Zhenzhen Fan, Liuan Li*, Mengran Qin,
Zhongmou Zhang, Keyan Zhang, Qian Wang, Chunnan Wu, Yuqiang Zhang and
Shuaiqiang Mao
Tianjin
Key Laboratory of Agricultural Animal Breeding and Healthy Breeding, College of
Animal Science and Veterinary Medicine, Tianjin Agricultural College, Tianjin
300384, China
*Correspondence author: anliuli2003@163.com
Received
01 September 2020; Accepted 15 September 2020; Published 10 December 2020
Effect of dietary tea polyphenol
(TP) on the content of epigallocatechin gallate (EGCG), catechin (C) in egg
yolk, and impact on egg quality and production was investigated. For this
purpose, 315 healthy Gallus
domestiaus aged 42 weeks were selected and randomly divided into 7
groups. The experimental group added 0.02, 0.05, 0.09, 0.14, 0.19 and 0.24% TP
to the basic diet. The control group (CK) was fed basal diet. After 10, 20 and
30 days, 15 eggs were randomly selected from each group for egg quality
testing, and 20 eggs were selected for EGCG and C content test in the yolk. The
results showed that in the 0.24% TP group, the content of EGCG in egg yolk was
significantly higher than that of CK group and the 0.02, 0.05, 0.09 and 0.14%
TP groups (P < 0.05), and reached
the highest on the 30th day (19.171μg/g). The content of C in
egg yolk was significantly higher than that in CK group and the 0.02, 0.05,
0.09 and 0.14% TP groups (P < 0.05);
and reached the highest on 30th day (7.071 μg/g). The egg weight of the 0.14% TP group on the 10th
day and of the 0.19% TP group on the 20th day were significantly
lower than that of the CK group (P < 0.05);
the egg yolk weight of 0.14% TP on the 10th and 20th days
were significantly lower than that of the CK group (P < 0.05). On the 30th day, compared with the control
group, the egg weight of the 0.14% TP group was significantly reduced (P < 0.05), the egg yolk color of 0.05
and 0.14% TP groups was significantly increased (P < 0.05). During the whole experiment, the egg production of
0.24% TP group was significantly higher than that of control group (P < 0.05). In conclusion, adding high
concentrations of TP can increase the content of EGCG and C in the yolk;
however, it has a certain impact on egg weight, yolk color and eggshell
thickness. Adding high concentrations of TP may increase egg production. © 2021
Friends Science Publishers
Keywords: Catechin; Epigallocatechin gallate;
Egg yolk; Egg quality; Gallus domestiaus;
Tea polyphenols
Tea polyphenol (TP) is the
general term for a class of polyhydroxy phenolic compounds contained in tea,
accounting for about 30% of the dry weight of tea (Wang 1981), including
catechins, flavonoids, anthocyanins and phenolic acids (Wan 2003). Catechins
are an important substance in TP, and accounts for about 70% of the total TP.
There are 8 monomers of catechin compounds, including epigallocatechin gallate
(EGCG), epigallocatechin (EGC), catechin (C), epicatechin (EC), catechin
gallate (CG), gallocatechin (GC), gallocatechin gallate (GCG) and epicatechin
gallate (ECG) (Lu et al. 2018).
Catechin compounds have anti-microbial, anti-oxidant, anti-mutation,
anti-cancer, anti-diabetic and anti-viral effects (Dorota et al. 2004; Khan and Mukhtar 2007; Sharangi 2009). EGCG is the
polyphenol with the largest proportion of catechins that has the strongest
activity. Studies have shown that the antioxidant activity of EGCG is 20 times
that of vitamin E and 6 times that of superoxide dismutase (Huang et al. 2010).
The strong
antioxidant activity of EGCG is due to the trihydroxy group (on the B ring C3,
C4 and C5) and the esterified gallate (on the C ring C3) (Ahmad et al. 2014). In vitro studies have
found that C can scavenge free radicals, remove cytotoxic hemoglobin, and show
obvious antioxidant activity (Lu et al.
2011). In addition, C inhibits tumor-specific angiogenesis by regulating the
production of pro-inflammatory cytokines, nitric oxide, vascular endothelial
growth factor, interleukin-2, etc. (Guruvayoorappan and Kuttan 2008).
At present, many
studies focus on the improvement of livestock and poultry production
performance, immune function, antioxidant function, regulation of glucose and
lipid metabolism, antibacterial by adding TP to the diet (Wang 2017). Adding
300 mg/kg of tea polyphenols to broiler diets can increase the activity of
T-AOC in the blood of broilers and improve the antioxidant properties of meat
quality (Li et al. 2012). A proper
concentration dietary addition of tea polyphenols can improve the production
performance and carcass quality of Partridge shank Chickens, and improve the
blood biochemical indicators related to fat metabolism (Xu et al. 2011). Other studies have shown that adding green tea powder
to the diet can effectively promote the development of immune organs of white
feather broilers, enhance the activity of antioxidant enzymes and increase the
expression of immunoglobulin (Yin 2017).
