moving herd
- digestive tract best suited for forage diet
- small meals multiple times a day
- eat grasses that change with seasons throughout year
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DOmestication
- stall confinement
- meal feeding
- high amounts of concentrates (corn, oats)
-
Equine managment today has higher risk of health issues
- colic
- muscle-associated disease
- laminitis (hoof)
-
Hindgut fermentors
- cecum
- large colon
- small colon
- rectum
-
monogastric herbivore
- simple stomach - cant utilize forage (high fiber)
- Hindgut - extensive fermentation after primary sites of digestion and absorption, digest forage as primary source of nutrition
-
compared to human GI tract
- same except ascending colon is for fermentation
- appendix = cecum
-
amount of digestion and absorption of nutrients
- 40% forgut
- 60% hindgut (fermentation)
-
route of digesta
- stomach, duodenum, jejunum (same as most animals)
- Ileum (starts to change to fermentation)
- ileocecal Valve
- Cecum (start of fermentation)
- cecocolic orifice
- Right ventral colon
- sternal flexure
- Left ventral colon
- pelvic flexure
- Left dorsal colondiaphragmatic flexure
- Right dorsal colon
- Transverse colon
- Small colon
- Rectum
-
Duodenum
- short
- 3-7 ft
- dorsal
- on right side and goes behind right kidney
-
Jejunum
- 70 ft
- cranial mesenteric artery
- dorsal body wall mesenteric connects
-
Ileum
- avascular band of tissue continues with dorsal band on cecum
- iliocecal orifice to cecum
-
Cecum
- 1st part of fermentation
- caudal abdomen
- transistion time slows down for better absorption
- primary site of water absorption
- holds 30 L of fluid (more w/ disease) ~ 60 lbs
- cecocolic junction
-
rt arm example
- forward movement to diaphragm
- around rt ventral colon
- sternal flexure on bottom
- left ventral colon (narrows) and goes up
- pelvic flexure
- back toward diaphragm
- left dorsal colon
- diaphragmatic flexure (on right)
- rt dorsal colon
-
conversion
1L ~ 1kg
1kg ~ 2.2 lb
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Transverse colon
- very short <1 meter
- little nutrient effects
- dorsal
-
Descending colon
- makes feces shape
- "apples"
-
species differences
- Small colon = descending colon
- Large colon = ascending only
-
Foregut
- digestion and absorption of non-fiberous feed ingredients
- protein
- fat
- sugar/starch (non structural carbs)
- water
- vit/minerals
- stomach
- small intestine
-
Hindgut
- digestion and fermentation of fibrous feed ingredients
- structural carbs
- cellulose
- hemicellulose
- Larger intestine
- cecum/large colon
- small colon/rectum
-
starch digestion
8% in stomach and Small intestine
-
Amino acids, fat, vitamins, and mineral
- 30%
- digested and absorbed in small intestine
-
-
Lips
- prehension (soft)
- bring food to mouth
- lips when eating from a manger
- teeth when grazing
- lips form suction for drinking water
- lots of sensation
-
Tongue
- propulsion of feed bolus to pharynx to be swalloed
- cranial nerve XII
- Hypoglossal
-
Teeth
- chew - lateral excursion (grind) on occlusal surface
- increases surface area
- chew continuosly (up to 60,000 times a day)
- allow enzymes to begin digestion
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Hypsodont Teeth
- 4 types
- Incisors - cutting 6 uppen and 6 lower
- Canine - tearing/fighting (males only) 2 upper and 2 lower
- Wolf teeth - on top before premolars, spikey, can be removed premolar 1
- Premolars - grind, 6 upper 6 lower
- Molars - grind, 6 uppen 6 lower
- grow entire life
- bottom jaw is more narrow
-
points on teeth
- cause problems
- malnutrition
- not able to grind feed properly
-
floating
- routine care
- remove sharp points
-
poor dental health
- Quidding - dropping feed
- abnormal head postion during chewing
- loss of condition
- Colic
-
Salivary glands
- parotid - largest
- submaxillary gland
- sublingual gland
- moisten feed, lubrication, amylase, bicarbonate (buffer for stomach acid)
-
Saliva
- < 40 L per day ~ 10 gallons
- flow rate affected by - parasympathetic, Increase then increase flow (more saliva
- Sympathetic - increase then decrease in flow
-
esophagus
- swallowing = degluttion
- requires intensive neurological coordination
- transport of food from mouth to stomach
- peristaltic contractions
- muscular tubular organ
- Proximal 2/3 - straited m.
- Distal 1/3 - smooth m
- propulsion of food bolus
-
"Choked"
wad of feed stuck in esophagus
-
esophageal sphincters
- upper esophageal sphincter - circopharyngeus m.
