Ruminant metabolism (question 110-116) and Ketogenesis + Ketolysis (q31 and 32)

What is the main component of saliva

Water (99%)

List the minor components of saliva

-Electrolytes

-Enzymes

-Mucins

-Immunoglobulins

-Antimicrobial agents

-Urea

Name the electrolytes present in saliva

Na+, K+, Cl-, HCO3-, Ca2+

Which electrolyte is especially important in ruminant saliva and why

Bicarbonate as it balances the pH of the stomach

Which enzymes are present in saliva

Lingual lipase and alpha-amylase

Which species do not have amylase in their saliva

Horses, ruminants, dogs and cats

Why do carnivores not have salivary amylase?

Amylase digests starch. Due to high protein, low carbohydrate diet of carnivores, there is no need for starch digestion

Why do horses and ruminants not have salivary amylase?

Their saliva serves mainly a lubricating and buffering role, while carbohydrate digestion occurs in the intestine and by microbial fermentation in the hindgut.

What are mucins

Glycoproteins that provide viscosity, aiding in lubrication and bolus formation

Which is the primary immunoglobulin present in Saliva

IgA

Name 3 antimicrobial agents present in saliva

Lysosome lactoferrin and peroxidase

Which species has Urea present in their saliva and why?

Ruminants. Urea is used for microbial protein synthesis, promoting fermentation and microbial activity in the rumen

Which animals have the highest mucin content?

Carnivores

Name the functions of saliva

1. Lubrication

2. Digestion

3. Buffering

4. Thermoregulation

5. Oral Health

6. Nitrogen recycling (ru)

Which part of the stomach is the primary digestive site in young vs adult ruminants

Young: abomasum

Adult: rumen

What is the esophageal groove

A muscular fold in the reticulorumen that directs milk/colostrum directly to the abomasum

Which enzymes have a role in milk digestion

Rennin (chymosin) and pepsin

What are the components of colostrum

-Immunoglobulins

-Fat and lactose (energy)

-Vitamins and GFs

-Enzymes

Which immunoglobulins are present in colostrum

IgG!, IgA, IgM

What are the main vitamins present in colostrum

A and E

Name 2 enzymes present in colostrum

Lactoferrin, lysozyme

Name 3 key functions of colostrum

1. Passive immunity

2. Nutritional support

3. Gut development (GFs)

How does rennin coagulate milk

cleaves k-casein into para-k-casein which then reacts with calcium ions to form a curd

Why must milk be coagulated in the stomach of young animals?

To slow the digestion of the milk, enhancing nutrient absorption

What are the main, non-water components of milk

Casein (protein), lactose (carbohydrate) and fat (energy)

Describe lactose digestion (location, enzyme, reaction, products)

Location: small intestine

Enzyme: lactase

Reaction: hydrolysis

Products: glucose and galactose

What 2 factors are needed to stimulate the development of the rumen?

1. Physical stimulation: from fibre

2. chemical stimulation: from VFAs during microbial fermentation

Name the 3 VFAs

acetate, butyrate, propionate

What stimulates the growth of ruminal papillae?

VFAs

What are the 2 ideal dietary components of a weaning ruminant?

-Starter grain with digestible carbs

-Hay

Name the 5 carbohydrates present in the diet of ruminants

1. Cellulose

2. Hemicellulose

3. Starch

4. Pectin

5. Lignin

Do ruminants directly produce the enzyme cellulase?

No

How is fibre (cellulose and hemicellulose) degraded in the rumen

-Bacteria: produce cellulase which breaks down cellulose/hemicellulose into simpler sugars e.g. glucose

-fungi and protozoa: degrade plant cell walls

give 2 examples of bacteria involved in production of cellulase

-Fibrobacter succinogenes

-Ruminococcus albus

How is starch degraded in the rumen

-Amylolytic bacteria break it down into maltose and glucose

-Glucose is then fermented into VFAs

Give 2 examples of amylolytic bacteria in the rumen

-Streptococcus bovis

-Prevotella

Whats the most common VFA in ruminants

Acetate (60-75%)

How is acetate produced?

Fermentation of cellulose and hemicellulose

Function of acetate?

Fatty acid synthesis and energy production in tissues

How is propionate produced?

Fermentation of starch and soluble sugars

Functions of propionate?

-Key precursor for gluconeogenesis in the liver

-Provides energy to tissues

How is butyrate produced?

Fermentation of cellulose by butyrate-producing bacteria

Function of butyrate?

-Serves as energy source for ruminal epitheliocytes

-Growth and repair of rumen mucosa

How does diet composition influence VFA production?

>High-fibre (forage-based)diet: increases production of acetate and butyrate

>High-starch (grain-based) diet: increased propionate production

How can low rumen pH occur and what can it lead to

Occurs due to excessive fermentation of starch. Can lead to acidosis which reduces microbial efficiency and inhibits fibre degradation

Is frequent feeding good or bad for VFA production?

Good: helps maintain pH in rumen

Which organs is acetate transported to?

