Safety of fluralaner oral solution, a novel systemic poultry red mite treatment, for chicken breeders’ reproductive performances
Huyghe et al. Parasites & Vectors
Safety of fluralaner oral solution, a novel systemic poultry red mite treatment, for chicken breeders' reproductive performances
Gaelle Le Traon
Background: Poultry mites are the most significant pest affecting production systems in the chicken egg-laying industry, altering the health condition of the birds, and causing stress, mortality and decline of egg quality impacting economic performance. Fluralaner is a novel systemic parasiticide that is effective against poultry mites (Dermanyssus gallinae, Ornithonyssus sylviarum) in chickens after oral administration. The evaluation of the safety of this new product in breeder chickens is particularly relevant because poultry mite infestation affects long cycle production systems, such as layers and breeders farms, for which the productivity heavily depends on the health of the reproductive function. This study was designed to investigate the safety for reproductive performances of fluralaner in male and female chickens at 3 times the recommended dose (1.5 instead of 0.5 mg/kg body weight) and 2 times the recommended duration (4 administrations instead of 2 administrations, with a 7 day interval between administrations). Methods: This randomized, parallel-group, blinded study included 432 Bovans brown parent stock chickens (48 males and 384 females, 17-week old). Birds were randomly assigned to 16 pens (three males and 24 females per pen), and then each pen assigned to one of the two treatment groups (8 pens, i.e. 216 birds per group). Fluralaner was administered via drinking water on a total of four occasions 7 days apart, at daily doses of 1.5 mg fluralaner/kg body weight, equivalent to 3 times the recommended dose of fluralaner per administration and 2 times the recommended number of administrations. Birds supplied with non-medicated drinking water served as controls. The treatments were given at time of peak egg production in the bird's life: i.e. at 30 to 34 week of age. During that period, all adult chickens were clinically observed. The reproductive performances were carefully monitored including the number of eggs laid, egg weight, fertility and hatchability. Furthermore, the health and viability (up to 14 days of life) of randomly selected chicks was also monitored. Results: There were no clinical findings related to fluralaner treatment. There were no statistically significant differences between the reproductive performances of treated and control groups, nor in their progeny chickens viability. Conclusions: Oral administration of fluralaner was well tolerated by breeder chickens with a safety margin of approximately 3-fold obtained. Fluralaner had no effect on the egg number, weight and fertility, and no effect on egg hatchability or chick viability. Based on these results, a safe use of the new mite treatment proposed with fluralaner administered via drinking water is expected in layer and breeder field industrial conditions.
Fluralaner; Breeder hens; Chickens; Safety; Poultry red mites; Drinking water; Parasiticide; Isoxazoline; Reproduction
The poultry red mite (Dermanyssus gallinae) is a
bloodsucking ectoparasite of domestic and feral birds, and is
particularly important in commercial layers and breeders.
Infestation by this parasite is associated with a decreased
health condition [
], stress and decline of egg quality.
Increased hen mortality is observed in severe infestations [
The egg production period (above 1 year) in the layers and
breeders industry contributes to the establishment of strong
parasite populations in facilities, which are difficult to
eradicate. The replacement of traditional cages by enriched cages
provides better hiding opportunities for poultry red mite
]. Consequently, PRM is widespread in commercial
layer and breeder facilities [
]. Few products are licensed for
use against mites in chickens [
]. Fluralaner is a novel
systemic parasiticide, inhibitor of ligand-gated chloride
channels (γ-aminobutyric acid (GABA) and L-glutamate gated
chloride channels) with significant selectivity for arthropod
neurons over mammalian neurons [
]. Fluralaner provides
efficacy against infestation with PRM in chickens after oral
administration via drinking water [
]. The recommended
treatment dosage of fluralaner oral solution for chicken is
two administrations of 0.5 mg/kg body weight, given at
7 days interval. The general safety of such fluralaner
treatment has been investigated in laying hen by Prohaczik et al.
]. The authors have shown that fluralaner is well tolerated
in poultry, with a high margin of safety. However, fluralaner
treatment against PRM is administered while birds are in lay
of infertile eggs (commercial layers) or of fertile eggs
(breeders), and no data are available on fluralaner impact on
reproductive performances in any avian species.
