Pre-mowing vs. topping: Which is the better option?

Trying to get the cows to graze out paddocks fully – during this time of year – can be difficult; so sometimes further action such as topping or pre-mowing is necessary.

We have reached the stage in the grazing season when the grass plant begins to head out and develop a seed head.

Once this happens, the base begins to form a stem to support this seed head. If residuals are not met the proportion of this poor-quality stemmy grass in the sward increases.

Grass growth rates have been high these past few weeks which has resulted in pre-grazing yields slipping that bit higher on farms.

The trouble with these high pre-grazing yields is trying to reach residuals, so that grass quality is maintained into the next round.

Topping

Topping the paddock post-grazing is a common method used by farmers to eliminate the amount of stemmy grass in the sward – to have good-quality grass coming back for the next rotation. However, topping has its pros and cons.

Although topping is a quick and effective way of eliminating the amount of stemmy grass left over in the paddock, it is very labour intensive, particularly if it has to be carried out more than once.

Topping can also affect the regrowth rate of the sward. If paddocks are left and not topped immediately after grazing the stemmy grass along with the regrowths will be cut.

Cutting the regrowing plant can impact negatively on the grass plant causing a delay in the regrowth of a paddock.

Pre-mowing

Pre-mowing is another technique used by farmers. This is commonly completed in New Zealand and involves mowing the paddock in front of the cows before they are let in to graze it.

However, just like topping pre-mowing also has its downfalls.

Cows are selective grazers; however, pre-mowing prevents the cow from selecting the high-quality grass over the poor-quality grass.

If the paddock was to contain a high amount of poor-quality stemmy grass this could cause a fall in milk production.

However, pre-mowing paddocks can also increase intakes because the grass is readily available to the cow which in turn can increase milk production – provided it doesn’t contain a high amount of poor-quality grass.

In any case, both options result in improved grass quality in the subsequent rotation; but both are associated with poor grass utilisation because grass is lost in both cases.

Furthermore, each are very labour intensive and should not replace good grassland management techniques to achieve target residuals through grazing.

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