RELATIONSHIP OF RUMEN MICROFLORA WITH HEALTH & PRODUCTION OF DAIRY COWS
Dr.Mukesh Sharma, Dairy Consultant,Raipur
A healthy rumen isn’t just a good way to avoid digestive upsets. Rumen health is a good yardstick of overall cow well-being. Without a well-functioning rumen, your dairy herd is open to all manners of costly health complications. New research that analyses microbes in cows’ stomachs could help boost meat and milk production leading to greater food security in the future. Though hidden from view, the rumen and its microbes hold a central role in feeding of cattle. During ruminal fermentation, microbes break down fiber and other feed components and produce volatile fatty acids (VFA). In the process, microbes generate adenosine-tri-phosphate (ATP, energy) for themselves, then harness part of this ATP to produce microbial protein. The VFA so produced meet up to 70% of the animal’s energy needs (Bergman, 1990), and microbial protein meets 60 to 85% or more of protein needs.
Ruminants can degrade fiber thanks to the synergistic actions of different microbial populations inside the rumen, including bacteria, fungi, protozoa and methanogens. This ecosystem ferments both fiber and other nutrients, such as sugars and carbohydrates (CHO), into short-chain fatty acids, (SCFAs). These represent the main energy source for the cow for both maintenance and milk production. Fermentation also fuels microbial growth and in-turn the synthesis of protein.
Energy and protein availability
Milk production depends directly on metabolizable energy and protein available to the animal, after the need for growth and maintenance. Modern, dynamic formulation systems such as the Cornell Net Carbohydrate and Protein System (CNCPS) or platforms such as Nutritional Dynamic System (NDS) calculate milk production forecasts based on metabolizable protein and the amino acids profile available at the intestinal level. This approach is becoming more widespread due to their strength in forecasting subsequent production.
Rumen microbial protein production offers additional benefits, including:
• a high rate of digestibility of 75% to 80% (similar to soybean meal)
• a constant and reliable amino acid profile (important for stable milk production and milk protein quality)
• Energy from rumen fermentation through improved fiber digestion.
Optimizing rumen protein production
To the extent that we are able to maximize milk protein production through good rumen function and health, we can optimize the cost of our protein diet. In this light, producers and nutritionists should pay particular attention to rumen pH, proper cultivation techniques and harvesting time in order to optimize neutral detergent fiber (NDF) digestibility of forages and to the choice of ingredients that best meet a cow’s and rumen bacteria’s needs.
From a formulation perspective, a profitable ration for high producing cows should have at least half of all metabolizable protein coming from rumen bacteria and more than 70% of the starch efficiently fermented in the rumen. Both these parameters are good indicators of proper rumen efficiency.
There are several opportunities for improving microbial protein synthesis, just as there are several bottlenecks that can limit the quantity of microbial protein that rumen microflora create. Some of these are reported in Tables 2 and 3.
RUMEN-——
The capacity of an adult dairy cow’s rumen is about 184 litres (49 gallons) and the reticulum is about 16 litres (4.25 gallons). It is one of the most dense microbial habitats in the world. Microscopic organisms called rumen microbes break down (or digest) ingested feed by a fermentation process. The rumen is the major site of fermentation in the cow. There are1,000,000,000 to 10,000,000,000 bacteria per ml, 1,000,000 protozoa per ml, and a variable amount of fungi. The cow does not secrete any of her own acids or digestive enzymes in the rumen. Rather, all rumen digestion is done by the microbes.
It is because of the rumen and its microbes that dairy cows can digest plant fibers, such as hemicellulose and cellulose. This allows the dairy cow to convert forages and industrial byproducts that humans cannot digest into nutritious foods for humans. Mammalian enzymes and acids cannot digest fiber. The rumen microbes ferment fiber, starch, sugar, and protein to form volatile fatty acids and microbial protein.
The rumen wall (or mucosa) is a major site of nutrient absorption. It is convoluted to give it tremendous surface area for absorption. Rumen papillae (thousands of finger-like projections on the inside surface of the rumen) are responsible for absorbing the volatile fatty acids from the rumen for use by the cow. Volatile fatty acids (VFA’s) are absorbed from the rumen and used as an energy source for the cow. Microbial protein(the actual bodies of the microbes) is not absorbed from the rumen. It absorbed from the cow’s intestine and is used as a source of quality protein for the cow.
The reticulum is located in front of the rumen and it is known for its characteristic “honeycomb” surface. If a cow accidentally eats hardware, such as screws or nails, it usually ends up lodged at the bottom of the reticulum. If the hardware punctures through the reticulum wall, it causes the often deadly “hardware disease”.
