A smother in a poultry shed is something that every producer dreads. Claire Knott of Crowshall Veterinary Services details the advice.

Smothering incidents can result in heavy losses, and it is not always easy to discover the cause and put preventive measures in place.

Smothering occurs when birds group together or pile up to such an extent that birds at the bottom of the pile suffocate or become crushed. Following a smother, other birds may die from stress, or as a result of scratching damage. Yolk peritonitis, or bacterial infection entering via skin scratches, can also add to losses.

What is smothering?

Bird behaviour leading to smothering falls into two distinct categories:

Sudden smothers

These occur most commonly when birds have suffered a fright. It can be caused by a sudden noise, hot-air balloons, helicopters or birds of prey in the vicinity, strangers walking into the sheds, or marked changes in lighting.

Night-time feed deliveries may also disturb the flock. Smothering can occur in cold weather, when birds huddle together for warmth.

Smothered birds normally pile up in corners. Although losses may be significant, a smother is usually a one-off incident. However, if there is some prolonged stress factor, smothering may occur repeatedly. In such cases, it is important to try and identify the trigger factors.

Measures aimed at reducing the risk of birds suffering a fright are normally of a practical nature. Arranging daytime deliveries to avoid lorry lights shining into the house is one example. A reduction in the number of visitors entering the house may also help, especially if a particular flock appears nervous.

Unfortunately, removal of the cause may not always solve the problem, as sudden smothers can become habitual in some flocks.

One danger period occurs when flocks are coming into lay. It is possible to see nestbox smothers, especially when birds come into production rapidly and there is competition for nestbox space. Even in a house with ample nestboxes, birds may favour a particular nest. It may be necessary to close off problem nests, until full nesting behaviour and better bird distribution has developed.

Creeping together

The second type of smothering is often referred to as "creeping together." Birds may pile up in the middle of sheds, or even outside on the range.

It can be very difficult to pinpoint the reason for this behaviour. Although mortality may often be lower in these cases, this form of smothering can occur periodically on the same farm. It may be more common in some breeds than others, possibly related to docility, as well as the tendency of some strains to want to flock together more, compared with more "aloof" strains.

When is smothering most likely to occur?

Smothering incidents are most commonly reported in rearing birds aged between 10 and 13 weeks, and at the onset of production at between 20 and 28 weeks, with the latter being the peak risk period.

Stress is believed to be a trigger, and there have been cases seen with all brown egg layer strains. The majority of smothers occur in the afternoon, following egg laying.

Peak risk period for smothering is at the onset of production, between 20 and 28 weeks.

What are the possible causes?

Fear

While experts do not fully understand the triggers for smothering in all cases, fear is thought to be one of the principal causes. Sudden frights which cause birds to panic and pile up are to blame in some cases.

However, there may be more subtle triggers, which make birds feel uncomfortable or apprehensive about their surroundings, encouraging them to huddle together for security.

In the wild, hens are attracted by shade, which affords a degree of protection from predators from above. It is possible that light intensity within a shed may play a role in influencing smothering behaviour.

Stress factors

Stress may occur in a flock for many different reasons, for example, if birds are underweight, if feed or water is restricted, or if feed intake is too low for other reasons. High production flocks may be more vulnerable to stress, because of the demands placed on their bodies during egg laying.

General ill health through red mite, worms or other diseases may also lead to dull birds seeking solace in the company of others.

Feeding

Nutrition may also play a part in smothering, particularly if the content of the feed does not meet the birds' requirements. Feeding at inappropriate times, such as when the birds are using the nesting area, may also increase the risk.

Other possible causes

Draughty sheds or exposure to extremes of temperature may also trigger smothering. There is no evidence to show that a single house type or design appears to make the birds more vulnerable to smothering.

How can I reduce the risk of smothering?

Risk reduction relies on identifying trigger factors, wherever possible. Time feeding activity, so that birds get into the habit of virtually clearing the tracks in the break between feeds in the middle of the day. This will keep them occupied, and encourage them to look for feed when they are given their afternoon ration.

Care must be taken, however, to make sure that feed intake is never restricted. If it suspected that nutritional stress may be the involved, increasing the crude fibre content of the ration may also be helpful.

If birds smother in the same area of a shed more than once, a pallet placed on the floor in that area will discourage the behaviour and allow birds at the bottom of a smother to breathe.

Running an electric wire along walls and corners of the housing, using low voltage netting or wires, is another way to physically prevent birds from entering problem areas.

Changing the time clocks is another potentially useful intervention. For one day, adjust the lighting to an hour early. A break in routine may break the smothering habit.

Ask staff and visitors to speak to the birds or knock on the door before entering the shed. Where flocks are very flighty, do not permit large numbers of visitors in the shed at any one time.

When walking through the shed to collect eggs or inspect the birds, vary the route taken. It may be advisable to increase the number of flock inspections, particularly at times when smothering has occurred in the past.

Walk through the house reasonably quickly, but not so fast as to alarm the birds. This will avoid the problem of birds congregating in one area.

If blood samples need to be taken, it is better to remove birds to the service area, rather than spending a prolonged period in one part of the shed. The desire to perch may also be a trigger; therefore additional perches can reduce the risk.