AFBI Hillsborough Feeding Information System- Assess your grass quality
The 2009 grass growing season started badly on farms, with poor weather conditions through late April and May resulting in disappointing grass growth. The wet conditions through the early part of the season made grassland management difficult with many farmers having to re-house animals or limit grazing. This resulted in longer grazing intervals and in some cases heavy grass covers. However, the recent excellent weather through late May and early June has allowed silage harvesting to progress and has seen most animals return to grazing.
Harvesting of quality grass at Hillsborough to produce high quality winter forage.
For the past 13 years the Hillsborough Feeding Information System (HFIS) which was devised and based on practical research at AFBI Hillsborough, has offered a service to assess the quality of grass. There are two separate services, Grass Monitoring for grazing areas, and Grass Ensilability for swards intended for silage making.
The Grass Monitoring Service predicts dry matter, crude protein (CP), sugars (WSC), fibre and metabolisable energy (ME) content of grass. The AgriSearch & DARD funded GrassCheck report published weekly from March to October is based on samples from sites around Northern Ireland which have been analyzed using this Grass Monitoring Service.
For grazing animals, it is essential to assess current grass quality and hence the potential of grass for milk production, or to support growth in beef cattle and lambs. Regular monitoring of grass quality is essential as considerable changes in grass quality occur through the season as shown in Figure 1.
Monitoring of grass quality is also important for farmers feeding concentrates at grass. Changes in grass composition during the grazing season, and in particular, changes in the protein and the fibre fraction have significant implications for concentrate type. For example, DARD funded research at AFBI Hillsborough has shown that lower protein concentrates (14 – 16%) can be used in some instances, particularly where grass protein content is high (above 18% DM).
The Grass Ensilability Service estimates the suitability of grass for ensiling by predicting dry matter, crude protein, sugars, nitrate levels and buffering capacity. While silage making is dependent on many factors, not least the weather, there is always a trade off for bulk against quality. Research at AFBI Hillsborough over the last 25 years has consistently shown that grass will lose quality from mid-May onwards at a rate of approximately 3.5 digestibility units per week which will equate to feeding 1.5 kg extra concentrate per day to sustain milk yield or growth rate during the subsequent winter. After ensiling, the fermentation process converts grass sugars to lactic acid which lowers pH, effectively acting as a preservative in a well-sealed silage pit. For this process to work effectively you will need high residual sugars in your grass so it is best to cut in late morning and in dry sunny weather when the sugar levels have had time to build up. While much has been published about high nitrate levels and subsequent poor fermentation, results from AFBI Hillsborough suggest that nitrate levels are not a problem when nitrate nitrogen concentrations in the grass are below 1000ppm or 0.1%, and buffering capacities are less than 500. Therefore for consistent results when making silage, cut early, preferably in May when grass is still growing strongly, and analyse your grass to check that the nitrate levels and buffering capacity are low, and that sugar levels are greater than 2.5% of fresh weight.
Many of the samples currently being received have shown relatively low nitrate levels and particularly over the last couple of weeks the sugars at high levels. However it is important to remember that under specific conditions; i.e. where pastures were grazed over the spring and closed up and fertilised late, there may still be a need for sampling to monitor suitability for ensiling.
The AFBI Hillsborough Feeding Information Grass Service is available today. If samples arrive before noon, we guarantee to have results back on the same day usually by FAX or telephone, or if after noon, by noon the next day. The cost of the service is £10 excluding VAT for monitoring grass and £12 excluding VAT for ensiling grass.
For sampling packs and further information, please contact Kyla or Linda on 9268 2484.
by Kyla Whiteside, AFBI Hillsborough
