Rainy season syndrome

Broiler farmers in Africa will agree that the constant change in weather conditions affects farm production. As the continent’s climate transforms, it alters rainfall patterns, the ambient temperature, and even the level of carbon dioxide in the atmosphere. Broiler farming depends on suitable climatic conditions such as humidity and temperature. However, over time the industry has developed a hybrid bird that has been intensively selected for rapid growth and high feed conversion efficiency. With their higher metabolic activity, these birds produce more body heat and consequently require more attention on broiler farms.

These hybrid birds are very sensitive to sudden changes in temperature and humidity, especially if either exceeds a certain range. Growing broilers will respond to excessively high temperature and humidity with increased heat dissipation by means of panting and a higher respiratory rate than we normally observe. Farmers in Zambia are experiencing such problems. Each year, from October to February, most broiler outgrowers suffer from poor growth, low feed intake, wet droppings, and dysbacteriosis. These inferior performance sends most of us on a hunt for answers, and we normally end up empty-handed.

From the latest research published by The Journal of Avian Pathology, it is clear that heat stress can cause bacterial diseases in the lower gut of broilers. The researchers, Tsiouris et al (2018), used a sample of 240 broiler chicks to test their hypothesis. They subjected each group of broiler birds to one of four treatments. The first group was a negative control, conducted at 25 degrees Celsius, which is below the heat stress threshold for broiler birds. The second group was subjected to cyclic acute heat stress at 35 degrees Celsius (in theory, challenging the birds on maintaining feed intake as well as their gut health). The third group was exposed to a bacterium, and the fourth group was subjected to heat stress as well as exposure to a bacterium.

The intestines and gizzards were later collected from each bird and inspected and scored for gross lesions. The researchers also collected intestinal digesta to determine its pH and viscosity. When they analysed the results, they could not prove that the lesions in the intestines and gizzards were directly related to the bacterial disease in the birds in the third and fourth groups above. However, they did establish that heat stress had induced necrotic enteritis outbreaks in the second, third, and fourth groups.

At Novatek Animal Feeds we refer to this occurrence as ‘rainy season syndrome’ as so many broiler farmers struggle with performance during the rainy season in Zambia. The high humidity and extreme heat induce suffering, and the birds struggle to consume the right amount of feed. Eventually we discover wet litter and identify dysbacteriosis.

The frequency of this occurrence, taken together with the above-mentioned study, provides evidence that cyclic acute heat stress is an environmental stressor which can significantly affect gut health. It should therefore be taken into account in warmer areas of Africa, where poultry farming is becoming a major industry.