- lower esophageal formed from distal esophageal musculature
- esophagus obliquely enters stomach (can kink)
-
Esophagus problems
- stomack can cause esophagus to kink
- lots of tone in lower esophagus
- horse very rarely vomits and if so is a sign of morbitity
- stomach will rupture before vomiting
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Stomach
- 8-12 L : small volume b/c small infrequent meals
- rapid gastric emptying (2-12hr) b/c of forage diet
- similar to human stomach
-
function of stomach
- reservoir for controlled release of digesta to SI
- Mix/mechanical break down of feed (hydrolytic digestion by acid and enzymes)
- HCl- parietal cells, acetlycholine + gastrin + histamine 2 receptors = all have to be bond to parietal cell to produce HCl
- gastrin (g-cells) also in pancreas and duodenum
- pepsinogin (chief cells)protein break down
- HCl - makes low pH, bacterialcidal
-
Anatomy of stomach
- cardiac sphincter
- squamous portion
- margo plicatus
- glandular portion and fundic region
- pyloric spincter and outflow
- greater and lesser curvature
-
margo plicatus
separates top squamous from bottom glandular
-
Feed bolus
- in pyloric region
- protects squamous epithelium from exopsure to HCl and bile acids
- prevents HCl from splashing up on to squamous mucosa in nonglandular region
-
greature curvature
ruptures b/c weakest when distended
-
Glandular mucosa defense against acid
- mucus barrier bilaryer
- bicarbonate secretion
- rapid regeneration and repair
- reflux of duodenal secretions (from common bile duct, pancreas/hepatocytes) neutralizes HCl in stomach
-
Small intestine
- duoenum + jejunum + ileum
- 30 % of GIT
- 70 ft
- 40 - 50 L
- 3-4 hr for transit
-
duodenum
- common bile duct - continuous release in horses
- NO gallbladder
-
Small Intestine
- primary site of digestion and absorption of protein, fat, vitamins and minerals
- CHO (sugars, starch, non structural), limited digestive capacity b/c not enough amylase
- * to much non structural changes microb pop = COLIC
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Large meals
- promotes rapid transit to cecum
- incomplete pre-cecal digestion = COLIC
-
Cecum
- 30 L
- slow rate of passage
- initiation of fermentation
- bacterial, protozoa, fungi
- microb health determined by diet
- microb determine GI health
- 50 % of forage
-
Microbial fermentation
- VFA - Metabolized for energy - liver for further breakdown
- Gas - waste energy
- B-vitamins
- vitamin K
-
high lactic acid
lowers pH = COLIC
-
Fermentation of Cellulose
- ultra-abundant
- easy to obtain
- plant cell wall and fiber high in energy
- Cellulase - only found in bacteria and some protozoans and is needed for cellulose break down
- indigestible by mammalian digestive enzymes
-
Fermentation digestion
- mammals have little capacity of utilization of fiber
- fermentation is related to the fraction of total digesta contained in fermentative compartments of the GI tract
- horse - cecum, mainly colon and rectum
- Cattle and sheep - mainly reticulum
-
Large Colon
- additional site of microbial fermentation
- primary site of water absorption (cecum also)
- microbial production of vit B and Vit K
-
Transverse colon
- very little significance
- very short time
-
Small Colon
- absorbs water
- creats fecal ball "road apples"
- rectum stores and expels feces
-
Balanced diet
- water
- energy - fiber + non structural CHO + fat
- protein
- vitamins
- minerals
-
equine nutrition
- feed good quality hay/ pasture, water and a trace mineral salt block
- meets most requirements
- NRC - book at 6th edition, new info on equine nutrition
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water
- 50 ml/kg/day
- > 6 gallons per day
- average horse 500 kg
- 500 kg x 50 ml/kg = 25,000l/day
- 25,000ml = 25 L per day
- 1 L = 1 quart
- 4 quarts = 1 gallon
-
water
- maintenance
- replace insensible - sweat, feces, urine, lungs (happens no matter what horse is doing)
- daily metabolic processes
- periprandial drinking
- primary site of water absorption - cecum, large and small colon
-
water intake
- varies with environmental conditions, workload, diet, lactation
- increase fiber increase water intake
- always provide fresh, clean, potable water
- make sure not frozen - use proper working ehat pump if necessary
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encourage water consumption
- provide electrolytes
- oral electrolyte paste
- trace mineral salt block
- offer warm water in winter months
- sweat too much - sweat is hyperontic to plasma, causes decrease in electrolytes
- always provide plain water in addition
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energy
- maintenance, growth, pregnancy, lactation, work
- excess energy causes - developmental orthpedic disease
- equine metabolic syndrome (type II diabetes)
- laminitis
- obesity
- reduced performance
- colic
-
energy units - digestible energy
- calorie - 1 g of water to 1 degree Celsius
- kilocal - 1000 cals
- Megacal - 1000 kcals
-
maintenance
- 16 Mcal/day
- rest, no work, or use
-
light work
