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Transcript of Ruminant Nutrition
Food moves down tube in "peristaltic" waves / muscular contractions
Food can be moved down tube, or up (regurgitated) Mouth
SALIVARY GLANDS are located in the cheeks and at the rear of the mouth.
Food enters the mouth where it is chewed and it is mixed with saliva.
This forms a "bolus" which is swalled down the OESOPHAGUS.
Saliva contains sodium bicarbonate which buffers the activity of the acidity of the rumen. Up to 150L of saliva can be made each day! (~3kg sodium bicarb) Rumen The rumen is the largest stomach compartment and is found on the left hand side of the cow.
The inside surface is covered in "papillae" (fine projections) which increase the surface area for absorption.
The rumen contains a range of microbes which break feed down through a process called "fermentation".
The walls of the rumen move continuously to mix the injested feed with the microbes and the fluid in the rumen.
Temperature = 39C pH = 6.7
Size (100-200L) is dependent on size of the cow and her diet (more fibrous diet -> larger rumen)
Feed separates in the rumen so that the fibrous, coarser/longer feed floats on top and the more digested feed makes a soup-like on the bottom. The top section will be regurgitated. The contractions of the rumen and reticulum help the flow of finer food particles into the omasum.
The rumen is where most VFAs are absorbed. Reticulum The inside surface of the reticulum is known for its "honeycomb" appearance, where fine projections make up a distinctive pattern.
The reticulum is much smaller than the rumen.
The reticulum works with the RUMEN to mechanically break down food and to mix it with the microbes.
The reticulum ensures particles are small enough to pass into the OMASUM (as the opening from the reticulum to omasum is small and hence limits the passage of particles ~ <1-2mm).
Hardware disease. Oesophageal groove The OG is a smooth line of muscle that leads from the oesophageal sphincter to the opening of the OMASUM.
In young calves, the groove extends upwards to form a TUBE which allows milk to pass directly to the ABOMASUM. (Tube can no longer form once calves are weaned to solid food.)
In young calves, the rumen is undeveloped.
Suckling stimulates the OG to close, directing milk from the OESOPHAGUS straight into the ABOMASUM.
Access to hay and grain in the first week of life helps develop the rumen so that by week 3 the rumen can be fully functional and calves are able to digest forages. Omasum The inside surface of the omasum has numerous folds (this stomach compartment is know as the "bible" as the folds look like pages of a book).
The 100 (approx.) folds are covered in projections also, which direct flow of food particles towards the ABOMASUM.
The role of the OMASUM is to extract water from the digesta and further grind it down.
The digesta enters the OMASUM with about 90-95% water, and leaves at approx. 20%.
Abomasum The inside surface of the abomasum is covered with ridges and folds.
The folds increase the secretory capacity, as the lining produces gastric juices (HCl and ensymes) which allow the acid digestion of feed which occurs in the ABOMASUM. (NOTE: acid digestion, not microbial digestion, occurs in this compartment.)
pH ~ 2
Microbial protein and UDP are also broken down by enzymes in the abomasum. Small Intestine The inside surface of the small intestine is covered in "villi", which are small, finger-like progections, which increase the surface area of the small intestine.
Blood vessels surround the small intestine.
Length ~40m (or 20x body length)
The SI is the main site for nutrient absorption.
Undegraded UDP can be broken down here, and fat is digested in the SI also. Large Intestine The large intestine is wider than the small intestine.
10-15% of energy is absorbed from the LI.
Feed that is indigestible at the SI is fermented for a second time in the LI.
At the LI, water, vitamins, minerals (eg Na, Cl, K, P, Mg) are absorbed.
This is the last site for absorption before entering rectum.
VOLATILE FATTY ACIDS
(VFAs) The three main VFAs are:
VFAs are the major energy source for the cow. Microbial Fermentation The microbes in the rumen break down feed in a process called "fermentation".
This fermentation is the main way that ruminants (cows) digest their feed.
The nutrients in feed when it enters the cow are Carbohydrates, Proteins and Fats.
These need to be broken down into products that the cow can absorb and use (or the microbes can absorb and use for themselves). 75% of plant tissue DM is in the form
of carbohydrates (COH).
Microbial fermentation breaks COH
down into simply sugars.
The main end products of COH digestion are VFAs and gases. Carbohydrates Microbes Microbes are not all the same. Microbes include bacteria, fungi, protozoa, yeasts, etc. (Microbes = micro-organisms, that is, organisms you need a microscope to see).
Microbes all have specific functions. One group will be responsible for breaking down soluble carbohydrates, a different group for breaking down storage carbohydrates, one for breaking down structural carbohydrates, one for breaking down proteins, etc etc etc! Gases The main gases produced are:
- Carbon dioxide Methane is wasted energy as the cow cannot use it,
and as such it is simply burped out. Carbon dioxide is used by the microbes and by the cow
to help maintain the bicarbonate levels in saliva. 50% of the energy needed for fat synthesis comes from ACETATE.
