Effect of dietary Artemisia argyi powder on egg production, egg quality and nutrients, serum biochemical indices in laying ducks

ABSTRACT

A total of 240 laying ducks at 24 wk of age were randomly assigned to 4 groups with 6 replicates of 10 layers each according to a completely randomized design. The control group were fed a basic diet, and three treatment groups were fed a basic diet supplemented with 2%, 4% and 6% Artemisia argyi powder (AAP). The adaption period was 7 d and the main experimental period was 35 d. The addition of 2% and 4% AAP increased ALR and PLR, while decreased FCR (P < 0.05) but did not affect (P > 0.05) ADFI compared to the control group. Supplementation with AAP enhanced (P < 0.05) the eggshell thickness but did not affect the egg shape index, yolk ratio, albumen height and Haugh unit (P > 0.05). Compared to the control, the concentrations of PUFA and DPA in the 4% AAP and 6% AAP groups were increased (P < 0.05). SFA were higher in 2% AAP while MUFA were decreased in three experimental groups (P < 0.05). Accordingly, GSH-Px, T-SOD in all experimental groups, IgG and IgM in the 4% APP group displayed higher levels, while MDA was not affected when feeding AAP diets. It can be concluded that Artemisia argyi powder positively affects egg production, enhances the antioxidant and immune capacity of laying ducks.

KEYWORDS:

• Artemisia argyi
• egg production
• egg quality
• serum biochemical indices
• organ indexes
• fatty acid
• amino acid
• laying ducks

1. Introduction

Artemisia argyi (A. argyi) is a well-known medicinal herbaceous plant, belonging to the genus Artemisia, one of the largest genera of the family Asteraceae, consisting of about 400 species. There are 186 species along with 44 varieties grown in China (Lin 1991). Some species of this genus such as Artemisia argyi Levl. et Vant (Tan and Zhongjian 1992), Artemisia annua Linn (Klayman 1985; Baraldia et al. 2008) and Artemisia capillaris Thunb (Wu et al. 1998) are used as famous traditional Chinese medicines for the treatment of malaria, hepatitis and cancer and infections by fungi, bacteria and viruses (Han et al. 2002). Recent studies reported that the A. argyi extract can induce apoptosis in human gemcitabine-resistant lung cancer cells via the PI3K/MAPK signalling pathway (Su et al. 2022). A. argyi can also exhibit anti-ageing effects by decreasing senescence in ageing stem cells (Ho et al. 2022). Moreover, dietary fibre from A. argyi has been proven to be advantageous in preventing type 2 diabetes, cardiovascular diseases and colorectal cancer (McGuire 2016). These studies suggest that A. argyi leaves and their extracts will have broad application prospects in the medical field in the future.

On the other hand, in the context of global restrictions on the use of antibiotics, there has been increased research on natural plant-based ingredients as feed additives.

A. Argyi, as a traditional low-cost Chinese herbal medicine, will have potential in animal feed additive applications because of its variety of active substances (Song et al. 2019). Several studies on the use of A. argyi in livestock feeding have been implemented in the previous decades. In rabbit, it was found that adding A. argyi can improve intestinal immunity (Liu et al. 2019). A study on the aqueous extract of A. argyi as an additive has been conducted, which was found that adding 1000 mg/kg A. argyi aqueous extract to broilers can improve the antioxidant capacity of the small intestine (Zhao et al. 2016), and this result is consistent with that reported by Zhang et al. (2020a). Yang et al. (2021a) reported the effects of A. argyi flavonoids on growth performance and immune function in broilers, and the results demonstrated that dietary A. argyi flavonoids significantly improved the body weight and alleviated immune stress in broilers. A. argyi leaves at appropriate concentrations can significantly up-regulate the quantities of Akkermansia and Bifidobacterium, thus positively regulating animal growth (Ma et al. 2022).

To our knowledge, the previous studies mainly focused on the use of A. argyi as an additive in broilers, there were few reports on the application of A. argyi powder in laying fowls. Particularly, there was little information on the changes in duck egg quality and nutritional nutrients closely related to human health when adding of A. argyi powder to the diet of laying duck. Therefore, the aim of the present study was to investigate the effects of different levels of A. argyi powder in diets on laying performance, egg quality, egg nutritive components, serum immunological and antioxidant indices and internal organ parameters in laying ducks, and to find the optimal proportion of APP supplement in the diets, so as to provide an application reference of A. argyi in poultry production.

2. Materials and methods

2.1 Materials

The feeding trial was conducted at the farm of Guizhou University (Guiyang City, Guizhou Province, China). A. argyi powder was purchased from Jiexi Yibai Pharmacy Co., Ltd. (Guangdong Province, China). A. argyi powder (AAP) was acquired by crushing the dried plant materials, and sifting through 40 mesh sieve. The basic chemical composition of the AAP was determined according to AOAC (2019). The chemical constituents of A. argyi powder were as follows: dry matter (DM) 88.15%, crude protein (CP) 15.55%, crude fat 2.84%, crude fibre (CF) 21.3%, crude ash (CA) 10.15%, calcium 1.23%, total phosphorus 1.68%, gross energy 14.81 MJ/kg and total sugar 5.13%.

2.2 Animals, diets and experimental design

A total of 240 (24-week-old) laying ducks from the Guangxi Zhuang Autonomous Region of China were randomly assigned to the control group and three experimental groups with six replicates and 10 ducks each according to a completely randomized design. The control group ducks were fed a basal diet, and the experimental group ducks were fed the same diet further supplemented with 2%, 4% and 6% A. argyi powder. The feeding trial lasted for 6 weeks, consisting of 1-week preparation period and a 5-week formal experimental period. The nutritional levels of the control and experimental diets, including crude protein, metabolic energy, etc., were basically similar and were formulated according to the Criterion of Nutrients Requirements of Egg duck (SAC, GBT/41189-2021) (Standardization Administration of China(SAC) 2021). The ingredients and chemical composition of the experimental diets are shown in Table 1.

Table 1. Ingredients and chemical composition of the experimental diets (DM basis).

Ingredients,%	Experimental group
	Control	2%	4%	6%
Corn	64.6	63.4	62	60
Soybean meal	19	19	19	18.5
Wheat bran	3.5	2.5	1.5	1.5
Rapeseed cake	2	2	2	2
Palm oil	1.1	1.3	1.7	2.2
CaHPO4	1	1	1	1
Limestone	7.5	7.5	7.5	7.5
NaCl	0.3	0.3	0.3	0.3
Premix1	1	1	1	1
Artemisia argyi powder	0	2	4	6
Chemical composition
Crude protein	15.24	15..29	15.31	15.23
ME(MJ/kg)	11.46	11.44	11.46	11.45
Crude fibre	2.74	2.81	2.88	2.98
Calcium	2.94	2.97	2,99	3.02
Available phosphorus	0.31	0.33	0.31	0.30
Lysine	0.66	0.66	0.65	0.63
Methionine	0.23	0.23	0.23	0.22

(1) The premix provides the following micronutrients (per kilogram of complete diet): Cu 10 mg, Fe 80 mg, Mn 60 mg, Zn 60 mg, I 0.4 mg, Se 0.2 mg, vitamin A 4000 IU, vitamin K₃ 2 mg, vitamin B₁ 3.5 mg, niacin 50 mg, folic acid 1.0 mg, calcium pantothenate 10 mg, vitamin B₆ 2.5 mg, vitamin B₁₂ 0.01 mg and biotin 0.1 mg.

(2) Crude protein, crude fibre and metabolic energy were measured values, while other chemical components were calculated values.

The experiment was conducted in a chamber consisting of 24 single-layer wire cages (1.2 am × 1.0 am × 0.4 am) with a trough and two nipple drinker in front of the wire cage. Each cage was considered as a replicate of 10 ducks and diets and water were available ad libitum during the experimental period. Ducks were fed twice a day (08:00 and 16:30) freely and water was available through a nipple-type dispenser, natural lighting and artificial lighting in the morning and evening were also provided to ensure the constant 16 h lighting time every day. The relative humidity was maintained at about 65%. All eggs were collected on time at 7:30 and 16:00. The immunization procedure was carried out in accordance with the provisions of duck farm epidemic prevention.

At the end of the experiment, blood samples were collected from a vein in the duck’s wing. Eight samples were collected per treatment, and a total of 32 blood samples were collected. All the blood samples were centrifuged at 3500 rpm for 15 min at room temperature, then removed into micro tubes and stored at −20 °C until they were used to measure immunological and antioxidant parameters.

2.3 Egg laying performance and egg quality measurements

When the formal trial period started, the feed intake was recorded daily in the morning. The feed conversion ratio (FCR) was calculated after the experiments were completed. Mortality was recorded as it occurred. The feed conversion ratio and average daily feed intake (ADFI) were calculated using weekly feed recorded values. Egg production was recorded daily per cage, and the average daily laying ratio (ALR) and peak laying ratio (PLR) were calculated at the end of the laying experiment. The average egg weight (AEW) was determined by dividing the total weight of the collected eggs by the number of eggs laid per replicate. FCR was calculated based on feed intake and egg production data.

At the end of the laying experiment, 72 eggs from each treatment were collected and marked differently, weighed individually. The following egg quality indicators were measured: egg shape index, eggshell strength, eggshell thickness, albumen height, yolk colour, Haugh unit (HU), using the Egg Analyzer (model EA- 01, ORKA Co., LTD, Israel) and Egg Force Reader (model EFR-01, ORKA), the yolk weight was recorded individually and expressed as yolk ratio.

2.4 Analysis of fatty acids and amino acids in eggs

With regard to fatty acids and amino acid ingredients in eggs, 72 duck eggs were collected in the same way. The whole egg was dried to constant weight by a vacuum freeze drier (Lyoque-85PLUS, Shanghai Taishida Electromechanical Equipment Co., Ltd., China), and then fully ground by a high-speed multi-functional crusher (800Y, Wuyi Haina Electric Co., Ltd., China).

Fatty acids were extracted using a chloroform-methanol solution according to GB 5009.168-2016 (National Food Safety Standards of the People's Republic of China). Individual fatty acids were detected using a gas chromatography-mass spectrometer (GC–MS; Thermo Fisher Scientific, U.S.A.). The following fatty acid combinations were calculated: omega-3 (n-3) fatty acids, omega-6 (n-6) fatty acids, total saturated fatty acids (SFA), total monounsaturated fatty acids (MUFA), total polyunsaturated fatty acids (PUFA), PUFA/SFA and n-6 PUFA/n-3 PUFA ratio.

Amino acids analysis was conducted according to the external standard method GB/T 5009.124-2016 (National Food Safety Standards of the People's Republic of China). The content of amino acids in eggs was determined by an automatic amino acid analyser (Biochrom 30, UK). Sixteen amino acids were detected: aspartic acid (Asp), threonine (Thr), serine (Ser), glutamic acid (Glu), glycine (Gly), alanine (Ala), valine (Val), methionine (Met), isoleucine (Ile), leucine (Leu), tyrosine (Tyr), phenylalanine (Phe), histidine (His), lysine (Lys), arginine (Arg) and proline (Pro). The following amino acid combinations were calculated: total amino acid (TAA), essential amino acid (EAA), non-essential amino acid (NEAA), EAA/TAA and EAA/NEAA ratio.

2.5 Serum biochemical indexes determination

The commonly used biochemical indexes, involving total superoxide dismutase (T-SOD), glutathione peroxidase (GSH-Px), malondialdehyde (MDA), total protein (TP), albumin (ALB), immunoglobulin G (lgG), immunoglobulin A (IgA) and immunoglobulin (IgM), were measured using commercial assay kits provided by commercial kits (Jiancheng Biotechnology Institute, Nanjing, China). The automatic micro-plate reader (BioTek Instruments Inc, U.S.A.) was used to measure the serum immune and antioxidant parameters. All measurement procedures were strictly in accordance with the manufacturer’s instructions.

2.6 Organ indexes determination

At the end of collecting blood samples, 12 ducks (three ducks per treatment) were euthanized by carbon inhalation and their internal organs, including thymus, spleen, bursa and liver were removed, and weighed after stripping fat and irrelevant issues. Finally, the organ index was calculated by the following formula:

Organ index = organ weight/body weight × 100%.

2.7 Statistical analysis

Data were analysed using one-way ANOVA of SPSS 19.0 (SPSS software for Windows, SPSS Inc., Chicago, IL). The model was $\mathrm{Yij}=\mu +\mathrm{Ti}+{\epsilon }_{\mathrm{i}}$where Yij = egg production index; µ = population mean; Ti = diet effect and ϵ_ij =random error.

The results were indicated in means ± standard error of the mean. Duncan’s test was used for multiple comparisons. Differences were declared significant at P < 0.05.

3. Results

3.1 Egg laying performance

The effect of AAP on egg production in laying ducks is shown in Table 2. No differences (P > 0.05) in ADFI were observed among treatment groups except for a slight decrease in ducks fed 6% of AAP, whereas the addition of 2% and 4% of AAP to diet significantly improved ALR, PLR, while it decreased FCR (P < 0.05). In addition, the egg production in all treatment groups was higher (P < 0.05) than that in the control group (data were not listed).

Table 2. Effect of Artemisia argyi powder on egg performance in laying ducks.

Item	Diet				SEM	P-value
	0	2%	4%	6%
ADFI (g)	132.01^a	130.18^a	129.42^ab	127.52^b	0.412	0.017
AEW(g)	61.58^a	60.07^ab	59.91^ab	58.36^b	0.361	0.014
ALR(%)	75.83^b	82.87^a	84.33^a	80.73^ab	0.008	0.046
PLR(%)	91.98^b	93.75^a	93.68^a	92.24^ab	0.003	0.056
FCR	2.94^a	2.76^bc	2.68^c	2.87^ab	0.021	0.025

^a,b,c Values within a row with different superscripts differ significantly at P < 0.05.

ADFI, average daily feed intake; AEW, average egg weight; ALR, average egg laying ratio; PLR, peak egg laying ratio; FCR, feed conversion ratio.

3.2 Egg quality

As shown in Table 3, supplementation with dietary AAP in diets did not affect egg shape index, yolk ratio, albumen height and Haugh unit (P > 0.05). However, the eggshell thickness values in the three experimental groups were higher (P < 0.05) than those in the control group. Ducks fed 6% of AAP showed improved eggshell strengthen, whereas they exhibited lower (P < 0.05) yolk colour values, compared to the control group.

Table 3. Effect of A. argyi powder on egg quality in laying ducks.

Items	Diet				SEM	P-value
	0	2%	4%	6%
Egg shape index	1.36	1.35	1.35	1.33	0.006	0.483
Eggshell strength(N)	45.52^ab	44.54^b	46.54^ab	49.72^a	0.724	0.062
Eggshell thickness(mm)	0.22^b	0.29^a	0.31^a	0.30^a	0.005	<0.001
Yolk weight(g)	19.00^ab	18.78^ab	19.29^a	17.94^b	0.184	0.054
Yolk ratio	30.92	30.75	30.17	29.83	0.335	0.651
Albumen height(mm)	6.84	6.67	6.23	6.18	0.145	0.282
Yolk colour	10.61^a	10.67^a	10.89^a	9.50^b	0.152	0.004
Haugh unit	80.72	79.86	76.65	77.27	1.044	0.454

^a,b,c Values within a row with different superscripts differ significantly at P < 0.05.

3.3 Fatty acid and amino acid profiles in duck egg

The effect of dietary AAP on fatty acid composition in egg yolk is presented in Table 4. A total of 10 saturated fatty acids (SFA), 6 sorts of monounsaturated fatty acids and 10 sorts of polyunsaturated fatty acids were examined. In terms of SFA, the inclusion of AAP in 4% and 6% AAP groups improved the levels of C15:0, C17:0 and C24:0, whereas it resulted in a decrease in the levels of C16:0 and C22:0, compared to the control group. However, the total SFA contents were similar among the experimental groups (P > 0.05) except for a slight increase in the 2% AAP group. Supplementation with AAP led to a decrease (P < 0.05) in total monounsaturated fatty acids (MUFA) levels, while C17:1 levels in 4% and 6% APP groups were higher (P < 0.05) than that in the control group. With regard to polyunsaturated fatty acids (PUFA), in ducks fed with AAP diets the concentrations (P < 0.05) of C20:2, C18:2n6c, C20:3n6 and DPA(docosapentaenoic acid) were increased compared to the control group. Accordingly, the total PUFA in 4% and 6% AAP groups was higher than the control group (Table 4).

Table 4. Effect of A. argyi powder on fatty acid composition in egg yolk of laying duck.

Items	Diet				SEM	P-value
	0	2%	4%	6%
Saturated fatty acid(SFA),%
C12:0	0.02^ab	0.02^a	0.02^ab	0.02^b	0.001	0.095
C14:0	0.40^b	0.51^a	0.43^b	0.42^b	0.014	0.002
C15:0	0.02^b	0.02^b	0.03^a	0.03^a	0.001	<0.001
C16:0	24.44^b	24.75^a	23.84^c	23.69^c	0.134	<0.001
C17:0	0.06^c	0.07^b	0.09^a	0.10^a	0.004	<0.001
C18:0	5.41^b	5.91^a	5.93^a	5.91^a	0.088	0.063
C20:0	0.03^b	0.03^a	0.03^a	0.04^a	0.001	0.033
C21:0	0.03	0.02	0.02	0.02	0.003	0.555
C22:0	0.29^b	0.30^a	0.28^c	0.28^c	0.003	<0.001
C24:0	0.03^b	0.04^ab	0.04^a	0.04^a	0.001	0.008
Total SFA	30.73^b	31.68^a	30.73^b	30.53^b	0.137	<0.001
Monounsaturated fatty acid (MUFA), %
C14:1	0.04^b	0.06^a	0.04^b	0.03^b	0.003	<0.001
C16:1	2.83^a	3.03^a	2.56^b	2.52^b	0.069	0.003
C17:1	0.07^c	0.07^bc	0.08^a	0.08^ab	0.002	0.006
C18:1n9t	0.21^b	0.23^a	0.20^b	0.21^b	0.004	0.007
C18:1n9c	56.00^a	54.76^bc	54.35^c	55.16^b	0.198	0.001
C20:1n9	0.21^a	0.02^a	0.23^a	0.02^a	0.043	0.120
Total MUFA	59.37^a	58.16^b	57.45^c	58.03^b	0.212	<0.001
Polyunsaturated fatty acid (PUFA), %
C20:2	0.16^d	0.16^c	0.19^b	0.19^a	0.004	<0.001
C18:2n6t	0.08	0.09	0.08	0.08	0.001	0.431
C18:2n6c	7.36^b	7.45^b	8.87^a	8.83^a	0.222	<0.001
C18:3n6	0.17^b	0.18^a	0.14^c	0.15^c	0.005	<0.001
C18:3n3	0.26^b	0.35^a	0.37^a	0.37^a	0.014	<0.001
C20:3n6	0.18^d	0.19^c	0.22^a	0.21^b	0.005	<0.001
C20:3n3	0.06^a	0.06^a	0.05^b	0.05^b	0.002	0.008
C20:4n6	1.43^b	1.46^b	1.66^a	1.36^c	0.035	<0.001
C22:6n3(DHA)	0.13	0.07	0.07	0.04	0.015	0.201
DPA	0.09^d	0.12^c	0.15^a	0.15^b	0.008	<0.001
Total n-3	0.54^b	0.62^ab	0.66^a	0.62^ab	0.017	0.055
Total n-6	9.21^c	9.37^c	10.98^a	10.63^b	0.234	<0.001
Total PUFA	9.91^c	10.16^c	11.82^a	11.44^b	0.249	<0.001
n-6/n-3	17.14	15.25	16.72	17.02	0.335	0.154
PUFA/SFA	0.32^b	0.32^b	0.38^a	0.37^a	0.009	<0.001

SFA = total saturated fatty acids; MUFA = total monounsaturated fatty acids; PUFA = total polyunsaturated fatty acids; DPA = docosapentaenoic acid; n-6 = omega-6 fatty acids; n-3 = omega-3 fatty acids.

^a,b,c Values within a row with different superscripts differ significantly at P < 0.05.

The amino acid composition of eggs is presented in Table 5, and the amino acid proportions in all treatment groups were significantly higher (P < 0.05) than those in the control group, indicating that dietary supplementation with AAP could significantly increase the amino acid levels, including essential acids and non-essential amino acids.

Table 5. Effect of A. argyi powder on amino acid composition in duck egg.

Item	Diet				SEM	P-value
	0	2%	4%	6%
Asp	3.99^c	4.24^a	4.28^a	4.14^b	0.035	<0.001
Thr	2.57^c	2.79^a	2.80^a	2.68^b	0.029	<0.001
Ser	3.41^c	3.64^a	3.60^a	3.50^b	0.029	<0.001
Glu	5.65^c	6.04^a	5.98^ab	5.87^b	0.048	<0.001
Gly	1.50^b	1.60^a	1.60^a	1.54^b	0.013	<0.001
Ala	2.17^b	2.29^a	2.27^a	2.19^b	0.017	0.001
Val	2.83^b	3.00^a	3.01^a	2.87^b	0.025	<0.001
Met	1.94^b	1.95^b	2.11^a	1.36^c	0.087	<0.001
Ile	2.06^c	2.21^a	2.18^a	2.12^b	0.018	<0.001
Leu	3.68^b	3.93^a	3.89^a	3.75^b	0.033	<0.001
Tyr	2.07^b	2.22^a	2.24^a	2.10^b	0.023	<0.001
Phe	3.31^b	3.48^a	3.48^a	3.33^b	0.026	0.001
His	1.01^c	1.10^a	1.09^a	1.05^b	0.011	<0.001
Lys	3.23^c	3.45^a	3.47^a	3.32^b	0.031	<0.001
Arg	2.45^d	2.66^a	2.60^b	2.52^c	0.025	<0.001
Pro	1.70^b	1.79^a	1.78^a	1.75^ab	0.012	0.008
TAA	43.56^b	46.38^a	46.38^a	44.07^b	0.410	<0.001
EAA	20.63^b	21.91^a	22.03^a	20.47^b	0.223	<0.001
NEAA	22.93^c	24.47^a	24.34^a	23.60^b	0.198	<0.001
EAA/TAA %	47.36^ab	47.24^b	47.50^a	46.45^c	0.123	<0.001
EAA/NEAA %	89.93^b	89.53^c	90.50^a	86.70^d	0.444	<0.001

TAA = total amino acid; EAA = essential amino acid; NEAA = non-essential amino acids;

^a,b,c Values within a row with different superscripts differ significantly at P < 0.05.

3.4 Serum biochemical indices

The effect of AAP on the serum immune and antioxidant function of laying ducks is presented in Table 6. No significant differences (P > 0.05) in serum ALB, MDA and IgA were detected among all groups when adding dietary AAP to diets. However, the TP and GSH-Px contents of the three experimental groups were higher (P < 0.05) than those of the control group. The serum T-SOD levels in the 2% and 4% groups were higher (P < 0.05) than that in the control group, while there was no significant difference (P > 0.05) between the 6% AAP group and the control group. The 4% AAP group showed higher (P < 0.05) serum IgG and IgM levels compared to the other groups.

Table 6. Effect of A argyi powder on serum biochemical indices in laying ducks.

Items	Diet				SEM	P-value
	0	2%	4%	6%
ALB (g/L)	10.73	13.43	12.95	13.50	0.451	0.095
TP (g/L)	26.17^b	32.70^a	35.42^a	32.47^a	1.008	0.007
MDA (nmol/mL)	8.94	6.98	5.45	7.90	0.546	0.136
T-SOD (U/mL)	44.06^b	55.18^a	52.66^a	49.73^ab	1.181	0.004
GSH-Px (U/L)	254.42^b	316.19^a	308.21^a	313.69^a	7.670	0.008
IgG (g/L)	1.78^b	1.56^b	2.12^a	1.69^b	0.048	<0.001
IgA (g/L)	0.22	0.22	0.23	0.23	0.003	0.466
IgM (g/L)	0.38^b	0.37^b	0.45^a	0.36^b	0.012	0.025

^a,b,c Values within a row with different superscripts differ significantly at P < 0.05.

3.5 Internal organ parameters

Table 7 shows the effect of AAP on internal organ parameters. The hepatosomatic index was not affected (P > 0.05) when adding AAP to diets in the three treatment groups, whereas the thymus index, bursa index and spleen index in the 4% AAP group showed higher (P < 0.05) values compared with the other groups.

Table 7. Effect of Artemisia argyi powder on internal organ parameters in laying ducks.

Items	Diet				SEM	P-value
	0	2%	4%	6%
Hepatosomatic index	2.9734	3.0540	3.2838	3.0579	0.0621	0.341
Thymus index	0.0180^b	0.0205^b	0.0281^a	0.0201^b	0.0010	0.014
Bursal index	0.0262^b	0.0275^b	0.0332^a	0.0270^b	0.0009	0.011
Spleen index	0.0601^b	0.0725^a	0.0730^a	0.0634^ab	0.0020	0.031

^a,b,c Values within a row with different superscripts differ significantly at P < 0.05.

4. Discussion

Egg production is one of the most important economic indicators for laying ducks. Previous studies revealed that supplementation with several medicine plants or their extracts could improve egg production and feed conversion ratio (Yang et al. 2020). However, it is hard to find reports on the effects of adding AAP to the diet on laying performance, although egg weight, egg white weight and antioxidant capacity were improved (Chen et al. 2022). Additionally, it has been found that dietary 3% AAP could improve laying performance and egg quality, and promote the antioxidant capacity of laying hens (Zhang et al. 2020b). In the current study, supplementation with 2% and 4% AAP improved the average laying rate, peak laying rate and FCR. AAP contains some bioactive substances such as flavonoids, volatile oils and polyphenols, which promote follicle development, regulate uterine contraction and promote egg production. In addition, Zhao et al. (2016) reported that feeding of A. argyi could improve production performance and feed conversion ratio in broilers. Ultimately, A. argyi may inhibit the intestinal pathogenic microflora, and promote the digestion and absorption of nutrients (Ma et al. 2022). We noted that the ADFI and AEW were lower when AAP was fed to 6%, the reason for this might be the bitter taste of A. argyi led to a decrease in feed intake(P < 0.05). The lower AEW is relatively reasonable when the laying rate is high.

Egg quality is an extremely important economic trait in egg production. Its external and internal qualities are directly related to consumer health and egg market value. The egg quality is affected by a number of factors, such as the type of the husbandry system (Radu-Rusu et al. 2014). For instance, hens housed in large furnished cages had lower productivity and higher egg quality than those housed in small furnished and conventional cages (Meng et al. 2014). Some well-known environmental factors affecting egg quality are storage temperature (Fikiin et al. 2020), relative humidity and storage time (Yimenu et al. 2018). Besides, many studies demonstrated that Chinese herbal medicines not only affected egg production but also egg quality, antioxidant capacity and immune indices, depending on what active ingredients the herb contains. In the present study, ducks fed with AAP groups increased the eggshell thickness and eggshell strength, but did not result in the changes of the other egg quality indexes. Our results are not in accordance with those of Chen et al. (2022), who reported that the addition of 2% and 3% A. argyi to the hen’s diet increased egg weight and egg white weight. The difference in results needs to be verified by further experimental recommendations.

MUFA and PUFA have the functions of promoting growth, stimulating body development and strengthening immune regulation. Strandvik et al. (2016) reported that the oleic acid in MUFA has beneficial effects on infant growth, development and neural activity, and PUFA has various functions such as anti-cancer, anti-oxidant, improving immune regulation, promoting growth and development, and lowering blood sugar (Jordan 2010). Long-chain n-3 PUFA, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) have been widely researched, and shown to have cardio-protective effects by the anti-inflammatory effects of their meditators, reduce plasma triglyceride levels and platelet aggregation (Mozaffarian and Wu 2012). Recent reviews have summarized the possible role of docosapentaenoic acid (DPA) intake related to cardiovascular health benefits, mental health, cancers and lower blood pressure (Dyall 2015). The present study found that 10 kinds of SFA, 6 kinds of MUFA and 10 kinds of PUFA were determined in Guangxi laying duck eggs (Table 4), which is inconsistent with the results of Ruan et al. (2018), who reported that 3 kinds of SFA, 3 kinds of MUFA and 6 kinds of PUFA were examined in Longyan laying duck eggs. The reason for the different fatty acid composition might be due to the different laying duck breeds or different rearing methods. However, the total SFA and PUFA values in ducks fed with 4% and 6% AAP in this study are similar to those in ducks fed with double-low rapeseed meal with corn in the report of Ruan et al. (2018). We found that supplementation with 4% and 6% AAP could increase the levels of total PUFA, total n-3 and total n-6, compared to the control. In particular, C18:2n6c was the most abundant PUFA in the current study (Table 4), which is in agreement with the report of Ruan et al. (2018). DPA n-3 is the predominant n-3 PUFA in beef, goat and lamb flesh and certain marine species such as abalone and menhaden (Kaur et al. 2011). To our knowledge, no reports on DPA in poultry eggs could be found. In our study, DPA could be examined among all the group, feeding of AAP in three experimental groups led to DPA increase (P < 0.05, Table 4) compared with the control group.

Adequate supplies of essential amino acids and the balance of amino acids play an important role in the nutritional value and flavour of food. World Health Organization (WHO) and the Food and Agriculture Organization of the United Nations (FAO) in 1973 recommended the EAA quantity in food, which is an important criterion to evaluate the nutritional value of food protein. Table 5 shows the effect of feeding of AAP on amino acid composition in duck eggs, indicating that ducks fed with 2% and 4% AAP groups exhibited higher (P < 0.05) EAA and TAA levels than that in the control group, the EAA/TAA were 47.24%, 47.50%, respectively, which met with FAO and WHO requirements(>40%). A significant difference was detected between the amino acid composition in eggs from Guangxi laying ducks in our study and eggs from Nanchang, Jiangxi, in the report of Zhao et al. (2014). However, both EAA/TAA values in our study and in the report of Zhao et al. (2014) were similar. A different amino acid composition of Jingding duck eggs in the study of Sun et al. (2019) was observed. Probably because eggs used in several experiments came from different duck breeds.

Umami has a unique savoury taste and is often used as an indicator of meat quality (Yasumatsu et al. 2015), the key compound that produces umami is inosine monophosphate (IMP) and its degradation products (ribose and hypoxanthine) (Bagnasco et al. 2014). Glutamic acid (Glu) and aspartate (Asp) are umami amino acids (Liu et al. 2015). Besides, glycine (Gly) and alanine (Ala) are also thought to contribute to the umami taste of seafood providing some sweetness (Gong et al. 2016). In the current study, supplementation with 2% and 4% AAP could increase the levels of the umami amino acids such as Asp, Glu, Gly and Ala (P < 0.05, Table 5), compared to the control group. The content of glutamic acid in the control group(5.65%) in this study was higher than that (1.31%) in the study of Sun et al. (2019), whereas lower than that (12.93%) in the report of Zhao et al. (2014).

Blood biochemical parameters reflect conditions of the internal microscopic, status of digestion, metabolism and health of the animal. Therefore, it is related to the production performance and nutrition level of livestock to a certain extent (Guo et al. 2021). Serum total protein (TP) and albumin (ALB) are important indexes reflecting the metabolism and absorption of protein in the animal body, while the changes of TP and ALB are associated with the functional state of the liver and the nutritional status of the animal body. When the content of serum TP increases, it can promote the absorption and metabolism of various proteins in the animal body, improve the feed conversion ratio and promote the growth and development of animals (Sawale and Ghosh 2011). The effect of supplementation with dietary AAP on serum biochemical indices in laying ducks is presented in Table 5. TP values of the three experimental groups were higher than those in the control group. Accordingly, ALB values in all trial groups were higher than the control group. SOD and GSH-Px, as the key enzymes of the antioxidant system, play a crucial role in eliminating free radicals, reducing oxidative damage and maintaining cell structure. The activities of SOD and GSH-Px in the serum were decreased, whereas the level of MDA increased under oxidative stress (He et al. 2016). As can be observed from Table 5, SOD levels increased in all treatment groups while MDA values did not affect after AAP was added to the diet. This result is consistent with our previous study (Yang et al. 2020), which found that dietary supplementation with 2% and 4% Moringa oleifera stem in duck diets improved SOD whereas decreased MDA. The current results suggest that dietary AAP could enhance the antioxidant capacity of laying ducks. Immunoglobulin is the main antibody involved in humoral immunity, and its serum content is one of the important indicators to judge the humoral immune function of animals. In the present study, the contents of IgG, IgA and IgM in the 4% group were higher than that in the control group, which is consistent with Zhang et al. (2022), who found that the contents of IgG and IgM in the serum and liver of broilers in the high dose of Artemisia argyi polysaccharide group were significantly increased. Our results suggest that AAP promotes the immune system and enhances the immune function of laying ducks. It has been found that flavonoids and other bioactive substances in A. argyi powder can enhance the immune function of the body, which explains the reason why serum contents of IgG, IgA and IgM increased when ducks were fed with AAP.

The liver, thymus, spleen and bursa are important immune organs in the body, which can participate in immune regulation and response to the immune status of the body. Rivas and Fabricant (1988) believed that the liver is an important organ involved in the metabolism and reflects the health status of laying ducks; the thymus is involved in the non-specific immune process and thus plays a regulatory role in humoral and cellular immunity; the spleen promotes the production of sensitized T lymphocytes and is the main organ for antibody production; the bursa of Fasciola induces B lymphocyte differentiation and maturation and promotes humoral immunity (Stutz et al. 1983). Changes in the size and structure of internal organs can be indicative of the effect of diet and its components on the development and function of the organs. It was observed that the addition of AAP to the diet increased the thymus index, spleen index and bursa index of ducks in the 4% AAP group in the current study, the observed organ parameters could be confirmatory of the notion that the AAP could have been positively influential. Similar observations were made in other studies (Yang et al. 2021b). It has been reported that flavonoids added to the diet can increase the weight of the thymus, bursa and spleen (Chen et al. 2014). The flavonoid content of AAP may be responsible for the increase in hepatosomatic index, thymus index, spleen index and bursa index in this study. The addition of 4% AAP to the diet could promote the development of the immune organs and enhance the resistance of laying ducks to diseases.

5. Conclusion

The results of the current study indicate AAP can be used as source of natural functional additives for laying ducks because (1) AAP can improve the average laying rate, feed conversion ratio and eggshell strength; (2) AAP can improve the total PUFA contents of egg yolk, especially in C18:2n6, total n-3 and n-6, DPA; (3) AAP can increase the amino acid levels of eggs and (4) AAP can enhance the serum antioxidant capacity and immune indices. Further studies are necessary on how AAP active substances increase egg nutrients and regulate antioxidant and immune capacity.

Ethical consideration

The authors carefully checked all ethical issues concerning plagiarism, consent to publish, misconduct, data fabrication, falsification, double publication or submission, and redundancy of the manuscript.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by National Natural Science Foundation of China: [grant number 31960682]; Special Project for Chinese Government Support Local Government: [grant number [2019]4021].