Protein & Metabolism in the Rumen Flashcards
What nutrients do different dietary components produce in the small intestine as a result of the ruminant digestion process?
Nonprotein N (NPN) > Amino acids
Feed proteins > Volatile fatty acids (VFA) & amino acids
Carbohydrates > VFA & glucose
Fats > Fatty acids & glycerol
What are the 2 main types of protein in milk?
Microbial protein
Casein
What type of relationship do ruminants have with ruminal bacteria?
Symbiotic
What conditions must be maintained in the rumen to support microbial growth?
- Temperature (30℃), moisture, pH buffered
- Constant supply of nutrients
- Continuous removal of by-products of digestion/fermentation (eg, gases (methane), VFA, ammonia)
What process produces the bulk of the energy to ruminants?
Fermentation
(over digestion)
Which volatile fatty acids (VFA) are present in the rumen, in order of concentration?
- Acetate
- Propionate
- Butyrate
List some characteristics of acetate
Milk fat precursor
Lipogenic - stored as fat (via acetyl-CoA)
High fibre diets favour acetate production
Absorbed across the rumen wall intact & converted to acetyl CoA in liver > enters Krebs citric cycle
List some characteristics of propionate
Glucose precursor
Gluconeogenic - stored as glycogen
High concentrate diets favour propionate production
20% of propionate converted to lactate during absorption across rumen wall, enters gluconeogenic pathway in liver via phosphoenolpyruvate (PEP)
Remaining propionate passes into liver & converted into glucose via oxaloacetate & PEP intermediates
List some characteristics of butyrate
Lipogenic - stored as fat (via acteyl-CoA)
Production less controlled by diet, but slightly favoured on high forage diet - presence of protozoa increases production
Butyrate converted to beta-hydroxybutyrate during absorption across rumen wall & passed into liver > converted into acetyl CoA
Beta-hydroxybutyrate may also be used as an energy source by heart & skeletal muscle
What are 2 reactions that produce methane (CH4)?
CO2 + 4H2 -> CH4 +2H2O (CO2 reduction)
CH3COOH -> CO2 + CH4 (acetate decarboxylation)
What type of diet produces less methane (CH4)?
Diets low in concentrate (H2 sink)
Why must volatile fatty acids (VFA) be removed from the rumen?
How are they removed?
Maintain rumen pH
Too many VFA = acidosis
Passively absorbed across rumen wall
What are the 2 types of protein involved in ruminal digestion?
Digestible Microbial True Protein (DMTP)
Undegraded Dietary Protein (UDP)
What are the 2 ways rumen microbes are produced?
Non-protein N (NH3) -> microbial protein
Hydrolyse dietary proteins -> peptides/amino acids -> microbial protein
What do Low Fermentable Metabolisable Energy (FME) diets use for energy?
Amino acids
What are branched-chain Volatile FatAcids (VFA) utilised from?
Amino acids
What is valine the precursor for?
Isobutyric acid
Describe the metabolisable protein system
What is a key intermediate in nitrogen metabolism?
Why?
Ammonia
It regulates the use of dietary nitrogen
How does low dietary protein lead to less energy generation?
- Low dietary protein
- Less ammonia
- Slow microbial growth
- Reduced carbohydrate breakdown
- Less energy generation
What is a result of rapid degradation of dietary protein or insufficient FME?
Increased ammonia levels at rumen level
What is the fate of urea?
Rumen via saliva, converted to ammonia by bacterial urease (N recycling)
Excreted in urine
What is the optimum rumen ammonia concentration?
8mMol
What %’s of dietary nitrogen from forage ends up retained in thee rumen, in urine or in faeces?
Forage = 100%
Retention = 20%
Faeces = 30%
Urine = 50%
