The new broiler welfare rules which came into force in 2010 attached great importance to bird stocking rates.
But one other aspect, which some producers have been inclined to overlook, is the calculation of cumulative daily mortality rates (CDMR).
Under the regulations, any farmer stocking conventionally-reared meat chickens above 33kg/sq m is required to calculate the CDMR for each flock for each house.
This information must be supplied to the slaughterhouse on the Food Chain Information form (FCI) at least 24 hours before the arrival of the birds.
Batches that do not have a correctly completed FCI form cannot be slaughtered. Random checks will also be made to see if the mortality rate reported is CDMR rather than standard house mortality.
“A stumbling block to providing CDMR is that it is seen by some to be complicated and time-consuming to calculate,” says Alison Wintrip of consultants ADAS. “But that need not be the case, as CDMR can easily be worked out with just a calculator.
“It is worked out using figures that are already being recorded – the number of birds placed, daily mortality figures, the number of birds thinned.
“The only difference with CDMR is that you need to adjust the number of birds left in the house every day and use this figure to calculate the next daily mortality.
“As such, it is a more accurate measure of mortality over the life of the flock. It is not, however, a substitute for informed and consistent monitoring by the grower of the level and changes to the pattern of day-to-day mortality.”
During the early stages of the crop, CDMR and daily house mortality will be very similar. But towards the end of the crop and, in particular after thinning, the difference between the two figures will be greater.
This is demonstrated in the worked example, based on a typical daily house record sheet.
|Day||Number of birds at the end of the |
previous day (A)
|Number of birds thinned||Total found dead||Total culled||Daily mortality|
(total dead on the day) (B)
|Reasons for death/culled if known||Daily mortality rate (%) (C)||CDMR (%) (D)|
|Continue as above until depletion or thinning|
|Continue as above until the end of the flock|
|At the end of Day 1, divide the total number of birds that have died (Column B) by the number placed (Column A) and multiply that figure by 100 to give the percentage daily mortality (Column C).|
You then need to adjust the number of birds remaining in the house by subtracting the number of dead on Day 1 (Column B) from the original number placed (Column A).
Carry this figure forward to Day 2 (Column A).
On the following day the same procedure is performed to work out daily mortality % (Column C).
CDMR is then calculated by adding the daily mortality figure you have just worked out (Column C) to the cumulative mortality figure from the previous day (Column D).
This calculation is then repeated on a daily basis until either the end of the flock or until thinning.
If part of the flock is to be depleted early, the number left after depletion has to be adjusted for the number of birds thinned.
For example, if 5,000 birds are removed on Day 35, the total number remaining on Day 36 will be 26,390 (Column A), less mortality (Column B), less the number thinned number (5,000), ie, 21,376 birds remaining.This figure is carried forward to Day 36 and this reduced number is used for the subsequent calculations for daily and CDMR.
Both at thinning and at the end of the crop cycle, the final figure in Column D is the CDMR value that must be included on the FCI form.
An Excel spreadsheet that producers can use to calculate CDMR by computer is available on the archived DEFRA website.
Putting it into practice
Mark and Louise Forster have produced broiler chickens as a business for the past 30 years.
Louise is managing director and acting company administrator and deals with the day-to-day running of the office and accounts.
Prior to June 2010, Louise received information from Defra stating that it would become a legal requirement for producers like her to provide CDMR data for each flock on the FCI form. “It was a statutory requirement, so it had to be done,” she said.
Although working out daily mortality was not difficult, asking the staff to calculate cumulative percentages on a daily basis was more problematic.
So using the spreadsheet Defra supplied on its website as a template, she developed her own system for recording and calculating CDMR using her computer. “This means that staff have only to add the total mortality for each day into a column and the computer works out the rest,” she said.