Acetate is the VFA formed during the breakdown of fibrous feeds,
such as hay. In the liver, propionate is converted into glucose.
Most of the energy used for liveweight gain and milk lactose synthesis somes from PROPIONATE.
Propionate is the VFA formed from the digestion of feeds such as cereal grains. In the liver, BUTYRATE is converted to ketone bodies.
These ketones are used for fat and body tissue synthesis. VFAs are absorbed through the rumen wall into the liver. Microbe populations The diet of the cow siginificantly affects the numbers of microbes in each group.
For example, a diet with a large proportion of cereal grains will require more of the bacteria (microbes) that produce Propionate. If the cow is then changed to a diet that requires more of the bacteria that produce Acetate (such as a higher proprotion of forages and hay in her diet), then the population of acetate-producting bacteria will increase, while the propionate-producing bacteria population will decline in numbers.
This is the reason why we should GRADUALLY make changes in diet, as otherwise the microbe populations cannot keep up with the digestion demands and can result in various illnesses. Remember also, that the gases produced during microbial fermentation, namely carbon dioxide, is important for maintaining sodium bicarbonate levels in saliva. The sodium bicarbonate allows the saliva to have the buffering effect on acids, keeping the rumen pH normal. Protein Common gut problems Protein is made up from Nitrogen and other components.
Crude Protein is an estimated amount of protein in feed, which is calculated by using the nitrogen content of the feed (available through feed testing).
CP = N x 6.25
Protein digestion Microbes are responsible for breaking down proteins.
First they break the proteins into smaller pieces called "amino acids".
In ruminants, most amino acids are then broken down further, into ammonia which the microbes use to build their own protein. (Microbes need protein for reproduction and growth).
Some protein is not broken down in the rumen by these microbes, so instea it is digested in the small intestine and then absorbed. CP, RDP, UDP, NPN CP = crude protein (an estimate of the total protein in a feedstuff which has been calculated using the Nitrogen value from the feed test results). RDP = Rumen degradable protein (protein which is broken down in the rumen). UDP = Undegraded dietary proten (protein which passes through the rumen without being attacked by microbes, and instead needs to be broken down in the small intestine). NPN = non-protein Nitrogen (100% degradable in the rumen). Urea. BLOAT Bloat is a condition where an excessive amount of foam is produced in the rumen.
This foam captures the gas that is produced in the digestion process, rather than allowing the cow to burp out these gases.
The pressure rises in the rumen and can lead to a number of symptoms of ill-health, and severe cases can lead to cardio-respiratory failure and death.
Why is bloat more common in cows grazing clover?
Legumes, as well as some fast-growing grasses, have natural foaming agents in them. Therefore, when the cow is grazing a high proportion of legumes in a young, lush pasture, there is a higher risk of her experiencing bloat.
Treatments? Can be targeted at dispersing foam (eg. paraffin oil), or reducing methane production (eg rumen modifiers). Rumen modifiers - there are two main active ingredients used as rumen modifiers:
- monensin (eg. Rumensin): inhibits microbes that are less efficient at digestion (less efficient = produce a higher than average amount of methane)
- virginiamycin (eg. Eskalin): inhibits microbes that produce lactic acid (relevant to acidosis) LACTIC ACIDOSIS Many starches are digested almost completely and very quickly.
Microbes that digest starch produce lactic acid while producing VFAs.
Normally, this lactic acid is used by microbes, however, when a high starch diet (such as large grain portion) is fed, this can result in a large amount of lactic acid being produced.
The microbes that do this fermentation grow rapidly as they have the high supply of their feed (starch), and hence larger amounts of lactic acid are produced, and as such the acid amount reduces the pH in the rumen.
A diet high in easily fermentable starch that is not combined with a good fibre source, is likely to lead to acidosis. Without a reasonable fibre content, the cows chews less and hence the amount of saliva produced is less. With the low pH, many of the microbes responsible for digesting fibre are also inhibited.
It takes about 1-2 weeks for microbe populations to grow and adjust to changes in diet, particularly grain levels.
It is recommended to introduce new feed at 0.5kg/day. DISPLACED ABOMASUM (TWISTED STOMACH) There is no single cause of displaced abomasum (DA).
DA is where the abomasum is moved out of its normal position.
DA causes the abomasum to be kinked and can vary in the level of restriction to digesta movement.
The abomasum fills up with gas, which makes the stomach produce abnormal sounds.
DA is most common in the few weeks following calving, as the dry matter intake of cows is lower than usual.
Rolling the cow and surgery are the common treatments, yet neither is guaranteed successful.