Putting a size on paddocks
Published 22/07/2014 | 00:00
While grass growth has been excellent over the past three months, maintaining quality has been difficult. It doesn't help that many farmers have increased stock numbers, without amending paddock sizes.
Having a good paddock design and layout will help you get the most from your grass by allowing you to manage it efficiently.
Pat Clarke and Tom Ryan, Teagasc dairy specialists, recently outlined the most important points to remember when setting up a paddock system.
Whether you are re-designing an existing block or adding to it, start off with getting a good map of the farm. Aerial picture maps from the SPS are useful as are the more detailed ones which can be printed from Bing or Google maps. Web based software with measuring tools, such as ArcView are ideal. A number of commercial companies specialise in mapping and use GPS to get exact paddock sizes.
Number of grazings
Decide how many grazings you will get per paddock mid-season. One grazing is normally allocated to the herd in the spring and autumn. This allows for good grass utilisation and helps reduce damage to paddocks when weather and ground conditions are most challenging. For the remainder of the year allocating grass every 12 hours is time consuming. If the correct amount of grass is not allocated cows may be underfed. This especially impacts on heifers as the cows will generally pick the best of the grass at every grazing. Allocating grass for more than 48 hours allows cows back over grazed grass and you will end up hitting re-growths.
Two to three grazings per paddock, is less time consuming, protects re-growths and gives cows, especially heifers, a chance to be fully fed in two out of every three grazings. It is also much more efficient when spreading fertiliser, topping or taking out bales in larger paddocks.
Four grazings per paddock will allow for future expansion where you can revert back to three grazings if necessary. You will also require fewer water troughs and fewer paddocks overall.
Number and size
Establish the ideal number of cows for your farm in the long term. Work out what your daily demand will be for grass. If you have medium-sized cows intakes will generally be about 18kgs of dry matter per cow (18kgs/DM/cow) for every 24 hours. Research trials have shown that ideal pre-grazing yield is 1,400kg of dry matter per hectare in mid-season. This allows cows to graze excellent quality grass which maximises milk solid production. It also allows the grass plant grow to the three-leaf stage which means that you maximise the amount of grass grown.
The number of paddocks required will depend on the number of grazings you plan to get per paddock and the length of your rotation mid-season. So if you have three grazings per paddock in a 21-day rotation you will need 14 paddocks. However if you only have two grazings per paddock, you will need 21 paddocks. The remaining ground can be divided similarly, left in to silage fields or smaller paddocks for young stock.
Multiply the number of cows by their daily intake and multiply this by days in the paddock. Then divide this by the ideal pre-grazing yield (PGY).
(cows) x (intake in kgs DM) x (number of day's) / 1400 (ideal PGY) = ____ha
80 cows x 18kgs DM intake x 1.5 day's / 1400 = 1.54ha
So if you have 80 cows with intakes of 18kgs DM/cow, in a paddock for three grazing's the paddock should ideally be 1.54 hectares (3.8ac) in size.
Ideally keep paddocks square /rectangular with the ideal depth to width ratio of 2:1 and not more than 4:1. Cows walk less in rectangular paddocks which minimises soil damage in wet weather.
Layout and Troughs
Use the maps to determine the most suitable road layout and appropriate positioning of water troughs in paddocks. These will impact on cow flow to and from the parlour. Consider the depth of the paddocks. Ideally there should be a maximum of 250m from the road to the end of the paddock on dry farms. In wet paddocks this should be closer to 100-150m.
Multiple entrances and cow paths are especially important in wet paddocks and if possible these paddocks should also be accessible from the back. Take account of physical features such as slopes and wet areas when designing the farm's paddock layout.. Getting a second opinion on this is invaluable whether it's your advisor or another farmer.
The main benefit of an efficient paddock structure is the ability to grow and utilise more grass. It will also provide you with a pleasant easy to manage farm. But the cost involved is substantial so make sure that you take the time to plan this important project properly.
Nora O'Donovan is a Teagasc dairy advisor in Co Kerry