This study was designed to investigate more
specifically the safety for reproductive performances of this
novel parasiticide, fluralaner, in male and female
chickens at 3 times the recommended dose (1.5 instead of
0.5 mg/kg body weight) and 2 times the recommended
duration (4 administrations instead of 2 administrations,
with a 7 day interval between administrations). In this
study, the treatments were given at time of peak egg
production in the bird’s life, when the reproduction
system is the most stressed.
This randomized, parallel-group, blinded study included
parent stock chickens. Half of the chickens received
fluralaner medicated water (treated group), the other half
received standard water as negative control (control
group). The study design was based on VICH GL 43
target animal safety requirements for veterinary
pharmaceutical products [
]. This study was conducted
in USA in compliance U.S. FDA Good Laboratory
Practices (GLP) for Nonclinical Laboratory Studies 21 CFR
Seventeen week-old Bovans brown parent stock chickens
were used. A total of 648 individually identified birds
(576 females and 72 males) were assigned to a total of
24 pens. Three males and 24 females were assigned per
pen, reaching a male to female ratio of 11%, consistent
with the 9–11% recommended for the breeder industry
]. At inclusion, males weighed 1.9–2.05 kg and females
weighed 1.35–1.45 kg. Neither vaccinations nor systemic
medications were administered during the study.
Breeding conditions for parents
Pens were 8.5 m2 (equivalent 0.29 m2/bird), and
contained 4 egg nests, feeders (one for males and one for
females) and drinking nipples. Wood shaving litter
covered the pen floors. Housing conditions were in line with
the Bovans management guide [
]. Pens and litter were
inspected daily. Daily temperatures were recorded and
ranged from 1.7 °C to 22.8 °C. Daily relative humidity
was recorded and ranged between 12 and 85%. The
minimum amount of light the animals were exposed to
was measured weekly and ranged between 44.5–56.6 lx.
Birds were fed with feed according to their age,
manufactured specifically for the study according to the
Bovans management guide [
]. The same ration was
proposed to males and females during the course of the
study. The amount of feed proposed was controlled (as
per management guide), and feed consumption
recorded. Birds had free access to well water from 4
individual drinking nipples in each pen. For the water
consumption measurement and treatment periods, the
pipes connecting each pen nipple were derived for
connection to a plastic can placed above each pen.
Handling conditions for eggs and chicks
Part of the eggs laid during the study was allowed to
hatch, and some of the derived chicks were monitored
over 2 weeks post-hatching. Eggs allowed to hatch were
incubated for 21 days: eggs were set for 18 days in a
commercial incubator controlling temperature (36.7–
38.9 °C) and humidity (62–69%), then the eggs were
transferred and set for 3 days in a commercial hatcher
controlling temperature (36.1–37.2 °C) and humidity
(62–68%) to hatch the progeny. On the day of hatching,
selected trays of eggs were briefly removed from the
hatcher, evaluated, and then returned to the hatcher in
order to monitor the progress of hatching at
approximately two-hour intervals. Completion of hatching was
determined based on the number/% of chicks that
hatched, if the navel/yolk sac area was dry, and if the
feathers were dry. Hatching was considered complete
when approximately 95% of the hatched chicks had dry
feathers, and all of the eggs were removed from the
hatcher at the same time. When monitoring of hatched
chicks was required, chicks were housed in a barn, daily
temperatures and humidity were recorded and ranged
between 18.9–35.6 °C and 18–81%, respectively.
The different phases of the study are presented in Fig. 1.
Selection of treatment groups
From 17 to 29 weeks of age, the total 24 pens were
monitored for egg production and general health. All the eggs
laid during the 24th week of age were collected, and
allowed to hatch. On week 30 of age, 16 pens were selected
treatment, based on egg production, egg weights, daily
observation records, and the highest number of live chicks
hatched from eggs laid during the 24th week of age. After
randomization of the 16 pens to the two treatment groups,
all the eggs laid during the 30th week of age were collected,
allowed to hatch and 32 of the hatched chicks per group
were observed (body weight and clinical conditions) for
2 weeks post-hatching. These chicks data, together with
adult data recorded during the 30th week of age (see
Records section), were considered as baseline data.
as a 10 mg/ml solution, diluted into drinking water at 3
times the recommended treatment dose, i.e. 1.5 mg
fluralaner/kg body weight (treated group). Both groups
received a total of 4 administrations (A1 to A4) 7 days
apart, starting on first day of Week 11, until first day of
Week 14. Four administrations correspond to two times
the recommended duration of treatment. The treatment
period (4 weeks) extended for at least one estrous cycle
in females (1 day, [
]), one egg formation period
(11 days, [
]), and one spermatogenic cycle in the
males (13 days, [
]). On first administration day, the
average body weight was 2.56 kg and 2.47 kg for the
males, and 1.81 kg and 1.81 kg for the females, in the
control and treated group respectively. The body weights
of the parents were in line with the Bovans parent
performance guide [
], for birds of that age.
