The experiment was run at the Lincoln University Research Dairy Farm (LURDF) from October 2016 to February 2017.
Key preliminary results:
Data is still being analysed but these are the first preliminary results to be presented.
- There was no benefit of pre-graze mowing on cow performance (BCS or milksolids production).
- Cows offered lower pasture mass (2900 vs 3500) produced 6% more MS over the experiment.
- Rotation length was 8 days longer (29 vs 21 days) for the high mass treatments.
- There were 0.2 more leaves (2.7 vs 2.5) for the high mass treatments.
- Pasture disappearance (pre-graze – post-graze yield) was greater in mown vs grazing treatments (+ 2 kg DM/cow/day) BUT mowing reduced pasture utilisation by 2 kg DM/cow/day and thus, there was likely no difference in DMI.
- There was a numerical increase in pasture growth rate in grazing vs mown treatments and in high vs low pre-graze covers.
- More silage was purchased for the mowing treatments and more silage was made in the grazing treatments and the high pre-grazing covers.
- Cows grazing high covers spent more time eating than cows grazing low covers, and cows eating mown material spent less time eating than cows grazing. There was no effect on rumination time.
Data from the experiment has been compiled and results from the initial analyses are available. The following results are preliminary only and some data has not yet been analysed.
Pre-grazing covers and post-grazing residuals
There was an effect of pre-graze cover height and harvesting method on residuals. Mowing treatments had lower residuals than grazing treatments, and the higher pre-grazing cover treatments had higher residuals than low pre-grazing cover treatments.
These results are based on the plate meter reading, using the winter formula. We achieved pre-grazing cover targets in all but the HM treatment. During the experiment the mowing farmlets had periods where paddocks struggled to reach pre-grazing targets and consequently had to be topped up with silage.
When using the winter formula, residuals were higher than planned, but this is because this formula does not take the calibration cuts into consideration. When these calibration cuts are applied, it indicated the winter formula was over scoring the mown paddocks. The calibrated formula also indicated we struggled to achieve target pre-grazing cover for both mowing treatments. See discussion in the growth rate and silage sections.
Utilisation of mown material
There was substantial mown material left behind in the paddocks. On average 190 kg DM/ha (HM) and 143 kg DM/ha (LM) of mown pasture was not utilised.
Example photos below demonstrate the range observed. On average over the whole experiment, this was equivalent to 2 kg DM/cow/day, and indicates, pre-mowing doesn’t minimise wastage, which had been promoted as an advantage over post-grazing topping.
There was a 7-8 day difference between the high covers and low covers, with no effect of harvesting method.
Rotation length was calculated using the daily area grazed plus the area cut for silage. There was an interaction due to the amount of silage cut on the LG farmlets making the rotation length slightly faster than the LM farmlets.
The difference in rotation length resulted in a greater proportion of the farm being mown in the LM farmlets than the HM farmlets, which has implications for cost. The small amount of mowing on the grazing farmlets is due to silage being cut and a handful of paddocks post-grazing topped.
Using the winter formula growth rate was numerically lower in the mown treatments and the low pre-graze yields. When the calibrated equations were used, the difference between growth rates in the low graze treatments was greater. Although the differences were numerical, large variations in growth rate from week to week reduces the ability to detect significant differences. The increased use of silage in the mown farmlets to achieve target pre-graze yields supports a reduced growth rate in the mown treatments.
Growth rate was calculated for each paddock during the weekly farm walk. It compared the previous cover with the current cover and the number of days between. No growth rate was calculated for the paddocks grazed during that week. This data is currently being explored further.
There was an effect of harvesting method, with mowing reducing the number of ryegrass tillers produced during the experimental period. There was an effect of pre-grazing cover height on the number of leaves on ryegrass plants pre-grazing. The aim of the higher pre-grazing covers/longer rotation lengths was to take pasture through to 3-leaf stage and potentially capture additional growth. However, during the period that this experiment was conducted, the 8 day longer rotation, and higher pre-grazing covers, did not reach three leaf stage.
Silage (made and fed)
There were treatment differences between grazing and mowing in the amount of silage made and fed out, with more silage being made in the grazing farmlets and more being fed out in the mowing farmlets.
The net silage (silage made minus silage fed) resulted in a surplus of silage in the grazing farmlets and a deficit in the mowing farmlets.
In terms of the silage fed, this was equivalent to 0.2 kg DM/cow/day for the grazing farmlets and 1.2 kg DM/cow/day for the mowing farmlets, averaged over the whole experiment. Converting this to a growth rate value estimates that the 1 kg DM/cow/day extra fed to the mowing treatments was equivalent to a growth rate of 3 kg DM/ha/day, once again in support of the small decrease in growth rate with mowing, although difficult to detect statistically due to the large fluctuations in growth rates throughout the experiment.
