There are several ways of doing this. The best way is as follows:

- Add up the total amount of milk produced by the herd in one month including waste milk.
- Add up the total amount of concentrates used in the month, exclude minerals.
- Moist feed purchases are controversial but generally feeds like Vitagold and Trafford gold are moist concentrates and should be included in the figure by dividing the volume by 2.5 (Vitagold) and 1.5 (Trafford Gold) in order to level up the dry matter.
- Take the total volume of the concentrates and multiply by 11.5 ME. This is equivalent to a 13 MJ average for the concentrates. Yes it’s a rough figure that works if you forget to take out the minerals. Dividing by 12 would equate to a 13.64 MJ average for the concentrates without minerals.
- Once you have a total ME figure for the month divide it by 5.3. This is the energy needed to produce a typical litre of good quality milk.
- The figure you are left with is the total amount of milk produced from concentrates.
- Subtract this figure from the total amount of milk produced and you have your milk from forage for the month.
- Divide this by the average total number of cows in milk for the month and you have it per cow.
- Now divide by the days in that month and multiply by 365 and you have it on a per cow per year basis. (it’s better and a bit more accurate if you calculate it month by month and then add them up after a year).
- The result is always a rough figure and different organisations use different equations. Some of which are way off the truth.