Farm Ireland

Thursday 19 July 2018

Maximising killout on lambs

Achieving a consistent killout weight can make a big difference to the sheep farmer's bottom line

Good condition: Lambs with better conformation for example U grade lambs will normally have higher KO pc than 0 and R grades
Good condition: Lambs with better conformation for example U grade lambs will normally have higher KO pc than 0 and R grades

Every farmer's aim is to maximise the price they are getting for their lambs by selecting young stock that will produce carcases as near as possible to the maximum factory pay weight.

This aim will increase output per ewe, while cutting costs and delivering a stronger overall gross margin/ha.

Sean Conway, who farms at Lavagh, near Ballymote, Co Sligo, has been aiming to achieve the maximum possible price per carcase since he weaned his lambs from the mature ewes at the end of June.

Sean, who is part of the STAP The Lights sheep discussion group, is aware there can be a huge variation in lamb kill out (KO) percentages between individual lambs in the flock.

However, he was aiming for consistency and made every effort to reduce the range and maximise carcase value.

His heavier carcases are produced at relatively low cost as lambs are finished off grass.

Sean has been using the PastureBase programme to measure grass growth and use it to identify paddocks to take out as grass surpluses this year.

Average liveweight

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So far he has drafted 14pc to date at an average liveweight of 44kgs and KO pc of 49pc producing an average carcase weight of 21.56Kgs.

Sean, who takes his lambs to Irish Country Meats (ICM) in Navan, was targeting a weight of 22.5kg.

The average price received to date is €99.67, with a difference of €11 in the latest lot of lambs with lamb 10 (in the graphic) hitting the top price and lamb 2 the lowest.

The lamb KO pc will ultimately determine the final carcase weight.

When selecting lambs for slaughter Sean takes account of the factors that affect KO pc.

Gut fill

The more feed in the gut will result in lower KO pc. The greater the time from the lamb's last feed, the lower the gut fill which will result in higher KO pc.

Lambs housed without food the evening before being transported to the factory could weigh up to 4kgs less the following morning.

Likewise lambs weighed in the evening will have poorer KO pc than those weighed early in the morning prior to grazing.

Sean weighs his lambs at the around the same time on the same day of each week to reduce the influence of gut fill.

Fat cover

Lambs that are lacking flesh or fat cover, such as lambs of fat score 2 will have poorer KO pc than those in fat classes 3 and 4.

Sean tries to select lambs that are fat class 3.


Dirty soiled and wet fleeces will increase lamb liveweight and lower KO pc.

Sean aims to keep his lambs as clean as possible and makes an allowance for lambs weighed with very wet fleeces.


Ram lambs will normally have lower KO pc than wethers due to the weight of the testicle and ewe lambs will normally have higher KO pc than rams or wethers.

Sean normally selects ewe lambs at lighter weights than rams, they can become over fat at lighter weights.


Lambs with better conformation for example U grade lambs will normally have higher KO pc than O and R grades.

Sean selects the more muscular lambs at lighter weights provided they have adequate fat cover. In 2014 U3 grade lambs had a 4pc higher KO pc than R2 lambs.


Lambs killed directly off the ewe early on in the season will generally have higher KO pc than weaned lambs.

As the season progresses and the lambs mature their stomachs enlarge as does their grass consumption, this will lower the KO pc.

Sean will increase the live selection weight as the season progresses as he aims to have carcases as near as possible to the factory pay weight.


Lambs consuming concentrate will normally have higher KO pc than those on grass only.

The majority of lambs are finished off grass on the Conway farm.

Carcase damage

Carcase damage due to rough handling or abscesses will reduce the carcase weight.

Sean avoids grabbing the lambs by the fleece when handling.

The variation in KO pc can be seen in the 12 ram lambs slaughtered in ICM Navan by Sean on the August 4 last (see table).

The lambs were weighed on the evening prior to slaughter and ranged in live weight from 41-46kgs.

The KO pc ranged from 44 to 51pc and carcase weights from 19.7kgs to 22kgs.

Indo Farming