Evaluation of Feeds as Source of Energy | Animal Husbandry & Veterinary Science Optional for UPSC PDF Download

Evaluation of Feeds as a Source of Energy Overview

Various methods are used to evaluate the energy content of feeds for dairy cattle. These methods help in predicting animal performance accurately and determining their energy requirements. The different systems used to express the energy value of feeds include Total Digestible Nutrients (TDN), Starch Equivalent (SE), Digestible Energy (DE), Metabolizable Energy (ME), Net Energy (NE), Scandinavian Feed Units, among others.

Total Digestible Nutrients (TDN)

• TDN is a measure of the energy value of feeding stuffs determined through digestion experiments that calculate the digestibility coefficients of organic nutrients like carbohydrates, fats, and proteins.
• The advantage of TDN is its ease of determination in feedstuffs by subjecting the feed and feces to proximate analysis.
• To calculate TDN, the digestible nutrients from all four principles (crude protein, ether extract, crude fiber, and nitrogen-free extract) are added, with the weight of digestible ether extract multiplied by 2.25.
• However, TDN suffers from inaccuracy as it only considers digestion losses in animals, leading to overestimation of roughage energy value and underestimation of concentrates.
• Feeding standards in America are primarily based on the TDN system, with the Morrison standard being extensively used, although there is a gradual shift towards the ME system.

Starch Equivalent (SE)

• SE is a system of feed evaluation developed by Kellner, widely used in Europe.
• It quantifies the amount of feed needed to produce the same amount of animal fat as a unit of starch when added to the maintenance ration.
• For example, if linseed cake has a starch equivalent of 74 kg, it means that 100 kg of linseed cake can produce as much animal fat as 74 kg of pure starch.
• SE is similar to net energy systems in stating the productive value of feed, with SE expressed in terms of starch and net energy in terms of calories.
• Kellner determined SE values of feeding stuffs by conducting experiments in an animal calorimeter to accurately measure heat losses and energy production.
• The efficiency of utilization of fibrous feeds like straws differs from less fibrous oilcakes due to varying crude fiber contents affecting energy expenditure during digestion.

Calculation of Starch Equivalent in Feeds:

• Starch equivalent is determined for feeds without deducting for fiber.
• Value numbers, ranging from 95 to 1, are utilized for oilcakes.
• For linseed cake: SE = 78.4 kg per 100 kg, using a Value Number of 0.97.

Digestible Energy and Total Digestible Nutrients:

• Digestible energy refers to the energy content of food minus fecal energy.
• Total Digestible Nutrients (TDN) may overvalue roughages due to energy loss considerations.
• Net energy and starch equivalent are preferred over TDN, considering energy losses in digestion.

Evolution of Energy Measurement Systems:

• Until 1972, TDN and SE systems were used, later replaced by TDN and Metabolizable Energy (ME).
• ME values vary based on feed species and composition, correcting for nitrogen balance.
• Feed processing, feed intake levels, and feed composition impact ME values.

Factors Affecting ME Values:

• ME values differ between ruminants and non-ruminants due to energy losses in methane production.
• Feed composition's amino acid balance affects ME values and nitrogen excretion.
• Processing, feed intake levels, and nitrogen balance corrections influence ME values.

Scandinavian Food Unit System:

• In Scandinavian countries, the system uses one kg of barley as a food unit instead of starch.
• This system allows for a practical comparison of food values beyond protein and energy content.
• Practiced in Scandinavian countries, East Europe, and the CIS for feed evaluation.