CHARACTERISTICS OF THE RUMEN ENVIRONMENT—–
A number of characteristics about the rumen allow for the growth of the rumen microbes and for their fermentation process that digests feed and forages for the cow. Any disruption to the delicate balance of the rumen environment will result in poor growth of the microbes, poor digestion, and ultimately, lower milk production.
First of all, the rumen is anaerobic. This means that there is little or no oxygen in it. The rumen microbes cannot grow in outside air. They will tolerate a small amount of oxygen so long as the fermentation is going strong enough so that they can get rid of the oxygen quickly. Some oxygen does, of course, get into the rumen through feed and water. Secondly, the rumen temperature is one degree above body temperature at39°C (102.5°F). Luckily, it’s fairly easy for us as farmers and nutritionists to maintain an anaerobic, warm environment deep in the belly of the cow!
Rumen pH ranges between 5.7 and 7.3. The high side of this pH range (> 7) will be seen on poor quality forage diets supplemented with urea. In high-producing dairy cows,acidosis (rumen pH<6.0) is a common problem. This occurs when the cow eats too much rapidly digestible starch or sugar that creates acid and overwhelms the rumen’s buffering system. Most of the buffer in the rumen comes in the form of saliva that is generated when the cow chews her cud. Inadequate intake of long fiber that promotes rumination (cud-chewing) can also result in acidosis because it provides less salivary buffer to counteract the acid produced by grain fermentation. The rumen microbes, especially those that primarily digest fiber, are acid intolerant. They do not grow well in acid and they don’t digest feed, especially forages, well under acid conditions.
END PRODUCTS OF RUMEN FERMENTATION———–
1. Volatile Fatty Acids (VFA’s):———-
The rumen microbes make three primary volatile fatty acids: acetate (CH3COOH),propionate (C2H5COOH), and butyrate (C3H7COOH). Acetate is formed primarily from the fermentation of fiber. Large amounts of propionate are formed from grain fermentation. Butyrate is produced to a lesser extent than acetate and propionate. Sometimes lactate is also formed, especially under acidic conditions in the rumen. VFA are actually waste products from the rumen microbes but the cow absorbs them from her rumen and uses them as major source of energy.
2. Gases:————
Dairy cows produce 30-50 liters (8-13 gallons) of gas per hour. Carbon dioxide (CO2) (about 60%) and methane (CH4) (about 40%) are the main waste gases produced by the rumen microbes. Hydrogen (H2) usually makes up less than 0.05% of the total rumen gases. Gas is primarily found on top of the solid and liquid contents of the rumen. Methane bacteria actually grow on CO2 and H2 and other byproducts from the other bacteria in the rumen. The methane bacteria commonly produce methane in this way:
4H2 + CO2 —> CH4 + 2H2O
Cows get rid of these excess gases by a process called eructation (a kind of silent belching) and by absorption through the rumen wall and lung exhalation. The cow eructates using a process which is slightly different from the normal contractions of the reticulum. Once gas pressure stimulates pressure receptors, the reticulo-ruminal fold and the cranial pillar stop the rumen digesta from getting into the oesophagus. The cardia and diaphragmatic sphincters relax, gas enters the oesophagus and is released through the cow’s mouth.
If a cow is unable to get rid of excess gases, she can bloat. When the rumen contents foam excessively, the cow has difficulty getting rid of the gas because it is trapped inside the foam. The rumen keeps expanding. It creates pressure on the cow’s lungs and the cow can die of asphyxiation. Many legumes (white clover and alfalfa), especially those that are young and freshly cut, can cause bloat. A chronic type of bloat also occurs in beef cattle on feedlots when they are fed a lot of grain. Oils or low-foam detergents have been used to reduce the stability of foam in the rumen and prevent bloat.
3. Microbial Mass—————
The rumen microbes grow in the rumen and their bodies are passed down to the intestine of the cow. Thus, they make up a large portion of the cow’s diet and the largest portion of the cow’s protein supply. This microbial protein is high quality, meaning that the amino acid profile is fairly similar to that of milk and meat. Therefore, the cow can easily and efficiently convert microbial protein into milk and meat.
4. Heat——————–
As the microbes digest ingested feed and forages and grow, they release heat. This is called the “heat of fermentation”. Except for when the cow needs this heat to warm her body, this heat is a waste of energy to the cow. The fermentation of forages creates more heat than the fermentation of concentrate feeds.
Rumen Structure and Movements:————-
Rumination—————
Rumination, also called cud-chewing, is the process by which the cow regurgitates (casts up) previously consumed feed and masticates it a second time. The re-chewed feed with saliva is formed into a bolus and swallowed a second time. It is the floating, large particles on top of the rumen which are re-chewed. One purpose of rumination is to decrease particle size and increase surface area of the feed. This results in an increase in digestion rate of feed and a decrease in the lag time prior to fermentation. The fibrous particles will stay in the rumen longer causing the rumen to feel more full if the cow is not ruminating enough. This will reduce the total intake of the cow and negatively impact milk production. Another purpose of rumination is to make saliva (98 to 190 liters (or 26-50 gallons) per day) to buffer the rumen and decrease rumen acidity.
