Cows tucking in to premown grass back in 2012
Today's post is all about the "sexy" topic of premowing grass for grazing. Just from my own conversations with fellow grazers, it seems the majority have dabbled with premowing at some point, with a range of success. My own opinion is that it's an important tool to help manage grass quality heading into the summer. Others are slightly more sceptical. With this in mind I thought I'd share my tips and thoughts on the practice.
Five years ago we sold our topper and instead bought a mower. This was not to cut silage with, but to specifically premow grass. Topping worked OK, but in some situations the dead grass would lie on the ground and prevent the regrowth shooting through. Here was our justification for the change:
Despite the best management in the world cows will not hit 1500kgDM residuals every time, for a range of reasons, some within our control, others not. Over allocation, inclement weather or just plain bad luck! The decision then is to either try and correct the residual mechanically or hope the cows will graze better 'next time'. The problem is the deck is stacked against us if we use the 'next time' approach. Grazing to 1800kgDM for example, shifts the 'growth point' up to this height, with everything below, low quality, unpalatable stem. At this point we saw premowing as a simple correctional tool to reset the paddock. But what if there were other benefits we hadn't considered?
We soon noticed that when the grass was mown, cows were finishing grazing quicker and lying down full. Then there was the jump in milksolids. Cows went from 1.8 to 1.94kgMS almost overnight. During our surplus months we could now allocate more grass to the cows, knowing they could hoover it up, expending less energy walking the paddock pulling the grass themselves. Capturing the benefits of more feed for less effort.
Costing the exercise is a lot harder. Fuel, labour, repairs and depreciation all have a cost. However, the cost of doing nothing, we have seen time and again, as milk output declined every summer. To this day we now take an aggressive approach to residuals. Any paddock which doesn't meet the standard is put on a list and, weather permitting, will be premown in the next round.
Here are my Dos and Don'ts for those wishing to try it out:
- Don't mow in a deficit. Mowing slows regrowth, especially when mowing higher covers.
- Don't mow covers over 3700kgDM. Grass above this cover has lost a lot of its quality and palatability.
- Don't mow more than 24 hours in advance during dry weather. Grass will overwilt.
- Do mow 12-24 hours in front of cows. Some wilting will increase the dry matter of grass without losing quality. In very dry weather, the cows can go in straight after mowing.
- Do mow early in the year. The sooner you can start mowing, the sooner you can stop grass pushing towards heading.
- Do mow high quality lush grass. The better the grass, the more profound the impact from increased intakes.
- Do mow low. Use a plate meter to measure your mowed residual, the closer to 1500kgDM the more effective it is.
I hope these helped. Ultimately whether you use a mower, topper, or a second mob of stock to tidy paddocks doesn't matter. The important thing is to recognise poor residuals and remedy them before it's too late!