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Profitable Growth from Grass
By Ranald Fowler, Editor for Mole Valley Farmers
Given that the EBLEX costings show that few costed lowland flocks make a profit once the Single Farm Payment has been deducted and that this will be reduced in 2013, now is a good time to consider how best to reduce flock management costs by then. Optimising the use of good grassland offers the greatest opportunity, though for some, this may mean changing lambing dates to do so. As it is many sheep farmers have insufficient grass for their flock at turnout and too much by May leading to stemmy pastures and lower growth rates from June onwards. The best graziers target at least 6cms at turnout and maintain this height into April by utilising a rotational grazing system to maximise ewe milk production. Ideally the grass should not be grazed below 4cm.
As the sward height reduces the ewes compensate by grazing for longer until it drops below 4cm when intake is reduced, ewes body condition and milk yield falls and with it, lamb growth rate unless expensive concentrates are offered to make up the nutritional deficit. Lambs will attempt to compensate for the fall in milk by grazing earlier and of necessity, tighter, but as worm larvae are concentrated at 2-3cm from the ground at this time of year, the lambs are exposed to an unnecessary parasite challenge when they are also under nutritional stress. The challenge is greater for ewes with twins and their lambs, but having sufficient grass would prevent this.
Last autumn we suggested closing up a proportion of the grazing swards; these rested pastures carry some autumn growth and are also thicker and better able to respond to early nitrogen. Fields that have been rested will produce twice as much grass as those grazed through winter.
Previous studies at the Athenry sheep research farm in Ireland have shown that for each days delay in Autumn closing date, herbage DM yield in spring is reduced by 22kg/ha. Consequently, a weeks delay in closing pasture after 1st November would reduce grass DM availability in the following spring by 154kgDM/ha, which is equivalent to 50 ewe grazing days! The closing date reflected recovery right through to spring grazing. Fields closed in early November had the same sward height on 29th January, as swards closed on 28th November had on 20th March. All ewes are housed by mid December, with lambing starting 1st March after which the aim is to feed no concentrates.
Early Nitrogen
Ideally nitrogen should be applied 6 weeks before turnout; hence the reference earlier to deciding on an appropriate lambing date to coincide with managed early spring growth. Suckling ewes, like dairy cows, have an immediate demand for a large intake of grass. A ewe suckling twins, each of which is gaining over 300gm/day is almost equivalent to a cow yielding 27 litres/day.
On heavily stocked sheep farms (12 ewes/ha+) nitrogen needs to be spread over the whole grassland acreage at 30kg N/ha (24 unit/acres) 5-6 weeks before the due lambing date, with a further application in late March or early April to keep the grass growing well. Grazing the silage ground until early April enables the grazing fields to get sufficient cover to maintain flock demand. The response to a January-February application may only be 5-10kg grass DM/kg N applied, but it does get the grass moving and responsive to the second application. Spread when ground is sufficiently dry not to mark with the tractor wheels and rain is not forecast for 48 hours to prevent run-off or leaching. Urea is cheaper and less likely to leach, but CAN will probably give a faster response from the end of March on lighter soils that may dry out faster.
Research done in Scotland 80 years ago and recently revisited has shown conclusively that where soils are deficient in phosphate, applying a nitrogen/phosphate compound to low index soils, shows a greater and faster grass response than to N on its own. This is because phosphate is necessary in the early part of the year to boost root growth and especially so on winter grazed pastures. At Athenry, 90% of the total ewe and lamb diet is grazed grass. The ewes are rotationally grazed and no concentrates are fed after turnout, though last year there was a grass shortage in mid April and for 5 days paddocks were grazed down to 2.8 cm, before growth recovered.
Grass height is measured on entering and leaving each paddock and post grazing target in April is 4cm; May 5cm and June 6cm. The mean post grazing achieved in May was 4.5cm, increasing from 3.9cm to 5.8cm by the end of the month and illustrating the rapid increase in growth enabling land to be closed for silage.
It is essential to graze paddocks bare in April and May to maintain herbage quality otherwise grass throws up seed heads and becomes fibrous, reducing palatability and intake which reduces lamb growth rate in the last few weeks prior to weaning. Set stocking requires higher grazing heights. Fields are not closed for silage until May when growth erupts; a leafy silage crop is taken before the aftermaths are returned to grazing for the lambs at weaning. Typical daily grass DM growth rates were March 10kg/ha; April 40kg/ha; May 90kg/ha; June 50kg/ha/day respectively.
Lamb performance at Athenry
| Litter Size | Single | Twin | Triplet |
| Lamb weight (kg) birth | 5.8 | 4.9 | 3.8 |
| Lamb weight (kg) weaning | 38.5 | 33.4 | 33.2 |
Lamb lwt gain (g/day)
| Litter Size | Single | Twin | Triplet |
| Birth to 5 weeks | 386 | 306 | 311 |
| Five to 10 weeks | 267 | 331 | 348 |
| 10 to 14 weeks | 245 | 229 | 204 |
| Birth to weaning | 337 | 292 | 296 |
- triplets fed 300gm/day to weaning
- at weaning 27% of lambs were drafted for slaughter
- being 53% of singles and 21% of the twins
These figures are a good example of what is being achieved with good grazing management.
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