Energy supplements for dairy cows

Date: 4 Jul 2003 Author: Brad Granzin

Introduction

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.

Effect of energy content of grain supplements on milk production

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.

Do some grains have a higher energy content?

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.

Table 1. Typical reference values for the metabolisable energy (ME) content of various grains
Grain ME content*
(MJ/kg dry matter)
Wheat 13.5–14.5
Maize 13.0–13.8
Barley 12.8–13.8
Sorghum 12.8–13.2
Oats 12.0–12.5

*These values are expressed on a dry matter basis.
Grains usually contain 88%–90% dry matter.
Source: National Research Council (1989); Standing Committee on Agriculture (1991).

There are, however, several factors that can affect the ranking shown in Table 1. Two of these are protein content and bulk density.

Protein content and bulk density of grains versus energy content

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:

  1. Within a grain type, a higher bulk density usually means more energy.
  2. Within a grain type, a higher crude protein content usually means more energy.
Table 2. A guide to the metabolisable energy content of Australian grains based on their crude protein (CP) content (dry matter basis)
CP (%)

Metabolisable energy (MJ/kg)

SorghumMaizeOatsWheatBarley
6 10.2 11.4 12.4 12.7 13.2
7 10.6 12.0 12.9 13.0 13.5
8 10.8 12.4 13.1 13.4 13.7
9 11.0 12.8 13.3 13.6 13.9
10 11.1 13.0 13.6 13.8 14.0
11 11.4 13.2 13.7 14.1 14.0
12 11.5 13.3 13.8 14.2 14.2
13 11.6  – 13.9 14.3 14.2
14 11.7  – 14.0 14.4 14.3
15 11.9  – 14.1 14.5 14.3
16 12.0  – 14.1 14.5 14.3

Source: Derived from the NSW Agriculture Feed Evaluation Database.

Figure 1. Relationships between the bulk density of grains and their metabolisable energy (ME) content

Buying grain on bulk density and protein

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:

  1. Accurately weigh 1 L of the grain (e.g. using a kitchen jug and scales) to give you a value in grams of grain per litre.
  2. Divide this value by 10 to give a bulk density value in kilograms per hectolitre (1 hectolitre = 1 hL = 100 litres).

Example: If 1 L of barley weighs 620 g, then the bulk density of that grain will be 62 kg/hL.

Effects of processing on energy content of grains

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:

  1. Easily digested grains. These include wheat, barley and triticale. It is generally recommended that these grains be rolled or cracked. Finer processing provides little advantage in terms of energy content. For example, in an experiment at Wollongbar with cows in mid-lactation, there was no difference in energy responses to feeding hammermilled barley as opposed to rolled barley.
  2. Less easily digested grains. These include maize and sorghum. These grains should be finely rolled or hammermilled. Reference values indicate that hammermilled maize has approximately 8% more energy available for a lactating cow than does rolled maize. However, if these grains are ground too finely, palatability can be reduced.