Farm Ireland
Independent.ie

Thursday 25 May 2017

Use spring rotation planner to develop grazing programme

Dr Mary Kinston

As February draws nearer, so too does a need to have a management plan in place for your spring grazing. This is important because if you are grazing during early spring, you are generally managing a feed deficit, in that the demand for grass (intake per hectare per day) is higher than the supply (growth per hectare per day).

This results in a decline in average pasture cover and, therefore, a plan is required to control the rate at which this declines. However, the trick to this plan is also to manage grass in such a way that your system is ready for the magic day, when grass growth meets demand.

Due to the rapid rise in growth rates in late spring, pasture cover at the magic date essentially determines the quality and quantity of grass available at mating.

If not managed accordingly, the quality of pasture is often lost and the diet quality and intake potential of the cow is reduced. As a result, the grazing management implemented in the first two months after calving is crucial.

So in this article, and in next week's management piece, I am going to outline the use of the spring rotation planner (SRP), which helps remove the guesswork from spring-grazing management.

However, the SRP should not be used in isolation. It is by combining the decisions from the SRP with your spring feed budget, while actively monitoring your pasture cover, that you will make the most of spring milk production off grass.

What is the SRP?

The SRP allocates a set area per day (or per week) from when the cows calve to the magic date, starting on a slow rotation and gradually speeding up the rotation until you finally reach the fastest rotation with which the farm will be grazed during spring. As I have stated in previous articles, rotation length relates to the area grazed per day, eg 1/60 is a 60-day rotation. On a 30ha milking platform, the rotation is calculated by 30ha/60 days, which equates to 0.5ha/day.

First of all, point A is the start of calving. Point B is your estimated 'magic date'. It's usually in the first three weeks in April, depending on where your farm is located. Grazing data from previous seasons will help you pin-point this date even more accurately. To determine the optimum rotation length between Point A and B, simply draw a line between the two points as shown on the graph.

Ireland vs new zealand

An important point to note is that because of the slower spring-growth rates experienced in Ireland in comparison to New Zealand, where the planner was initially developed, you must add between seven and 10 days onto your predicted magic date (Point B) when drawing the line from your longest to shortest rotation.

Using the rotation lengths from this graph for each weekly interval results in a target area to be grazed per day (farm area divided by rotation length = ha/day). Please note that this area is for all the grazing stock during this time (milking cows and dry cows etc). This is then used to set management targets for the area grazed per week and the cumulative area grazed over the spring period as shown in the table for a 60ha farm example.

Looking at the data, it is clear that around 30pc of the farm is grazed by March 1 and 100pc in the first week of April. Next week I will develop this topic further by discussing how the plan should be combined with your spring budget and how it should be altered when facing a tough spring such as last year.

Dr Mary Kinston is a farm consultant based in Co Kerry. Email: mary.kinston@gmail.com

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