However, up to now,
there are few reports on the in-depth study of the effect of adding TP to the
diet on the enrichment of TP active components in egg yolk. Therefore, this
experiment took the local breed of Gallus
domestiaus laying hens, and added different levels of TP to the diet to
explore its effect on the catechin compound EGCG content and C content in egg
yolk, as well as egg quality indicators and egg production. This article aims
to provide a basis for the production of TP-rich functional eggs and the
optimization of dietary additives for animal husbandry.
This study was carried out at
the chicken breeding base of Tianjin Jinwa Agricultural Technology Development
Co., Ltd. from October to November in 2019. 315 healthy Gallus domestiaus aged 42 weeks were randomly selected and randomly
divided into 7 groups (45 chickens in each group), raised indoors on flat
ground (with an activity area of 50 m2 for each group), with free
eating and drinking. The control group was fed with the basal diet, the rest 6
groups were the experimental groups, with 0.02, 0.05, 0.09, 0.14, 0.19 and
0.24% TP added to the basal diet, respectively. The pre-test period of all
groups was 3 days, and the formal test period was 30 days. The composition of
the basic diet is shown in Table 1.
Main materials, regents and
equipment are listed in Table 2.
Around the 10th, 20th
and 30th days, 35 eggs were randomly collected from each group, 15 eggs
of which were used for the determination of egg quality, and the remaining 20
eggs were used for the detection of EGCG content and C content
in the eggs. Before testing, the eggs are stored at 4°C for later use.
Eggshell color were measured
using an eggshell color tester of the sharp end, blunt end and middle of the
eggshell, and take the average value. Use an electronic balance to measure the
egg weight, yolk weight, egg white weight and eggshell weight of the eggs. Egg
shape index was measured using an egg shape index tester to measure the
vertical and horizontal diameters of eggs, egg shape index = vertical diameter
/ horizontal diameter. The relative density of eggs is measured with sodium
chloride aqueous solutions of different specific gravity. The higher the
relative density, the fresher the eggs. Use an eggshell thickness tester to
measure the thickness of the three parts of the eggshell at the sharp end, the
blunt end and the middle, and take the average value. Egg yolk color was
measured by the yolk colorimeter. Use the 15 egg yellow grades of the Roche yolk color fan
for comparison; higher the grade, the darker the egg yolk. Haugh unit: break
the egg and pour it on a glass plate, use a protein height measuring
instrument, avoiding the lace to measure the middle of the thick protein layer
around the yolk, and take the average of three equidistant points to be the
protein height, according to the formula calculate the corresponding Haugh
unit.
Haugh unit=100 log
(H-1.7W0.37+7.57)
Note: H is the height of
concentrated protein (mm), and W is egg weight (g).
The egg production of each group
was recorded every day, and the egg production of each group on the 10th,
20th and 30th day was counted and the data was analyzed.
Table 1: Basic diet composition
Component |
Content (%) |
Component |
Content (%) |
Corn |
60 |
Stone powder |
4 |
Soybean meal |
20 |
Fish meal |
2.5 |
Sorghum |
5 |
Bone meal |
2.5 |
Bran |
4 |
Premix |
2 |
Table 2: Main materials, regents and equipment
Name |
Producer |
Tea polyphenols |
Wuxi Century Biological Engineering Co., Ltd.
(Batch No.: FP190702) |
Epigallocatechin Gallate (EGCG) |
Tianjin Xiensi Biochemical Technology Co., Ltd.(CAS
No.989-5-15) |
Catechin (C) |
China Institute for Food and Drug Control (CAS
No.7295-85-4) |
Methanol (chromatographically pure) |
Merck Inc., Germany |
Phosphoric acid (analytically pure) |
Tianjin Fengchuan Chemical Reagent Technology
Co., Ltd. |
Protein height meter (NFN382) |
FHK Inc., Japan |
Analytical Balances (FB223) |
Shanghai Shunning Hengping Scientific
Instrument Co., Ltd. |
Multi purpose vortex mixer (VORTEX-6) |
Haimen qilinbeier Instrument Manufacturing
Co., Ltd. |
Egg shell reflectivity (TSS-QCR) |
Beijing Tianxiang Feiyu Technology
Co., Ltd. |
Ultrasonic cleaning machine ( SB-100D) |
Ningbo Xinzhi Biological
Technology Co., Ltd. |
High performance liquid chromatograph
(Agilent-1260) |
Agilent Technologies Co., Ltd. |
Column: C18 (250 mm Χ 4.6 mm, 5 μm) |
Shimadzu-GL Sciences (Shanghai) Laboratory
Supplies Co., Ltd. |
Fig. 1: Effect of adding different content of TP in diet
on EGCG content in egg yolk.
