17 December 2025
A farm-based study in Wales shows that pre-mowing the grazing platform delivers no financial or feed quality advantage in certain dairy systems.
At Moor Farm, near Holywell, the Davies family have a policy of pre-mowing paddocks up to four times a year when covers exceed 3,100kgDM/ha, when the sward is stemmy and at its reproductive stage.
With only limited published research on pre-mowing, through their work as a member of the Farming Connect ‘Our Farms’ network, the Davies’ embarked on a study to test suggested benefits, including whether it really does improve pasture quality and cow intakes during the grazing season and reduce weed burden.
The findings have now been published and are revealing, indicating that pre-mowing had no economic benefit, and did not increase grass production and quality.
Even though tidying up the sward “looked nice’’, it didn’t increase grass metabolisable energy (ME), D-value or crude protein levels, says Farming Connect Dairy Sector Officer Osian Hughes, who led the project.
When grass production levels were analysed, data revealed that pre-mowing reduced it by 0.4 tonne DM/ha in the Moor Farm study compared to swards where there was no mechanical intervention, he adds.
“This work has indicated that there are few gains to be made through mowing of paddocks pre-grazing,’’ says Osian.
Moor Farm supports the spring calving Ffrwd Holstein Friesian herd, with milk production from grazed grass a principal feature of the system.
This cow type produces higher milk yields than cross-bred animals and has a higher feed intake. These factors, in combination with limited research on pre-mowing in a medium-output grass-based dairy system like theirs, were reasons why the Davies family were keen to establish the performance of operating this policy on their own farm.
A field was divided into two one-hectare paddocks – one to act as a control, and the other pre-mown 6-12 hours before every grazing round.
Grass production was measured weekly or fortnightly with a rising plate meter and samples cut and weighed to establish the quantity of dry matter (DM) produced.
Pre-grazing samples of grass from each paddock were analysed with near-infrared spectroscopy (NIRS), and pasture quality and density and weed burden visually assessed.
There were several key findings:
ME in the pre-mown section varied between 10.8 MJ/kg and 11.2 MJ/kg and from 10.9 and 11.3 MJ/kg in the control
Crude protein range was higher in the control – between 16.9% and 21% compared to 16.1% and 20.4% after pre-mowing
Analysis of digestibility (D)-value established that pattern too – between 69.2 - 72g per kg in the control and from 68.5 - 71.2g per kg in the mown area
Volume of grass grown was down in the pre-mowing section – 39.7tDM/ha over the grazing season compared to 46.8kgDM/ha in the control.
But does pre-mowing encourage greater intakes? According to this piece of research, data captured from 10 cows fitted with collars that examine rumination, intakes and grazing and lying times, there was no noticeable difference in behaviour between cows grazing pre-mown swards and the control plot.
The cost associated with pre-mowing is not insignificant - between £50-£90ha an hour factoring in labour, fuel, machinery depreciation and wear and tear, the study estimates.
Giving his evaluation of the study, Osian acknowledges that pre-mowing does still have a place in certain situations.
“It can be used as a tool to manage covers exceeding 3,400 kgDM/ha and improve utilisation in the grass wedge when you cannot afford to take paddock out as surplus, it can for example be used effectively in a drought situation,’’ he says.
While the findings don’t paint a picture favourable to pre-mowing, it is a system that will be maintained at Moor Farm, including for reasons other than those considered by the study.
Rhys Davies, who farms there with his parents, Dei and Heulwen, says their paddock sizes are small for the number of cows milked and, as such, simply taking some out of the rotation to cut as silage is not straightforward.
“If we didn’t pre-mow we would need to top a couple of times a year, once before the last rotation because it is important to get the covers cleaned off before the valuable spring growth and it’s not a case that the cows will do that tidying up even when they do the best job they can.’’
His cow type, some of which produce 50 litres of milk a day at peak lactation, requires an intake of 24kg/DM/day but it is generally accepted that a cow is only capable of capturing around 18kg from standing grass.
“By mowing we are making it easier for our cows to get their required intakes, when all they need to do is stand there and eat grass that has already been cut and laid out before them.’’
Rhys’s own observations suggest that when grass is pre-mown, to satisfy their feed requirements cows spend 45-60 minutes less time grazing, and it is the mature, higher yielding cows that graze for the shortest period, and his heifers for the longest.
“Those older cows get the first bite so if we can reduce competition for heifers by pre-mowing, it is a good reason to do it.
“The evidence we have seen in terms of cow behaviour shows it helps our cows, but whether it would have the same benefits for smaller grazing cows with intakes of 18kgDM a day is another matter.’’
Rhys also uses pre-mowing strategically when grazing conditions are not perfect. “We try and recreate those 'perfect grazing days' when cows can graze and maximise intakes during long, warm summer days.’’
Pre-mowing is one of several options farmers utilise to manage grass when covers are high and swards stemmy.
Topping is one but has a similar cost to pre-mowing and, as Osian points out, it can hamper regrowth if it isn’t done immediately after grazing.
Baling is another tool when a good supply of grass exists across the farm.
There is also the option of moving cows more frequently from one grazing break to the next.
“Shifting the herd two or three times within a 12-hour period can lead to better utilisation of higher covers and the fuel and machinery costs are lower compared with pre-graze mowing,’’ says Osian.