Wageningen University: Indicators for bird flu on duck farms

Wageningen Bioveterinary Research (WBVR) investigated if and to what degree mortality and production data could signal possible outbreaks of avian influenza on duck farms. Research shows that a daily mortality rate of 0.3% is a reliable indicator for a possible bird flu infection. Moreover, a decrease of 9% or more in daily egg production also indicates a possible outbreak.

This study was commissioned by the Ministry of Agriculture, Nature and Food Quality (Dutch acronym LNV) and is published in Pathogens.

Value of early bird flu detection
Avian influenza is the cause of serious illness and high mortality in poultry. Increased mortality, decreased production, stunted growth and reduced food and water intake could be used as indicators to report a suspected outbreak to the veterinary authorities. Reporting a suspected outbreak as early as possible is essential in preventing the disease from spreading.

Rules for reporting suspicious situations
Dutch law stipulates that a veterinarian and the government veterinary services must be consulted for hens, breeding animals, broilers and turkeys when certain criteria pass a critical threshold. To date, similar legislation had not been determined for ducks. The general rule that the appropriate parties must be informed if the weekly mortality exceeds 3% is insufficient as this results in a considerable delay in reporting, allowing the infection to spread before it is reported. Avian influenza in commercially farmed ducks and geese generally does not cause serious illness, further contributing to delays in reporting suspicious situations. In recent years, however, several countries, among which the Netherlands, have seen increased mortality rates and decreased production on duck farms during outbreaks of the bird flu.

Collecting data
Wageningen Bioveterinary Research has collected data on the daily mortality, egg production, feed and water intake of flocks of breeding and broiler ducks. The data was collected from ducks that were infected with avian influenza and those that were healthy, both in the Netherlands and abroad. Data from the healthy ducks was used to establish a baseline in the daily mortality and production parameters, and thus the threshold values that could indicate an infection with bird flu. Data from infected birds was used to see what the effect of infection is on the daily mortality and production and to evaluate the accuracy of the early detection thresholds.

Indicators for avian influenza in ducks
Armin Elbers, who works as an epidemiologist at WBVR, states: ‘A daily mortality rate of over 0.3% (after the first week of life at the farm) could be an excellent indicator for broiler ducks. A decrease in the daily food and water intake of more than 7 grams or 14 ml respectively are also accurate indicators of avian influenza infection. For breeding ducks, the available data is limited. The mortality in three flocks of breeding ducks in Germany was very limited after an infection. The British flock, however, showed rapid mortality. Applying the threshold value of 0.3% mortality is recommended for all breeding and reproduction ducks. A decrease in egg production of over 9% is also a very effective indicator of a bird flu outbreak in breeding and laying ducks.’

The established thresholds can be used to inform duck farmers and veterinarians to report suspected outbreaks of high pathogenic avian influenza (HPAI) in commercially kept ducks.