One of the most significant environmental challenges facing livestock farming is high temperatures, which can cause animals to suffer from heat stress if appropriate protective measures are not taken. In poultry farming, hot summer days combined with high humidity can have a negative impact on the health and welfare of the animals. Recent summers suggest that this problem will continue to be a concern for local poultry farmers in the future. This can result in high animal losses, as heat stress places a significant strain on poultry.

But how can heat-related discomfort in animals be detected at an early stage? What measures should be taken to prevent or reduce heat stress in animals?

The North Rhine-Westphalia Chamber of Agriculture provided answers to these questions in an online event organised as part of the nationwide Fokus Tierwohl network, attended by around 90 participants.

To begin with, Dr Kristian Düngelhoef, a veterinary specialist in poultry from the veterinary practice on Güterstraße, and Dirk Wonning, spokesperson for the Management Group of the Federal Association of Mobile Poultry Farming (Bundesverband mobile Geflügelhaltung e.V.), spoke about the detection and consequences of heat stress in poultry houses. Animals that are too warm can be recognised by their reluctance to move. They pant, spread their wings to increase their surface area and display highly vascularised (head) skin, according to Dr Düngelhoef. Dirk Wonning added that during heat stress, the animals’ water consumption increases whilst feed consumption decreases. Weight loss in the poultry is a further consequence.

Risk of heat stress

From an outside temperature of around 28 °C, the risk of heat stress rises sharply. “The critical upper limit is an enthalpy value of 67 kJ/kg,” said Dr Düngelhoef. Enthalpy is the measure of the thermal load of the air, taking humidity into account. These values can be accessed daily on the German Weather Service’s website and should be monitored during the summer months.

Heat-related death can occur due to circulatory failure and dehydration (insufficient water intake and loss of electrolytes) or overheating of the body. Death predominantly occurs in the evening, once the day’s maximum temperature has already been exceeded, reported Dr Düngelhoef. Long-term consequences in laying hens include reduced egg size, a decline in laying performance and poor shell quality. This can lead to neck moulting, feather pecking and cannibalism, as well as E. coli infections. In broilers, reduced growth performance and respiratory infections can occur as long-term consequences.

According to experts, the most effective management measure against heat stress is the use of spray cooling. From 8 am onwards, feed can be withdrawn from broilers to avoid placing unnecessary strain on the circulatory system due to a full gastrointestinal tract. The animals and the housing systems should be monitored continuously. Similarly, following consultation with the vet, the night-time dark period can be omitted to allow the birds to catch up on feed intake. To encourage the resting birds to move about, careful inspection rounds should be carried out during the day. Cold water should be flushed through the drinking lines several times a day at increased pressure. Ideally, the airflow should be directed straight at the animals so that heat can be dissipated. Additional fans can help in dead corners. It is also helpful to water the barn roofs and their surroundings.

If a heatwave is expected, Dr Düngelhoef recommends feeding liver protection supplements to relieve the liver and vitamin E as an antioxidant for several weeks in advance. For acute phases of heat stress, he advised stirring vitamins C, E and A, along with electrolytes, into the fresh drinking water several times a day. After a heatwave, the drinking water pipes must be cleaned, as the nutrients from supplementary feed promote the formation of a biofilm.

Spray cooling as an effective management measure against heat stress

As a practical example, Geflügelhof Höckel GmbH und Co. KG then presented their newly designed spray cooling system, developed in collaboration with Dipl.-Ing. agr. Frank von der Haar (Agrarhygiene-Wassertechnik, Ankum). In 2004, the farm switched from cage rearing to floor rearing with winter gardens. As the existing high-pressure spray cooling system in the barn area also moistened parts of the litter in the winter garden, this was replaced with external low-pressure spray cooling systems. In other barns, winter gardens were fitted with an additional corridor on the eaves side, complete with windbreak netting and low-pressure spray cooling, to ensure optimal evaporation of the water in a barrier-free space with reduced air velocity. Supply air sections with plastic cool pads serve as droplet separators and ensure that the litter does not get wet. The damp cool pads also cool the air flowing into the barn through surface evaporation and ensure a diffuse, draught-free mixing of the cooled air with the ambient air.

In the barn, a relative humidity range of 60 to 85% can be utilised for cooling. The spray cooling system consists of low-pressure nozzles and generally operates without a booster pump, using only the existing water pressure. The mist nozzles spray approx. 5 litres of water per hour at a pressure of 3 bar, whereby approx. 6 ml of water per m³ of air can evaporate within the humidity range, depending on air velocity and ambient temperature. The system is controlled by a barn computer. “It is crucial to work with short cycles. Under no circumstances should the humidity in the house be allowed to rise above 85%,” says von der Haar. He recommends spraying for a maximum of 1 to 2 minutes indoors, followed by a break of approximately 5 minutes to allow the ventilation system to remove the introduced moisture from the house. This ensures optimal utilisation of the evaporative energy.

Low-pressure cooling only works for laying hens; for broiler poultry, however, Frank von der Haar recommends high-pressure cooling. The advantages of the significantly cheaper low-pressure cooling system are its operational reliability and the possibility of using water-based disinfectants or essential oils. One recommendation is to always use hygienically impeccable fresh water of drinking water quality and to avoid using Coolpad recirculation systems with pumps and circulating service water. Increasing contamination and bacterial load then contaminate the supply air, and the constantly warming recirculating water also reduces cooling performance. In emergencies, roofs are frequently sprayed with water. It should be borne in mind that this solution involves wetting hot roof surfaces (up to 70 °C) with water at around 6 °C, which places extreme stress on the roofing material and can drastically reduce its lifespan. 

Author: Viola Erfkämper, North Rhine-Westphalia Chamber of Agriculture

Published in Land & Forst, Issue 24/2021