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Energy is measured in Mega Joules (MJ) or Mega Calories (Mcal). In the SI system, joules should be used, although calories are also common. The factors below can be used to transform one unit into the other.
1 Mcal = 4,18 MJ
1 Kcal = 4,18 KJ
Only about 20% of the cow’s total energy intake is used for milk production. The cow uses the remaining 80% for maintenance and losses through heat, gases, feed and urine. The higher the milk yield, the higher the percentage of total energy intake is used to produce milk.
The cow’s two main energy sources are carbohydrates and fat.
The energy concepts of digestible energy (DE), metabolizable energy (ME) and net energy (NE) are used to describe the animal need and to formulate rations. Net energy is most widely used.
Utilisation of the energy consumed by a cow.
Carbohydrates are the cow’s main energy source. They are vital for maintenance, body fat and milk production. Different types of carbohydrates are transformed into different volatile fatty acids that are absorbed as energy in the rumen.
Carbohydrates can be classified in many ways: for example, sugar, starch or fiber.
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Sugar
Sugar is quickly digested in the rumen. Many feedstuffs that contain plenty of sugar, such as molasses, are tasty and can increase the feed intake of the cow. Sugar is classified as a non-fiber carbohydrate (NFC) (see picture below).
Starch
Starch is a type of carbohydrate that can be quickly digested, and is classified as a non-fibre carbohydrate. All grains and corns contain a high percentage of starch. In the corn plant, starch is stored in the corn grains. |
Starch is a carbohydrate that can
be degested fairly quickly. It is classified as a non-fibra carbohydrate. |
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Fibres
Fibres are cell-wall carbohydrates of four parts: pectin, hemicellulose, cellulose and lignin (see picture below). Pectin is quickly fermented and has a digestibility similar to sugar.
Hemicellulose and cellulose are available in the cell walls (see picture below). They contain lignin, which is solid and bound to cellulose and hemicellulose. This bond makes the cellulose and hemicellulose less available for the micro-organisms in the rumen. The result of high lignin content is that the digestibility of the feed decreases. |
Fibre are cell-wall carbrohyrates made up of four fractations. |
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The fermentation speed of carbohydrates.
Neutral detergent fibre (NDF)
As shown in picture 10, the NDF contains cellulose, hemicellulose and lignin. In practical feeding, the NDF value is closely related to the total dry matter intake. When most of the NDF in the ration comes from immature forage and by-products, the relation to dry matter intake becomes less relevant.
Acid detergent fibre (ADF)
The ADF fraction contains cellulose and lignin. The lignin is a measure of the digestibility of the feedstuff. Straw has a high ADF value.
*Lignin is not a carbohydrate, but it is closely related.
Description of the carbohydrates and their elements.
Carbohydrates are fermented in the rumen and transformed into different volatile fatty acids (VFA). VFA are absorbed through the rumen wall and serve as the main energy source for the cow. The box shows the proportions of different acids when the cow is fed a normal ration.
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Carbohydrates:
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- Acetic acid, 60-70%
- Propionic acid, 15-20%
- Butyric acid, 10-15%
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Acetic acid is vital for the production of milk fat. A sufficient amount of acetic acid must therefore be produced in the rumen. The primary source for acetic acid fermentation is digestible fibre, which comes from early cut silage or hay.
Another important acid is propionic acid. Propionic acid affects total milk yield and milk protein content. Since propionic acid is needed for fattening, it is important when feeding beef cattle. The production of propionic acid is stimulated by starch in grain, for example.
Buturic acid is important for milk fat production. The production of buturic acid increases when sugar beets and barley are fed to the cow.
Fat contains twice as much energy as carbohydrates. The fatty acids are transported through the rumen and absorbed in the small intestine. Fat can be used to increase the energy density of the ration. When feeding high levels of fat to ruminants it is important to use protected fat, so as not to upset fermentation in the rumen.
What is protein?
Proteins are built up by amino acids. The most important amino acids are the essential amino acids: lysine, methionine and tryptophane. A lack of amino acids can be a limiting factor in milk production.
The functions of protein:
- building and repairing tissue;
- growth;
- reproduction; and
- milk production.
Protein supply
The protein value of feed is calculated by multiplying its nitrogen content by 6.25, based on the presumption that most proteins contain approximately 16% nitrogen.
Protein supply
The figure you get is the crude protein value of the feed. Crude protein represents a combination of true protein and non-protein nitrogen (NPN).
The cow has two types of protein source: microbe protein and undegradable protein.
