Hindgut Fermenters Flashcards
(40 cards)
Enzymatic digestion
Bonds between molecules susceptible to mammalian enzymes (secreted by the animal)
Carbohydrates (CHO) Dry Matter (DM) Proteins Fats/lipids Soluble CHO (α linkages)
Microbial fermentation
Bonds between molecules are not susceptible to mammalian enzymes but are to enzymes secreted by microbes
Insoluble CHO (β linkages)
GIT and feeding strategy of hindgut fermenters
Natural diet of herbivores is low in nutrients compared to the diet of carnivores
Diet of herbivores is high in CHO, low in protein and low in energy
➢Consume large quantities to satisfy nutrient and energy requirements
➢Spend vast amount of time eating (species variations – rabbits dawn and dusk, behavioural
considerations)
• Need a GIT that enables enzymatic digestion of soluble compounds and microbial fermentation of insoluble compounds
• Enzymatic digestion is a relatively quick process (0.5-2 hours in equids) takes place in the stomach and/or small intestine
• Microbial fermentation is a much slower process (24-48 hours in equids) so requires large
fermentation chambers
➢Ruminant = foregut (rumen)
➢Hindgut fermenters = caecum and colon
Small mammals
Known as caecal fermenters
Guinea pig • Hamster
• Rabbit
• Koala
Large mammals
Known as colon fermenters
- Orangutan • Equids
* Rhinoceros • Elephant
Omnivore species also utilise hindgut fermentation although benefit from a diet higher in
protein and soluble CHO
Key features of the GIT of hindgut fermenters;
oDentition suitable for biting and grinding plant material oSmall stomach
oEnzyme production
oSmall intestine for absorption of soluble molecules oLarge fermentation chambers
oMicrobial populations
Dentition of hindgut fermenters
• Due to the high food intake the teeth of herbivore
animals continually grow (rabbits/guinea pigs) or
erupt (equids)
o Rat - only incisors continually grow
• Incisors for cutting leaves and twigs
• Flat molars positioned close together to create one occlusal surface for grinding fibrous ingesta to small enough particles to swallow
• Implications for management – must provide fibrous foods/materials for chewing to wear down teeth
Salivary glands of hindgut fermenters
Role of saliva is to lubricate food when swallowed and buffer the acidic content of the stomach (most species have parotid, mandibular and sublingual glands, rabbits also have zygomatic glands)
• In rabbits saliva is produced continually from the mandibular gland, and in response to food intake and chewing by the remaining glands
• In horses saliva is only produced in response to chewing
• Saliva composition varies between species;
o Bicarbonate = buffers acidic stomach contents = present in most hindgut fermenters
o α-amylase = present in rabbit and rat saliva but not horse = starch digestion although action is low o Water and mucus = lubrication
Small stomach of hindgut fermenters
The stomach of hindgut fermenters takes up a small proportion of the total GIT volume 10% horse < 53% sheep (rumen)
15% rabbit 69% cat
• Have a trickle feeding strategy, not large meals
• Ingesta passes relatively rapidly through the foregut compared to foregut fermenters
although dependent on diet o 0.5-2 hours for horse
o 3-6 hours for rabbit
o 2 hours for guinea pig o 0.25-2 hours for rat
• Hindgut fermenters are thought of as simple stomached compared to foregut fermenters which are compartmentalised
Stomach
• Entrance to the stomach is through the cardiac sphincter = prevents regurgitation in horse, rabbit, guinea pig and rats
o What they eat must pass through the GIT = management implications
• HCL secretion in equine stomach is continuous = ingesta helps to prevent gastric ulcers • Exit from stomach is through pyloric sphincter
Cardiac / oesophageal of stomach
Non-glandular region, pH 6-7, no secretions = no protective mucus lining
Fundic and Pyloric
Main secretory part, parietal cells secrete HCL, chief cells secrete pepsin, mucus secreted to protect again acid corrosion, pH 1-2 in horse and rabbit
Pyloric region of the stomach
Gastrin secretion = stimulates HCL production
Enzymatic secretions
• Enzymatic digestion takes place in the stomach and small intestine
• Breaks down the ingesta to their individual molecules to allow absorption
e.g. protein is not one solid mass of protein, it is made up of single molecules (amino acids) joined together to make protein units that form protein compounds
• The α bonds that link the individual molecules are the target of this breakdown action
• The enzyme forms a complex with the target compound causing the bonds to break and the individual molecule to be released
• The reaction must occur multiple times to break all the bonds and release all of the individual molecules
• Once released the molecules are able to be absorbed through the gut wall where they enter the circulation and travel to the liver for processing and use by the body
• The complexes formed between enzymes and compounds is not random o Particular enzymes form complexes with specific molecules
o Results in specific nutrients being broken down and available for absorption at particular locations in the GIT
Small intestine of hindgut fermenters
• Small intestine is the main location of enzymatic digestion and absorption of soluble molecules (proteins, lipids, vitamins, minerals, sugars and starch)
• Structure is comparable between species although differences in dimensions and GIT proportions exist
• Three main sections;
1) Duodenum – first section digesta reaches after the stomach (most acidic section)
2) Jejunum – middle and longest section where nutrients are absorbed
3) Ileum – final section where nutrients are absorbed (least acidic section)
the mucosa
The inner most layer of the small and large intestines is called the mucosa
