Grass is perceived as being fundamental to lamb production, but the UK sheep industry could do more to maximise its value. Debbie James reports
A combination of early lambing systems and a reliance on creep feed means rising cereal prices will have a major impact on the cost of sheep production. But by managing grazing efficiently, farmers can get more from their grass and reduce their dependence on bought-in feeds.
The benefits of efficient grazing management are many: the quality of ewe milk is improved and worm burdens can be reduced and therefore lambs finish quicker.
To achieve a good forage system, farmers must first concentrate on the basics such as sward height and pasture type, says EBLEX sheep scientist, Liz Genever.
“A one-point increase in the D-value of grass through improved varieties or better grazing management can lead to an additional 20g of liveweight gain a day for lambs through improved efficiency of digestion. This can mean at least two weeks taken off the days to finish,” says Dr Genever.
Teagasc looked at the effect grazing management, sward type and supplementation would have on the growth rates of lambs at pasture. The study demonstrated a decline in lamb growth rate in the month pre-weaning in June could largely be prevented if sward height was increased to between 6-8 cm, or if the flock is grazed on aftermaths at a similar height.
And lamb growth rates on pasture post-weaning varied greatly, from under 100g a day to over 200g a day, depending on the type of pasture grazed.
The study found creep feeding, at 250g a lamb a day, increased weaning weight by 2.7 to 3.8 kg, depending on pasture and year, while the response to forward creep grazing was more than 2kg.
With forward creep grazing, lambs should be leaders as they have the highest quality diet requirement.
Dr Genever suggests this grazing method works best with an eight-paddock, 24-day cycle. “Lambs are encouraged to feed through specially constructed gaps in the fences where they choose a high quality diet and are possibly less exposed to worms,” says Dr Genever.
“As grass consumption of lambs increases, the ewes receive a less digestible diet, which coincides with their declining lactation.”
Another option is rotational grazing which is possibly most applicable to ewes with older lambs or weaned lambs. A group of animals graze in one paddock at a relatively high stocking rate for a defined period, between two days and a week, depending on the pasture mass and quality and the feed requirements of the flock.
Pasture quality and growth rates will have a bearing on the number of paddocks in the rotation.
An advantage of this system is that it increases use, possibly to 70% from 50%, and can increase yield by 20%. The quality of grass in a well-managed grazing system can be maintained at 12 MJ of ME.
Pastures can recover because time is allowed for pasture re-growth between grazing cycles and parasite lifecycles can be disrupted. And the better the feed quality of grass under well-managed grazing systems the better animals will be able to cope with parasite challenges.
An important feature of this system is the length of the grazing rotation. When the rotation is too long paddocks will become long or rank by the time the sheep return to them.
During spring when grass is growing rapidly, the rotation can be shortened by closing paddocks for silage or hay. This will have the effect of increasing the stocking rate on paddocks left in the rotation.
Conversely, when the rotation is too short, pasture may not have had time to re-grow adequately when the flock returns to the field and this can restrict animal growth rates. Further grazing will reduce pasture mass to low levels resulting in slower re-growth and this cycle will continue with subsequent rotations.
Teagasc adopted a rotational grazing system when it conducted an experiment looking at the effects of tight grazing pre-weaning. It found it improved pasture quality and lamb growth rates post weaning. The optimum sward height for weaned lambs depends on how tightly the sward is grazed in the first half of the year, especially in June, and the resulting proportion of green leaf in the sward.
During the two-year experiment pasture was grazed by ewes and lambs to residual sward heights of 3.0, 4.5 or 6.0 cm from April to early July.
Sward heights were recorded weekly and the percentage of green leaf, in herbage samples cut to ground level, was measured.
Tight grazing pre-weaning improved pasture quality in the post-weaning period. The percentage green leaf in the herbage averaged 78, 69 and 66 for the swards grazed to 3.0, 4.5 and 6.0 cm respectively. Lamb growth rate rose with increasing sward height on each site. There was a significant difference between sites, with the highest growth rates on pastures grazed tightly in the first half of the year.
However very tight grazing will restrict lamb growth, in particular when lambs are between five and 10 weeks old and at weaning. This suggests tight grazing in April/May, when pastures are leafy, is less restrictive on lamb growth than in June when pastures tend to be more stemmy.
Dr Genever says grass measuring is important. “Various methods – a sward stick, a ruler on wellies, beer cans, matchboxes, golf balls or coins – can all be used. It is all about looking at sward height, monitoring weekly and acting on the information.
“Plate meters are an investment and can be used well on sheep farms but the information needs to be used to plan grazing,” she says. “There is a need to improve the understanding of basic grass management across the industry, and using a sward stick is simple and effective place to start.”
Managing pastures correctly in the spring will influence growth rates and grass quality throughout the season.
Dr Genever says 50% of all grass growth will happen by the end of May in southern regions of the UK and by the end of June in the north therefore managing spring growth is crucial.
“It’s important to keep control of grass before there is a massive peak in growth because digestibility and feed quality reduces if this happens,” she says. “If there is excessive grass the risk of grass going to head and losing quality is high, which will reduce use and may lead to the need for topping.”
Sward Height targets
|Rotational grazing – pre-graze (cm)||Rotational grazing – post-graze (cm)||Set Stocking (cm)|
|Ewes with lambs (Apr-May)||8-10||4-5||4|
|Ewes with lambs (May-weaning)||8-10||4-6||4-6|
|Weaned finishing lambs (Jul-Sep)||10-12||5-7||6-8|
Case Study Huw Davies, Carmarthenshire
For upland lamb producer Huw Davies, who supplies a local abattoir with a set number of lambs weekly, good grazing techniques are essential to achieving target finishing weights.
“Efficient grazing is as essential for lamb growth as it is for a dairy cow to produce milk well,” says Mr Davies, who runs a flock of 580 ewes in Carmarthenshire.
From late July, he supplies the Dunbia abattoir at Llanybydder with 50 lambs a week. He starts the process of managing grazing to achieve lamb finishing weights in mid-April.
The silage fields are closed between 20 April and 1 May; any earlier and the aftermath would be too advanced when the lambs are turned on to it to graze.
Mr Davies places great emphasis on nutrient management to achieving the correct level of grass growth. “We try to manage our fertiliser usage and cost so we set aside slurry and farmyard manure for 12 months and spread this on the silage fields once the silage is cut,” he explains. “It means we don’t get that great flush of grass we would get from using artificial fertiliser. It gives a more natural growth and doesn’t place stress on the lambs so we avoid the associated problems like scouring.”
Mr Davies’ land at Llandre Farm, near Lampeter, rises from 500ft to 1,000ft. When the Beulah Speckled Faced and Mule ewes lamb in mid-March they graze the silage ground first, before being moved up to the highest ground with a typical set-stocking system of 250 ewes and 400 lambs on 42 acres.
The lambs are weaned in the first week of July and turned on to the aftermath. Mr Davies selects the best lambs – those that will finish the quickest – to graze the more advanced grass.
The aftermath is again grazed on a set stocking system with 10 lambs to the acre. “We don’t keep them in a field for more than three weeks. They don’t like it when the field gets stale, they won’t eat the grass and get the intakes they need for growth,” he says.