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Heat Stress in Poultry: Recognising it, tackling it and the Insurance considerations

Heat stress losses can be significant for both poultry farmers and their insurers and are likely to rise because of the increasingly unpredictable weather caused by climate change. In this article Mike Clementson, Charles Taylor’s Director: Head of Agriculture, reflects on some of the technical and insurance considerations behind poultry heat stress losses.
Many of the same insurance considerations also apply to machinery breakdown claims. The most significant difference is that these can occur at any stage of the rearing cycle whereas heat stress incidents typically involve the heaviest birds later in the cycle.
Technical background
Like your pet dog, poultry have no sweat glands so the only way of governing their body temperature is by panting, which is an early signs of heat stress. The birds have an average body temperature of 41ºC and will succumb to death through heat stress if this rises by more than 4ºC. Poultry are also generally susceptible to sudden, large changes in temperature.
In our experience, 30ºC is an expected trigger point for heat stress losses to occur, usually in mid to late afternoon. We have seen stress incidents occurring with temperatures in the mid 20’s where the situation has been exacerbated by high relative humidity.
The temperatures given in weather forecasts, and historical records, are taken in the shade so most poultry houses, which are in direct sunlight, will experience higher actual temperatures than may be recorded.
It is important to differentiate between losses caused by heat stress and those caused by smothering which can occur regardless of the ambient temperature. Smothering results from an external shock like a loud noise such as low flying aircraft or collisions to the building. Even the presence of rats has been found to cause birds to panic and smother. The poultry usually congregate in large heaps in one corner of the shed, resulting in mass smothering of the lower birds.
This is in stark contrast to heat stress, where the birds typically remain motionless, dying where they lie. This difference, along with weather records, can form valuable proof of heat stress as the proximate cause. However, in most cases the dead birds are likely to have been removed long before a loss adjuster arrives on site. Therefore, photographic evidence taken before and during the carcass clearance operation should be requested.
We are dealing almost exclusively with intensively reared broilers (table birds), rather than free range birds and layers.
Some strains of broilers appear to be more susceptible to heat stress than others. However, there is insufficient evidence to allow a detailed analysis of any such differences. 
Heat stress in poultry can arise in two ways (i) acute stress caused by the intensity of the heat and (ii) chronic stress caused by prolonged exposure to heat.
In the absence of supplementary heating, the largest source of heat within poultry houses is the birds’ metabolic temperature which is one reason heavier birds tend to be more susceptible than lighter birds.
Air exchange is responsible for most heat loss from poultry houses in hot weather. Once ambient temperatures rise there is very limited potential for removing internal heat by artificial ventilation, even with the fans working at maximum capacity.
Ventilation design is crucial. This is a very complicated subject outside the scope of this brief. Suffice to say that modern poultry houses feature sophisticated environmental sensory, control and alarm systems which aim to govern internal temperatures as far as possible. However, these are offset to some degree by the increased thermal insulation characteristics of modern structures which limit the escape of heat through the walls and the roofs during periods of hot weather.
Temperature alarms are frequently set at 3ºC above the target ambient temperature, which is governed by the stage of growth of the birds. There comes a point when, even with all the fans working at maximum capacity and with all doors and vents open, temperatures breach this 3ºC allowance and the alarms activate. On well managed farms the risk of heat stress is often identified early by the scrutiny of Met Office forecasts warning of high temperatures.
The potential for heat stress losses should become apparent during the day, with the fans turned to maximum capacity and all the doors and vents opened. However, once the increasing ambient temperature overcomes the capacity of these measures to keep the birds cool, deaths can be expected, typically in mid to late afternoon because of the combined acute and chronic heat stress effects.
Heat stress in birds can be unpredictable. We have known cases where apparently identical poultry houses containing identical birds in similar numbers experience widely differing loss levels.
So, what risk reduction measures can be undertaken?
One is to anticipate periods of high ambient temperatures and to thin (clear at an earlier, lighter weight) as many birds as possible to reduce the overall stocking density. The problem is that all the birds are pre-programmed into the factories at specified weights so there may be little scope to accept any extra throughput. The factory will in turn have contracts with supermarkets to supply birds at specific weights over precise time scales so there may be little opportunity to market lighter birds at short notice.
Another possibility is through misting or “evaporative cooling” by the installation of misting jets in the poultry sheds to keep the birds cool. However, this also increases the relative humidity which needs very careful management and so is not widely adopted.
A third is “crop walking”, when employees walk slowly through the birds, causing them to move about to increase the air movement and particularly to release heat trapped beneath their bodies. This can be beneficial during the early stages of heat events but as the birds become increasingly stressed, they also become increasingly reluctant to move.
The introduction of extra fans can help by increasing the air flow over the birds, if these can be made available at short notice and during periods of high demand.
The aim of carcass disposal is to remove the dead birds from site as efficiently and humanely as possible. Thus, there is little time to take an accurate count of the numbers involved, so the figures recorded as lost during the clearance operation should be double checked against a stock reconciliation when the surviving birds have been cleared.
Despite the potentially significant losses through heat stress, in our experience it is unusual for there to be consequential loss claims arising from depressed performance in the survivors. Odd as it may seem, the birds appear to be virtually unaffected in terms of their subsequent performance.
Insurance considerations

