Silage 2020: The impact of harvest date on crop quality

Mowers, silage harvesters, balers and tractors and trailers have been on the move in recent weeks, as farmers aim to harvest first-cut silage during this spell of favourable weather conditions for the task.

The majority of first-cut silage will take place on farms throughout May and into June. As farmers act to harvest enough feed for the winter period ahead, we look at how a delay in harvest dates can negatively affect the quality of the crop at feed-out.

While a number of factors can affect pasture yield and quality, harvesting date is one of the main influences determining the feeding potential of the resulting grass silage.

The pattern of change in grass yield on silage swards over time is depicted in figure 1 (blue line). It shows a steady increase in yield throughout the month of May and a slower rate of accumulation in June.

The potential nutritive value of the crop slowly declines during the first three weeks of May, but typically stays above 75% DMD (dry matter digestibility).

However, later in the month (depending on sward age and grass varieties sown), the pasture begins to produce stems and seed heads.

Figure 1: Pattern of change in grass yield and digestibility. Source: Teagasc, Grange Beef Research Centre

As a result of the changing plant structure, its nutritive and feeding value declines considerably. By late June DMD can be less than 60%.

Depending on the animal type(s) to be fed and their target performance level over the winter, a decision relating to harvest date needs to be made.

Data from Grange (below) shows that as DMD increases, animal dry matter intake (DMI), liveweight gain, carcass gain and feed conversion efficiency all improve.

At a DMD of 70% or greater, finishing animals can achieve a liveweight gain in excess of 0.66kg/day on silage only.

Digestibility: What difference does it make for beef cattle? Source: Teagasc, Grange