2: Digestive physiology of horses Flashcards
What kind of digestion to horses do
Monogastric, hind-gut fermenters
What is the most significant part of the horse GI tract? Why?
The large intestine is 50% of the length of the small intestine (much larger than the ratio in dogs or cats)
They need to get sufficient energy from the diet that they eat
Fiber fermentation creates what?
SCFA (acetate, butyrate, propionate)
What type of fermenters are horses
Obligate hindgut fermenters
Large caecum for fermentation
What is colic? Six reasons
Horses are fed a lot of rapidly fermentable material = a lot of gas production in the colon = colon expands and rises in the body cavity and parts of the GI tract get blocked
Reasons: gas, simple obstruction, strangulation, impaction, inflammation, ulceration
Saliva in the oral cavity of the horse
Saliva secretion stimulated by mastication (intense chewing compared to dogs and cats)
Saliva contains a small concentration of bicarbonate (provides buffer against stomach acids, allows some microbial fermentation in stomach)
Horse saliva contains amylase
How many teeth do horses have?
Approximately 36 total
- 12 incisors, 12 premolars, 12 molars
- May have canines and wolf teeth
Three sections of the horse stomach, their epithelium and role
- Oesophageal region: squamous epithelium
- Fundic region: glandular epithelium
- parietal cells secrete HCl
- Zymogen cells secrete pepsin - Pyloric region: glandular epithelium
- secretes gastrin (incretin, stimulates release of HCl and pepsinogen)
Where does microbial fermentation occur in the stomach
Oesophageal and fundic regions
Describe digesta transport through the stomach
Stomach is a small organ in adult horses
Most digesta passes quickly into the SI
Relative emptying time of 120 mins (fast)
Segments of the small intestine
Duodenum (3m)
Jejunum (20m)
Ileum (45m)
Small intestine is the primary site of digestion and absorption of…
protein, starch and fat
Exocrine action of the pancreas
- secretes enzymes and bicarbonate salts into the gut
- enzymes: inactive proteases, lipases and amylases
Endocrine action of the pancreas
- secretes hormones into the blood
- hormones: insulin, glucagon
Role of the liver
Produce bile that continuously drains into the SI which emulsifies dietary fat and activates enzymes to aid in fat digestion
Why is there no gall bladder in horses?
Don’t need to break down large amounts of fat
Continuous flow of small amount of digesta, bile does not need to accumulate in large amounts for one large meal
Gradual release of bile
What is the caecum? Contains what? Is responsible for…
Start of the large intestine (very large)
Contains microbial population similar to rumen (protozoa, bacteria, other microorgs breakdown fiber)
Responsible for microbial synthesis of SCFA and protein
Name the four large compartments and three major flexures of the large colon
- Right ventral colon: sternal flexure
- Left ventral colon: pelvic flexure
- Left dorsal colon: diaphragmatic flexure
- Right dorsal colon
What is the small colon?
4-5m small traverse colon & distal dorsal colon that ends into the rectum
Intestinal histology of the SI vs LI
SI: villus, crypt
LI: no villi, crypts are deeper
What are the ways the intestine increases capacity?
Coils, folds, villi, microvilli
Look at slides 17, 18, 19
DO It
What is a peptide? consists of…
Chain of amino acids
N terminus, polypeptide chain, C terminus
Name two protein digesting enzymes, their location and primary action
Pepsin: stomach, cleaves bonds of aromatic AA at the N-terminus
Trypsin: pancreas, cleaves peptide bonds joining basic AA
What might be reasons for AA absorption to happen as single AA and small peptides
- small peptide absorption costs the same amount of energy as single AA
- transporters can only absorb certain aa; peptides are backups
Slide 21,22
LOOK
Why is brush border transport of proteins not limited in some young mammals
Antibodies are proteins found in colostrum that need to cross the brush border if there are no antibodies transferred via the placenta
Most AA transport is…
active transport
Slide 24-27
know
Enzyme involved in fat dig/abs? Location of origin? Primary action?
Lipase
Pancreas
Break down triglycerides into free f.a. and monoglycerides
How do fats get absorbed? Where do absorbed fats drain into firt?
Bile, emulsification breaks down triglycerides into f.a.
Lymph
Major site of SCFA production/abs? How much energy do horses get from SCFA
Large intestine
50-70% of energy from SCFA
Slides 31, 32
SCFA uptake*
Three methods of SCFA uptake
- Passive
- Facilitated
- Symporter
What are some physiological adaptations of horses?
No gall bladder, LI digestion, no vomiting, colic, molars/oral cavity
