Dermanyssus gallinae in Dutch poultry farms: Results of a questionnaire on severity, control treatments, cleaning, and biosecurity

In 2005 a questionnaire has been sent to 1,390 Dutch poultry farmers to investigate the severity of the poultry red mite (PRM) as a pest problem in The Netherlands. The response rate amounted to 31%. As the questions were not independent of each other, four clusters of questions were formed, based on two observed, discrete variables: (1) directly visible PRM infestation, and (2) indirect signs of the presence of PRM. Respondents were distributed over the most common housing systems in The Netherlands and reflected the Dutch situation with regards to housing of laying hens quite well. More than 80% of the poultry farmers reported infestations of PRM. Chicken flocks without PRM problems were significantly younger than flocks where (signs of) PRM infestation were observed. Where poultry was housed in battery cages, more farmers reported problems with PRM infestations, they tend to apply the first control treatment earlier, and repeat it more often than farmers with poultry in other housing systems. When PRM or signs of PRM were reported, farmers more often applied a combination of control treatments. The mean costs paid for control treatments and the costs incurred in terms of production losses were estimated to be € 0.43 per hen in an average flock. Given that there are 300 million layer hens in Dutch poultry houses and that ca. 85% of the flocks are PRMinfested, the overall annual cost to the national poultry industry is estimated at € 11 million. Since the answers to the questionnaire revealed a significant underuse of several measures that could prevent PRM infestation, there is room for improvement by more stringent management.