VEM
Definition
VEM (Voeder Eenheid Melk) is the Dutch energy parameter that represents the net energy content of feed for lactating dairy cows.
VEM is related to the energy content of 1 kg of standardised barley (barley with a specific hectolitre weight and starch content). By definition, the energy content of this kilogram of barley is set at 1,000 VEM. Because VEM is a relative value, it has no unit.
Energy levels
The choice to define an energy parameter without a unit makes comparisons easy in practice.
For example, a feed containing 1,100 VEM provides 1.1 times the energy of 1 kg of barley (or 10% more energy). In ration calculations, it is therefore easy to work with VEM, for example when the desired energy density is 1,000 VEM per kg dry matter.
In other feed evaluation systems, energy is expressed in megajoules per kilogram (MJ/kg). The Net Energy Lactation (NEL) value of 1 kg of barley is 6.9 MJ NEL, meaning that 1,000 VEM equals 6.9 MJ NEL.
Digestibility
VEM is calculated based on the levels of:
- Digestible crude protein
- Digestible organic matter
- Digestible crude fibre
- Digestible crude fat
- Digestible carbohydrates (sugars, starch and other carbohydrates)
This shows that digestibility, measured as the Digestibility Coefficient of Organic Matter (VC-OS), plays a major role in determining the VEM value.
The energy content of roughage such as grass can therefore be strongly influenced by the time of harvest. Older grass contains more lignin, has a lower digestibility and consequently a lower VEM content.
Energy requirements
To produce 1 kg of FPCM (Fat-Protein Correct Milk), milk with 4% fat and 3.3% protein, a cow requires approximately 460 VEM.
A cow producing 30 kg of milk per day requires about 19,000 VEM. Of this amount, approximately 5,300 VEM are needed for maintenance, with the remainder used for milk production.