• The mucosa is not flat:
o Finger-like projections called villi (singular = villus)
extend inwards towards the centre of the intestine
Villi are only present in the SI
o Depressions called crypts surround each villus
Villi
• Structure increases the intestine surface available for nutrient absorption
• Villi are covered with tiny projections called microvilli (often referred to as the brush border)
• Each villus contains a circulatory network for transporting absorbed nutrients into the blood
• Cells within the crypts produce enzymes for digestion - goblet cells within the mucosa layer produce protective mucus
Passage of matter through the small intestine in hindgut fermenters
• Ingesta passes through the small intestine of hindgut fermenters usually within 1-3 hours
• Considerably longer than a dog which pass ingesta through its entire GIT in approximately
8 hours
• The ileum joins the large intestines (caecum and colon)
• In equids this is a straight forward arrangement with ingesta passing from the ileum into the caecum through the ileocaecal valve and then leaving the caecum through the caecoventral colonic valve
• In rabbits the arrangement is more complex due to a three-way connection between the ileum, caecum and colon = ileocecocolic junction
The arrangement in rabbits facilitates selective retention of fluid and small particles and expulsion of fibrous material
• Adaptation by rabbits to avoid carrying large volumes of fibrous material in the GIT
Large fermentation chambers
Soluble nutrients within the ingesta should have undergone the majority of their digestion before reaching the hindgut
• Insoluble/fibrous portion is what remains and must undergo microbial fermentation to break the bonds linking the molecules
o Hemicellulose
o Cellulose
o Lignin (completely undigestible)
• Takes time so requires large chambers to store ingesta as goes through the process – caecum and colon
• The caecum and colon are the main sites of microbial fermentation in hindgut fermenters o Provide space for mixing of ingesta with microbial populations and a large surface area for absorption of
nutrients, fermentation products and water
• In most species the sites of fermentation are sacculated, increasing the surface area of the structure
o Some also have flexures involved in selective retention of ingesta
• The mucosa lining of the caecum and colon contains crypts but no villi
• Goblet cells produce mucus to protect against acids produced during the fermentation process
• Optimum pH for microbial populations is 6-7, therefore bicarbonate and phosphate are secreted into the large intestine to neutralise the acidic products of fermentation
Large fermentation chambers in Equids
• Microbial fermentation takes place in the both the caecum and the colon in equids
• Literature often refers to equids as colon fermenters (see slide 8) mainly because of their
enlarged colon
➢Caecum = 25-35 litres, 16% GIT capacity ➢Large colon = 81 litres, 38% GIT capacity
• Course particles high in fibre are selectively retained in the caecum and large colon
o Logical as main sites of microbial fermentation
• Absorption of fermentation products takes place in the caecum and colon
• Ingesta then passes through into the small colon
• Finalsiteofwaterabsorption
• Formationoffaecalballs
Large fermentation chambers in Rabbits
• Microbial fermentation takes place predominantly in the caecum of rabbits with selective retention of fine particles and fluids
o Known as caecal fermenters o Caecum = 40% GIT capacity
• These fine particles undergo microbial fermentation
o Products of fermentation are both absorbed in the caecum and expelled as cecotrophs (soft faeces)
• Fibrous material (insoluble CHO, >0.5mm in length) are selectively progressed through the colon for expulsion
o Important for promoting GIT motility as insoluble CHO promote GIT transit
• Rabbits have a number of unique GIT structures
o Thickened circular muscle between the proximal and distal colon called the fusus coli that controls
colonic motility
o Vermiform appendix at the end of the caecum rich in lymphoid tissue (immunity role) which also secretes bicarbonate and water
• Rabbits excrete faeces in two forms due to performance of coprophagy
Cecotrophs(softfaeces):
Excretedduringrestperiods(~4hoursafterfeeding)
Rich in amino acids, VFAs, enzymes, vitamins B and K, microorganisms (↑ protein)
Coated in mucus to protect against acid in the stomach (stay for 6-8 hours) Pass into the small intestine where contents are digested and absorbed
= pseudo ruminant
Hard faeces
excreted during feeding phase (dawn and dusk), indigestible fibre
Microbial populations
• Microbial populations are present in the caecum and colon of hindgut fermenters o Bacteria
o Fungi
o Protozoa
• The animal provides an environment in which the microbes can survive and grow in exchange for them breaking down the insoluble parts of the plants eaten
= symbiotic relationship
• Microbes have to adapt to changes in diet which can take a number of weeks o Requires dietary changes to be made gradually
o Equids = can cause colic due to disruption of the fermentation process
Microbes attach themselves to cell wall compounds Microbes then excrete their own enzymes that are able to breakdown the links between the individual molecules of cellulose and hemicellulose The individual molecules are then processed by bacteria to produce Volatile Fatty Acids (VFAs) and gases VFAs are absorbed through the gut wall into the blood for use by the body as energy sources • Products of fermentation of benefit to the animal o Volatile fatty acids (Butyrate, propionate and acetate) o Heat o B vitamins and vitamin K o Amino acids – only in those performing coprophagy o Gases are also produced – can cause issues if become trapped
