Meeting examines “Science and Silage – the forgotten feedstuff?”

Dr Conrad Ferris (AFBI) and Dr Peter Frost ( I Agr E Northern Ireland Branch chairman).
Dr Conrad Ferris (AFBI) and Dr Peter Frost ( I Agr E Northern Ireland Branch chairman).

Dr Conrad Ferris, an AFBI dairy scientist, was the speaker at a recent meeting of the NI branch of I Agr E held in AFBI Hillsborough.

Grass silage is the mainstay of the Northern Ireland ruminant livestock industry but relatively little new research had been carried out on it locally during the last 15 years. It was interesting to hear how practices have changed since Dr Ferris began his research career, at AFBI in 1988, when his PhD thesis examined the effects of using dry sugar-beet pulp ensiled with direct cut grass. This was to alleviate, in the era of direct cut systems, the release of effluent which was a significant environmental issue at that time.


Ruminant livestock enterprises occupy most of the agricultural land in NI. Stock are normally housed for at least five-six months of the year, during which silage is the main component of their diets. Feeding good quality silage reduces the need for bought-in concentrate feeding. Grassland management has always been at the centre of AFBI research and their latest major research project (co-funded by DAERA and AgriSearch) focuses again on grass silage quality.

During the last 20 years AFBI have analysed more than 70,000 separate silage samples from farms around Northern Ireland. While the dry matter of silages analysed have increased gradually over time, other indicators of quality have shown little evidence of improvement. For example, silage digestibility which is one of the key indicators of nutritive value has not improved. These findings have been one of the main reasons for AFBI to refocus their attention on silage quality.

The new research programme will focus on a number of specific areas. For example, an ongoing study is examining the impact of swards with excess cover in late autumn/early spring on the quality of first cut silage. In this study, swards with high covers have either been left ungrazed or were grazed tightly by sheep in late autumn to minimise the amount of dead material remaining in the sward. First cut silage will be made, from each of the two swards in May, and offered to dairy cows.

AFBI Survey

As part of its latest research initiative, AFBI carried out a survey among 174 dairy farmers, attending the 2018 CAFRE Dairy Open Days, about their silage making systems and their perceptions of the factors affecting silage quality. The published results may be viewed at afbi-survey-identifies-factors-influencing-grass-silage-quality.

Some of the key results were as follows:

Number of cuts

22% of the sample farms were taking two cuts, 65% three cuts, and 13% four or five cuts. More frequent cutting will result in higher quality silage, although costs will be higher. Early AFBI research has shown that digestibility drops by around three - 5% each week after ear emergence, and that livestock performance from early cut grass is superior. Moving from a two or three cut system to a multi-cut system will certainly result in higher quality grass silage. However, multi-cut systems tend to have lower total yields, while silage intakes will be higher. This could potentially increase the requirement for land by approximately 20% unless action is taken to maximise yields from existing land. The current research will look further at multi-cut systems both in the context of quality and how they can integrate with other management practices such as the timing and application of slurry between cuts.

62% of the farmers in the survey normally use a contractor, 9% do sometimes and 29 % make their own silage. 89% of the contract customers were charged per acre, 7% per bale, 2.4% (two farms) were charged per hour and one farm on the basis of the weight of herbage. A number of farmers cited the “per acre” charging system for contractors as a reason for delaying cutting to allow swards to “bulk up” and thus lower the cost per tonne.

However, the resulting loss in feed value can be considerable. Consideration needs to be given to alternative “yield based” charging systems to encourage earlier harvesting, including using new technology on the latest forage harvesters to measure and record herbage yields on the move. Whilst the necessary farmer confidence for this system may still need some support (64% of those surveyed said they might be interested) there is scope for quantitative on-farm research to demonstrate how it can work effectively. Research is also examining the potential of drone-mounted cameras to assess herbage yields from the air.

63% of the farms’ silage was made by self-propelled forage harvester (reflecting the popularity of that system with contractors), 13% by self loading forage wagon and 7% by wrapped big bales. Forage harvester/trailer teams are capable of high outputs and have the flexibility of adding additional trailers for longer haulage distances. Circumstances vary from farm to farm and, especially on short hauls, the forage wagon system using fewer tractors is capable of high output per person. Having both loading and haulage functions in the one machine enables an individual operator to do the two jobs simultaneously. This was demonstrated in work at AFBI Hillsborough during 2005 (by JP Frost and R C Binnie).

