Usefulness and limitations of feeding standards

USEFULLNESS AND LIMITATIONS OF FEEDING STANDARDS

  • Feeding standards serve as a guide in feeding animals and in estimating the  adequacy of feed  intakes and of feed supplies for groups of  animals .
  • In practical feeding operations, it is  frequently desirable to take economic factors  into account. Thus, modifications (in feeding standards) may be called for in the interest of obtaining the rate of gain or level of milk  production that seems the most economical in  terms of current feed costs and the market
    price of the product.
  • No standard can be a complete guide to feeding  because other factors such as palatability and the physical nature of the ration must also be taken into account.
  • Further, environment may change nutrient requirement.

Merits and Demerits of various feeding standards

  • The units used in feeding standards should be the same as those used in the evaluation of feeds.

Energy evaluation

  • It is not tenable to consider one nutrient more important than another, Since all must be available to the animal in adequate amounts if efficient production is to be maintained. However, an animal's requirement for energy is the primary consideration from a quantitative and economic position.
  • Energy is the most important factor which limits livestock production and meeting the energy requirement for maintenance and production is the major cost associated with feeding animals.
  • The best unit for expressing the energy value is the one which takes into account all the losses incurred by the animal in utilising the energy present in feeds.

TDN and DE Systems

  • The TDN and DE system of feed evaluation have been and continue to be used because these measures are useful as first approximations of a feeds value as a source of energy and a considerable and valuable volume of knowledge exists concerning the proximate composition and the TDN or DE value of feedstuffs.

Merits

  • TDN is a measure of apparent DE but is expressed in units of weight or percent rather than energy per se.
  • TDN value provides a relative measure of the DE content of feed:1 kg TDN =4.409 Mcal DE.
  • It is easy to determine the TDN content of feedstuffs: proximate composition of feed and faeces and digestion trial are to be done.
  • Digestible energy can readily be determined by using  a bomb calorimeter to measure the Gross energy of feed and faeces. No chemical analysis are required.

Demerits  

  • TDN systems takes into account only the losses of nutrients in the faeces but not the other losses from the body.
  • TDN system overevaluates the energy value of poor quality roughages in relation to concentrates specially so in hot environment because
    • TDN does not consider large amounts of energy wasted in the digestion of fibrous feeds in the form of gases and heat increment and
    • Ether extract of forages largely comprise other than true fat. So a kg of TDN in roughages has less value for productive purpose than a kg of TDN in concentrate.
  • Certain species of forage were found to have high gross energy and high TDN values due to essential oils but low ME values.
  • The measurement of DE takes into account the losses only through faeces.

Starch equivalent and metabolizable energy system

The total digestible nutrients (TDN) system in the USA, Canada and India and Starch Equivalent (SE) system in Europe have been widely used since early 1900s. The SE system was replaced by the ME system devised by Blaxter in the UK. The ARC has adopted the ME system since 1980. ME goes a step beyond DE or TDN (Since energy losses in urine and gasses produced during digestion are corrected) and provides a more accurate measure of the value of a feedstuff.
It has been common to use ME as a measure of feed value for poultry because their faeces and urine are excreted through a common orifice; it is actually easier to determine ME than DE for them.

Merits of ME system

  • ME represents a more accurate measure since losses in urinary and gaseous products of digestion are also accounted for.
  • ME provides a more satisfactory measure of nutritive value than do TDN or DE
  • ME is cheaper and easier to obtain than NE values.
  • The efficiency of utilisation of ME takes into consideration the purpose for which it is fed, level of feeding and caloric density of the diet.

Demerits

  • The requirement of the animal and feed value are given in terms of NE and ME, respectively.
  • The large differences in the efficiency of utilisation of ME are primarily due to wide variation in the energy losses as heat increment.
Last modified: Monday, 6 February 2012, 8:40 AM