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Adaptation of the digestive system (Herbivores (Browsers or grazers, Low…
Adaptation of the digestive system
Carnivores
Predators/scavengers
High energy content
Easily digestible
Long interval between short meals
Herbivores
Browsers or grazers
Low energy content
Microbial digestion
Digestive tract adapted for fermentation
Continuous eating
2 strategies (fore-gut/hind-gut)
Omnivores
Pig (&~bears)
Large species variation in digestive tract
Bears range from herbivore to carnivore
Degree of fermentation occurs in LI
Fermentation
Non-hydrolysable carbohydrate
Requires microbial degradation in absence of oxygen
Long, slow process
Fore-gut fermenters
Cattle/sheep = Ruminants
Stomach modified into fermentation chamber
Very efficient fermentation
Fermentation products absorbed in stomach
Microbial protein can pass into abomasum & small intestine for digestion/absorption
Hind-gut fermenters
Horses (& rabbits)
Large intestine modified into fermentation chamber
Moderately efficient fermentation
Fermentation products absorbed in colon
Microbial protein lost in faeces - rabbits practice coprophagy
Comparative fermentation
Hind-gut fermentation 70% efficient as fore-gut (lower degree of amylolytic fermentation, hind-gut lose microbial protein in faeces)
Hind-gut fermenters can alter transit time dependent on rate of fermentation
Ruminants more efficient on good quality forage, hind-gut more efficient on abundant poor quality forage (if short supply, ruminants predominate)
Ruminants nutritional strategies
Stems, blades, older leaves high in fibre
Ruminants have 3 substrategies
Grazers (grass/roughage eaters)
Intermediates
Browsers (concentrate selectors)
Fruit, seeds, buds, young shoots & leaves high in hydrolysable carbs
Ruminant adaptation
Browsers
Narrow muzzles
More mobile lips/tongue
Smaller fore-stomach
Ruminant browsers retain functional oesophageal/ventricular groove
SI glucose absorption remains high
Grazers
Wide muzzles
Less mobile lips/tongue
Larger fore-stomach
Ruminant grazers lose functional oesophageal/ventricular groove
SI intestinal glucose absorption declines
Oesophageal/ventricular groove
Present in all young ruminants
Retained only in browsers (to allow normal digestion hCHO
Enables milk to bypass fermentation chamber
Herbivore glucose absorption
Small intestine site of glucose absorption (via SGLT1)
SGLT1 regulated by diet
High in young, declines in grazers at weaning, remains high in browsers
Comparative digestion
Carnivores - No salivary amylase, high levels of enzymes from stomach/pancreas for proteins & fat
Omnivores - High levels of salivary amylase, high levels of enzymes from stomach/pancreas for proteins, fat & carbohydrate
Simple-stomached herbivores - Moderate levels of enzymes for carbohydrate prior to fermentation in large intestine, exploited in feeding concentrate diets high in hydrolysable carbohydrate
Ruminants - Low levels of enzymes for carbohydrates after fermentation in fore stomach. Moderate levels of enzymes for protein digestion of microbial protein in abomasum/small intestine
Comparative absorption
Carnivores/omnivores - Monosaccharides/peptides/monoglycerides and fatty acids absorbed in SI
Simple-stomached herbivores: Monosaccharides/peptides absorbed in SI, VFA in LI
Ruminant herbivores: VFA absorbed in fore-stomach, peptides absorbed in SI