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Towards a more reliable comparison of the FCR

Luc Maertens, the newest member of World Poultry's panel of experts, is a senior poultry researcher at ILVO, Belgium. In this column Luc looks at the feed conversion ratio (FCR) calculation for broilers and the need for change.


The feed conversion ratio (FCR) in broilers is largely dependent on their weight. To be able to compare different flocks, houses or diets, the FCR is corrected for weight differences. It is still common to recalculate the FCR towards a weight of 1500 grammes and then using a correction of 4 points for each 100 g deviation from this weight.However, slaughter weight and carcass composition of the modern broiler has changed dramatically over the last decades and a recalculation to a FCR 1500 makes no sense anymore.

A correction with 2 points per 100 grammes deviation from a reference weight of 2500 grammes is proposed.

The fast growing broiler of today is slaughtered at a weight of around 2.5 kg. For this fact alone a comparison and correction of the FCR in the range of the average slaughter weight is desirable. Moreover, a recalculated FCR 1500 favours highly the heavy flocks. An unrealistic FCR 1500 close to 1.0 can be obtained for a flock with a weight of 3.0 kg. This can - to some extent - be explained because the relationship between weight and FCR is not linear. By consequence; how larger the difference with the reference weight of 1500 grammes how bigger the error.

Carcass composition of modern broilers

Furthermore, the improvement of performance has led to a changed carcass composition of broilers. Modern broilers have much less fat and more muscles deposits at heavier weights than in the past. By consequence the effect on FCR is strongly overestimated when a correction is applied of 4 points (0.04) for each 100 grammes above or below the weight difference. By using the current FCR mentioned in the manuals of Cobb 500 and Ross 308, we calculated an effect on the FCR of about 2 points for each 100 g difference in the weight range of 2.3 – 2.7 kg. A comparison at a standard reference weight of 2.5 kg with this correction factor leads to a proper FCR 2500.

Therefore, we propose to no longer use the FCR 1500 but the FCR 2500 with the following formula:

FCR 2500 = FCR – Y with Y = (Average slaughter weight – 2500)/50/100.

Depending on the actual local slaughter weight a reference weight somewhat below or above 2500 grammes may also be used with our proposed correction factor of 2 points/100 grammes deviating weight.

Luc Maertens


  • Sayda Ali

    We usually calculate FCR on basis of live body weight and feed intake.
    We deine it as the ratio of feed consumed to weight gain during the same time (day, week or the whole period)

  • Greg Page

    Instead of a single correction factor for all weights, we should, as an industry agree on a common strategy where correction factors (adjusted periodically based genetic improvements) are weight-class specific (e.g. 1 point/100g for 1.5-1.9kg birds with a reference of 1.8 kg; 2 points/100g for 2.3-2.7kg birds with a reference weight of 2.5kg, etc...). This would bring uniformity, as well as flexibility to adjust FCR more accurately within ranges and make comparisons between studies more accurate.

  • S Chayon Barma

    In Bangladesh, we just divide total feed intake by live weight and no correction factor is used. We calculate FCR at any period of life of a flock.

  • ricardo hume

    The feed conversion rate (FCR) is nothing more than following up or down the growth curve of the bird.
    If we look at the Cobb or Ross performance tables we can conclude that between the range of slaughter weights the correlation of live weight (LW) and feed conversion (c) (r2=0.999) is linear.
    Instead of using points to correct the FC, I propose the following equation:
    FCR = (Actual LW - slope x (Actual LW - defined LW for correction). (*)
    slope = (Actual LW - defined LW) / (Actual FC - FC for defined LW)

    (*) Note: if the actual LW is lower than the defined LW the slope should be added.

    Ricardo Hume

  • ricardo hume

    Instead of FCR I should have put : Adjusted Feed Conversion.
    ricardo hume

  • Comment deleted by a moderator

  • Ali Ali

    Dear All
    The above formula for Adjusted FCR is absolutely correct. We have practically
    seen for correction it 2 point FCR for each 100 gms.
    Dr. Munawar Ali
    General manager
    Islamabad Farms Pakistan.

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