Piers' comments 4th July

Published 4 July 14

Piers Badnell, DairyCo technical extension officer, comments on this week’s grass growth results.

Below, is an example of how to calculate demand, against supply, how to reduce demand to match supply and therefore, how to calculate how much you need to supplement.

100 cows, eating 15kg DM = 1,500kg DM ÷ area available = demand/ha.

For example 100 cows x 15kg DM ÷ 20ha = a demand of 75kg DM

As an example, with a cover of 2,800kg DM and you want to graze to 1,500kg DM, that means you have 1,300kg DM available.  Divide that by a growth rate of 45kg DM it will give you around a 30 days rotation. It’s going to be 30 days before the grass is at the point you want to get back in and graze. Graze it earlier than that and you’ll lose that all important third lead.

For an example of how to reduce demand to match your supply - 100 cows x 9kg DM = 900kg DM ÷ 20ha = 45kg/ha. This shows you need to find that spare 6kg DM (to bring the total DM intake up to 15kg per cow) from somewhere, be it concentrate and/or silage.

Supplementing to preserve the length of the rotation will help you preserve grass for future grazings, and means it can bounce back once there is more moisture.

The two photos below were taken on the same day on different sides of the same valley. Photo one, shows a paddock which was rotational grazed. Photo two from a set stocking set up. Photo one shows grass green and ready to start growing again when it rains, while it will take much longer for the grass in photo two to recover.

Photo one

good grass in dry conditions


Photo two

drought grass