Dustbathing behavior: Do ectoparasites matter?

A presumed function of dustbathing behavior is to remove ectoparasites. Providing dustbathing substrates in furnished cages for laying hens might therefore offer an alternative to pesticide use to reduce ectoparasite populations. We investigated the effectiveness of dustbathing substrates for controlling northern fowl mites in individually caged beak-trimmed White Leghorn hens (N=32). Each cage contained a 32cm×32cm plastic tray that was either: (1) filled with 1200g of sand (SAND); (2) empty (CONTROL); (3) covered with Astroturf (AT); or (4) covered with AT on to which 150g of feed was delivered daily (ATF). AT and ATF are used in the dustbathing/foraging area of many newer commercial furnished cages. Hens were infested with approximately 35 mites at 25 weeks of age. Mite numbers were estimated weekly. Time spent dustbathing and dustbathing bout numbers and lengths in the tray and on the wire cage floor were determined from video recordings made for 2 consecutive days from 12:00 to 20:00h immediately before and after infestation and at weeks 1, 3, 5, and 7 post-infestation. Data were analyzed using a repeated-measures ANOVA in SAS. Treatment did not influence the total time spent dustbathing (average across substrates: 11.3min). However, there were treatment effects on the time spent dustbathing in the trays (F2,21=3.67, P=0.043) and on wire (F2,21=7.68, P=0.031). SAND and ATF hens spent more time dustbathing in the trays (11.4 and 9.1min, respectively) than AT (2.3min), and CONTROL and AT hens spent more time dustbathing on wire (11.6 and 4.7min, respectively) than ATF (0.4min). There was a treatment effect on infestation (F3,28=3.08, P=0.04), with ATF having more mites (back-transformed mean=1500) than AT (330), and with SAND (460) and CONTROL (447) intermediate. This study confirmed that the substrate type affected dustbathing behavior. SAND was a preferred dustbathing substrate but was not effective for controlling mite numbers, nor was the time spent dustbathing in any substrate or in total influenced by infestation levels. Our data also suggest that adding feed to the AT pad in furnished cages might lead to increased mite numbers in infested hens. The reason for this effect is unclear, but could be due to feed particles contributing to a change in feather structure that creates a more favorable mite habitat.