Farm Ireland

Friday 23 February 2018

Browned off but all's not lost

John Donworth

I walked my first farm of the year last Friday. A little late in the year, I know, but priority had to be given to other work commitments. Last November, grass quality looked really good on dairy farms. A fine October allowed swards to be grazed out really well. And while November was very wet, we still looked in good shape going into the winter.

Boy, has all that changed. The severe weather over Christmas has really taken its toll. The grass plant is very weathered-looking and a serious amount of leaf loss has taken place. Much of the grass leaf that was green in November is today brown and in this state it is not capable of trapping and responding to sunlight. While all the grass leaf in paddocks hasn't died off, it certainly has around dung pads or where heavy clumps of grass are to be found. This was due to the fact that there was a build up of dead material, which resulted in a lack of light getting down into the plant and so the plant keeled over. However, all is not lost here, as there could be viable growing points underneath the dead mass of leaves.

The most dead material is to be found in paddocks that were closed first. These have taken the biggest hit. Dead and dying leaves are to be found mixed in with green leaves. How much of the grass is absolutely useless from a nutritional point of view is anyone's guess. Cows going into such paddocks will, first off, walk around the paddock to see if there is anything more appealing on offer. If they don't find anything better, they will put their head down and do their best to sort the green leaf from the dead leaf.

Obviously both dead leaf and green leaf will wind up in the cow's mouth. Two things will happen there. The cow will be challenged, from a nutritional point of view, and her dry matter intake will also suffer. Since she will be attempting to sort the grass, she will eat less of it over any given period.

So what's the nutritional value of a sward that was closed in October and has between 15pc and 20pc dead material in it? Research carried out by Deirdre Hennessy in Moorepark found that this type of material had a DMD figure of between 72pc and 76pc. This would place this material way ahead of the vast majority of first and second-cut silage. Into the bargain the crude protein content of the herbage was 24pc.

So swards with up to 20pc dead material will be of reasonable quality. Because the leaf is brown, it doesn't mean it has no nutritive value. It hasn't totally decayed yet. This is especially true if the leaf only died in the previous few weeks.

Does the crude protein of the grass surprise you? It shouldn't. Grass that's green in October and November takes up nitrogen from the plant roots. The plant may shut down over the winter and no growth will take place. The nitrogen it has picked up is now stored in the leaf of the plant, hence the high crude protein content of grass in early spring.


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Can this nitrogen present in the leaf be used for grass growth? The answer is no. Growth of the grass plant can only come from nitrogen present in the root system.

So what's the best thing to do with swards that have anything from 15-30pc dead material in them? Graze the swards with the highest amount of dead material as soon as you can. Do as good a job as you can. It is essential to get light into the base of the sward. Next I would apply at least three quarters of a bag of urea to get the plant going. Spreading nitrogen on these swards pre-grazing is not recommended. It will just sit there. The canopy of grass must first be removed.

The fact that I am recommending that you graze the sward with the highest amount of dead material first means that you may have to come out of your normal rotation to do this job. It should also be borne in mind that these paddocks will be the slowest to recover and this could affect the amount of grass you have in your second rotation. Flexibility will be the key.

However, it is not all bad news. November-grazed paddocks have much less dead material in them due to the fact that they had very little leaf cover over the winter. These paddocks have the potential to grow at a much faster rate than the paddock that came into the spring with a lot of leaf.

Dry cows are the ideal type of animals to graze swards with anything up to 30pc dead material. If you have to use milkers to do the job, I would be recommending that you feed these cows an extra 2kg of ration going from 3kg to 5kg. In some cases, if the amount of dead material is approaching 35pc, the DMD of the sward could be as low as 65/66. Such swards will be a challenge.

Irish Independent