Equine Digestion Flashcards
Digestive tract
- def
- functions
= Tube lined with mucous membrane from lips to anus
- Chemical digestion – enzymatic + microbial fermentation
- Absorption
- Elimination of waste
Structure of tract reflects diet. Major differences between species
hind gut fermenting herbivore
Mouth
four func
- prehesion (lips, tongue, teeth)
~ 6 upper and lower incisors, premolar and molars
~ 4 canine teeth (tushes) in males and some females
~ teeth ridged and continuously erupt
~ wolf tooth (can cause problems and may need to be removed) and interdental space between premolars and canine (where bit sits but long head so eyes can be level with surroundings while eating)
- mastication
- insalivation = mixing of slaliva with ingesta
~ 12-100 litres/day
~ secreted in response to chewing
~ lubricant
~ buffer = contain bicarbonate with high pH
~ low amylase (starch digest)
- bolus formation = process of turning food into size for swallowing
Salivary glands
- parotid gland
- mandibular gland
- sublingual gland
- buccal or submaxilary gland
Stomach
- compared to other species
- physical description
- Major organ for storage and digestion. Big differences between species
- Horse: relatively small and inelastic (10% gut volume). Transit time quick (0.5 – 1.0 hour)
- stomach does not stretch, limit intake at one time
- enter via esophagus
- lined with squamous and glandular mucosa
- margo pilcatus = margin between glandular and squamous mucosa
- leave via pylorus and duodenum
Stomach - equine specific factors
Two distinct regions with different mucosa and pH
-Oesophageal/cardia/saccus caecus/non-glandular fundus:
~ Squamous epithelium; no gastric secretions
~ Significant fermentation of CHO
~ Susceptible to acid damage (ulcers)
- Glandular fundus:
~ Secretion of mucus, acid and enzymes
~ Digestion of protein begins
~ Can also get ulcers (peptic ulcers)
- Entrance and exit controlled by cardiac and pyloric sphincters.
- Little regurgitation.
- Cannot eructate (belch) or vomit
- gas production may cause colic
- Stomach rupture more likely than vomiting = cardiac sphincter with strong musculature, stomach enlarges
Normal cycle of food through stomach
- food enter
- bacterial fermentation
- gastric acid mixes
- pH drop
- fermentation stops
stomach - acids and ph in diff regions
- Saccus caecus
~ non-glandular stratified squamous epithelium
~ where most bac ferm occurs
~ soluble carbohydrates turn into lactic acid - fundic region
~ 1000x10^6 bac per gram of ingesta
~ mainly lactobacteria
~ pH 5.4 = enzymatic digestion of protein and fat starts
~ as pH drops microbial activity and degradation stops - Pyloric region
~ pH 2.6
~ proteolytic activity of pepsin is 15-20 x that in fundic region
Small intestine - general
- Longest part of gut (20 metres).
- Transit time quick (1 hour)
- Three regions
~ Duodenum
~ Jejunum
~ Ileum - Completes enzymatic digestion (duodenum) and absorption (ileum)
- 30% of gut volume
Small intestine - three secretions in duodenum
- Intestinal juice ~ Mucus, Maltase, Sucrase, Peptidases (chains to amino acids) - Pancreatic Juice ~ Bicarbonate - buffer = alkaline ~ Trypsinogen, Lipase, = protein and fat breakdown ~ Amylase (poor)* - Bile ~ bile (secreted by liver) No gall bladder (continuously produced)
*the horse has a limited ability to digest starch in the small intestine
Small intestine - surface and absorption
- Surface area of ileum increased by folding – villi and microvilli
- Absorption by diffusion, active transport or pinocytosis.
- Excellent blood supply by portal vein. (not fats = absorbed by lacteals = lymphatic cappilary in the vili)
large intestine - parts and functions
- Largest part of digestive tract (60 % of gut volume) Transit time slow (24 hours)
- Four parts
~ Caecum (15%)
~ Colon (40%)
~ Rectum (5%)
~ Anus - Functions
~ Hind gut fermentation of cellulose, hemi-cellulose and pectins (caecum and large colon)
~ absorption of water (small colon)
~ elimination of waste - over 60% gut volume
- 7m long
- have folds that go back on themselves = tend to get blocked = colic
Large intestine - hind gut fermentation
- Hind gut fermentation of major significance to horse.
- Material reaching hind gut indigestible (resistant starch and fibre)
- Vast microbial population in hind gut
~ Bacteria (1010/ml)
~ Protozoa (106/ml)
~ Anaerobic fungi (105/ml) - Symbiotic relationship, host ideal environment, microbes digest fibre = horse gets energy molecules
Microbial protein?
Unlike in the ruminant (abomasum, small intestine w/ enzymes to break down protein, absorb amino acids), protein produced by hind-gut microbes is not very available to the horse and is largely excreted in faeces.
large intestine - two stages
- complex carbohydrates to simple sugars using microbial enzymes, extra cellulear
- simple sugars to VFAs (volatile faty acids) using microbial enzymes, intracellualy
Large intestine - 3 main VFAs produced
- acetic acid (2c)
- propionic acid (3c)
- Butyric acid (4c)
allow for high pH within large intestinal contents
(also CH4 and CO2)
Healthy ratio = A = 70%, P= 21%, B=7%
but if starch reaches hind gut, converted to lactic acid = pH falls
