As over 17,000 lambs are sold through the live ring, many farmers are weaning lambs and putting the biggest away to slaughter. Fears that the lamb market could fall significantly after Eid al-Adha look to have been allayed, as abattoirs were at £4.60/kg for R grade lambs this week and some early store sales are starting in marts where average prices have been above £70/head.

When weaning, the typical weight of the lamb should be between 30kg to 32kg. To achieve these targets, you should to be aiming for 200g-250g growth per day for lambs. Aim for an eight week target weight of 20kg and a 12 week target of 30kg. The lamb’s DM intake requirement is roughly 4% of its bodyweight, for example 1.2kg DM/day for a 30kg lamb.

Lambs should be going onto pastures of around 10-12cm grass height and leaving at 5-7cm of grass. Set stock fields should be 6-8cm of grass.

Calculating grass growth

To calculate the daily grass growth rate, a very basic calculation is that 1cm of growth approximately equates to 250kg DM/ha of grass.

Therefore, if grass height has increased by 2cm in one week, then the daily growth rate is approximately 71kg DM/ha (2cm X 250kg DM/ha = 500kg DM/ha over seven days = 71kg/day). The higher the figure, the more growth there has been over the past week.

Once you have worked out daily grass growth, it should be used to good effect. Recording individual paddocks weekly will give you an early indication of when to apply fertiliser to prevent a grazing shortage.

Stock demand

Grazing demand can be calculated next. Again, a simple calculation can be used by working out the average liveweight of the group of lambs grazing on a block of land.

Lambs will typically eat around 4% of their body weight in dry matter. For a group of 100 lamb grazing 4ha (10ac) with an average liveweight of 33kg, daily grass demand is 33kg DM/ha/day (33kg X 100 lambs = 3,300kg X 4% = 132kg demand /4ha = 48kg DM/ha for daily demand).

If the grass growth rate is higher than livestock demand, then a grass surplus will build. This allows paddocks to be closed up for cutting. If there is a deficit, then spread more fertiliser or reduce the stocking rate.

After weaning, lowland farms will be able to stock fields with 25-30 lambs/ha in July/August, but this falls to eight to 12 lambs/ha in October/November. Be ready to adjust your stocking rates depending on the season, with poor grass growth needing reduced numbers or supplement feed.

Lambs will have the highest growth rates (150g-200g/day) on short, leafy swards with high intake characteristics, while performance on mature, stemmy swards can be as low as 50-60g/day. Table 1 summarises typical growth rates that can be expected on a range of forage diets.

When weaning at 32kg and drafting weight is a target of 45kg live, then at 200g/day (equal to 1.4kg/week), it will take 12 weeks from birth to get lambs away fat. But remember, during September and October the grass quality will be lower, so realistically another three or four weeks should be added to the target.

Banking grass for breeding

One of the key things for the second half of the year is to get as many lambs away to slaughter as you can and start building a grass bank for breeding. This should start by September, to get a good pasture for breeding time. Make sure you assess if there will be enough grass in October to carry lambs, as ewes should be taking the priority for breeding.

If grass looks to be short and you don’t want to sell the lambs, then concentrates can be used in autumn. For around 10kg of feed, lambs should be expected to make one kilo of liveweight gain.

So far, indications in the market show store prices could be good this year, and if a 36kg to 38kg store lamb is making £75/head in late September, then this may be more profitable than feeding for a further eight weeks to finish at 45kg. Remember, there is still no Brexit deal signed to guarantee tariff-free access to Europe for lambs, so the market in 2021 is still uncertain.