Utilising grass – The cheapest source of feed on the farm.

By Andrew McMenamin, Ruminant Nutrition Adviser

Spring is upon us and after a long winter on most farm attention has turned to grass and letting cows out to graze that grass.
But why risk letting cows out to lush swards and changing their diet when things are settled indoors, and we can maintain and regulate feeding with ease on a diet of concentrates and silage?

In Northern Ireland the typical grazing season can be short, and we need to capitalise on grazed grass as a way of reducing costs and increasing profit on farms. Grazed grass is 5 times cheaper than concentrates and 3 times cheaper than silage. Spring grass has a crude protein of 16-21% and an ME of 11.5-12 megajoules therefore it is paramount that we utilise it to the full potential.


On average grass grown in Northern Ireland yields around 7 tonnes of dry matter per hectare. There is however potential to grow more than 12 tonnes per hectare on most dairy farms and this can have huge financial savings.
The ability to grow this extra grass is affected by many factors including soil type, soil fertility, weather and age of sward to name but a few. How we manage the swards throughout the year is just as important as any of the above factors. Whilst for some it is important to carry over some grass covers from the previous autumn to eat in spring it isn’t until these covers are grazed off that growth is kickstarted and we see vigorous growth in the grass plant. Ideally complete the first rotation in April to have the second rotation growth coming back again for the end of the month so we ensure lush swards of this fresh grass in May and June. The first rotation is where we can achieve the greatest clean outs of paddocks as there is no spoilage or sour patches from dung pats in fields (weather dependant of course!).

Management of the sward is important in May as grass can get too strong and affect quality but also in cold periods where growth slows farms can run out of grass forcing the need to rehouse animals. Therefore, it is important to measure grass. Measuring can help predict a shortfall or surplus in advance allowing farmers to plan and either take out surplus grass for silage bales or spread more fertiliser.

Not all farmers have access to measuring devices such as a plate-meter or clippers and weigh scales, but there are simple assessments farmers can do to assess swards before and after grazing to maintain quality and predict yield. Farmers should aim for a pre grazing height of 10-15cm and post grazing height of 5-6cm. Marking these measurements on a stick or using your boot as a guide can be very effective. Each centimetre of height in the sward equals 250kg DM/ha.
• Subtract the ideal post grazing height (residual) from the height of grass in the paddock and multiply that figure by 250kg DM/ha.
Eg. If grazing height is 13cm and post grazing is 5cm (13cm – 5cm) then 8cm x 250kg DM/ha = 2,000kg DM/ha
• Assuming cows in peak lactation will eat approximately 16kg of forage dry matter (DM) then 2,000kg DM/ha/16 kg DM intake per head = 125 cows can graze 1 ha in 24 hours.

Pre-grazing cover 3300kg DM/ha
Pre-grazing cover 3000kg DM/ha
Post-grazing cover 1400kg DM/ha

An easy way to identify post grazing heights is by doing the simple “welly boot test” – if cows eat a paddock down to the top of the toe of your welly boot then a good clean out was achieved. Leaving a residual of 4-5cm encourages leaf production. If there was more residual left, then this will affect sward quality going forward and results in more stem in the plant and as we all know leafy grass is more nutritious than stemmy grass.

For more tips and advice on grazing management contact your local United Feeds Adviser or call 028 9075 9000.

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