Nutritional value – What is the optimum mowing and baling time? 

Harvesting the grass from the fields as well as possible and achieving the highest possible nutritional value. That is the whole purpose of using mowers, tedders and baler-wrapper combinations. There are two decisive factors: the crude protein percentage and the net energy for lactation.  

“First of all, make sure the grass does not start to head and flower. This means that proportionally the stem will account for too much of the grass and that will be at the expense of the net energy for lactation (MJ NEL) and the protein percentage,” says Gerard Abbink from consultancy Groeikracht BV. “To bale the best quality grass, make sure you cut it before it starts to head and produce flowering stems.” As the days grow longer, grass will head faster. From mid-May to mid-August, the day length is approximately 14 hours. This is sufficient for perennial ryegrass to start heading. Before that time, often at the time of the first cut, or during the autumn cuts, the grass will retain a high proportion of leafy growth. This naturally increases digestibility and means grass from these cuts has a higher nutritional value.  

Temperature influences time of harvesting 

The temperature especially can often postpone the moment of mowing the first cut. If there is not enough grass, it is not a problem to delay mowing for a week. “The only time absolutely not to delay mowing is once the days start to lengthen”, according to Abbink. “Regardless of the amount of grass after the first cut, I recommend mowing every four weeks. That might go against the farmer’s or contractor’s instincts, but a shorter mowing interval is better than waiting for longer for a larger volume.”  

Bale as soon as possible

The length of time the mowing process takes is crucial when it comes to the net energy for lactation. “Once the grass has been mown and dried to a dry matter percentage of 30-50%, the baler should come into action as soon as possible. This minimises quality losses in the silage. Research shows that mown grass left lying in the field loses 0.0069 MJ NEL every hour1. So, in the interval between mowing and baling some nutritional value will obviously be lost. But suppose you wait three days instead of two before baling, in that case the loss is 0.16 MJ NEL. Remember that a dairy cow that produces 30 kg of milk a day needs about 131.1 MJ NEL, of which 94,53 is directed to milk production. Every hour of waiting before baling and ensiling can therefore ultimately reduce production by around 700 grams. Grass usually needs about 48 hours to wilt and dry to a dry matter content of 40%. So, waiting an extra day for a dry matter content of 50% will cost you too much.”  

Groeikracht BV recently performed a study that measured how the method of preservation correlates to nutrient loss in silage. “If the grass is loaded into a clamp, dry matter will certainly be lost until the moment the clamp is covered with sheeting. This is an unavoidable process. It is therefore important to cover the clamp as soon as possible. In this respect, baling is a better way of storing grass, as it minimises the losses. Baling should also be done as soon as possible, as our research has shown that waiting longer before wrapping with film has a dramatic effect on the dry matter content. Every hour longer you wait before wrapping equates to a loss of dry matter of 1.5%.”