There are several ways to describe energy content in feeds.

1) Digestibility

• Measured as a percentage, digestibility relates to the portion of food that is not excreted in the faeces and is available for use by the cow.

• Digestibility is not a direct measure of energy but it is indicative of overall feed quality.

• The greater the digestibility, the more the benefit of that food to the cow.

2) Metabolisable energy (ME)

• Metabolisable energy is the energy in a feed that the cows can use for metabolic activities.

• Metabolic activities include maintenance, activity, pregnancy, milk production and gain in body condition.

• ME of a feed can be calculated directly from its digestibility.

• The higher the energy content of the feed, the more energy is available to the animal.

• It is measured by MJ ME/kg DM.

3) Total digestible nutrients (TDN)

• TDN is an old system used in US and some other Asian countries.

• It is less accurate than ME s it does not account energy losses via methane and urine.

• TDN content is expressed as a percentage while TDN intake is expressed in kg/day.