Yield and quality

The current average yield of grass in Northern Ireland is around five tonnes of DM/hectare but there is potential to grow and utilise up to 9.5 tonnes/hectare. To achieve this soil fertility and pH need to be correct and reseeding may also be necessary. Only 10% of farms have an up-to-date soil test and, with 40% showing less than optimum phosphate nutrient levels, there is a lot of scope for improvement. Many Northern Ireland farms rely on renting additional land for grass silage production. The incentive for reseeding and longer term sward management on conacre is reduced compared to ownership or long-term lease conditions.


Wilting is now common practice and its advantages include less risk of pollution from effluent, improved silage fermentation, faster field clearance rates and improved animal performance. Previous AFBI research has confirmed the benefits of rapid wilting with a mean milk yield response across eight harvests of approximately 3%, although the responses were extremely variable between harvests.

The average D M of first cut silages in Northern Ireland is now approximately 28%. The rate that grass wilts at is primarily dependent on the amount of solar radiation (sunshine) and the weight of herbage within the swath. Mechanical conditioning during mowing is effective and grass spread after mowing will dry faster. Wilting rates will be extremely slow in heavy undisturbed swathes.

Current advice is to aim for a herbage dry matter content of at least 30% with a maximum 24 hour wilt. During periods of broken weather, with risk of continued exposure to rainfall, achieving a herbage dry matter content of 25 -27% will minimise the risk of effluent being produced. There appears to be little evidence of benefits of wilting to very high dry matters, and indeed this can create problems when preparing a homogeneous TMR ( total mixed ration). With overly dry silages concentrates can separate out and this allows sorting to take place at the feed barrier. Very dry silages are also more likely to be subject to aerobic deterioration after opening.


The benefits of using a proven silage innoculant has been demonstrated in many studies. Additives can improve the stability of silages, and improve animals performance, often when little fermentation benefits are observed. 47% of the AFBI survey respondents always used an additive, 18% did sometimes and 35% never did.

Harvesting systems

Most now pick-up wilted grass using a meter chop harvester, baler or self loading forage wagon (SLFW). According to the AFBI survey 63% use a contractor (most with high output self propelled forage harvester based teams) producing shorter chopped material. The longer sliced-length grass from the SLFW requires more rolling when filling the silo and fermentation may be slower. However, studies have shown that chop-length in well made silages, over a range of chop lengths from 1.5cm upwards, had no significant effect on milk yields. This work needs to be repeated with higher yielding dairy cows.

Silage covering

The traditional standard polythene cover sheeting is partially impermeable compared with the new oxygen barrier film type which is now available. It can be used to reduce storage losses in both bulk silage and wrapped bales.

Health and safety aspects

The seasonal pressures of faster silage making on farms and handling larger tonnages pose dangers to personnel who do the work. Avoiding potential falls from higher clamps and possible collapse of bulk material requires extra vigilance. There is also a risk from gas generation so no one should ever reach, even for a short distance, under the silage covers. Nitrogen dioxide, a reddish/brown coloured gas with a bleach-like smell, can be generated from nitrates in the grass. It is highly corrosive and potentially fatal to people within a confined area.

Discussion period

As always, after an interesting topic has been presented at an I Agr E meeting, there is an interactive discussion around it. This time, the topics included :-

Storage losses and the relative cost of the new oxygen barrier film.

The practical aspects of charging for contract work by herbage yield

Silage quality aspects of feed for an anaerobic digester

Practical implications for applying slurry and nitrogen in a multiple silage cut regime

Possible yield effects of stubble cutting height and the use of disc or flail mowing.

Dr Ferris was thanked for making his expertise available to the meeting and presenting the topics in such an informative and enjoyable way.

The next I Agr E Northern Ireland branch technical talk is at 8.00pm, in AFBI Hillsborough, on Tuesday 19th March 2019 when Mr Sean Gorman (AGCO Area Sales Manager) will speak on the subject of “Fendt - our journey and vision for the future”.

Everyone is welcome to attend.