Lecture 13 -- Evolutionary Adaptation of the Digestive System

What is the digestive adaptation of carnivores?

→ Simple digestive tract
→ High energy diet → Long intervals between meals
→ Spacious stomach for storage
→ Low carbohydrates in diet → Absent of salivary amylase

What is the primary diet of omnivores and what is its digestive adaptation?

→ Omnivores have diets consisting of both plant and animal origin → Have combination of both digestive strategies of carnivores and herbivores
→ Large species variation e.g. Omnivores = black bear/ dark bear and pig; Carnivores = Polar bear; Herbivores = Panda bear

What is the primary diet of herbivores and what is its digestive adaptation?

→ Microbial digestion = Fermentation
→ Low energy content → Continuously eating

What are the requirement for fermentation?

1. Absence of oxygen → If fermentation is done under presence of oxygen, it leads to respiration instead of fermentation → End product = CO2 + H2O → No energy produced

2. Presence of microbes → help break down beta-glycosidic bond of non-hydrolysed carbohydrates in cellulose

Where does fermentation happen in omnivores?

Large intestine

Where does fermentation happen in carnivores?

Most of them happen in small intestine; little bit happen in large intestine

Where does fermentation happen in herbivores (ruminant and horses)?

In horses, fermentation occurs after the small intestine (Large intestine)
Ruminants ferment before the small intestine (Fore-stomach and stomach) → Ruminant also do a bit of fermentation in large intestine BUT not as much as horses

Where are fermentation products and microbial protein absorbed in fore-gut fermenters ?

Fermentation products absorbed in stomach and microbial protein passes through abomasum and small intestine for absorption

Where are fermentation products and microbial protein absorbed in hind-gut fermenters ?

Fermentation products absorbed in large intestine and microbial protein passes through faces

How efficient is fermentation in hindgut fermenters compared to foregut fermenters?

Hindgut fermentation (70%) is less efficient then foregut fermentation (90%)

Explain how the gut transit time influences forage consumption in ruminants and horses.

Horses have decreased gut transit time when there is poor quality of forage → Consume more BUT for fore-gut fermenters e.g. ruminants, their gut transit time depends on rate of fermentation and cannot be reduced whatever the nutrient quality of fibre

What is coprophagy and why do rabbits practice it?

Coprophagy is the practice of eating feces to re-digest nutrients, especially microbial protein, lost in the feces

What are the nutritional strategies of ruminants?

1. Browsers → Able to pick up fresh grass → More hydrolysed carbohydrates → These CHO can bypass the fermentation chamber → Directly get into abomasum and small intestine for digestion → End product: Glucose

2. Grazers → Cannot bypass the fermentation chamber → Everything get fed to the microbes → End product: VFAs

3. Intermediates → Able to bypass little but not very extensive

What morphological adaptations do browsers have compared to grazers?

Browsers:

→ Narrow muzzles
→ More mobile lips/tongue
→ Retain oesophageal groove
→ Small fore-stomach
→ Small intestinal glucose absorption remains high

Grazers:
→ Wide muzzles
→ Less mobile lips/tongue
→ Lose oesophageal groove
→ Large fore-stomach
→ Small intestinal glucose absorption remains declines

What type of carbohydrates do ruminants primarily rely on?

Ruminants primarily rely on fibrous carbohydrates that require fermentation.

How does digestion and absorption differ between carnivores and omnivores?

Carnivores have no salivary amylase and rely on pancreatic enzymes, whereas omnivores have high levels of salivary amylase and enzymes for digesting carbohydrates.

List the examples of browsers ruminant.

Giraffes; Small ruminant; Dear

List the examples of grazer ruminant.

Sheep; Cattle; Hippo

List the examples of intermediates ruminant.

Goats; Camels; Elk

What is oesophageal groove?

Groove with lips that runs from oesophagus to reticulo-omasal orifice
→ Present in all young animals to allow milk to bypass the fermentation chamber

What triggers the loss of the oesophageal groove in ruminants?

The groove function is lost by grazers upon weaning.

What types of animals have oesophageal groove/ ventricular groove

Young animals → Allow milk to bypass fermentation chamber

Browser ruminants → Retain groove function to allow diet high in hCHO

How does SGLT1 abundance change in relation to ruminant diet?

SGLT1 abundance is high in young ruminants, declines in grazers at weaning, and remains high in browsers.