Rumen-produced protein — microbe protein
The major part of the protein that a cow digests and absorbs is produced in the rumen by rumen microbes. When the cow reaches higher production levels she needs additional protein, which passes through the rumen and is directly absorbed in the small intestine (undegradable protein).
The micro-organisms use ammonia and carbohydrates as raw materials when producing protein. Ammonia originates from two different sources:
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Non-protein nitrogen, which is almost immediately transformed into ammonia in the rumen. Urea is a typical non-protein nitrogen.
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Degradable protein, which is a natural protein that contains nitrogen. In order to access the nitrogen, the micro-organisms start the process of degrading the feedstuff. Ammonia is a by-product from this process. Examples of easily degradable protein sources are grass and legume seeds.
The micro-organisms grow and multiply on the ammonia and carbohydrates, and when they die they become a protein source for the cow. The microbe protein passes through the digestion channel and is available for absorption in the small intestine.
Undegradable protein
Undegradable protein is also a natural protein that comes from feed. The protein that escapes degradation in the rumen is called undegradable or by-pass protein. It passes through the rumen and is absorbed in the small intestine.
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A cow also needs other nutrients, such as minerals and vitamins. Even if every other nutritional need is fulfiled, where there is a lack of minerals and vitamins milk production will be limited.
Minerals
Minerals are necessary for many of the cow’s significant body functions, such as water balance and milk production. Minerals can be divided into macro minerals and trace minerals. Macro minerals are needed in larger amounts than trace minerals.
| Macro Minerals |
Notes and Function |
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Calcium (Ca)
Phosphorus (P)
Magnesium (Mg)
Potassium (K)
Sodium (Na)
Sulphur (S)
Trace minerals |
Animals need calcium for bone and teeth formation and the transmission of nerve impulses. A high yielding cow needs about 0.6–1% calcium of total DM in her feed ration. Bones serve as a source of reserve calcium for exchange with soft tissue.
The high price of phosphorus can cause a deficiency of this mineral. A decrease in milk production is a result of insufficient phosphorus.
A lack of magnesium is not discovered until a tetany appears. Excessive levels of potassium may result in a lack of magnesium.
Potassium is required in large quantities. It is vital for the cow’s water balance, nervous system and for milk production. Note that excessive potassium levels reduce the availability of magnesium. If the potassium content of the ration exceeds 2%, the magnesium level will require extra attention. Otherwise, “grass tetany” might appear.
Sodium has the function of maintaining body fluid balance, osmotic pressure regulation and acid-base balance. When cows are fed a diet deficient in sodium, they will start licking and chewing various objects.
Sulphur is an essential component of protein.
Iron
Copper
Zinc
Manganese |
Cobalt
Iodine
Molybdenum
Selenium | |
Vitamins are organic combines that fulfil vital functions. There are two types of vitamins: water soluble and fat soluble. The cow can produce water soluble vitamins with the help of micro-organisms.
The fat-soluble vitamins are stored in the fat and used when needed. With high production, and a limited vitamin content in feed, additional vitamins have to be provided. Fresh feedstuff contains more vitamins than stored. Some of the vitamin content is destroyed when feed is stored. The necessary use of stored feedstuffs therefore necessitates provision of extra vitamins.
A high-yielding cow needs more vitamins due to the stress that comes with high yield. Important fat soluble vitamins are A, D, E and K. Water-soluble vitamins are B-vitamins.
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| A high producing dairy cow may need more than 130 litres of water per day and free access to fresh water is essential for milk production. Water is needed not only for vital body functions, such as regulation of body temperature, digestion, metabolism and excretion; it also affects total milk production. Scientific trials have shown that a 40% reduction of a cow’s normal water intake can result in a 25% decrease in milk yield (Allen et al., 1976). |
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Water needs of a dairy cow
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Water of high quality — cows are more sensitive to poor quality water than humans;
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Free access — a high yielding cow drinks up to 130 l/day. When feeding, water requirement can reach up to 20 l/min. This places requirements on both the dimension of the water system and the number of drinking places;
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Temperature — the optimum water temperature is 17 °C (Andersson, 1984). Very low water temperatures will result in a drop in milk yield. High temperatures will also negatively affect milk yield, although to a lesser extent; and
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Large drinking surfaces — a cow will drink most naturally from a large calm surface, such as a pool.
Bowls and troughs
There are primarily two ways of providing cows with water: in water bowls or in troughs. Water bowls are most commonly found in tied-up stalls. Their main advantages are that they are easy to clean and easy to find space for. Troughs are more common in loose housing. They have greater capacity and a larger drinking surface. On the other hand, they are more complicated to clean.
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