9.2: ruminant nutrition 1

1. Be able to explain the healthy GIT and its function. 2. Describe how ruminants break down carbohydrates/fibre into useful products. 3. Explain and understand how this energy is derived from the products of fibre digestion and are then utilised. 4. Describe how protein and lipids are utilised in the ruminant diet.

Name some things that nutrition affects in the ruminant.

• Milk yield: fat content and protein content

• BCS

• Diarrhoea

• Constipation

• Immunity

• Abomasal displacements

• Ketosis

• Fatty liver

• Fertility

• Acidosis

• Bloat

• Milk fever

• Hypomagesaemia

• Growth

• Support pregnancy

What is the percentage makeup of ruminant foodstuff?

• 60% forage: grass, brassicas (kale), roots, straw and maize

• 40% concentrates: cereals, cake, soya, rapeseed, molasses

  • Supplementation will depend on what is in forage

What are the relative volumes of the rumen and abomasum in neonates and adults?

• Neonates: 25% rumen, 60% abomasum

• Adults: 62% rumen, 22% abomasum

Discuss the rumen:

• What side of the cow is it found on?

• What is its holding capacity?

• What is its function?

• Left hand side

• Large holding capacity of 100-200 litres

• Contracts rhythmically to digest food - some is regurgitated and re-chewed.

• It ferments food and absorbs VFAs and ammonia to maintain pH

What are the normal conditions of the rumen, in terms of temperature, oxygen, pH, gases, flora and fauna?

• 38-40°C

• Anaerobic conditions - to allow fermentation

• pH 6.0-6.5 - buffered by bicarbonate and phosphate in saliva

• Produces CO2 and CH4 (methane)

• 10^6-10^10 per ml of bacteria

• 10^6 per ml of protozoa

In what way does the rumen function?

• It is a storage area allowing enough time for food to be properly digested.

• Food enters and the same volume leaves it again.

• Soluble components are fermented (like sugars)

• Insoluble components are gradually broken down by microbes

What happens to large particles in the rumen? Why is it important?

• They form a fibrous mat on the rumen floor until they are broken down.

• The fibre mat is important for rumen movements and saliva flow, via stimulation of the vagal nerve.

What size do particles need to be to leave the rumen?

About 3-4mm.

What effect do high roughage diets have? Therefore, how can ruminant diets be most efficient?

• They increase transit time due to higher salivation, but this decreases digestion.

• Diet should, therefore, have small-sized, quickly digestible concentrates that provide maximum energy quickly without rumen acidosis.

What is the function of the reticulum?

How is it innervated?

What is its proportional size in smaller ruminants?

• It has no absorptive capacity, but deals with mechanical breakdown and microbial fermentation. Its papillae can collect smaller particles to move to the omasum.

• Innervated by the vagus nerve (CN X)

• Proportionally larger in small ruminants

• What sort of contractions does the omasum undergo?

• What do the contractions do?

• How is the omasum innervated?

• It undergoes biphasic contractions.

• The first contractions remove fluid, along with VFAs and bicarbonate (stopping it from entering the abomasum). This is then absorbed.

• The second contractions expel solids into the abomasum.

• It is innervated by the vagus nerve.

• What is the function of the abomasum?

• Does it receive innervation?

• What is the nature of its contraction?

• What is its proportional size in smaller ruminants?

• Glandular for chemical digestion - releasing HCl and pepsinogen.

• Proteins are broken down to be absorbed in the small intestine.

• It does not receive much innervation from the vagus nerve, instead having a lot of intrinsic motility.

• Its contractions strengthen as they reach the pylorus to aid expulsion of contents.

• Proportionally larger in small ruminants.

What happens in the duodenum, jejunum and ileum of ruminants?

• Duodenum:

  • Stomach acid neutralised.

  • Pancreatic duct and bile duct release secretions for digestion of fat, carbohydrates and proteins.

• Jejunum:

  • Site of absorption.

• Ileum:

  • Absorbs remaining nutrients and vitamin B12

  • Also contains lymphoid tissue

What is the function of the large intestine in ruminants?

• Storage and further breakdown of foodstuffs.

• The colon is the primary site of water and Na absorption.

• The bacteria in the colon produce necessary vitamin K and thiamine.

• It is the channel for removal of waste.

• Contains the caecum in the right sub-lumbar fossa.

What are microbes and what are their functions in the ruminant?

• Includes bacteria, protozoa and fungi.

• Feeds on forages ingested, then uses anaerobic fermentation to produce end products that can be utilised by the cow and the microbes themselves.

• Different microbes have differing functions, some will digest sugars, some cellulose, etc.

What must the ruminant diet contain, in terms of microbe function?

