ruminant metabolism

metabolic adaptations of ruminants

• how are dietary polysaccharides fermented

• what is glucose metabolised into

• use symbiotic micro organisms to ferment dietary polysaccharides, like cellulose to VFAs

• glucose is metabolised to pyruvate and lactate in all mammalian cells- in ruminants this glucose is generated by gluconeogenesis using VFA as the substrate and not directly obtained from the diet

• foregut and hindgut

• ruminants and herbivores have adapted their metabolic pathways to utlilise VFAS as the substrate for energy production

• slower food passage

• fermentation relies on a constant env

• food intake is matched to the outflow of the GIT

• pH regulation via bicarbonate in saliva

foregut vs hindgut- rumination, stomach, primary fermentation site, digestive efficacy, food intake, microbial protein utilisation

3 stages including how the host absorbs vfa

1. microbial enzymatic digestion of polysaccharides to soluble hexose and pentose sugars

2. microbial metabolism of sugars by glycolysis and pentose phosphate pathways to produce VFAs. host absorbs VFAs via monocarboxylate transporters in the rumen epithelium

3. electron disposal to enable continuous fermentation. enables pH regulation and NAD+ regeneration for microbial glycolysis

main fermentation products

VFAs

• more than 95 percent total VFA production

• acetate 60-70 -increase with roughage

• propionate 15-20 - increase with concentrates

• butyrate 10-15

Gases (up to 30L/hr per cow)

• co2

• methane

butyrate- where and what is it used for

rumen epithelium use as a fuel source

glucose metabolism adaptations- gluconeogenesis

• continual gluconeogenesis

• regardless of fed/fasted state ruminant livers continually undergo gluconeogenesis to produce glucose for whole animal

• low, insignificant liver glycogen reserves- low glycogen synthase activity

glucose metabolism adaptations- hepatic glucokinase

• low expression and activity

• glucokinase is responsible for generating g-6-p from glucose as it enters cell

• prevents liver taking up glucose from blood circulation and ensures glucose produced by liver, leaves liver to supply extra heptatic tisse

protein digestion in ruminant

• some passes through rumen and digested in the absomasum and small intestine

• rest digested to amino acids in rumen which are either utilised by the microbial population in rumen or deaminanted generating volatile fatty acid and NH3

• other non proteinaceous nitrogen eg urea can be used by the microbial population to synthesise amino acids

• when the microbial population pass into the rest of the gi tract they are digested enzymatically and resultant amino acids are absorbed into the blood circulation

• so can thrive on low protein diet as they obtain essential and non essential from microbiome

• microbiome derived vitamins absorbed in the small intestine are suffiient to satisfy ruminant requirement

energy demands of lactation

• how does the liver generate the vast majority of glucose

• what is the major hepatic gluconeogenic subtrate

• other gluconeogenic substrate

• how much glucose needed

• liver generates vast majority of glucose via gluconeogenesis

• proprionate is major heptatic gluconeogenic substrate

• other gluconeogenic substrates are gluconeogenic amino acids and glycerol

• milk production need large amounts of glucose

• high producing may need 1.7kg of glucose a day

• high yield dairy cows usally fed a nutrient dense conc alongside forage to help increase percent of propionate produced by micorbiome of rumen

management - what do

• concentrates do and increase

• rumen bypass protein result in

• propylene glycol- dose and what is increased

CONCENTRATES

• result in increased propionate production

• increased gluconeogenic substrates to support gluconeogenesis

RUMEN BYPASS PROTEIN

• bypass the rumen for enzymatic digestion in the abomasum and small intestine

• amino acids directly absorbed by the cow increasing gluconeogenic subtrates to enable the liver to produce more glucose

PROPYLENE GLYCOL

• typically administered as an oral drench of 250-500ml/day

• femented by rumen microbiome to propionate - increased propionate production

• increased gluconeogenic substrates to support gluconeogenesis

ovine pregnancy toxaemia

• metabolic disease in ewes carrying multiple lambs where the high glucose demand of hte developing lamb not met and causes severe energy deficinecy

• insufficient gluconeogenesis in the liver result in rapid lipolysis of stored triacylglycerides in the adipose tissue

• beta oxidation of fatty acids result in excess acetyl coa formation which are converted to ketone bodies

• ketones accumulate in blood as extrahepatic tissues cannot utilise all that are produced- ketoacidosis

ovine pregnancy toxaemia management

• oral drench of propylene glycol to increase propionate production by rumen microbume to icnrease gluconeogenic substrates for use by liver

• prevetion- identify ewes carrying multiple lambs and separate for provision of increased concentrat ena drumen bypass proteins

how is butyrate used in the rumen epithelium

• how does it entered

• what is it converted to

• what by products are produced

• butyrate enters via a monocarboxylate transporter

• is converted to acetoacetyl coa to acetyl coa which enters the TCA cycle

• this contributes to ATP synthesis

• acetoacetate and beta hydroxybutyrate are produced as by products

• these ketone bodies leave rumen epithelium cells into blood for energy production in other cells