More pasture was offered to the cows through mowing. However, when wastage and silage fed were accounted for, 2 kg DM/cow/day wastage and 1 kg DM/cow/day extra silage fed, there is little or no difference in the amount eaten in the different treatments.
The amount of pasture disappearance (kg DM/cow/day) was calculated by subtracting the pre-grazing residual from the pre-grazing cover and dividing by the stocking rate and rotation length. This calculation is based on covers derived from the winter equation. Pasture disappearance does not equal intake.
Milk production and BCS
There was no effect of pre-graze mowing on milksolids production. Average milksolids production was 5% less for the high pre-grazing covers (3500 kg DM/ha) than low pre-grazing covers (2900 kg DM/ha).
However, the amount of silage made/fed influences the total potential production of the treatments. For example: an additional 0.8 T DM of silage was made in the HG farmlets over the LG farmlets, which if converted to milksolids (using 70g MS/kg DM response) is equivalent to approximately 56 kg MS over the experiment (0.03 kg MS/cow/day). if taken into consideration, this will reduce the difference in MS production to 4% (0.07 kg MS/cow/day) between the LG and HG treatments.
There was no difference in BCS between treatments.
There were differences in grazing behaviour, with cows grazing high covers eating for longer than cows grazing low covers.
Cows grazing high covers spent 42 min (7%) longer per day eating than cows grazing low covers, thus requiring more energy. There was no effect on rumination time.
Pasture composition data has not yet been analysed e.g. botanical composition, dry matters, ME and nutrient composition.
- The same amount of nitrogen was applied to all treatments, 146 kg N/ha over the course of the experiment. The average application rate over the experiment was 36 kg N/ha for the high-cover treatments and 29 kg N/ha for the low-cover treatments.
- Seventy percent of the paddocks on the farm were diploid
- We could mow at 0.75 ha/hour - this was due to small paddocks and our mowing costs would not be a good reflection of a commercial farm’s. Use the mowing calculator to calculate yours costs.
- Mowing made the farm look pretty
- Managing the grazing farmlets tended to be less stressful than the mowing farmlets. This is probably due to more consistent growth rates and paddocks reaching pre-grazing target more often than mown paddocks.
Discussion point on tactical or operational decisions to mow
This experiment specifically tested the use of strategic pre-graze mowing, i.e. that for a defined period of the year farm policy was that paddocks were mown pre-grazing. This differs from some farmers who use pre-graze mowing tactically, i.e. if in a surplus, then a paddock is mown, or operationally, if pre-graze covers are above targets, then that paddock is mown. While this experiment didn’t set out to test the effect of mowing tactically, or operationally the results can add to the discussion on this practice.
Pasture wastage following mowing indicates that if a paddock is above pre-grazing target (surplus), it does not matter whether it is grazed, and a higher residual left behind that is post-grazing topped, or whether is it pre-grazing mown – this surplus material will be wasted. Data from this experiment indicates there is no benefit of pre-graze mowing and this surplus pasture was not converted to milk. In fact, potentially, there are more benefits of post-graze topping is high quality pasture components are eaten and not wasted.
Additionally, due to the challenges of estimating pasture available if a paddock is above pre-grazing target it is beneficial to allow the herd to graze the paddock and attempt to hit residual in the desired time frame. If paddocks don’t meet residuals, post-graze topping may be used to meet residuals and this information can also be used to make decisions on subsequent pasture allocation, allow a surplus to be identified with the potential of shutting up paddocks for silage. On some occasions (particularly tetraploid pastures) residual may be hit without the assistance of mowing.
Cutting silage will also sustain some wastage and will incur a similar (or greater) cost than mowing, but, by skipping an appropriate area, will enable key KPIs for pasture management (e.g. pre-graze covers and residuals) to be met, without the need for continual mowing/topping.
Why pre-graze mow?
The perceived benefits of pre-graze mowing were:
- increased DM and ME intake
- reduced energy expenditure in foraging and harvesting pasture
- increased MS production
Pre-graze mowing is commonly used at a time of pasture surplus. For example, if a paddock is above target pre-grazing cover and it is anticipated the herd will not hit target post-grazing residual, the paddock is sometimes pre-graze mown to prevent the need for post-grazing topping. The theory being this gives the herd a chance to eat the surplus and convert it into milk instead of being topped to waste.
The concept of grazing paddocks on longer rounds and at higher pre-grazing covers (grazing at 3 leaf stage instead of 2.5), to capture additional pasture growth, has also generated interest.