Cows usually spend more time chewing during rumination than they do when they eat. Pressure of coarse material (or “scratch factor”) against the rumen wall stimulates the cow to ruminate. Therefore, the amount of time a cow spends ruminating is diet dependent. Feeding a lot of concentrates and/or finely ground feeds reduces rumination. It is critical, especially in high-producing dairy cows that consume considerable amounts of concentrate, that there is an adequate amount of long fiber present in the diet to stimulate rumination.
Stratification of Rumen Contents-————–
Dairy cows who are fed a diet containing long fiber have a large, dense, floating layer (or floating mat) located just under the gas in the top portion of the rumen. This mat contains the more recently consumed feed, especially the fibrous portion of the diet. As the ingested feed ferments and is ruminated, it becomes more water-logged and dense and gradually sinks toward the bottom of the rumen. Smaller, dense particles and liquid is located in the bottom portion of the rumen. This bottom layer is material that is nearly ready for passage out of the rumen, into the omasum, and on down the cow’s digestive tract. Diets high in concentrates or containing only very fine fibrous material may either have no floating mat or a very small one.
Rumen Mixing—————–
Mixing of rumen contents is very important to the cow. Contraction and relaxation of the entire rumen, especially the wall between the rumen and the reticulum, helps to mix contents. Also, ridged structures called rumen pillars act like baffles on the inside of a clothes washing machine and help to set up mixing motion in the rumen.
Rumen mixing helps to inoculate feed with microbes. It also aids VFA in reaching the rumen wall for absorption. The combination of mixing and rumination allows the cow to pass indigestible matter that might otherwise stay in the rumen and decrease total feed intake of the cow. It is interesting to note that finely processed diets that result in little mat formation actually increase the rate at which feed passes and increase the size of particles found in the manure.
Adding just a small amount of long hay to a diet, such as 1-2 kg (2-4 pounds) can greatly increase the size of the mat, stimulate rumen mixing, help VFA to reach the rumen wall for absorption and help to properly sort rumen contents. At same time, hay promotes rumination and the production of saliva to buffer the rumen.
The importance of rumen microbes-—–
Increasing the production of microbes in the rumen is the key to lifting milk production and composition. The microbes break down feed to produce volatile fatty acids, which are used by the cow as energy for maintenance and milk production.
The rumen microbes are also digested and absorbed in the small intestine of the dairy cow as the main protein source for milk production, providing up to 70-90% of a cow´s protein requirements.
Roles of different microbes-——
The three different types of microbes produced in the rumen are:
• fungi
• bacteria
• protozoa.
Different microbes have different digestive roles.
There are two main groups of rumen microbes: the slow-working fibre-digesters located on the fibre mat in the rumen, and the fast-working microbes that float around in the rumen fluid, looking for easily-digested nutrients like sugars and starches
Feed influences microbe type, digestion and intake———
Because each group of microbes has very specific functions – like digesting fibre, starch, sugar or protein – the numbers of each are directly related to diet.
A minimum amount of longer fibre particles to form the rumen mat is required for optimal microbe production.
The type of feed – especially its fibre content – influences:
• the type of microbe in the rumen
• the speed of digestion
• the total intake of dry matter and nutrients.
Concentrates and lush forage, which contain lower amounts of fibre, build up the quick-working ´floating´ microbe population and cause feed to move more quickly through the rumen and digestive system. The cow wants more food, and intake is potentially increased.
Mature forages contain higher fibre and lower soluble nutrients, which build up the slow-working, fibre-digesting microbes and cause feed to move more slowly through the system. The cow feels less hungry, and intake is reduced.
Importance of a consistent diet–————–
Microbe populations take time to recover and build up after sudden feed changes.
Forage fibre-digesting microbes may take 4-6 weeks to build up. Starch-digesting (grain-digesting) microbes take 4-5 days to build up. Lactic acid-producing bacteria (from slug feeding) take 2-4 hours to build up.
If a cow’s diet keeps changing every few days, the required microbes will not be present in sufficient numbers for optimum digestion. Therefore, a cow’s diet should be as consistent as possible.
Essential nutrients for the microbes
Water
Cows require up to 100 L of drinking water/cow/day. Water maintains the rumen liquid environment, supports microbe metabolism, and dilutes acids in the rumen.
Energy
Most energy for microbes to grow and multiply is sourced from:
• starches (e.g. cereal grains)
• sugars (e.g. lush forages, molasses and citrus pulp)
• digestible fibre (e.g. forages, cottonseed hulls, palm kernel extract and brewer´s grain).
Protein
Microbes use both true protein (e.g. protein meal and pastures) and non-protein nitrogen (e.g. urea) for growth and reproduction. In turn, rumen microbes become the largest source (greater than 70%) of dietary protein for the cow.
Minerals
Calcium, phosphorus, sulphur and magnesium are essential for microbes to grow and multiply.
FACTORS AFFECTING FEED INTAKE-—
Major drivers of feed intake-——
Feed availability
The amount of feed on offer must be sufficient to satisfy appetite and meet production targets. Provide equal access to feed for all cows, particularly at troughs or on a feedpad.
Feed quality-———-
Optimise nutrient content in the diet for intake and milk production (e.g. energy, protein and fibre). Feed quality and the palatability of a particular feed are affected by:
• freshness
• mould
• spoilage
• taste
• moisture
• temperature.
High neutral detergent fibre (NDF) in individual feeds and the total diet will restrict the cow’s ability to consume a high intake.
Feeding management————–
Provide feeds and total diets that are easy to eat and digest. Consider the:
• chop length
• degree and type of grain processing
• amount of green leaf available in pastures.
Ensure mixed rations are mixed thoroughly.
Neutral detergent fibre (NDF) content-——————
NDF in forages and the total diet determines dry matter (DM) intake. Diets need to be balanced to contain sufficient and effective NDF for healthy rumen function while not providing too much fibre, as this slows down digestion and limits intake.
Other important drivers of DM intake-————–
Other factors that influence DM intake include:
• cow size
• rumen health
• stage of lactation (in early-lactation cows require higher DM intake)
• water quality and accessibility
• heat stress
• overall animal health
• nutrient supply (should be constant and consistent to maximise rumen microbial activity and DM intake).
NDF intake rules of thumb-—————-
There are three rules of thumb for NDF intake:
• Optimum intake is achieved when NDF content equals 28% to 34% of total diet DM.
• Maximum NDF intake from forage should equal 1% of the cow´s body weight.
• Maximum intake of NDF in the total ration should equal 1.2% of the cow’s body weight (1.3% for a high-producing cow).
Estimating potential intake from NDF———————
The rules of thumb can be used to help evaluate the NDF content of a cow’s diet and see if it falls into the optimum range. The following example shows how to calculate all the figures you will need to do this.
Estimating intake from NDF on lush, low-fibre pastures-——————
Example: a 600 kg cow on a diet of lush, temperate pasture (45% NDF) and dairy meal (15% NDF).
In order to find the total percentage of NDF content in the cow’s diet, follow the steps below.
1. Use the rules of thumb to find the different maximum intake levels of NDF.—————–
Max. total diet intake of NDF = 1.2% of 600 kg (body weight) = 7.2kg
Max. intake of forage NDF = 1% of 600 kg (body weight) = 6 kg
Max. NDF intake from sources other than forage = 7.2 kg – 6 kg = 1.2 kg
2. Calculate how much lush, temperate pasture (45% NDF) the cow should eat.———————-
Calculate the max. DM intake of lush, temperate pasture (forage) using the figure for the max. intake of forage NDF (step 1). That is, if a cow can eat 6 kg of forage NDF, how many DM kilograms should it eat of a forage that is 45% NDF?
Max. DM intake of lush pasture (45% NDF)
= 6 x 100 ÷ 45
= 13.3 kg DM
3. Calculate how much dairy meal (15% NDF) the cow should eat.—————-
Calculate the max. DM intake of dairy meal using the figure for the max. NDF intake from sources other than forage (step 1). That is, if a cow can eat 1.2 kg of NDF from sources other than forage and dairy meal is only 15% NDF, how many DM kilograms of dairy meal should it eat?
Max. intake of dairy meal (15% NDF)
= 1.2 x 100 ÷15
= 8 kg DM
4. Calculate the total potential DM intake on this diet.——————–
Calculate the total potential diet DM intake by adding together the max. DM intake of lush pasture (step 2) and the max. DM intake of dairy meal (step 3).
Potential diet DM intake
= 13.3 (max. DM from lush pasture) + 8 (max. DM from dairy meal)
= 21.3 kg DM
5. Find the total percentage of NDF in this diet and see if it falls inside the optimum NDF intake range.-————–
Evaluate the total diet NDF by dividing the max. total diet intake of NDF (step 1) by the potential diet DM intake (step 4) and multiplying by 100 to find the percentage of NDF the diet contains.
Total diet NDF
= 7.2 ÷ 21.3 x 100%
= 33.8% = Good (inside optimum range)
Reference:On request.
