Gastrointestinal tract Flashcards
key features of equine digestion
- non-ruminant herbivore with significant fermentation in hind gut
- rely on microbes in GIT to break down fibrous portion of diet
development
underdeveloped large intestine at birth -increases over first year foals begin suckling at 1-2 hours after birth and spend 6-8% of day suclkking -by 8 weeks 2% of days -21 weeks 50% of day eating solids
coprophagy
- consumption of feces, common in horses
- possibly helps colonization of GIT
stomach
relatively small in horses and rarely empty
- 2x capacity of pig
- limited ability to vomit
transit times total
total 23-48 hours, 75% of time spent in hindgut’s cecum and colon
transit time stomach
- fast through stomach: 2-6 hours following ingestion, about 75% liquid and 24% dry passed out of stomach
- transit through stomach only 30 min to 1.5 hours
stomach digestion
- carbs, proteins, and fats mix with digestive enzymes and partially digested when passed to small intestine’s duodenum
- few microbes suited for acidic environment of stomach, but there are some anaerobic bacteria to help digest ready carbs
- as digesta approaches stomachpH falls, due to HCl secretion that initiates pepsin activity and reducing fermentatio
small intestine anatomy
duodenum, jejunum, and ileum
- total length 25 m
- attached to mesentery and mostly freely mobile
- where major digestion of proteins, fats, and non-structural carbs
- enzymes produced by pancreas enter duodenum
large intestine/hindgut anatomy and function
cecnum and large colon
- digesta reaches cecum by 30-45 minutes after leaving stomach
- insoluble carbs pass through small intestine and are fermented by microbes in cecum and colon
hindgut environment/microbes
major microbes include cellulolytic proteolytic, lactate-using, and glycolytic bacteria
- cecum more cellulotytic bacteria and less starch-using bac than colon as it is primary location of FIBER digestion
- horses LESS EFFICIENT than ruminants but donkeys are similar to rums
hindgut shape and function of delaying digesta passage
long feeding times maintain full stomach and continuous supply of nutrients to host and microbes
-increased retention times are associated with increased digestibility, aided by delay of rate of passage through sacculation, large volume, and pelvic flexure
selective areas of retention
pelvic flexure, diaphragmatic flexure, sternal flexure and colonic separation mechanism of GIT
-contractions and anatomy result in physical separation of courser particles from finer ones and fluid retention
pelvic flexure
-retains coarse particles (1 cm or more) in CECUM and ventral colon, while fine and liquids move to left and right dorsal colon
colonic separation mech of GIT
-fluid retained in right dorsal colon, contractions in muscular wall of colon results in fecal ball production and absorption of fluid
2 types of carbs digested
non-structural carbs (sugars) and structural carbs=fibers
non-structural carbs
- monosaccharides like glucose can be absorbed across the wall
- sugars are hydrolyzed in small intestine by pancreatic a-AMYLASE
structural carbs
- hemicellulose, cellulose, lignin and pectin
- made up of monosaccs joined by beta bonds that horses cannot break down
- rely on microbes in hindgut to produce enzymes that break this fiber into useable components
fermentation
- volatile fatty acids VFAs are byproducts and can be used as energy source for horse
- VFA produced from cellulose metabolized by microbes
- microbes proteins contribute minimally to horse nutrition
VFAs
> 50% of daily energy comes from them for horses
- include acetic, propionic, and butyric acids
- 7% of glucose production
excess of non-structural CHOs
- digestive capacity of small intestine can be exceeded when fed lots of cereal grains
- grasses=3.5% starch vs oats 44% starch
- recommendation: do not exceed 4g starch/kg BW/meal
- excess non-structural carbs result in large portion of undigested material entering colon
what happens when high starch content in stomach
-fermentation causes increaesed LACTIC ACID production, decreasing pH, disrupting microflora, and decreasing activity of FIBER-digestion
illness caused by excess starch
- lactic acidosis associated with laminitis
- colic
- diarrhea
- stereotypies like crib-biting and pacing
- reduced gut health
- rule of thumb: change diet over 5 day period
proteins
digested in small intestine
-protein of cells walls used as nutrition for microbes
liver
- metabolizes carbs, proteins, and fats
- breaks down and excretes potential toxins
- large storage capacity, esp for glucose
liver anatomy
- most cranial part is behind diaphragm
- divided into lobes
- NO GALL BLADDER
- continuous flow of bile enters duodenum
- most products of digestion pass through liver via portal vein
glucose metabolism
- liver maintains blood glucose in response to pancreatic hormones insulin and glucagon
- after meal excess glucose undergoes glycogenesis, converted into glycogen for storage
- glucose not stored is used to produce energy via glycolysis
glucose metabolism between meals
- blood glucose falls, liver responds via
a) glycogenolysis, converting glycogen into glucose
b) gluconegenesis, non-sugars like amino acids are converted into glucose
fat metabolism
- bile enters duodenum EMULSIFYING fats into smaller globules, which are broken down further by lipase enzymes
- when excess: LIPOGENESIS where fatty acids and glycerol and stored in subcutaneous tissue
- low energy: lipolysis in fat store cells convert back to glycerol and fatty acids, brought to liver
protein metabolism
-AA transported to liver
excess=
a)aa converted into fat and stored in fat depots
b) made into glucose for energy via gluconeogenesis
DEAMINATION=amino group excreated as urine
storage of vitamins and minerals
stored via hepatocytes
bile
- emulsifies fat
- metabolic wastes and drug products may form part of bile which are then excreted from body with faeces
- bilirubin, toxic end product of haemoglobin breakdown is removed via bile
