What is the net energy (NE) of fat

The NE of a feed ingredient represents the energy actually used by the animal for maintenance and productive purposes. The NE value is calculated based on efficiency of use of the ME and differs between different energy sources. 

While conversion efficiency of ME to NE for typical dairy diets will be around 65%, ME from fat is converted to NE in milk with an efficiency of approximately 80%, so reducing energy wastage. Fat therefore has a higher net energy of lactation (NEL) value than other ingredients. This efficiency is similar for all fats so the primary factor determining the NE of a fat supplement is the product’s ME value, which is turn is determined by its digestibility. 

Megalac rumen-protected fat has the highest measured NEL value of any feed ingredient, determined in a feeding study with lactating dairy cows. The NEL of Megalac is 27.3 MJ/kg dry matter (Andrew et al., 1991).