- 20 Mcal/day
- pleaseure, trail
-
Moderate work
- 25 Mcal/day
- longer, intense training, ranch work
-
heavy work
- >30 Mcal/day
- heavy work, racing, lactation
-
energy = fiber + CHO + fat
- fiber, basic for all equine diets
- structural cabs ~ forage feed
-
fiber = forage
- structural CHO
- Fermentable CHO - beta 1-4 linkages (glucose linkages, used by microbes)
- common forages - hay (legumes, grasses) pasture forage
- >50 % equine diet should come from forage feeds
- Ensures GI Health
- non structural - oligosaccarhides also need fermentation
-
forage feeds
- digestion of plant cell wall - cellulose and hemicellulose
- requires microbe fermentation - enzyme cellulase, pH 6.5
- fermenation - large intestine
- efficient, slow, time consuming
- Small intestine tract - some fermentation
-
-
fiber = energy
- volatile fatty acids
- primary source of energy
- 30 - 70 % of daily energy
-
Equine volatile fatty acids
- produced in cecum/arge colon - absorbed stright into blood stream
- acetate - immediate energy, decreases when increase in grain feed
- proprionate - gluconeogenesis(use other source to produce glucose) in liver, increase proprionate w/ grain feed,
- Butyrate
-
Absorption of VFA
- across intestinal wall - passive down pH gradient as free acids
- directly into the portal blood - liver to muscle
- rate of absorption related to molecular weight - acetate, proprionate, butyrate
- absorption maintains intestinal pH
- related to salt and water movement
-
meal feeding of horses
to much VFA, water into GIT decreases blood fluid, increase in renin production
-
VFA
- slow release for sustained energy - maintenance requirments
- if additional energy is needed - feed non structural CHO and fat
-
non structural CHO
- simple sugars - alpha 1-4, monosaccharides, polysaccharides (amylase)
- pancreas - brush border, enzymatic hydrolysis of CHO, amylase, sucrase, lactase, to duobenum by common bile duct
- digestion begins in stomach - SI, 50 to 70% is digested
-
Amylase
- primary starch digestion
- horse - limited production
- feed concentrates = colic b/c not enought amylase to digest
- non digested CHO goes to hind gut cecum
-
CHO non strucutral
- oats, corn, molasses
- sweet feed 50% non structural CHO
-
Concentrates = colic
- incomplete pre-cecal digestion (b/c of lack of amylase to digest)
- bacillus, lactobacillus, streptococcus - ferment starch, produce lactic acid, alters pH (decrease), injures mucosa, dysmotility
- gas distention of cecum/colon = colic
- normal microbes die - b/c of low pH, endotoxic shock (leads to laminitis), gas production
- burned mucosa from toxins, toxins into blood, leads to laminitis,
- some toxins from normal bacteria death - liver can handle
- to much bad bacteria - decrease pH, bad microbes work better, good die off in great quanitities, produce lots of toxins, leads to toxic shock, laminitis
-
prevent pre-cecal digestions
- feed NSC separatly from forage
- consider source of starch
- decrease amount of starch intake/meal/day
- processing of starch - oats highly digestible, corn requires processing to increase digestion (pop), grinding/popping/heat treatment(oats mainly)
- individual digestive variability - amount of amylase depends on each individual horse
- 5 lb of grain a day, increase colic by 6 times
- need 2 g per kg of body weight
-
NSC
- rapid energy for high energy required horses
- ex - underweight "hard keepers"
-
NSC
- avoid in certain disease states
- cushings - long shaggy coat, hyperglycemic
- equine metabolic syndrome
- laminitis - rock back onto hind quarters, 60% of body weight is usually on front limbs
-
excess energy
- "hot horse" - difficult to handle
- weight gain
- young horses - developmental orthopedic disease (endocrine problem)
-
structural CHO
- roughages
- low stratch
- high fiber
- low digestible energy
-
nonstarch CHO
- grains
- high starch
- low fiber
- high digestible energy
-
Glycemic index
- CHO on blood glucose
- high glycemic feeds - CHO break down quickly during digestion, releasing glucose rapidly into circulation
- Low glycemic feeds - CHO break down more slowly, releaseing glucose gradually into blood
-
Diabetes II in equine
- hypoglycemic
- need low glycemic feed
- lower peaks of glucose absortion
-
fat
- <2-3% fat/day
- good for energy w/o CHO overload
- fat = high energy density (2.25 to 1 CHO)
- triglycerides = 3 FFA + glycerol back bone
-
fat digestion
- lipolysis
- 100% absorption in SI tract by micelle (absorbed by brush border), w/in enterocytes, lipids form chylomicrons, travel through lymph
- bile acids - from hepatobiliary tract, released from common bile duct into duodenum, coat TG, pancreatic lipases surround TG (cleave TG = glycerol + FFA)
-
fat in liver
- depends on energy requirments
- TCA - ATP
- excess - esterified back to TG, stored at FA hepatocytes, limited space
- glycerol for gluconeogenesis
- made into ketone bodies
- made into very low density lipoproteins
- VLDL (very low) - adipose tissue, equine very efficient at making
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