Heat stress should be considered as a separate peril. It does not fall within a standard “accidental, visible, violent and external ….” policy definition. Nevertheless, in our experience it is unusual to find a definition of heat stress in the policy wording, or indeed a minimum temperature at which cover is triggered.
We also need to differentiate between losses caused by heat stress and those caused by smothering (which may not be covered) or indeed machinery breakdown, where lower excesses are the norm.
Some policy wordings define livestock to include poultry, whilst in other wordings poultry is defined separately. In some policies there is no specific exclusion of poultry from the livestock definition. Hence the Oxford English Dictionary definition of “Livestock” should be broad enough to include poultry under a generic “Livestock” definition. 
The Government regulate welfare requirements for many livestock classes, including poultry. These are not enshrined in law, but they are considered influential in Court when considering animal welfare cases. They are reflected, or frequently improved upon, in the welfare codes of supermarkets and the RSPCA for example.
These requirements are in turn reflected in policy warranties governing things including the maintenance and use of environmental control and alarm systems, back-up power supplies, and the regular testing and recording of those test results. 
We are aware claims have been declined because of the failure to comply with such warranty conditions.
If birds are thinned as a standard procedure, and if heat stress (or mechanical breakdown or smothering) losses occur before thinning, remember to allow for those birds which would have been sold at thinning to calculate the average saleable weight of the birds lost.
There is an argument that early thinning to help prevent heat stress comprises loss mitigation which is not covered under the policy. This is obviously a disincentive for poultry farmers to adopt this approach, and it may be difficult to convince the policyholder that such a decision is reasonable.
There would be no heat stress mortality claim under these circumstances, but a claim for the revenue loss arising from these birds being sold at a lighter weight.
The calculation of loss on a revenue basis is then reasonably straightforward. The number of dead birds recorded at the time of carcass clearance can be unreliable so a stock reconciliation should be used to calculate the figure. Any adjustment for additional mortality should then be made to calculate the net number lost after allowing for rejects and birds dead-on arrival.
The average weight at slaughter can be taken from the factory returns, taking care not to confuse liveweight and dead weight criteria. This enables the loss of weight to be calculated, to which we apply the return per kilogram to arrive at the gross loss of revenue.
This calculation assumes that the policy covers the birds at their anticipated final sale weight so there are two elements here (i) the weight/value of the birds at the time of the loss and (ii) the net loss of income represented by the loss of weight/value between then and their anticipated final weight.
Feed savings relating to (ii) above can be calculated from breeders’ tables, ensuring not to confuse hatched flocks with those comprising single sex birds only.
Some policies are underwritten to cover the sale weight/value of the birds at the time of loss only, and not the resultant losses arising from the lost weight gain between then and the anticipated clearance date. Under these circumstances there are no feed savings to deduct.
Thinning aside, it is characteristically the largest birds which succumb to heat stress, so one can expect modest (at best) savings in feed and additional mortality because there is usually only a very short period between the birds dying and their planned depopulation date if the policy is written to cover (i) above.
Depending on the farmer’s contract, any savings in catching costs can then be considered, but these may be met by the factory.
Ancillary savings such as water or litter are unlikely to be significant.          

Heat stress covers typically carry high excesses or co-insurance clauses.

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