Grassland conservation

Grass may be a relatively cheap feed option for livestock producers, but there is great scope to use it more efficiently, as IGER’s Raymond Jones shows in this grassland academy.

Nitrogen use

Production costs for grass can range from £30/t to £50/t dry matter depending on utilisation efficiency. With fertiliser costs approaching £150/t, monitoring nitrogen use by grassland is important. During the growing season using the formula of 2.5 kg of N/ha a day utilisation is a good rule of thumb for fertiliser application in both rotational grazing systems and grass for silage.

An example of the latter would be 125 kg N/ha for a 50-day closing period for silage harvesting. These are the targets for high quality grass silage.

• High sugars (above 3%@20%DM) to provide an energy source to drive fermentation
• Low nitrate-N% (below 0.02) to prevent production of ammonia nitrogen that will increase buffering capacity and restrict fermentation
• D value – the digestibility of grass is directly related to its energy level – target above 67 D for growing/fattening animals and dairy cows.

The high quality of grass pre-ensiling, with D value, crude protein and sugar content (% DM) averaging 68.6, 18.8 and 3.9 respectively during the 2005 season, indicates good characteristics for ensiling.

Output from UK grass-based livestock production tops £8bn – more than 60% of the total agricultural output of the UK. It is estimated that more than 2m ha of land has been reseeded during the past seven years. Of the total land reseeded to grass, almost 90% was ryegrass species with establishment costs of £200/ha.

Maintaining swards with good quality grasses is essential to provide high seasonal yields, which on average need to exceed 11t DM/ha/year. These swards will provide a high protein and energy feed for livestock. Examples of the main species and varieties of grasses bred at IGER are shown in table 1. Further information on grass varieties may be obtained from the NIAB recommended list of grasses and herbage legumes.

  Silage Technology

Silage making has become increasingly expensive process with the value of silage now approaching £70/t DM. However, it still remains the cheapest winter feed for livestock and there is the opportunity to reduce costs by attention to detail. As an example grass silage can be made for £55/tDM or as expensive as £93/tDM depending on nutritive quality, yield and conservation losses.

The most popular method of harvesting forages for silage making in the UK is the precision chop harvester (36m t) and storage in clamp silos, although increasingly, significant amounts of grass silage are now harvested, wrapped and stored in plastic film using big baler technology (14m t). The average dry matter content of clamp silage is 25%; big bale silage averages 35%.

IGER in collaboration with Dow Europe has developed a net economic benefit model for costing baled silage in comparison to clamp silage. The model predicts that for high quality ryegrass silage (D value of 70) the net economic benefit in favour of baled silage is £12/ t of dry matter harvested for milk production. This would represent an increased income from milk sales of £12,000 from 1000t of silage prepared and fed as bales compared to feeding clamp silage. The main factor influencing the reduced costs was silage dry matter loss observed in the two systems with bales varying between 0.2-8% and clamp silage between 18-25%.

More recent work sponsored by Bpi-agri has shown considerable benefits in wrapping high quality baled silage with six layers of film. The additional film layering provided a more robust oxygen barrier resulting in less spoilage of bales by yeasts and moulds, as well as more stable and consistent silage at feed out.

Silage Inoculants

When an additive is to be used, it is essential the additive is applied evenly and is thoroughly mixed throughout the grass. This is achieved by spraying the additive onto the sward at the point of baling on a number of points across the sward or pumped directly on to the shoot of a precision chop harvester.

When selecting an additive, it is important to purchase one which has been shown to improve animal performance under similar conditions to those being experienced locally. Consultation of the UKASTA forage additive approval scheme will assist in the decision making process.

Experimental studies indicate the application of an effective inoculant, under a range of conditions, will also improve animal production. There is little evidence to show that additives based on enzymes, molasses or sulphuric acid will improve animal performance. An example of animal improvements from inoculated baled whole crop oat silage conducted at the Irene Centre in Africa is shown in table 2.

Improved animal performance and reduced milk urea nitrogen indicates better ruminant use of the silage protein fraction. Other research at IGER has shown that treating silage with a biological inoculant based on predominantly homofermentative lactobacillus plantarum not only provides a means of improving fermentation of silage, but also improving feed value by increasing forage digestibility and providing feed of higher true protein content for optimum animal performance.

Nitrogen Utilisation Efficiency (NUE)

NUE is an efficiency value (%) of the use of nitrogen on a whole farm basis and can be calculated as NUE% = total N exported (milk or meat) divided by the total N imported on a farm in terms of concentrates and fertiliser. On most dairy farms in the UK the average NUE is 25%. This means that up to 75% of the imported nitrogen on farm is lost to the environment as leached nitrogen in the soil or lost in animal excreta. Balancing energy and protein feeds for ruminants has a major beneficial effect on increasing NUE (see table 3).

To improve the NUE on farm it is necessary to regularly monitor efficiency and aim to increase NUE to a target value of 35%. IGER NUE models have demonstrated that for every 10% improvement in efficiency this will result in 10% more profit from milk. It has also been shown that providing more balanced diets of energy and protein for livestock not only improves efficiency but may be also cheaper feeds. raymond.jones@bbsrc.ac.uk