Assessment of laying-bird welfare following acaricidal treatment of a commercial flock naturally infested with the poultry red mite (Dermanyssus gallinae)

Abstract

The poultry red mite (PRM), Dermanyssus gallinae, a potential vector of pathogens to animals and humans, causes impaired bird welfare. A study investigated changes in behavioural variables, physiological biomarkers, and health parameters following acaricidal treatment of PRM infestation of laying hens on a commercial farm. Mite traps determined the challenge to 12,700 hens before and after drinking water administration of the acaricide, fluralaner (Exzolt®, 0.5 mg/kg; Weeks 0 and 1). Weekly daytime direct observations and night-time video recordings monitored bird behaviours from Weeks -6 through +6. Blood samples were collected from randomly-selected birds (Weeks -6, -1, and +6). Following treatment, mite count reductions (>99%) were statistically significant (P < 0.0001), as were night-time reductions in the percent of hens showing activity, preening, head scratching (all P < 0.0001), and head shaking (P = 0.0007). Significant daytime reductions were observed in preening and head scratching (both P < 0.0001), head shaking (P = 0.0389), severe feather pecking (P = 0.0002), and aggressive behaviour (P = 0.0165). Post-treatment, comb wounds were significantly reduced (P = 0.0127), and comb colour was significantly improved (P < 0.0001). Heterophil/lymphocyte ratio was significantly reduced at Weeks 1 and 6 (P = 0.0009 and P < 0.0001, respectively). At Week 6, blood corticosterone (P = 0.0041) and total oxidant status (P < 0.0001) were significantly reduced, and haemoglobin and mean corpuscular haemoglobin significantly increased (P < 0.0001). Farm production records indicated that those post-treatment improvements were accompanied by significant reductions in weekly mortality rate (P = 0.0169), and significant recovery in mean weekly egg weights (P < 0.0001) and laying rate (P < 0.0001). The improvements in behavioural variables, physiological biomarkers, and health parameters that were observed following the elimination of PRM on a commercial farm indicate that infestations can be a cause of reduced hen welfare.

Assessment of fluralaner as a treatment in controlling Dermanyssus gallinae infestation on commercial layer farms and the potential for resulting benefits of improved bird welfare and productivity

“…In the current study, the finding on both farms that mite elimination or near-elimination was followed by an improvement in nighttime hen resting behaviour, reductions in preening and head shaking and, on the aviary farm, head scratching aligns with similar findings from a recent study on an enriched cage farm in Spain [ 17 ]. Similarly, the current study and the Spanish study both align with earlier work showing that PRM infestation results in increases in those stress-related behaviours and provide further confirmation of the effects of PRM infestation in reducing bird welfare [ 5 , 8 ].…”

“…Just a single mite was detected after Week 1 on the aviary farm, on which a calculation error resulted in administration of a dose rate 11% higher than recommended. As fluralaner efficacy on the free-range farm was equivalent to that on this farm, and as efficacy at the recommended dose rate has been consistently shown to approximate 100% on other layer farms, it can be concluded that this increase in dose rate did not affect the results, and there were no treatment-related adverse events [ 15 – 17 ]. Nonetheless, the error emphasizes the need for careful calculation of the appropriate product volume to ensure accurate delivery of the correct dose rate.…”

“…As with the daytime findings in our study, the report from Spain also described daytime reductions in head scratching, head shaking and preening following mite elimination. Physiologically, stress-related behaviours have been linked to markers of somatic stress, including increases in plasma corticosterone with the potential to lower humoral immunity, and increases in the heterophil:lymphocyte ratio [ 17 , 24 ]. However, in the current study blood and egg levels of corticosterone increased from pre-treatment to the week of treatment and increased further at the final assessments, as did the H:L ratio on the aviary farm.…”

“…All camera recordings were evaluated by a single trained observer. Hens were scored, higher scores indicating greater stress, for the behaviour categories of body shaking, vertical wing shaking, gentle feather pecking, severe feather pecking, aggression, head shaking, head scratching and preening [ 17 ]. Behavioural categories were mutually exclusive.…”

“…Adult mites are killed quickly, while any egg or non-feeding larvae present at the time of treatment are subsequently killed as they mature to nymphs and take a blood meal, with mite populations reported to decline by as much as 99% within 3 days of the first fluralaner administration and up to 100% within 2 days of the second administration [ 16 ]. Elimination of the mites in this way may reduce or remove the welfare and productivity effects of infestations [ 4 , 16 , 17 ]. A study was conducted in Europe to generate further evidence of the potential benefits of elimination of PRM infestations.…”