However, in some instances, the use of higher pre-grazing covers can make achieving target residuals challenging. Pre-graze mowing has been proposed by some as a way of meeting target residuals and maximising pasture utilisation, particularly for those with a lower stocking rate.
To test the theory an experiment with four treatments - with two replicates - has been designed (eight individual farmlets in total). The treatments are shown in the diagram.
- There were 8 farmlets in total, 2 for each treatment
- Each farmlet started with 18 cows and 4.9 ha
- The stocking rate was 3.7 cows/ha
- There were 13 paddocks per farmlet
- The experiment ran for 4 months
- Due to fluctuating growth rates in November, each farmlet was reduced to 16 cows (3.3 cows/ha) in December for the remainder of the trial to ensure farmlets were in surplus
- Each of the 8 farmlets were managed individually, i.e. decisions weren’t the same for the two farmlets in the same treatment
- Target residuals were 8 clicks on the rising plate meter
- Rotation length was flexible
- Pasture was mown as close as possible to a new break being offered
- Most breaks were for 24 hrs
- Similar nitrogen and irrigation regimes were used between farmlets
- Cows could be moved onto a new break if they had finished their current break, or returned to the paddock if pasture remained.
- Pasture allocation was initially based on energy requirements for starting milk production
- If cows grazed below target residual then the area offered could be increased (up to 20% more than previous week) and rotation was sped up.
- If cows grazed above target residual then cows could be returned to the paddock and allocation adjusted for upcoming breaks.
- If target residuals were not met in the grazing farmlets (e.g. poor weather) they could be:
- Shut up for silage in next round
- Post-graze top
- The aim was to:
- Maintain average pasture covers in these ranges
- Low mass treatments = 2050 – 2350 kg DM/ha
- High mass treatments = 2350 – 2650 kg DM/ha
- Maintain pre-grazing pasture covers in these ranges
- Low mass treatments = 2900 ± 100 kg DM/ha
- High mass treatments = 3500 ± 100 kg DM/ha
- Harvest surplus for silage if > 5% above target yields
- Low mass treatments > 3000 kg DM/ha
- High mass treatments > 3600 kg DM/ha
- Pasture allocation was initially based on energy requirements for starting milk production
The following data was collected/calculated during the experiment:
- Individual cow milk volume and liveweight
- Time required to mow (due to the numerous small paddocks, we were not very speedy!!!)
- Farm walk/pasture covers
- Feed wedge
- Growth rate (from pasture cover change)
- Pre and post grazing pasture cover for each paddock
- Refused pasture in mown paddocks
- Pasture disappearance (from pre and post covers)
- Pasture botanical composition (from standing and mown pasture)
- Pasture nutritive value
- Individual cow milk composition
- BCS was scored fortnightly
- Tiller plugs were taken at the start and end of the experiment
- Grazing behaviour was recorded using SensOor eartags
- Impact of time from mowing to grazing on pasture nutrient value was measured
Your questions answered
Previous mowing research
There have been some queries and comments regarding previous pre-graze mowing trials. Below is a summary of previous research and what’s different with the current experiment.
There have only been a few experiments that have investigated the effect of mowing (pre and post-grazing) vs. grazing on cow and pasture performance. One consistent finding from these trials was that mowing reduced pasture regrowth; however, there were also several inconsistent results. Only one experiment reported improved intakes and MS production, following a 12 week period of pre-graze mowing, two reported no change in MS production with pre-graze mowing, and a fourth reported reduced intake and MS production when pastures were mown pre-grazing. Therefore, there is a need to quantify the effect of pre-graze mowing, taking into consideration how it is being incorporated into farm systems today.
The current experiment is investigating the use of mowing with different pasture management strategies (e.g. longer rounds, pushing out to the 3-leaf stage, and grazing at higher than recommended pre-graze yields) to try and grow more grass. The question that we are wanting to answer is “does pre-graze mowing allow more grass to be grown and harvested, while still maintaining pasture residuals and quality in subsequent rounds, and if so, what is the cost/benefit of this?”
In line with trying to better replicate how pre-graze mowing is currently being incorporated into farm systems. The present trial has:
- shorter intervals between mowing and grazing (previous research mowed pastures 12 – 24 hrs prior to grazing) which may have impacted on pasture quality and palatability.
- continual mowing during a period of pasture surplus (October – February).
In summary, the current experiment will allow us to investigate the effects of different pasture management strategies (increased round length and higher pre-grazing covers) and the impact (cost/benefits) of pre-graze mowing within these strategies.