For each treatment group, the water consumption of
each pen was measured during 6 consecutive hours for
2 days prior to each administration. On each
administration occasion, the medicated water to be provided to
treated group was prepared by dilution of fluralaner
10 mg/ml solution into well water, based on (i) the
target dose rate (1.5 mg fluralaner/kg body weight); (ii) its
total body weight; and (iii) its overall pen 6-h water
consumption. Confirmatory analyses of the batches of
medicated water prepared were conducted to determine the
actual concentrations of fluralaner supplied to pens. On
each administration day, the amount of medicated water
provided to each pen was weighed, as well as the
amount remaining after 6 h, to determine the amount of
medicated water ingested actually by each pen. The
actual fluralaner doses consumed per pen were calculated.
The pens from the control group received
nonmedicated well water. Analysis confirmed that no
fluralaner was detected in any of the batches of water
provided to the chickens from the control group. At each
administration date, the mean fluralaner dose per pen
(treated group) achieved was 1.4 mg/kg (corresponding
to 2.8 times the recommended dose).
The 16 selected pens received either non-medicated well
water (negative control group) or, fluralaner, formulated
General health observation of the birds (including
external examination of the feathers, eyes, and beaks, as well
Negative control group
aBaseline is Week 10 (pre-treatment); post-treatment is Week 14, after the 4th treatment
as any abnormalities in behavior, locomotion and
mortality) were performed twice daily during the course of
the study, for adults and chicks.
Between week 10 to 15 of production the birds were
weighed weekly by pen.
The following variables were recorded/ calculated per
(i.) number of eggs laid (daily);
(ii.) individual egg weight (daily);
(iii.) fertility at incubation day 7 (viable eggs);
(iv.) hatchability (on incubation day 21): total (number
of chicks / number of eggs transferred ×100),
and viable (number of chicks / number of viable
eggs × 100);
(v.) chick viability on newly hatched chicks (on incubation
day 21), based on the following binomial
variables: stance, deformity, navel aspects,
hydration, down feather: color, length
(continuous variables) and dryness;
aBaseline is Week 10 (pre-treatment); post-treatment is Week 14, after the 4th treatment
Abbreviation: SD standard deviation
(vi.) chick viability at 14 days old (post hatch):
mortality rate and based on the following binomial
variables: stance, deformity, navel aspects,
hydration, down feather: color, length (continuous
variables) and dryness;
(vii.) chick body weight (at hatch and at 14 days old).
mean egg weight. Chick hatch weight, chick feather
length, and 14-day old chick weight were analyzed with
an analysis of variance. Finally, linear model was used
for adult mortality, egg fertility binomial variables
(presence of deformity, navel healed …) and 14-day old chick
Analysis of the results
The study data were evaluated for fluralaner-related
effects on the reproductive safety parameters by
comparison to the negative control group. The parameters of
primary importance in this study were: fertility,
hatchability, and chick viability/survival. The study design did
not provide for differentiating effects specific to the male
or the female. The reproductive parameters collected
before treatment period (Week 10, baseline) and at the last
week of the treatment period (Week 14, post-treatment)
were statistically compared between groups. The
duration of the treatment period (4 weeks) ensured that
eggs collected for hatching during the last week of the
treatment period were issued from ovum and sperm
exposed to fluralaner during their formation.
All statistical comparisons were performed at the 0.1
level of significance. Statistical analyses were performed
using SAS version 9.4. The pen was considered as the
statistical unit and used as random effect in the
statistical analysis. Treatment, time and sex were used as
fixed effects. Data from Week 10 served as baseline.
