Grass is claimed to be the cheapest feed available on the dairy farm. However, the yield of grass utilised either by grazing or cut for silage is a key determinant of the cost of grass on your farm. Analysis of data from Greenmount Dairy Benchmarking would indicate that the annual average utilised yield of grass on N. Ireland dairy farms is about 6.5 tonnes of dry matter per hectare (approximately 13 tonnes fresh weight per acre at 20% DM). Based on costings produced by AFBI and CAFRE, the target utilised yield should be over 10 tonnes of dry matter per hectare (20 t FW/acre). This is one of the targets set for the Future Herd managed in partnership with Thompsons at Greenmount Campus.

Why is the average dairy farmer only achieving about 60% of the potential output from their grass? There can be a number of reasons:

• Late turnout to grazing and early housing

The number of times a paddock is grazed during the year has a major impact on the yield from a grazed sward.  Getting cows out early to start grazing also reduces the wastage of grass associated with grazing swards with excessive cover in spring.

• Soils compacted and damaged by machinery and livestock

Poaching damage and compaction from heavy slurry spreading and silage harvesting machinery is often not addressed through either regular ploughing and reseeding or soil loosening through mole-ploughing, the use of shakerators or soil aerators.

• Insufficient liming

A high proportion of soils analysed in recent years have been shown to have a pH of well below 6.0. The use of lime has been in decline in recent years.

• Large, infrequent and late silage cuts leads to loss of ryegrass

Looking for too much bulk from individual cuts not only reduces silage quality and winter feed bills but also leads to faster sward deterioration.

• Lack of reseeding frequency

Many old swards, particularly those cut regularly for silage, will have poor ryegrass content. In addition, in many heavy soil types prone to soil compaction drainage, the lack of regular reseeding exacerbates drainage problems.

Financial benefit of reseeding

Despite the initial establishment costs, the financial benefit of reseeding considerably outweighs the cost through the improvements to be gained in both grass yield and quality.  The increased yield of newly reseeded swards reduces the cash cost of producing 3 cuts of silage from £102/t DM to £72/t DM if the top yielding varieties are used.  The increased yield also means that the area required to grow the 225 tonnes of silage dry matter required for 100 cows is reduced by 9 hectares with a potential saving in conacre cost.

Together, this means that the cost of producing 225 tonnes of silage DM is reduced by around £9,000 in swards reseeded with the best varieties compared to old swards. In addition, the best varieties of grasses will lead to increased silage quality with higher ME values.  This will consequently lead to lower levels of concentrate use to achieve the same level of performance with a potential saving of around 19 tonnes concentrate per year for 100 cows.

Table 1: Financial benefit of reseeding 3-cut silage swards

Together, the increased yield and improved quality of new reseeds compared to old swards is worth around £12,500 per year (£665/ha/year).  The annual benefit from regular reseeding with one of the best varieties is worth around £100/ha/year more than reseeding with an average variety.  Therefore, the long-term benefit of reseeding with the best varieties considerably outweighs the cost and offers the potential to increase the amount of high quality grass grown cost effectively on the farm.

By Martin Mulholland Greenmount Campus, CAFRE and Jonathan McCaughan, John Thompson & Sons Ltd.