LPM 121: Fodder Production and Grassland Management (1+1)

Nutrient requirement of Cattle

NUTRIENT REQUIREMENTS OF CATTLE

• The first need of animal's life is energy and the central element for this is carbon. Carbon occurs in starches, sugars and other carbohydrates, fats, oils, proteins and even in plant pigments and vitamin compounds. All these are present in forage.
• Depending upon the animal's capacity, the forage is the main source of energy which aids in the support of life, growth, secretion of milk, work performance and reproduction. The portion of the nutrient that is digested and absorbed by the body is called digestible nutrient.
• Some of the nutrients are essential (not synthesized in sufficient quantity) which must be supplied by the diet. Non-essential materials are those that are required by the animal for physiological functions. They can be synthesized by the body tissues or microflora in the digestive tract.
• For example, a young calf with rudimentary rumen must depend on B-Vitamins from the diet. On the other hand, a mature cow can synthesize sufficient B-vitamins to supply her needs. Simple stomached animals depend on the diet for essential vitamins, aminoacids and fatty acids.
• For normal Physiological functions such as respiration, muscular contraction, heart beat, body heat, digesting feeds and body movements energy, proteins, vitamins and minerals are required. Protein is needed daily to replace cells that are broken down.
• To replenish minerals for formation of bones and new tissue cells minerals are needed. If the feed is reduced a dairy cow will use available energy for maintenance and reproduction at the expense of growth and lactation. Therefore, it is important to supply adequate nutrition if normal growth, high milk production and profits are to be obtained.
• Energy: The most important nutrient in the formulation of rations for dairy cattle is energy. The energy values are expresed in different ways.
  • Total Digestible Nutrients (TDN) content of a feed is expressed as a percentage. It is estimated in a digestion trial in which feed and faeces are analysed for crude protein (CP) = (N x 6.25), Crude fibre (CF), Nitrogen-free extract (NFE) and either extract(EE) (Fat x 2.25). The data are used to calculate TDN.

% TDN = (CP + CF+ NFE+(EE X 2.25) X 100) / 100 KG Feed

• This formula ignores gaseous and urinary energy and losses due to heat production. Extensive TDN data on many feeds are available and long tradition insure its continued use in practice.
• Digestible energy (DE):
  • Gross energy of feed is the total amount of heat liberated when it is completely combusted.
  • The difference between gross energy in the feed and that in faeces is termed digestible energy.
• Fibre and energy:
  • Fibre is necessary in a ration although it is not a nutrient. It controls feed intake, stimulates rumination, maintains pH in rumen and digestion.
  • Lignified fibre is less digestible. It also decreases dry matter intake. The stimulating rumination of fibre is destroyed by reducing particle size in grinding, pelleting or excessive chopping of fodder. An increase in fibre content decreases the energy value.
• Protein:
  • In the animal's diet provides aminoacids for its physiological functions. The cow does not depend on its diet for protein because the rumen is capable of converting nitrogen from the feed and non-protein - nitrogen (NPN) sources into aminoacids.
  • The protein requirement of a mature cow depends on the amount of protein in the diet, which is broken down to ammonia by microbial digestion.
  • The rumen microbes convert ammonia to microbial protein. All the feed protein sources are not degraded in the rumen to the same extent.
  • The optimal ration meets the nitrogen requirements for maximum rumen microbial protein synthesis, avoids losses of excess ammonia from the rumen and provide undegraded protein.
  • When microbial synthesis is inadequate to meet protein demands of high production by-pass protein becomes important in lactation. The synthesis depends on feed intake, feed type, protein level, digestibility and feeding method.
  • NPN is any compound that contains nitrogen not in the form of amino acid.
  • Common NPN compounds fed to dairy cows are feed grade urea, ammoniated straw, mono ammonium phosphate and liquid supplements having molasses, urea, minerals and vitamins. NPN in the ration is cheaper than feed protein sources per unit of nitrogen.
  • Urea is limited to 1 percent of grain mixture or 200 g/cow/day. Protein is one the most expensive ingredient of dairy ration and hence overfeeding is avoided.
  • Excessive nitrogen intake may affect delayed conception, embryonic death or increased services/conception. Protein requirements for different classes of animals are computed with data available on digestible crude protein.
• Fat:
  • Ruminants ingests and digests large quantities of forages and since fat can be formed from other nutrients, dietary fat needs are nominal.
• Minerals:
  • Inorganic elements are needed for cattle for various physiological functions such as for
    1. Bone and teeth formation,
    2. Enzyme systems,
    3. Maintenance of osmotic relationships and acid-base equilibrium,
    4. Functioning of muscles and nerves and
    5. To serve as constituent of proteins and lipids in muscles, organs, blood cells and soft tissues.
• Vitamins:
  • Dairy cattle require no dietary B vitamins and vitamin K as these are synthesized by microorganisms in the rumen. Vitamin C is synthesized by the body tissue.
  • However, until the rumen of young calves become functional at about 6 weeks of age, the calves need dietary B vitamins. The dietary needs of cattle are vitamins, A,D and E. These vitamins or their precursors are present in natural feeds in varying amounts.
• Digestible crude protein (DCP ):
  • From the digestibility coefficient of protein in a feed, the amount of DCP can be determined. For instance suppose an animal consumes 10 kg of a good hay (Guinea grass) containing 7.5% crude protein, then the quantity of crude protein ingested/day is 0.75kg.
  • The animal is found to pass daily 6 kg dung. The moisture content of the dung is 50% so that 3 kg of dry matter is being excreted. If the crude protein content of the dung is 8% on dry basis, the animal excretes daily 0.24 kg of protein as undigested.
  • Therefore from 10 kg hay, only 0.51 kg of protein is being digested giving a digestible protein content 5.1%.
• Total digestible nutrients (TDN):
  • It has been explained before that the major organic nutrients help in producing heat and energy in an animal. Thus, the TDN estimation provides an index of its energy yielding capacity.
  • Suppose a feed like ground nut cake contains 42 kg digestible protein. 12 kg digestible carbohydrate and 8 kg of digestible fat in 100 kg, its TDN will be 42+12+ (8 x 2.25) = 72 kg/100 kg.