• Sufficient energy and protein to allow microbes to grow and multiply to maximise rate of digestion.

Why must ruminant diet switches be done slowly?

To allow the rumen flora to adjust.

What are the end products of microbes in the rumen?

• VFAs - the main energy source of the cow

• Ammonia - used to form more microbial proteins. Microbial bacteria are digested and are the cows main source of protein.

• Gases - waste, then eructated (CO2 and CH4)

What is CF, NDF and ADF?

• CF - crude fibre: traditional measure of fibre in feeds.

• NDF - neutral detergent fibre: structural components of the plant (specifically the cell wall). These are slowly digested. An increased NDF → decreased intake, because it takes longer to digest.

• ADF - acid detergent fibre: the least digestible plant components, like lignin and cellulose. They usually are poor in energy and are excreted in the faeces.

How are carbohydrates digested and used in ruminants? What is specific about straw, lush pastures, potatoes and molasses?

• First fermented in the rumen, producing VFAs, then later digested to make glucose that will enter the Krebs cycle in the liver.

• Straw/fibrous hay: mostly cellulose, so slowly, producing lots of acetate

• Lush pastures: hemi-cellulose, digests faster

• Potatoes/beets etc.: rapidly digested, increasing levels of propionate

• Molasses/glucose etc.: most rapidly - don’t produce VFAs

What are VFAs and what is their purpose?

• Volatile fatty acids

• The end products of anaerobic fermentation of carbohydrates in ruminants.

• Readily absorbed into the blood stream and transported to the liver where they are converted to other sources of energy.

• Used for hepatic gluconeogenesis, lipogenesis and milk synthesis.

Discuss acetate:

• What proportion of VFAs produced are acetate?

• What diet produces the most acetate?

• What is its use?

• How many moles of ATP are produced per mole of acetate via the CAC?

• 55-65% of VFAs produced are acetate

• Predominates on a high roughage diet

• Used for the synthesis of fatty acids in adipose, some also used for muscle metabolism and body fat.

• 10 moles of ATP to one mole of acetate

Discuss butyrate:

• What proportion of VFAs produced are butyrate?

• What foodstuff is it found in?

• What is its function?

• How many moles of ATP are produced per mole of butyrate via the CAC?

• 10-15% of VFAs produced are butyrate.

• Found in poorly fermented silage, usually due to poor storage.

• Provides energy to the rumen wall

• The liver turns it into a ketone body to be used by muscle.

• 25 moles of ATP per mole of butyrate

Discuss propionate:

• What proportion of VFAs produced are propionate?

• What diet is it found in?

• What is its function?

• How many moles of ATP are produced per mole of propionate via the CAC?

• 18-21% of VFAs produced are propionate

• Predominates in a high concentrate diet

• It is a precursor of glucose, therefore providing energy by glucose conversion in the liver

• Used in lactose synthesis

• 18 moles of ATP per mole of propionate

What are UDPs?

Undegraded dietary proteins: proteins not broken down in the rumen so pass to the abomasum.

• What are rumen degradable proteins?

• What are the products used for?

• Does the rumen need a lot of these?

• What happens if they are not sufficient?

• Proteins broken down in the rumen, by microbes

• The nitrogen and amino acids are used by the rumen microbes to grow.

• Microbes can use any source of nitrogen, so the rumen does not require many RDPs - can be a waste of money if too much

• But sufficient is needed otherwise microbe and carbohydrate breakdown is needed

What are microbial crude proteins?

• The flow of protein contained in the rumen bacteria, which is then passed to the intestine for digestion.

• The protein that reaches the abomasum and SI is either MCP or UDPs.

What happens if there is excessive RDP? If there is insufficient protein in the diet? What is done to prevent this?

• Excessive RDP: excessive ammonia then absorbed into blood, liver turns it into urea to be excreted.

• Insufficient protein: more ammonia is then returned to the rumen, which is then turned into microbial crude protein.

• This may cause more protein to reach the SI than is consumed.

• Therefore urea is added to the diet, so a constant stream of protein passes to the SI.

What happens if ammonia levels are too high?

• It can overload the liver capacity, causing toxic levels of ammonia in the blood.

Discuss lipids:

• What can too much lipid in the rumen cause?

• What are most fats consumed by ruminants?

• What can the rumen not absorb?

• What happens to fats in the rumen?

• Too much lipid in the rumen (more than 100g/kg) can inhibit microbe action.

• Most consumed fats are triacylglycerides (TAGs), which are hydrolysed by lipases.

• Long chain fatty acids are not absorbed by the rumen.

• Fats in the rumen are saturated then pass to the SI for digestion.

  • Dietary fats can be treated to remain unsaturated when they get to the SI and therefore alter milk fat content.