Tommy Boland: Grass management is a powerful but undervalued tool in sheep farming

Now is the perfect time to get on top of your flocks health
Now is the perfect time to get on top of your flocks health

Conditions have improved somewhat at Lyons since my last article. We had received our total average April rainfall by April 12, but experienced more normal rainfall for the final two weeks of the month.

Temperatures were around average for the remainder of April and soil temperature also improved as the month progressed.

Up to the time of writing, May has been favourable for grass growth. Grass growth in the week to May 10th was averaging 104 kg of DM per ha per day.

For a farm stocked at 12 ewes per ha with each ewe rearing 1.75 lambs daily herbage demand is in the region of 50 kg DM per ha, so there is ample opportunity to close up area for silage where these types of growth rates are being achieved. It is important to note that not all fields will grow grass at the same rate.

At the simplest level, the most recently grazed fields/paddocks will grow at a slower rate than those with a higher cover of grass, but where an average growth rate of 80 to 100 kg DM per ha per day is being achieved ample opportunity to close ground for silage exists.

From talking to farmers who are carrying out grass measurement and grass budgeting on sheep farms, they have seen big surpluses develop in the last 10 days and have responded by closing ground for silage.

This is important for a number of reasons, firstly it allows rotation length to be shortened which prevents pre grazing herbage mass from becoming excessive and thus reducing the quality of grass consumed by ewes and lambs and finally it provides important winter fodder stocks on farms.

The assumption underpinning the above advice is that grass measurement and budgeting is taking place. The uptake of the grass measurement and budgeting technologies has been disappointingly low amongst livestock farmers in general and sheep farmers in particular are no exception.

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One of the key messages coming from the Teagasc Better Sheep Farms program is the benefit that is achieved by a stronger focus on grassland management. This focus includes correcting soil pH and fertility, improving grazing infrastructure (ie smaller and more numerous paddocks), grass measurement and budgeting and finally reseeding.

A common mistake is that reseeding is the first step taken in an attempt to improve grassland management, however if the other pieces of the puzzle are not in place then the benefits of reseeding will soon be lost, if ever achieved at all.

So what are some of the key targets or focus points in managing grass at this time of the year?

This year has proved, as if any proof was required, that managing animals at grass is extremely challenging. The months of May and June are the traditional months for making first cut silage on farms. The primary piece of information required in this process is how much silage is required. This is particularly appropriate this year as most forage reserves have been exhausted.

To calculate your silage requirement you must know how many sheep you will over winter, how many days they will be housed for and how much silage they require per day. Each farm must then build in their own safety net to allow for extreme circumstances. 

So let’s assume a daily requirement of 1.3 kg DM per ewe per day (allowing for some moderate wastage) at the average flock size of 108 ewes for a four month winter. This gives a total silage requirement of approx. 17 tonnes of DM. So if you are using pit silage this is 68 tonnes of fresh pit silage at a DM content of 25% or 87 bales of silage.

By closing silage ground, rotation length also becomes shortened, as is sensible with higher growth rates. Data from Pasturebase would show that average growth rate during the four main grass growing months averages around 65kg DM per ha per day.

If your target pre grazing herbage mass is 1200 kg DM per ha then at a growth rate of 65 kg DM per day it will take approximately 18 days for a field to regrow this amount of grass after grazing.


As the season progresses and growth rates begin to decline, rotation length will need to be extended to allow for sufficient grass build up. It is also important to maintain grass quality by achieving low post grazing sward heights, though the grazing severity should not be as hard as that achieved in the first and second rotation.

For the average mid-season flock at this time of year, the contribution of milk yield to lamb requirements and intake is declining rapidly.

In situations where grass still remains scarce there is little benefit to supplementing ewes with concentrates in week 8 of lactation or later. It is better to prioritise the lambs in this situation.

This can be achieved by forward creep grazing of the lambs where infrastructure allows, or even advancing the weaning date to reserve the available grass for the weaned lambs.

One of the keys to good and successful grassland management is making decisions early, whether it is in times of deficit or surplus, and this is greatly helped where measurement and budgeting is taking place.

Professor Tommy Boland is a associate professor in sheep production at Lyons Farm, University College Dublin. @Pallastb

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