Muscles, adipose tissue and liver

Function of acetate in adipose tissue

fatty acid synthesis

(converted to acetyl-coA -> fatty acid synthesis -> FAs are converted to triglycerides for fat storage)

function of acetate in muscle tissue

energy production

(converted to acetyl coA -> enters krebs cycle -> prod. of ATP)

% of propionate in total rumen VFAs

15-25%

where is propionate transported to?

liver

main function of propionate?

gluconeogenesis

what is propionate converted into during gluconeogenesis?

succinyl coA

Name 2 other functions of propionate in the liver

-Regulation of insulin sensitivity

-Regulation of lipid metabolism

Where is butyrate transported to

liver, muscle and ruminal epitheliumq

function o f butyrate in the liver

converted to ketone bodies (beta-hydroxybutyrate and acetoacetate)

-> used for energy during fasting/lactation

function of butyrate in muscle

converted to acetyl-coa which enters krebs cycle for ATP synthesis

function of butyrate in ruminal epithelium

growth and maintenance of ruminal epithelium; cellular differentiation and repair of rumen lining

how is lactate produced

produced during anaerobic mtb of glucose in the muscles and by lactic acid bacteria in the rumen

which conditions contribute to lactate production in the rumen

high starch fermentation or low pH

Where is lactate transported to

liver, heart and muscles

function of lactate in the liver?

converted back to glucose via gluconeogenesis

function of lactate in heart and muscles?

converted back to pyruvate and used for energy in TCA cycle. or pyruvate goes to liver for gluconeogenesis

What is the primary source of nitrogen for ruminants?

dietary proteins from forage (grass, hay) and concentrates (grain)

What are the products of protein degradation in ruminants

amino acids, peptides and ammonia

what does NPN stand for

Non-protein nitrogen

name some NPNs

urea, ammonia, amino acids and nitrates

What is urea broken down into? where does this happen?

Into ammonia in the rumen

Give an example of a ureolytic bacteria

Selenomonas ruminantium

Whats the name of the condition where theres a high level of ammonia in the bloodstream?

Hyperammonemia

How is urea produced? (organ and pathway name)

Produced in the liver through the ornithine (urea) cycle

How is Urea used in ruminants?

-Recycled back into saliva to supply nitrogen to rumen microbes

-Excess is secreted through urine

Whats the most common form of dietary fat

Triglycerides (TAGs)

Name 3 other types of lipids (not TAGs) that are commonly part of a ruminant diet

-Galactosylglycerols

-Phospholipids

-Phytosterols

What is biohydrogenation?

process where dietary polyunsaturated fatty acids are converted into more saturated fatty acids by action of ruminal microbes

What is the role of microbial lipase in biohydrogenation?

breaks down triglycerides into free fatty acids and monoglycerides

What happens to the FFAs once they've been released from TAGs?

They are hydrogenated by rumen bacteria (esp. by Firmicutes phylum) which reduces double bonds and makes them more saturated

What is the main reason/function of biohydrogenation of FFAs?

Defensive reaction against the toxic effect of Unsaturated FAs

What are Galactosyldiacylglycerols broken into?

Galactose, FAs and glycerol

What are TAGs broken down into?

FAs and glycerol

What are phospholipids broken down into?

FAs and glycerol

What are galactose and glycerol converted into?

VFAs

Whats the most common TAG in rumen diet?

C18 PUFA (linoleic and linolenic acid)

What % of linoeic and linolenic acid undergo biohydrogenation?

70-90% Linoleic acid and 85-100% of linolenic acid

What is the product of biohydrogenation of FFAs?

Stearic acid

Give 3 sources of hydrogen in the rumen

-NADH + H+

-FMNH2

-FADH2

Which 2 enzymes are involved in ruminal biohydrogenation

isomerase and reductase

Where does lipogenesis occur in ruminants

adipose tissue (90%), liver (5%) and mammary glands during lactation

What is lipogenesis

Synthesis of fatty acids and triglycerides in the body

What are the precursors for lipogenesis

Acetate (primary), propionate and glycerol

Describe lipogenesis pathway (simplified)

-Acetate produced in rumen is transported to liver and adipose tissue

-Its then converted into acetyl-CoA and enters FA synthesis pathway

-Acetyl-CoA forms Malonyl-CoA which undergoes elongation reactions until it forms Palmitic acid (C16)

Describe Triglyceride synthesis

FAs formed during lipogenesis are esterified to glycerol to form TAGs

What is Ketogenesis

Conversion of acetyl-CoA (derived from FAs) into ketone bodies

What are the main sources of ketone bodies in ruminants?

-Butyrate converted to BHB

-Acetate

-NEFA, which is oxidised to produce Acetyl-CoA

-AAs, which are oxidised to produce Acetyl-CoA

Which Amino acids can be oxidised to produce Acetyl-CoA

Phe, Tyr, Leu, Lys, Trp

Name 3 important ketone bodies produced in ruminants

-Beta-hydroxybutyrate

-Acetoacetate

-Acetone

Which organ is the primary site for ketone body formation

Liver

Describe simplified process of ketogenesis

-Lipomobilisation in adipose tissue releases FFAs

-FFAs are transported to liver where they are broken down into acetyl-CoA

-When there is an excess of acetyl-CoA it is converted into acetoacetate, BHB and/or acetone

Name 3 key enzymes involved in ketogenesis

-Acetyl-coa acyltransferase (ACAT)

-HMG-CoA reductase

-BHB-dehydrogenase

What are ketone bodies used for?

An alternative energy source by extrahepatic tissues when glucose levels are low