produces the highest DM yield (about 45%). So you need to be grazing the third to get its full DM yield potential. The optimum post graze target is about 5cm, which on a rising plate meter will measure about 1500kg DM.
Leaving grass above 5cm results in lower production as it leaves more stalk in the base of the sward. The ryegrass plant will only support three live leaves, as another appears at the top of the plant the lowest leaf will die. More leaves also mean more stalk reducing the overall quality of the plant.
Cows need to learn to graze, but by putting good quality grass in front of them they will want to go out and eat it. Ideally, only allocate enough grass for one feed so that cows move on to a new, fresh patch of grass every 12 hours. When buffer feeding do so before afternoon milking so cows always enter pasture with a keen appetite.
There will of course be periods when you will need to supplement the diet of higher yielding cows, but by optimising grazing there will be less need to waste expensive feed when grass can provide what cows need and supplementation can be reserved for when lactation curves and grass conditions require it.
What is extra milk from grass worth?
Here is an example of what grass can do. A 600kg cow producing milk at 4% fat and 3.3% protein requires 70 MJ ME for maintenance and 5.3MJ ME for every litre of milk produced.
So, 5kg dry matter grass at 12 ME gives 60 MJ and 12kg dry matter grass at 12 ME gives 144 MJ. By taking away the 70 MJ required for maintenance the 12kg of dry matter will allow the cow to produce 14 litres.
When intakes are up at 17kg of dry matter (the maximum intake likely at grass) at 12ME, then the cow is getting 204MJ from grass, giving 134MJ available for milk production and resulting in 25 litres from grass, the cheapest feed. One thing that needs to be addressed is unnecessary buffer feeding when grass quantity is not limiting and intakes of 17kg DM are achievable. In this scenario and using the calculation above it is clear that buffer feeding is unnecessary.
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Cows need to learn to graze, but by putting good quality grass in front of them they will want to go out and eat it
Buffer feeding teaches the cow to be a lazy grazer as she knows feed will be provided instead of her working for it, so where supplementation is required for extra yield or small shortages of grass use concentrate in the parlour and only buffer when grass is limiting.
A lazy grazing cow will not clear out the sward and will waste grass and lead to poor utilisation, waste and deteriorating sward quality through the season.
THE JOURNAL JUNE 2015 35
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