Methods adopted to estimate protein requirements for maintenance

METHODS ADOPTED TO ESTIMATE PROTEIN REQUIREMENT FOR MAINTENANCE

  • The estimation of maintenance requirement for protein as compared with that of energy is more complicated because of the following reasons.
    • Protein may also be used as a source of energy in case of energy shortage.
    • An excessive supply of protein results in deamination of protein and utilisation of the resulting N free-substances as a source of energy, since deposition of protein in reserve tissue of mature animals is limited.
  • The protein requirements can be estimated for maintenance based on calculations of the factors causing nitrogen losses from the body during maintenance. These factors include endogenous urinary nitrogen and metabolic faecal nitrogen.
  • Losses of hair, feathers and scurf are other factors that are involved. Although not strictly required for maintenance, factors such as growth of wool, feathers or hooves do occur in animals otherwise being maintained.
  • The term ‘adult growth’ is used to refer the growth and renewal of these epidermal tissues.
  • Protein requirements have been calculated by conducting nitrogen balance trials, feeding trials and factorial method where endogenous urinary nitrogen, metabolic faecal nitrogen, nitrogen loss through skin and biological values (BV) of proteins are estimated to assess the protein requirements.

1.  Nitrogen balance method

  • Various rations containing different levels of protein are fed to the various groups of non producing adult and healthy animals.
  • The rations are otherwise adequate in energy, minerals and vitamins required by the animals.
  • Nitrogen balance is determined in the experimental animals.
  • The minimum protein intake at which nitrogen equilibrium is achieved is the maintenance requirement.
  • The experimental animals chosen for the studies must be in adequate protein nutrition at the start of the experiment.

Disadvantages

  • It is a short-term measurement carried out under closely controlled conditions and thus question always arises as to how accurately the results apply to the long-term feeding.

2. Feeding trial method

  • Long term feeding trials are conducted with non producing adult, healthy animals which are kept on different levels of protein with adequate intake of energy, minerals and vitamins.
  • The level of protein at which the animal maintains its body weight without loss or gain over an extended period is considered the maintenance requirement of protein.

3. Factorial method

  • Protein requirement can be determined accurately by factorial method.
  • Mostly this method has been followed throughout the world.
  • In India many workers have followed factorial method where EUN and MFN are estimated to assess protein requirement. Dermal losses of hair and scuff (2.2g N/d) are also included.
  • The net requirement, however only covered replacing these losses and the efficiency with which the absorbed protein is utilized (BV value) also must be considered.
  • ARC assumed BV values of 70% for cattle and 65% for sheep.
  • Since animals are being fed for productive purposes, the biological values for the combined function of maintenance and production are the ones of practical importance.
  • For pigs and poultry, protein requirement are usually stated for maintenance and production together.
Last modified: Friday, 30 March 2012, 11:02 AM