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What is a reduction in days to slaughter worth for a spring lambing flock?

Notes from Samuel Boon, Signet Breeding Services and AHDB

Within our terminal sire breeding programmes we are often asked to put a commercial value on the genetic improvement we make in enhancing growth rate and conformation.

While it is relatively easy to understand the value of increasing a lamb’s carcase weight, carcase conformation grade or changing fat classification, it is far harder to determine the impact of reducing days to slaughter.

The Direct Costs

In finishing spring born lambs there are direct costs and savings associated with

  • A reduction in forage and/or concentrate consumption
  • A potential reduction in vet and med costs

Forage costs are clearly influenced by the cost of producing grass for grazing in-situ and the lamb’s expected intake. However, whilst the cost of grass is often quoted, it frequently relates to the costs of forage conservation (hay/silage) for feeding the ewe flock over the winter. This cost is not directly influenced by faster lamb finishing.

An indirect and probably more significant saving will arise through reducing grazing pressure when lambs are slaughtered, lifting the performance of the remaining lambs in the flock and more importantly reducing the competition between lambs and ewes for grass at mating time and heading into the winter. 

While it is instinctive to place a low value on the cheap summer grass being eaten by lambs, in reality this has a higher real value, as the grass consumed from September onwards directly impacts on the cost of wintering the ewe flock or preventing additional lambs being finished.

Costs currently range from 5p/kg DM (for hill grazing in the summer) through to 12p/kg DM for winter grazing, with 8p/kg DM currently being quoted for summer grass costs. Assuming lambs are eating 1.6kg/day (about 5% body weight) then typical grazing costs would be as follows.  

Grass cost

5p/kg DM

7.5p/kg DM

10p/kg DM

Cost per lamb, with intake of 1.6kg DM

8p per day

12p per day

16p per day

Concentrate costs will vary tremendously between farms, with feed ranging between £250-£350 per tonne in recent years; and the amount fed varying from farm to farm. Many farms will aim to finish the bulk of their lambs from grass. Creep supplementation in the spring and summer at 10kg/lamb, probably means an average supplemented intake of 100g/day. This would entail extra daily costs as follows.

Creep costs for early season production would be considerably higher and a further complication arises where farms only resort to feeding concentrates to late finishing lambs when grass growth has reduced. By this time their feed conversion rate has already dropped and the relative cost of gains from concentrates is higher.





3p per day

3.5p per day


4.5p per day

5.25p per day

Ref: Nix quote 11kg/lamb at £360/t, ABC handbook quote 8kg at £385/t

When it comes to both grass and concentrate costs, we should also probably bear in mind that bigger, faster growing lambs will tend to require a great daily intake which may reduce some of these savings a little.

Reduction in vet and medicine costs

Depending on their speed of finishing, fast growing lambs may perhaps require one less drench for internal parasites and potentially less preventative treatment for fly strike and lameness, but as many of these treatments are applied at a flock level, savings are likely to be small when finishing lambs just a week or two earlier.

 The Indirect benefits

 The challenge when placing a value on faster finishing lambs is that many of the savings are subtle and indirect

  • Labour does reduce as lambs leave the farm, but these are initially small incremental changes up to the point that large draws of lambs leave the farm. The cost of this labour will vary, particularly where family labour is available.
  • The longer lambs are on the farm the greater the risk of lamb mortality or the chance lambs will encounter factors that may limit performance, such as drought or worm challenge.
  • The early sale of lambs can give rise to the opportunity to use the land for other purposes, such as the finishing of store lambs or overwintering extra ewes. However, this type of system change won’t tend to arise from a small reduction in days to slaughter of just a week or two.

 Selling onto a rising or falling market

One of the major benefits of keeping lambs that have the genetic potential to finish quickly is the ability to sell early on a falling market. Where prices are falling at 2p, 4p or 6p/kg a week a 38kg lamb is losing 11p, 22p or 33p per day – and of course the converse it true.

Many flocks lamb in the spring and those faster finishing systems will be selling lambs over the summer and into the autumn. While every year is different, lamb prices tend to fall between a seasonal peak around May through to October.

Looking at data from recent seasons, over this 150-day period a 38kg lamb has fallen in value by around 15p per day over the summer.










Max Value (Usually by May)








Min Value (Usually by October)
























Days over which change arises (5 months)








p per day change








Reduction in value of a 38kg lamb per day in p








Data from AHDB Economics Team

So what is the value of faster finishing, well even the direct benefits are hard to put an exact figure on; but on a grass finishing system feed and forage will typically be in the region of 10-20p per day, while the change market may increase its value by another 15p per day.


Sheep Ireland had values calculated in 2010 as part of their bio-economic model used to derive index weightings. In this scenario reducing lamb growth rates resulted in an increase in feed and veterinary costs and included assumptions about a reduction in lamb prices. The cost of increasing days to slaughter was €0.25/day/lamb (about 22p).

About the author

Samuel Boon

Samuel Boon

I am the Manager of Signet Breeding Services, within the AHDB.

Enthusiast on all things genetics to do with sheep and cattle and currently also supporting Bridget Lloyd in running the @RamCompare progeny test with ~18,000 lambs/annum.

I am also involved with the:-

  • Relaunch of Terminal Sire Breeding Programmes (Sheep)
  • AHDB lead for the Welsh Sheep Breeding Project run by HCC - working with Innovis, HCC and Janet Roden
  • Database design and development for this website
  • National Sheep Breeds Survey
  • Development of Carcase Trait EBVs in Beef Cattle
  • Formerly involved with the delivery of the Welsh Sheep Strategy, Northern Upland Sheep Strategy, Suckler Cow Project, Highlands and Islands Sheep Strategy

I can be followed on Twitter @SamBoonBreeding