Date: 4 Jul 2003 Author: Brad Granzin
Over time, a small difference in the energy content of supplements can result in a large difference in milk production. Measuring the energy content of grains is expensive and generally not practical on a day-to-day basis. However, there are some guidelines that can be used. This article discusses the effect of energy content of grain supplements on milk production, some of the differences in energy content between grains, and the effects of processing on the energy content of a particular grain.
One litre of milk is equivalent to about 5 megajoules (MJ) of metabolisable energy (ME). Therefore, a difference of 1 MJ ME/kg grain is equivalent to potentially 200 L milk/tonne grain (1000 kg = 1 tonne). See the reasoning below:
5 MJ ME = 1 L milk
1 MJ ME = 200 mL milk
1 MJ ME difference per kg grain = 200 mL difference in milk production
Therefore, 1000 kg grain, i.e. 1 tonne grain, with a difference of 1 MJ ME per kg = 200 L difference in milk production.
Table 1 shows some typical international energy reference values for grains. On average, wheat has the highest energy content followed by maize, barley, sorghum and oats.
|Grain|| ME content*|
(MJ/kg dry matter)
There are, however, several factors that can affect the ranking shown in Table 1. Two of these are protein content and bulk density.
The protein content and bulk density of grains can be used to indicate the energy content of grains (see Table 2 and Figure 1). At best, these values should be used as a guide only, as other factors also influence energy content, such as fibre and oil content, and how grains are processed. However, there are two points to make:
Metabolisable energy (MJ/kg)
Grain traders often sell grain on protein content, but selling on bulk density is less common. It is fairly easy to measure the bulk density of grain yourself:
Example: If 1 L of barley weighs 620 g, then the bulk density of that grain will be 62 kg/hL.
With the exception of oats, some form of processing is required in order for a cow to be able to utilise the energy available from grains. The effects of processing on the energy content of grains is complicated by various factors such as the type of grain and the levels of grain intake and forage intake. In addition, there has been relatively little research looking at how processing can affect the energy content of grains when fed to lactating cows. So, at best, the following can only be used as a guide.
The grains commonly fed in Australia that require some sort of processing can be divided into two categories: