R E S E A R C H Open Access
Nutritional effects of the dietary inclusion
of partially defatted Hermetia illucens larva
meal in Muscovy duck
, Sihem Dabbou
, Ilaria Biasato
, Maria Teresa Capucchio
, Elena Colombino
, Josefa Madrid
, Silvia Martínez
, Francesco Gai
, Christian Caimi
, Sara Bellezza Oddon
, Angela Trocino
, Riccardo Vincenzi
, Laura Gasco
and Achille Schiavone
Background: The present work is aimed at evaluating the effect of different inclusion levels of a partially defatted
black soldier fly (Hermetia illucens, L.; HI) larva meal for ducks. A total of 192 female 3-day-old Muscovy ducklings
(Cairina moschata domestica, Canedins R71 L White, Grimaud Freres Selection, France) were divided into 4 groups,
assigned 4 different dietary treatments (6 replicates/treatment and 8 birds/replicate) and reared from 3 to 50 days
of age. HI larva meal was included at increasing levels (0, 3%, 6% and 9%, HI0, HI3, HI6 and HI9, respectively) in
isonitrogenous and isoenergetic diets formulated for 3 feeding phases: starter (3–17 days of age), grower (18–38 days of
age) and finisher (39–50 days of age). The growth performance and apparent total tract digestibility were evaluated
during the trial using titanium dioxide as an inert marker (0.3% of inclusion). At 51days of age, two birds per pen were
slaughtered and histomorphological investigations were performed.
Results: The live weight and average daily gain showed a quadratic response to increasing HI meal in the grower
period (minimum corresponding to the HI6 group). No effects of dietary inclusion levels were observed for the daily
feed intake or feed conversion ratio. The apparent dry matter and organic matter digestibility were not affected by the
dietary treatment. A linear decrease was observed for the crude protein apparent digestibility in the starter period
(minimum for the HI9 groups). The ether extract apparent digestibility increased linearly during the grower and
finisher periods (minimum for the HI0 group). The morphometric indices were not influenced by the dietary
Conclusions: The inclusion of up to 9% of HI partially defatted larva meal in the diet of ducks did not cause any
effect on growth performance, as well as the apparent digestibility. Moreover, dietary HI inclusion preserved the
physiological intestinal development.
Keywords: Black soldier fly, Digestibility, Ducks, Histopathology, Insect, Performance
With an increase of 1.8% per year estimated until 2050,
poultry production is one of the fastest growing sectors .
The production of duck meat has undergone a great ex-
pansion in recent years, passing from 2.23 million tonnes
in 1996 to over 4.5 million tonnes in 2016 . Duck
production plays an important role in Italy, with 3.27 thou-
sand tonnes being produced in 2017 . Duck farming has
ducers of animal proteins and may contribute to the future
nutritional needs of the growing world population .
The reduced availability of natural resources and the
environmental impact of vegetable production require
the research of alternative forms of protein for animal
production. Considering the feeding habits of birds, in-
cluding poultry (chicken, duck, turkey and geese), in-
sects can represent a valuable alternative to the common
© The Author(s). 2019 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0
International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and
reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to
the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver
(http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.
* Correspondence: email@example.com
Department of Agricultural, Forest and Food Sciences, University of Turin,
largo Paolo Braccini 2, Turin, Grugliasco 10095, Italy
Institute of Science of Food Production, National Research Council, largo
Paolo Braccini 2, Turin, Grugliasco 10095, Italy
Full list of author information is available at the end of the article
Gariglio et al. Journal of Animal Science and Biotechnology (2019) 10:37
protein sources, thanks to their nutritional characteris-
tics . The use of insects in feeds leads to advantages
from both an environmental and nutritional point of
view. Compared to conventional vegetable protein
sources, insects rearing requires very little soil and water,
and their low emission of greenhouse gases and ammo-
nia implies an overall low environmental impact. A
study conducted by an EU initiative PROteINSECT esti-
mated that 1 ha of land can produce up to 150 tons of
insect protein per year. Instead, 1 ha of land can produce
less than 1 ton of soybean protein . Moreover, insects
can be reared on organic waste (such as fruit and vege-
table) and can converting them into nutrients of high
biological value, thanks to their high feed conversion ef-
ficiency [7,8]. Researchers have recently been evaluating
the use of insects in animal feeding, and they have
highlighted that insects could be used as a partial or
total substitute for the currently used protein sources.
The most promising species are Hermetia illucens (HI)
[9–12], Musca domestica [13,14] and Tenebrio molitor
(TM) [15–18]. Thanks to the favourable nutrient com-
position of HI, in terms of protein content (37–63%),
amino acid profile, fat content (7–39%) and other
macro- and micronutrients, it could be considered a
valuable alternative to common protein sources, such as
soybean meal (SBM) . The effects of the inclusion of
HI larva meal and oil on growth performance have been
investigated in many studies [10–12,20–22], with con-
flicting results being obtained. Only a few works are
available regarding the digestibility of HI meal in poultry
[9,10,22–24] and these show extremely variable results
in terms of dry matter (DM), crude protein (CP) and
ether extract (EE). In these studies, nutrient digestibility
was frequently influenced, according to the authors’in-
terpretation, by the chitin content of the diets, which
can negatively affect digestibility. Despite the limited
availability of studies, the evaluation of the gut histomor-
phometry represents a relevant research topic, since it
could affect the growth performance and the digestibility
of a diet , depending on the protein source and level
of the diet [26,27]. A recent study by Cutrignelli et al.
 has found that the inclusion of HI larva meal in lay-
ing hen diets significantly affects the gut histomorpho-
metry, resulting in a lower villi-to-crypt ratio than SBM
group. The above-mentioned studies have shown a wide
variability and more research is required to obtain a bet-
ter understanding of the effect of the inclusion of HI in
To date, no research has investigated the possibility of
including insect meal in duck diet. Therefore, the aim of
the study was to evaluate the growth performance, di-
gestibility and intestinal morphology of female broiler
ducks (Cairina moschata domestica) fed diets including
Materials and methods
Birds and husbandry
The present trial was performed at the poultry facility of
the University of Turin (Italy). The experimental proto-
col (Prot. No. 380576, 4
December 2017) was approved
by the Bioethical Committee of the University of Turin
(Italy). The poultry house was 7 m wide × 50 m long × 7
m high, and was equipped with a waterproof floor and
walls, completely covered by tiles and had an automatic
ventilation system. A total of 192, 3-day-old, females
Muscovy ducks (Canedins R71 L White, Grimaud Freres
Selection, France) were housed in 24 pens and randomly
allotted 4 dietary treatments, each group consisting of 6
pens as replicates with 8 birds per pen (average live weight
(LW): 71.32 ± 2.95 g). Each pen was 1.20 m wide × 2.20 m
long and was covered with rice hulls as litter. During the
first 3 weeks, the animals were heated by infrared lamps.
The lighting schedule was 23 h light : 1 h darkness until
day 3 of the trial, and thereafter the dark period was grad-
ually increased to 6 h and maintained constant until
slaughtering. The environmental parameters were moni-
tored daily during the whole period of the trial.
Four dietary treatments were obtained in which increas-
ing levels of a partially defatted HI larva meal (Hermetia
Deutschland GmbH & Co KG, Baruth/Mark, Germany)
were included. In order to assess the effect of HI meal
inclusion in the diets, HI meal was included as a substi-
tute to gluten meal, a commonly used raw material in
commercial duck feeding, which nutritional value is
comparable to HI meal.
The control group (HI0) was fed a diet without insect
meal (9% inclusion of corn gluten meal); 3%, 6% and 9%
of the gluten meal was substituted with HI larva meals
in the HI3, HI6, and HI9 diets, respectively (Table 1).
The diets were isonitrogenous and isoenergetic and
were formulated using the apparent metabolisable en-
ergy (AMEn) values for a partially defatted HI, which
had been calculated by Schiavone et al.  and accord-
ing to INRA for the other ingredients  both for
broiler chickens. The essential amino acids requirements
were calculated with matrix value for digestible amino
acids according to Schiavone et al.  for HI meal and
Pingel et al.  for the other ingredients, for chickens and
ducks, respectively. Feed and water were provided ad libi-
tum throughout the trial. A 3-phase feeding program was
applied: a starter diet (days 3 to 17), a grower diet (days 18
to 38) and a finisher diet (days 39 to 51).
Chemical analysis of the HI meal and experimental diets
The experimental diets were ground to pass through a
0.5-mm sieve and stored in airtight plastic containers.
Gariglio et al. Journal of Animal Science and Biotechnology (2019) 10:37 Page 2 of 10
HI larva meal and the experimental diets were analysed
for DM (AOAC, method number #934.01), ash (AOAC,
method number #942.05), CP (AOAC, method number
#984.13), neutral detergent fiber (NDF; AOAC, method
number #2002.04) and acid detergent fiber (ADF; AOAC
method number #973.18) . The EE (AOAC, method
number #2003.05) was determined according to Inter-
national AOAC .
Table 1 Ingredients (g/kg as fed) and nutrient composition (%) of the experimental diets
Ingredients Starter period (days 3 to 17) Grower period (days 18 to 38) Finisher period (days 39 to 50)
HI0 HI3 HI6 HI9 HI0 HI3 HI6 HI9 HI0 HI3 HI6 HI9
Corn meal 600.0 600.0 600.0 600.0 638.0 638.0 638.0 638.0 670.0 670.0 670.0 670.0
Soybean meal 212.0 212.0 212.0 212.0 160.0 160.0 160.0 160.0 100.0 100.0 100.0 100.0
HI larva meal 0.0 30.0 60.0 90.0 0.0 30.0 60.0 90.0 0.0 30.0 60.0 90.0
Bran 42.5 42.5 42.5 42.5 36.3 36.3 36.3 36.3 66.2 66.2 66.2 66.2
Corn gluten meal 90.0 60.0 30.0 0.0 90.0 60.0 30.0 0.0 90.0 60.0 30.0 0.0
Soybean oil 16.5 16.5 16.5 16.5 28.5 28.5 28.5 28.5 34.5 34.5 34.5 34.5
Dicalcium phosphate 10.0 10.0 10.0 10.0 13.0 13.0 13.0 13.0 4.0 4.0 4.0 4.0
Calcium carbonate 8.0 8.0 8.0 8.0 14.0 14.0 14.0 14.0 17.4 17.4 17.4 17.4
Sodium chloride 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5
Sodium bicarbonate 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0
DL-methionine 2.5 2.5 2.6 2.8 1.7 1.8 1.9 2.2 0.3 0.4 0.5 0.8
L-lysine 3.9 3.9 3.8 3.6 3.9 3.8 3.7 3.4 3.0 2.9 2.8 2.5
5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0
Choline chloride 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1
Optifos 250 bro 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0
Avizyme 1500× 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0
Titanium dioxide 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0
Total 1,000 1,000 1,000 1,000 1,000 1,000 1,000 1,000 1,000 1,000 1,000 1,000
, kcal/kg 2,897 2,892 2,888 2,884 2,994 2,990 2,986 2,981 3,052 3,048 3,044 3,040
DM, % 89.3 89.8 90.1 89.7 88.8 89.2 89.1 89.1 88.7 89.0 89.3 88.9
CP, % DM 25.1 24.7 25.2 24.8 23.0 22.5 22.5 22.4 20.2 20.2 20.1 20.1
EE, % DM 4.7 4.8 4.9 5.1 6.2 6.2 6.4 6.6 7.3 7.4 7.6 7.7
NDF, % DM 12.7 12.3 12.7 12.4 12.9 13.1 12.6 12.7 12.7 13.1 12.7 12.9
ADF, % DM 3.4 3.5 3.7 3.3 3.5 3.5 3.7 3.5 3.4 3.5 3.5 3.4
Ash, % DM 5.6 6.0 5.6 5.8 7.8 7.5 7.5 8.0 6.5 6.4 6.9 6.7
Fatty acid composition, % of total FAME
SFA 19.0 20.7 23.9 26.9 17.7 20.2 22.5 25.5 17.3 19.4 22.2 23.7
MUFA 27.6 26.1 25.5 24.6 25.8 24.9 24.2 23.5 24.9 24.8 23.8 23.8
PUFA 52.8 52.6 49.9 47.9 55.9 54.4 52.7 50.5 57.2 55.3 53.5 51.8
PUFA/SFA 2.78 2.54 2.08 1.78 3.15 2.69 2.34 1.98 3.31 2.85 2.40 2.18
∑n-3 3.3 3.4 3.4 3.3 4.1 4.2 4.1 4.1 4.5 4.5 5.3 5.0
∑n-6 49.1 48.9 46.1 44.3 51.6 49.9 48.2 46.1 52.3 50.4 47.9 46.4
∑n-6/∑n-3 14.88 14.38 13.56 13.42 12.58 11.88 11.76 11.24 11.62 11.20 9.04 9.28
HI Hermetia illucens,AMEn apparent metabolisable energy, DM dry matter, CP crude protein, EE ether extract, NDF neutral detergent fiber, ADF acid detergent
fiber, FAME fatty acid methyl esters, SFA saturated fatty acids, MUFA monounsaturated fatty acids, PUFA polyunsaturated fatty acids
Four dietary treatments: HI0 = control; HI3 = 3% inclusion level of Hermetia illucens; HI6 = 6% inclusion level of Hermetia illucens; HI9 = 9% inclusion level of Hermetia illucens
Mineral-vitamin premix: vitamin A (retinyl acetate), 12,500 IU; vitamin D
(cholecalciferol), 3,500 IU; vitamin E (DL-a-tocopheryl acetate), 40 mg; vitamin K
(menadione sodium bisulfite), 2.0 mg biotin, 0.20mg; thiamine, 2.0 mg; riboflavin, 6.0 mg; pantothenate, 15.21 mg; niacin, 40.0 mg; choline, 750.0 mg pyridoxine,
4.0 mg; folic acid, 0.75mg; vitamin B
, 0.03 mg; Mn, 70mg; Zn, 62.15 mg; Fe, 50.0 mg; Cu, 7.0 mg; I, 0.25mg; Se, 0.25 mg
Calculated according to Schiavone et al.  for HI meal and INRA  for the other ingredients
The chemical analyses were carried out on three replicates of each feed sample
Gariglio et al. Journal of Animal Science and Biotechnology (2019) 10:37 Page 3 of 10
The chitin content of HI meal was determined accord-
ing to Finke et al.  using ADF adjusted for its nitrogen
In order to perform the amino acids determination in
HI meal, samples were prepared using a 22-h hydrolysis
step in 6 mol/L HCl at 112 °C under a nitrogen atmos-
phere. Performic acid oxidation occurred prior to acid
hydrolysis for methionine and cystine. The amino acids
in hydrolysate was determined by means of HPLC after
postcolumn derivatization, according to the procedure
described by Madrid et al. . Tryptophan was not de-
termined. The lipid extraction and fatty acids profiling
of the experimental diets [34–36] were carried out at the
laboratory of the Department of Animal Medicine, Pro-
duction and Health, University of Padua, Legnaro, Italy
according to the method of Christie . All the analysis
were performed in triplicate (Table 1).
The chemical composition of the HI meal was the fol-
lowing: DM, 92.41 g/kg; CP, 56.71% DM; EE, 10.70% DM;
ash, 16.38% DM; chitin, 6.43% DM; DL-methionine, 0.63%
DM and L-lysine, 1.89% DM.
Birds were individually labeled with a wing mark and
weighed at their arrival. Mortality and clinical signs of ill-
ness were monitored daily throughout the trial. The live
weight (LW) of the animals was recorded at an individual
level at the beginning and at the end of each feeding phase
(3, 17, 38 and 50 days of age), and the feeds were removed
2 h before the birds were weighed. The average daily gain
(ADG) and average daily feed intake (DFI) were recorded
at a pen level at the end of each growth period.
The feed conversion ratio (FCR) was calculated for
each growth period and for the overall experimental
period. All the measurements were made using elec-
tronic scales (Sartorius-Signum®, Bovenden, Germany).
The digestibility trial was performed at the end of each
feeding phase using titanium dioxide (TiO
, 0.3 g/kg) as
an indigestible marker in each experimental diet (Table 1),
in order to evaluate the apparent total tract digestibility
coefficients (ATTDC). The Kaczmarek et al. method
was used to collect the excreta, with slight modifications,
as reported by Dabbou et al. . Briefly, all the birds were
removed from each pen and housed in wire-mesh cages
(n= 6 replicates) for approximately 1 h/d for four con-
secutive days to collect fresh excreta samples.
After collection, the excreta samples, from which the
feathers and litter had been removed, were immediately
frozen at −20 °C. At the end of each collection period, the
excreta were pooled, lyophilized, grounded and stored at
4 °C. All the analyses were carried out on two replicates
for each sample. The ATTDC was evaluated for DM, CP,
EE and OM. The uric acid (UA) content in the excreta
samples was determined spectrophotometrically (UNI-
CAN UV–Vis Spectrometry, Helios Gamma, the United
Kingdom) according to the Marquardt method . The
nitrogen contained in uric acid is the 33.33%. The CP
amount in the excreta (CP corrected) was calculated using
the excreta CP, corrected for UA as follows:
CP corrected ¼total nitrogen UA‐nitrogenðÞ6:25:
content was measured on a UV spectropho-
tometer (UNICAN UV–vis Spectrometry, Helios
Gamma, the United Kingdom) following the Myers et al.
 method .
The ATTDC of the dietary nutrients was calculated
using the following method :
ATTDC Xdiet ¼Total X ingested−total X excretedðÞ
total X ingested
Digestibility ¼%Xdiet =%TiOdiet
where Xrepresents DM, CP, EE or OM.
At 50 days of age, the final LW of the birds was recorded
individually and 12 ducks per diet (two birds per pen)
were chosen on the basis of the LW pen average and
identified by means of a shank ring. Then the feed was
removed and, after 12 h of fasting (at 51 days of age), the
selected animals were transferred to a commercial abat-
toir and slaughtered by electrical stunning and bleeding,
according to the standard EU regulations. The plucked
and eviscerated carcasses were obtained, the head, neck
and feet were removed.
Gut segments (approximately 5 cm in length, 12 animals
per each group) of the duodenum, jejunum and ileum
were sampled during slaughtering and flushed with 0.9%
saline to remove all the contents. The collected intestine
segments were the loop of the duodenum, the tract be-
fore Meckel’s diverticulum (jejunum) and the tract be-
fore the ileocolic junction (ileum). The gut samples were
fixed in a 10% buffered formalin solution, routinely em-
bedded in paraffin wax blocks, sectioned at a 5-μm
thickness, mounted on glass slides and stained with
Haematoxylin & Eosin (HE) for morphometric analysis.
The evaluated morphometric indices were as follows: vil-
lus height (Vh, from the tip of the villus to the crypt),
crypt depth (Cd, from the base of the villus to the sub-
mucosa) and the villus height-to-crypt depth (Vh/Cd)
ratio . Morphometric analyses were performed on 10
Gariglio et al. Journal of Animal Science and Biotechnology (2019) 10:37 Page 4 of 10
well-oriented and intact villi and 10 crypts chosen from
the duodenum, jejunum and ileum .
The statistical analyses were performed using the SPSS
software package (version 21 for Windows, SPSS Inc.,
Chicago, IL, USA). The mortality rate was analysed by
means of a Chi-square test, using the HI0 group as the
reference. Shapiro-Wilk’s test established normality or
non-normality of distribution. The assumption of equal
variances was assessed by means of Levene’s homogen-
eity of variance test. The experimental unit was the pen
for growth performance and digestibility, while the duck
was used for the intestinal morphology. The collected
data were tested by means of one-way ANOVA. Polyno-
mial contrasts were used to test the linear and quadratic
responses to increases in the HI inclusion level in the
diet. Intestinal morphometric indices were analysed by
fitting a general linear mixed model (GLMM). GLMM
allowed the morphometric indices (Vh, Cd and Vh/Cd,
separately) to depend on three fixed factors (diet, intes-
tinal segment and interaction between diet and intestinal
segment). Animal was included as a random effect to ac-
count for repeated measurements in the same duck. The
interactions between the levels of the fixed factors were
evaluated by means of pairwise comparisons.
Differences among treatments were considered statisti-
cally significant when the Pvalues ≤0.05.
The cumulative mortality rates of the HI0 (4.16%), HI3
(2.08%), HI6 (2.08%) and HI9 (2.08%) groups were not
influenced by the dietary treatments (P> 0.05). The
growth performances of the broiler ducks are summa-
rized in Table 2. Overall LW was not influenced by the
dietary treatments (P> 0.05), except at 38 days of age,
when a quadratic response was observed in LW for in-
creasing HI meal levels with a minimum being observed
for the HI6 group (P< 0.05).
ADG was not affected by the dietary treatments (P>0.05),
with the exception of the HI6 group in the second period
(18–38 days of age), where the ADG showed a quadratic
response (P< 0.05). DFI and FCR were not affected by the
dietary treatment nor in the different feeding phases or
over the whole experimental trial (P>0.05).
The apparent digestibility coefficients are reported in
Table 3. DM digestibility was not affected by the dietary
treatment throughout the trial, as well as the OM
(P> 0.05). In the starter period (3–17 days of age) the CP
digestibility decreased linearly with a minimum
corresponding to the HI9 groups (P<0.05)(–4.11%
compared to HI0, respectively), whereas the EE digestibil-
ity decreased linearly with the inclusion of HI in the diets
Table 2 Effect of the dietary HI larva meal inclusion on the growth performance of female ducks (n=6)
Items Age Dietary treatments
HI0 HI3 HI6 HI9 Linear Quadratic
LW, g 3 d 70.70 70.41 72.65 71.51 0.60 0.405 0.733
17 d 575.44 567.31 572.56 575.74 4.76 0.893 0.582
38 d 1906.79 1861.96 1797.10 1900.12 14.18 0.426 0.005
50 d 2540.57 2511.14 2456.14 2554.84 20.13 0.946 0.123
ADG, g/d 3–17 d 36.05 35.49 35.71 36.02 0.32 0.974 0.529
18–38 d 63.40 61.65 58.31 63.07 0.69 0.417 0.011
39–50 d 52.81 54.10 54.92 54.56 1.14 0.582 0.738
3–50 d 52.55 51.93 50.71 52.84 0.43 0.926 0.125
DFI, g/d 3–17 d 53.69 53.45 52.16 51.85 0.59 0.226 0.979
18–38 d 142.03 139.06 136.99 139.92 1.28 0.481 0.273
39–50 d 167.48 170.82 160.32 171.80 2.83 0.924 0.485
3–50 d 120.58 121.32 117.58 121.48 1.20 0.927 0.530
FCR, g/g 3–17 d 1.49 1.51 1.46 1.44 0.01 0.099 0.489
18–38 d 2.24 2.26 2.35 2.22 0.03 0.913 0.159
39–50 d 3.17 3.17 2.93 3.18 0.051 0.639 0.220
3–50 d 2.29 2.34 2.32 2.30 0.019 0.925 0.406
HI Hermetia illucens,SEM standard error of the mean, LW live weight, ADG average daily gain, DFI daily feed intake, FCR feed conversion ratio
Four dietary treatments: HI0 = control; HI3 = 3% inclusio n level of Hermetia illucens; HI6 = 6% inclusion level of Hermetia illucens; HI9 = 9% inclusion level of
Gariglio et al. Journal of Animal Science and Biotechnology (2019) 10:37 Page 5 of 10
In the periods from 18 to 38 days of age and from 39
to 50 days of age, the EE digestibility showed a linear in-
crease, with a maximum corresponding to the HI9 group
(P< 0.001) (+ 1.94% and + 3.05% compared to HI0 in the
grower and finisher periods, respectively). However, CP
digestibility was not affected by the dietary treatments in
the grower and finisher periods (P> 0.05).
The effects of the diet, gut segment and interaction be-
tween the diet and gut segment on the gut morphomet-
ric indices of the ducks are summarized in Table 4.The
intestinal segment significantly affected Vh, Cd and Vh/Cd
(P< 0.001). On the other hand, no influence of diet or inter-
action between the diet and intestinal segment (P> 0.05)
were observed on the morphometric indices. The
duodenum showed higher Vh and Cd values (P<0.05and
P< 0.01, respectively) than the ileum, and the morphomet-
ric indices were also greater (P<0.05 and P< 0.01, re-
spectively) in the jejunum than in the ileum. The
duodenum also showed a greater Vh/Cd (P< 0.05) than
the other gut segments.
Currently, no literature is available regarding the use of in-
sect meals in duck feeding. For this reason, all the com-
parisons with literature data referred to other poultry
species fed with HI meals and other insect meals.
The final LW of the birds was in line with the weight
reported by Pingel et al. . The results showed that
HI meal could be a valuable alternative to corn gluten
meal, and HI meal can be included in duck diets by as
much as 9% without any negative effects on the final
LW, ADG, DFI and FCR of the animals. Despite the
lower LW and ADG of HI6 birds in the grower period
(18–38 days of age), DFI and FCR were not influenced
by the dietary treatment, and the final LW of the HI6
group was in line with the weight of the other treat-
ments. Similarly, Cullere et al.  did not observe any
differences in the final LW of broiler quails (Coturnix
coturnix japonica) fed two different diets at 10% and
15% of inclusion levels of HI meal (in substitution of
SBM protein and oil). Our results also agree with what
Bovera et al.  previously reported for laying hens fed
25% and 50% HI in substitution of SBM (73 g/kg and
146 g/kg of inclusion, respectively), thus showing that
LW and DFI were not influenced by the dietary treat-
ments. The inclusion of up to 10% of HI larva meal in
the diet of broiler chickens influenced their final LW
and also improved the DFI of chicks in the starter period
. As far as other insect species with potential interest
as feeds are concerned, Adenjii  did not observe any
dietary effects on the performance of broiler chickens
when groundnut cake was substituted with housefly
maggot (M. domestica) meal. Biasato et al. ,
Ramos-Elorduy et al.  and Bovera et al.  also re-
ported that the inclusion of TM meal in broiler chicken
diets (from 5% to 15% of inclusion) did not affect the
final LW and DFI of the birds. On the other hand, the
replacement of SBM with 25% and 50% of HI meal (100
and 190 g/kg of inclusion, respectively) and 25% TM
meal (120 g/kg of inclusion) in Barbary partridge (Alec-
toris barbara) resulted in a higher LW than the control
. Finally, the results reported by Khan et al. , per-
taining to broiler chicks fed with silkworm (Bombyx
mori), housefly maggot and TM in substitution of SBM
Table 3 Effect of the dietary inclusion of HI larva meal on the nutrients apparent digestibility of Muscovy ducks (n=6)
HI0 HI3 HI6 HI9 Linear Quadratic
3–17 d DM 0.960 0.960 0.960 0.953 0.002 0.174 0.315
CP 0.852 0.872 0.828 0.817 0.007 0.010 0.195
EE 0.945 0.967 0.963 0.962 0.002 0.003 0.085
OM 0.963 0.963 0.966 0.962 0.001 0.853 0.453
18–38 d DM 0.953 0.956 0.962 0.960 0.002 0.086 0.511
CP 0.800 0.802 0.802 0.828 0.005 0.085 0.269
EE 0.958 0.966 0.968 0.977 0.002 < 0.001 0.891
OM 0.958 0.964 0.967 0.963 0.001 0.215 0.168
39–50 d DM 0.943 0.948 0.952 0.953 0.002 0.099 0.703
CP 0.733 0.682 0.715 0.718 0.012 0.913 0.259
EE 0.953 0.958 0.965 0.983 0.003 < 0.001 0.092
OM 0.950 0.953 0.958 0.958 0.002 0.072 0.642
HI Hermetia illucens,SEM standard error of the mean, DM dry matter, CP crude protein, EE ether extract
Four dietary treatments: HI0= control; HI3 = 3% inclusion level of Hermetia illucens; HI6 = 6% inclusion level of Hermetia illucens; HI9 = 9% inclusion leve l of Hermetia illucens
Gariglio et al. Journal of Animal Science and Biotechnology (2019) 10:37 Page 6 of 10
(7.8%, 8.0% and 8.1% of inclusion, respectively), pointed
out a higher LW in insect-fed chicks than in the control.
In this trial, the FCR was not affected by the dietary
treatments, according to the results of Elwert et al. 
and Cullere et al.  pertaining to broiler chickens and
broiler quails, respectively, fed with increasing levels of
defatted HI meal. On the contrary, an improved FCR
was observed in Barbary partridge fed diets with 25%
and 50% of substitution of SBM with HI and TM meal
. An improved FCR was also reported by Khan et al.
 (silkworm, housefly maggot, TM) and Bovera et al.
 (TM), who found that the FCR of broiler chickens
was lower in chicks fed insect meal than the control diet
meal results to be suitable in Muscovy ducks feeding.
During the whole experimental period, the growth perfor-
mances observed in the present study were not influenced
by dietary inclusion levels of HI meal, as already observed
by other researches in quails and laying hens [10,24]. Fur-
thermore, the absence of gut histomorphological alterations
can also explain the growth performance results, as well as
the slightly affected nutrient digestibility.
The herein obtained results show that the inclusion of HI
larva meal in Muscovy duck diets partially affected the ap-
parent digestibility coefficients of the nutrients. Consist-
ently with our results, Cullere et al. didnotreport
any differences in DM and OM total tract apparent digest-
ibility in broiler quails as a result of the HI inclusion level
in the diet. On the contrary, in laying hens fed 17% HI
meal in the diet, the apparent ileal digestibility of DM was
lower in the group fed HI meal than in the control .
Results reported by Bovera et al.  showed that the in-
clusion of HI meal by up to 7.3% in laying hen diets did
not affect the apparent DM ileal digestibility, compared to
the control with vegetable protein meal, whereas the in-
clusion of 14.6% reduced the apparent DM ileal digestibil-
ity. In another study, the use of TM in broiler chicken
diets worsened the apparent ileal DM digestibility com-
pared to the control with SBM .
In our trial, the CP and EE apparent digestibility in the
starter period (3–17 days of age) showed an opposite linear
trend, with a reduction in CP digestibility (up to −3.5% in
HI9, compared to the control) and an improvement in EE
digestibility (+ 2.0 in HI9, compared to the control) follow-
ing the increasing inclusion levels of HI meal in the diet.
The lower CP digestibility for the HI6 and HI9 groups in
the starter period could be related to the higher chitin con-
tent of the diet, because of the higher inclusion level of HI
meal . In fact, Cutrignelli et al.  and Bovera et al.
 also observed a reduction in the apparent ileal CP di-
gestibility of laying hens compared to the control diet with
SBM, and explained this result as a consequence of the
presence of chitin in the diet. Indeed, De Marco et al. 
assumed that the chitin, the structural component of the
exoskeleton of insects, can negatively affect the nutrient di-
gestibility, resulting as an indigestible fiber for domestic
poultry. However, no differences in CP total tract apparent
digestibility were reported by Cullere et al.  for broiler
quails, after a substitution of protein/fat sources with HI
larva meal of up to 15% of inclusion. However, in our trial,
the apparent CP digestibility was similar during the grower
(18–38 days of age) and finisher (39–50 days of age) pe-
riods, thus suggesting an adaptation to the chitin levels in
the diet. The studies conducted by Tabata et al. [49,50]
showed that the birds have acid chitinase genes in their
genome. In particular, in poultry (such as ducks), the acid
chitinase is expressed mainly at the level of the glandular
stomach. The level of acid chitinase mRNA in stomach tis-
sue is regulated by feeding behaviour, which was higher in
omnivorous species than in herbivorous and carnivorous
species . Moreover, it could be speculated that the chi-
tin level in the diet could influence the acid chitinase ex-
pression with an overall improvement in feed digestibility.
In our trial, the EE apparent digestibility was higher in
HI groups than the control group. However, despite this
positive result, the EE apparent digestibility was only 2.2%
and 1.9% higher than the control in the starter and grower
periods respectively (3–17 and 18–38 days of age) and
3.0% higher than the control in the finisher period (39–50
days of age). This result partially agrees with the results of
Cullere et al. , who found that the EE total tract
Table 4 Intestinal morphometric indices in the ducks in relation to diet and intestinal segment (n= 12, end of the trial)
Index Diet (D)
Intestinal segment (IS)
HI0 HI3 HI6 HI9 DU JE IL D IS D IS D × IS
Vh, mm 1.55 1.51 1.52 1.63 2.12
0.06 0.06 0.442 < 0.001 0.508
Cd, mm 0.16 0.14 0.15 0.15 0.18
0.01 0.01 0.346 < 0.001 0.782
Vh/Cd 9.80 11.06 10.67 10.83 12.62
0.60 0.45 0.469 < 0.001 0.966
Vh villus height, Cd crypt depth, Vh/Cd villus height-to-crypt depth ratio
The means with different superscript letters (
a, b, c
) within the same row per fixed effect (i.e. diet, intestinal segment) differ significantly (P< 0.05)
Four dietary treatments: HI0 = control; H I3= 3% inclu sion level of Hermetia illucens; HI6 = 6% inclusion level of Hermetia illucens; HI9 = 9% inclusion level of Hermetia illucens
Three intestinal segments: DU duodenum, JE jejunum, IL ileum
Gariglio et al. Journal of Animal Science and Biotechnology (2019) 10:37 Page 7 of 10
apparent digestibility in broiler quails fed with a 15% in-
clusion level of HI was higher than a 10% group, but simi-
lar to the control diet. On the other hand, Cutrignelli et al.
 and Bovera et al.  found that the apparent ileal EE
digestibility in laying hens was similar for HI meal- and
SBM-fed birds. The linear increase in EE digestibility is
not supported by the fatty acids profile, in particular by
the polyunsaturated fatty acids (PUFA) content, that is
usually related to an EE digestibility improvement . In-
deed, in the present study the dietary PUFA content, as
well as the ratio polyunsaturated fatty acids/saturated fatty
acids (PUFA/SFA ratio), decreased following the HI larva
meal inclusion (Table 1). The highest EE digestibility at
the maximum inclusion level (HI9 group) could be related
to the overall amount of EE in the diets (+7.84%, + 6.06%
and + 5.19% higher in HI9 group than HI0 group in
starter, grower and finisher periods, respectively) .
As a whole, the absent or moderate effects on nutrient
ATTDC had no impact on the ducks’growth perfor-
mances, without affecting final LW, ADG, DFI and FCR.
