Rejection sites in grazing paddocks

Published 19 July 13

Rejection sites in grazing paddocks

Rejection sites are appearing in paddock swards now cows have been grazing for up to five months. In grazing-based systems, cows are expected to graze up to the cow pat and take a few bites out of the grass growing round it, but Piers Badnell, DairyCo extension officer, looks at what you can do to reduce the impact and severity of dung pats, and thus rejection sites in higher yielding-type cows.

Soils – biology and chemistry – if the soil is working, a wide diversity of fauna will be present in the soil, which will breakdown the dung and disperse it. If soil structure and soil chemistry, in terms of pH, P, K etc are correct, and there are no compaction and drainage issue, it is far likelier there will be a healthy population of fauna, including worms, to break down dung pats and reduce the impact and quantity of rejection sites.

Grazing pressure – follow the fundamentals of grazing – allocate the correct area and teach the cows to graze hard, reducing their selection.

Correct entry covers – of about 2800 Kg of DM/ha – this is basic grazing management to achieve a good residual, but also benefits rejection sites. If cows enter higher covers there is more chance of muck landing on a thick wedge of grass, which will act as a barrier between the muck and the soil. This reduces the ability of soil fauna to get to the muck and break it down.

Cow diet – The higher the proportion of grass in the diet, the looser the dung is, and when she defecates the muck is spread over a wider area rather than in just a big solid lump. This solid lump is a concentrated area of nutrient which develops a strong and unpalatable growth around it.

When dung is spread over a wide area it is easier for soil fauna breakdown and rain to wash it in. Just think about the difference between muck from grass and muck from a dry cow fed straw. The dry cow leaves elephant-like dung which will take months and months to breakdown.

Grass put into bales at time of surplus in May, as it goes over the correct entry cover, will be very nutritious and a lot less likely to be fibrous than later cuts.

If you are supplementing grass, firstly think “Do I need to?”  If you do, you need to make sure you get the supplement right. Ideally, supplements are for supplementing grazing to get higher energy intake when there is plenty of grass is available and buffer feeding is for when grass supply is short. In this case, be aware that very fibrous silages will mean more solid dung consistency and the problems mentioned previously.

Cow training – you choose what the cow eats, not her. Allocate the area and train her to graze. Good grazers equal good residuals equal less rejection site problems.

Surpluses – This time of year, especially with the dry weather we have been experiencing, means more rejection sites, some seed heads and some more stem as the plant has been under more pressure. A really good way to manage this is pre mowing and wilting.

Take out any surpluses and put into bales to recreate good residual and regrowth.

Some people successfully rake pastures. A couple of days after cows come out go across the paddock with a rake / grass harrow to disperse muck. This knocks it about and the muck ends up in small bits, increasing its surface area, aiding breakdown and avoiding concentrated lumps of nutrient. This method works very well.