A spring rotation planner (SRP) is a key tool for allocating grass and managing pasture quality at a time of the year when grass growth is increasing.
And it is not just valuable to spring grazers – all herds can benefit from using one including autumn and all year-round calving herds, with the aim being to maximise grass in the diet throughout the season.
Debbie James spoke to farm consultant Piers Badnell to find out more about how to use one.
An SRP provides guidelines for grass allocation to cope with energy demand from the spring milking herd increasing post calving.
At the start of calving grass growth has not taken off, but demand quickly increases as more cows calve. If this is not managed correctly grass will run out, warns LIC Pasture to Profit consultant Piers Badnell.
“Grazing management two months post-calving determines production achieved through to early summer and very importantly how well fed the cows are coming into mating.’’
Yet the principles of getting it right in terms of quality and quantity of grazing are equally important for autumn or all-year calvers, he adds.
“They might not have to contend with getting the cow back in calf at that time of year, but milk from grass and putting condition back on the cow are vital. A rotation planner provides an environment for maximising quality and quantity of grass.’’
Below he summarises how to use one in this simple, six-step guide.
Key steps to using a spring rotation planner
1. Start date
Quantify the size of the dairy grazing platform and identify the date when you expect the herd to start calving.
2. Figure out your rotation length at the start of grazing
The rotation length – the proportion of the farm that is grazed in a single day – is normally set at 100 days at the start of calving. On an 80ha grazing platform, for instance, a 100-day rotation at that point means that one hundredth of the farm is grazed daily – 0.8ha. As more cows calve and come into the rotation, the rotation length reduces and a larger proportion of the platform will be grazed daily.
3. Identify your balance date
This is the date when you expect supply to equal demand – also referred to as magic day. This date will be influenced by stocking rate, soil fertility and geographical factors. In the UK, balance day is usually reached between 1 and 20 April.
4. Use a graph to plot it
Draw a simple graph (see below) with dates from 1 February to 1 May on the X axis and rotation length of 1-100 days on the Y axis. Plot a straight line from turnout at 100 days to the balance date on, perhaps, 1 April at a 20-day rotation.
5. Plan the rotation using the graph
From this graph, it is now possible to plan the rotation length on any given day. For instance, on the above graph, on 1 March the rotation length is approximately 60 days or 1/70th of the farm.
6. Plot your average grazing covers
With the rotation planner framework in place, the next step should be to measure average grass covers and plot these on a graph (see below). These ideally should be 2300kg DM/ha at the start of calving, dropping to 1900kg DM/ha by balance day.
Q. Why is it important to know your average grass covers (AGC)?
The basic SRP does not take account of variation from what is normal in terms of growth so measuring pasture with a plate meter is important.
The combination of the SRP and the plate meter provides accurate information for making good decisions.
Although the SRP shows what the daily grass allocation should be, this can be complicated if growth slows during an extremely cold spring or accelerates in a very warm spring.
This creates a situation where grass is in short supply or there is too much, compromising residuals and quality.
Q. What happens if average grazing covers are below or above target?
If average cover is below target, you should supplement with silage or concentrates until growth picks up. This will help build covers.
If average cover exceeds the target, then speed up the rotation length and stop supplementary feeding.
Allocate a larger area to bring average cover under control. If this does not fix the problem then the option is to cut the grass for silage to help increase demand to get back to the appropriate cover.
Q. What residuals should you target in the first round?
Aim to achieve residuals of 3.5–4cm – the equivalent of 1500kg DM/ha.
The importance of maximising grass intake
Data from AHDB Dairy Forage for Knowledge shows the first rotation of grass in February and March has the potential to be extremely high value at 12-12.5 metabolisable energy (ME) and 20%+ crude protein (CP).
If pasture is in short supply and grass silage is used to supplement grazing cows, it is unlikely the silage fed will be above 11.5 ME.
Therefore, every kilogramme of dry matter fed as silage is potentially lowered by 1ME/Kg of DM lower than that of grazed grass.
At point of calving, a 500-550kg cow can only eat 10-11kg DM per day, but this increases to a maximum 17 or 18kg DM per day over 12 weeks.
It requires 5.7mj/litre to produce milk at 4.5% fat and 3.5% protein. Therefore, if the diet is half grass and half grass silage – 11kg DM dry matter intake in total with 5.5 Kg DM of silage and an equal amount of grass – this means there is *5.5 MJ less being fed than if the diet was all grass.
This 5.5 MJ is almost the intake it takes to produce an extra litre of milk. So, if there is less grazed grass in the diet it impacts on yield. The shortfall could also lead to a cow losing body condition if the gap is not supplemented with concentrates.
11kg DM of grass x 12.5 ME/kg DM = 137.5 MJ ME
5.5kg DM of grass x 12.5ME = 68.75
5.5kg DM silage x 11.5ME = 63.25
=132 MJ ME
137.5 – 132 = 5.5MJ less than grass diet