The following variables were analyzed with a repeated
measures analysis of covariance: feed consumption,
water consumption, pen weight, mean egg number and
Results and discussion
The hen day egg production was 94.2–96.9% (1266 to
1303 eggs were laid per group during Week 10 or Week
14 for 1344 possible eggs at a 100% hen day egg
production). These figures are higher than the production
standard proposed by Meijerhof [
] for breeders. The
hatching per egg ranged between 80.1–84.8%; in line
with the 78–90% interval for 30–34 weeks-old breeders
proposed in Meijerhof [
]. These production figures
attest to the representativeness of the study for the
breeder industry. The number of eggs and chicks per
group are presented in Table 1.
Water consumption was not affected by fluralaner
administrations (ANCOVA: F(1,13.2) = 0.00, P = 0.9622).
This is consistent with the results of Prohaczik et al. [
where no effect on water consumption was detected up
to 5× the recommended dose. Fluralaner administrations
had no detectable effect on feed consumption. No
statistical analysis was performed on feed consumption as
100% of the feed was consumed in all pens, regardless of
the group. There was no mortality observed during
the study among the adult birds, and no
treatmentrelated effects on adult bird clinical observations or
No statistically significant differences were detected
between groups for egg production and for egg weights.
Egg production and egg weights are presented in Figs. 2
There were no treatment-related differences in egg
fertility and in egg hatchability. Fertility was between 96.7–
97.4% in both groups at Week 10 and at Week 14.
Hatchability was between 84.1–87.5% in both groups at
Week 10 and at Week 14. Egg fertility and egg
hatchability results are presented in Table 2.
There were no treatment-related differences in chick
viability (newly hatched or at 14 days old) and chick
clinical observations. Chicks’ mortality at 14 days (from
eggs laid week 14) was 0% in both the treated and
control groups. For chick viability binomial variables (newly
hatched or at 14 days-old), the majority of responses
were the same and abnormal data were too sparse for
analysis (only one chick (control group) from Week 10
(baseline) was abnormal for all binomial viability
variables). Newly hatched chicks weight at week 14 chicks
was 41.7 ± 0.1 g and 41.4 ± 0.1 g in the control and the
fluralaner-treated groups respectively. Fourteen days
later, the chicks had grown to 106.1 ± 4.3 g and
104.1 ± 2.9 g for females and 105.9 ± 4.7 g and
112.1 ± 2.1 g for males, in the control and the
fluralaner-treated groups respectively. No differences
were detected between groups for chick weight (at
hatching or at 14 day-old) and down feather length.
Results are presented in Table 2.
This detailed evaluation of the reproduction safety of
fluralaner, a novel systemic parasiticide drug, following
oral administration at doses much higher than the
recommended treatment dose, did not reveal any adverse
effects in laying breeder hens. Oral administration of
fluralaner via drinking water to laying hens at dose rates
of up to 3× the recommended dose and 2 times the
recommended treatment duration did not lead to any
treatment-related findings that could be detected
through careful clinical observations of reproductive
performance of parents and health of the progeny chickens.
Oral administration of fluralaner via drinking water was
well tolerated by breeder chickens, a safety margin of
approximately 3 was demonstrated. Based on the present
results, the use of the new fluralaner treatment against
mites, administered via drinking water, is expected to be
safe for breeder chickens under field industrial
conditions, and to have no negative impact on their
CFR: Code of Federal Regulation; FDA: Food and Drug Administration;
GABA: γ-aminobutyric acid; GLP: Good laboratory practices; PRM: Poultry red
mite; VICH: Veterinary International Committee on Harmonization
The authors thank HMS Veterinary Development Inc., 3346 Avenue 248, Tulare, CA
93274, USA for assistance with the study. We very much appreciate the careful
technical support of B. Draney and J. Slightom in conduct of the research.
Availability of data and materials
The data generated or analyzed during this study are included partially in
this published article. They are the property of the sponsor and will not be
BH, AFS and GLT authored the study design. BH monitored the study and
interpreted the results. All authors revised and approved the final manuscript.
This study was conducted in the USA, in compliance with local ethical regulation,
after obtaining the authorization from MSD Animal Health Innovation ethical
Consent for publication
Authors are employees of MSD Animal Health Innovation or Intervet Inc. USA.
Springer Nature remains neutral with regard to jurisdictional claims in published
maps and institutional affiliations.
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