The most common and economically significant ectoparasite in laying hen houses is the red bird mite. This parasite, which measures approximately 0.7–1.1 mm in length, primarily attacks its host at night to feed on blood. While the laying hen is the main host for the red bird mite, other poultry species can also be infested. Controlling the red bird mite is a long-standing problem in laying hen farming. The parasites can sometimes go without food for months and thus survive for months even in unoccupied houses. Controlling them is particularly challenging due to their rapid development of resistance and tenacious ability to survive.

Dr Thorsten Arnold explained in a webinar that controlling these mites is only successful if treatment is consistently repeated after at least seven days. This is because this corresponds to the typical life cycle of the mites. However, the development cycle of mites is temperature-dependent and may vary. For example, no eggs are laid at temperatures below approximately 9°C, and eggs already laid do not develop further. In contrast, at temperatures of 32°C or above, the first mite eggs are laid after just 8 hours, and these hatch after 36 hours.

But why do these parasites pose a problem in poultry farming? On the one hand, the parasites cause restlessness in the flock, behavioural disorders and dirty eggs. On the other hand, a mite infestation leads to reduced weight gain, a drop in laying performance and can even result in the loss of birds due to anaemia. Furthermore, the parasites also transmit diseases between the hens. Thus, a mite infestation can severely impair the flock’s health. Another point is that mites can also affect human health (among animal carers), for example more frequently through allergies or, very rarely, through bites. To manage the negative consequences of a severe mite infestation in a laying hen flock, the following points should be observed in mite prevention and control:

Even whilst the house is empty, all surfaces should be sprayed with mite-effective agents before the equipment is removed, so that most mites and eggs are destroyed. Subsequently, all movable equipment should be removed from the house, as well as all nesting material, so that all corners and thus hiding places for the parasites are exposed. The walls and fixtures should then be thoroughly cleaned with a high-pressure washer to flush out any remaining mites. These measures should be carried out promptly after the flock has been removed, whilst the house is still warm and before the mites can hide deeper within the crevices of the house fixtures. Before the coop is restocked, all potential mite hiding places should be sprayed intensively once more to ensure that any mites present are killed before the next batch of birds is introduced. Generally, the vet recommends drawing up a hygiene plan setting out the exact procedures.

There are generally four different control strategies for the red bird mite:

Chemical control

In this group, there is a prescription-only product for control with a 0-day waiting period for eggs, which is highly effective but very expensive. For treatment of the animals, the product can simply be administered via the drinking water. Furthermore, there are products that may be used in occupied stables but not on the animals themselves.  These vary greatly in effectiveness and should only be used after careful consideration. The mite population develops resistance to these products very quickly, so the active ingredients should be changed regularly. In cases of frequent, severe infestation, it is advisable to test the mites for resistance to these agents.

Biological control

This involves administering various herbal extracts via the drinking water or using predatory mites. However, it should be noted that predatory mites react to other mite control agents. Accordingly, predatory mites should not be used in conjunction with other agents effective against mites. The use of predatory mites requires particular care on the part of the animal keeper, as the predatory mite needs to be looked after when it is introduced. The use of herbal extracts requires a high degree of consistency, as it must be carried out regularly and the mites are only partially killed, but prevented from feeding on blood. These products help to reduce mite pressure and can form part of a mite control strategy.

Physical control

The entire barn is heated to around 60°C or the surfaces in the barn are cooled significantly by applying liquid nitrogen. However, this method is very costly.

Biophysical control

In this method, for example, amorphous diatomaceous earth is applied as a dust or in liquid form. This penetrates the mites’ respiratory organs, causing them to dry out. Furthermore, the fine dust blocks the joints, leading to the immobilisation of the parasites.

At the end of the seminar, Dr Thorsten Arnold reiterated: “The key to successful mite control under practical conditions is not only the selection of the right product, but also professional application by motivated staff.”

Author: Regine Revermann, Lower Saxony Chamber of Agriculture