Dietary HI meal inclusion did not affect the gut morph-
ology of the ducks of our study. Since the rapid growth
of chickens has been reported to strictly depend on the
morphological and functional integrity of the digestive
tract , it is reasonable to hypothesize that insect meal
utilization does not negatively influence gut develop-
ment and, as a consequence, animal performance. The
greater mucosal development observed in the duodenum
than in the other gut segments is also in agreement with
the previous studies available on broilers [11,14–17,53,
54], thus suggesting that insect meal utilization leads to
the preservation of the physiological intestinal morph-
ology. Indeed, the duodenum is the intestinal tract that
undergoes the fastest cell renewal, and is also the first
gut segment to receive the physical, chemical and hor-
monal stimuli caused by the presence of the diet in the
lumen . The obtained results about the preservation
of gut histomorphology in all dietary groups contributes
to validate what has been previously discussed in terms
of nutrient digestibility and growth performances.
To the best of the authors’knowledge, this is the first
study that has evaluated the possibility of including in-
sect meal in duck nutrition, and to have demonstrated
how HI larva meal can be a valuable protein sources for
ducks. Increasing inclusion levels of a partially defatted
HI meal in Muscovy duck diets did not affect the growth
performances of the birds, which showed similar LW,
ADG, DFI and FCR to the control group fed with corn
gluten meal, and only had weak effects on the apparent
total tract digestibility during the first stages of growth.
Moreover, these increasing levels did not affect the intes-
tinal morphology or cause histopathological alterations.
From this preliminary investigation, it appears that HI
larva meal can be included in duck feeding at levels of
up to 9% of the diet, with no negative effects on growth,
digestibility or animal health. Furthermore, the obtained
results help to expand the information available about
the use of insects in poultry nutrition.
ADF: Acid detergent fibre; ADG: Average daily gain; AMEn: Apparent
metabolisable energy; ATTDC: Apparent total tract digestibility coefficients;
Cd: Crypt depth; CP: Crude protein; DFI: Average daily feed intake; DM: Dry
matter; DU: Duodenum; EE: Ether extract; FAME: Fatty acid methyl esters;
FCR: Feed conversion ratio; GLMM: General linear mixed model;
HE: Haematoxylin & Eosin; HI: Hermetia illucens; IL: Ileum; JE: Jejunum;
LW: Live weight; MUFA: Monounsaturated fatty acids; NDF: Neutral detergent
fiber; OM: Organic matter; PAS: Periodic acid-Schiff; PUFA: Polyunsaturated
fatty acids; SB: Sudan Black; SBM: Soybean meal; SEM: Standard error of the
mean; SFA: Saturated fatty acids; TM: Tenebrio molitor; Vh: Villus height; Vh/
Cd: Villus height-to-crypt depth ratio
The authors would like to thank Mr. Heinrich Katz, the owner of Hermetia
Baruth GmbH, Baruth/Mark (Germany), for providing the black soldier fly
meal and A.I.A. Agricola Italiana Alimentare S.p.A (Fossano, CN, Italy) for
providing the feed ingredients. The authors are also grateful to Mr. Dario
Sola and Mr. Mario Colombano for the bird care and technical support.
Research supported by the University of Torino (Italy) funding: SCHA_RILO_16_02.
Availability of data and materials
The datasets analysed in the current study are available from the corresponding
author on request.
MG, SD, FG, LG and AS conceived and designed the experiment. MG, SD, LG,
FG, CC, SBO, VR and AS prepared the diets, performed the trial and collected
the experimental data. MG, SD, FH, JM and SM performed the digestibility
determinations. IB, MTC and EC performed the morphometric investigations.
AT established the fatty acids profile. MG, SD, IB and MM performed the
statistical analysis. LG, FG, AS, MG, SD, AT analyzed and interpreted the data.
LG, MG, SD, IB, AS, FG and AT wrote the first draft of the manuscript. All the
authors critically reviewed the intellectual content of the manuscript and
gave their approval for the final version to be published.
Ethics approval and consent to participate
The experimental protocol was approved by the Bioethical Committee of the
University of Turin (Italy) (protocol number: 380576, 04/12/2017).
Consent for publication
The authors declare that they have no competing interests.
Department of Veterinary Sciences, University of Turin, largo Paolo Braccini
2, Turin, Grugliasco 10095, Italy.
Department of Agricultural, Forest and Food
Sciences, University of Turin, largo Paolo Braccini 2, Turin, Grugliasco 10095,
Department of Animal Production, University of Murcia, Campus de
Espinardo, 30071 Murcia, Spain.
Institute of Science of Food Production,
National Research Council, largo Paolo Braccini 2, Turin, Grugliasco 10095,
Department of Comparative Biomedicine and Food Science, University
of Padua, viale dell’Università 16, Padua, Legnaro 35020, Italy.
Italiana Alimentare S.p.A, via Val Pantena 18G, 37142 Verona, Italy.
of Interdisciplinary Research on Sustainability, University of Turin, via
Accademia Albertina 13, 10100 Turin, Italy.
Gariglio et al. Journal of Animal Science and Biotechnology (2019) 10:37 Page 8 of 10
Received: 19 December 2018 Accepted: 15 March 2019
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