Note: The lowercase
letters represent the significant differences among different groups (P < 0.05). The same applies below
High performance liquid
chromatography (HPLC) was used to determine the content of EGCG and C in egg
yolk. The sample preparation was carried out according to SN/T3848-2014 (SN/T
3848-2014) with slight modifications. Weigh 2g egg yolk sample into a 10 mL
graduated centrifuge tube, add methanol to the volume to 10 mL, mix well,
vortex for 2 min, sonicate for 20 min, freeze in the refrigerator at -20°C for
10 min, centrifuge at 5000 r/min for 8 min, filter the supernatant with 0.45 μm organic microporous membrane,
and the filtrate is used for detection by high performance liquid
chromatography. The liquid phase conditions during the determination are:
Chromatographic column: C18 (4.6 mm Χ 250 mm, 5 μm); Mobile phase: 0.1% phosphoric acid aqueous solution:
Methanol = 68:32 (V:V); Flow rate 0.9 mL/min; Column temperature: 30°C;
Detection wavelength: 279 nm; Injection volume: 15 μL.
The test data are all expressed as
"mean ± standard error". Using SPSS 22.0 software, one-way
ANOVE analysis (DuncanD) was used to perform multiple comparisons between
means, and a significance test was performed. P < 0.05 was considered significant.
Table 3: Effects of different concentrations of TP on egg
quality on the 10th day
Egg quality Index |
CK |
0.02% TP |
0.05% TP |
0.09% TP |
0.14% TP |
0.19% TP |
0.24% TP |
Egg weight (g) |
54.134a
± 1.512 |
51.012ab
± 0.956 |
51.553ab
± 1.080 |
52.126ab
± 1.007 |
50.201b
± 1.030 |
51.133ab
± 1.184 |
52.066ab
± 0.959 |
Egg yolk weight (g) |
16.467a
± 0.318 |
16.113ab
± 0.241 |
15.842ab
± 0.501 |
15.854ab
± 0.294 |
15.073b
± 0.310 |
15.673ab
± 0.427 |
15.849ab
± 0.242 |
Egg white weight (g) |
29.442
± 1.230 |
27.470
± 0.654 |
28.346
± 0.703 |
29.376
± 0.716 |
27.539
± 0.826 |
28.239
± 1.208 |
28.738
± 0.925 |
Eggshell weight (g) |
7.052a
± 0.211 |
6.476ab
± 0.178 |
6.622ab
± 0.181 |
6.444ab
± 0.207 |
6.101b
± 0.180 |
6.680ab
± 0.238 |
6.495ab
± 0.202 |
Eggshell color |
48.500
± 1.885 |
53.371
± 1.396 |
48.679
± 1.492 |
50.273
± 1.074 |
52.740
± 1.226 |
49.814
± 1.802 |
51.536
± 1.662 |
Egg Shape Index |
1.419a
± 0.019 |
1.413a
± 0.015 |
1.372b
± 0.012 |
1.343b
± 0.012 |
1.345b
± 0.012 |
1.383ab
± 0.013 |
1.353b
± 0.014 |
Relative density (g/mL) |
1.086
± 0.001 |
1.085
± 0.002 |
1.086
± 0.002 |
1.138
± 0.054 |
1.080
± 0.002 |
1.084
± 0.002 |
1.084
± 0.001 |
Yolk color |
6.800
± 0.442 |
7.267
± 0.248 |
7.600
± 0.235 |
7.333
± 0.270 |
7.333
± 0.252 |
7.333
± 0.211 |
7.333
± 0.232 |
Haugh unit |
85.565
± 4.526 |
85.066
± 1.646 |
85.028
± 1.890 |
89.741
± 1.579 |
87.606
± 2.586 |
87.748
± 1.742 |
84.613
± 1.965 |
Eggshell thickness (mm) |
0.375a
± 0.005 |
0.349b
± 0.006 |
0.349b
± 0.008 |
0.349b
± 0.006 |
0.326c
± 0.005 |
0.349b
± 0.009 |
0.353b
± 0.005 |
Fig. 2: Effect
of adding different content of TP in diet on C content in egg yolk
It
can be seen from Fig. 1 that the EGCG content in the egg yolk of the 0.24% TP
group was significantly higher than that of the control group and the 0.02,
0.05, 0.09 and 0.14% TP groups (P < 0.05).
And reached the highest on the 30th day (19.171 μg/g), which was significantly higher than the 0.19% TP group
(P < 0.05).
It
can be seen from Fig. 2 that the C content in the egg yolk of the 0.24% TP
group was significantly higher than that of the CK group and the 0.02, 0.05,
0.09 and 0.14% TP groups (P < 0.05);
on the 10th day, the 0.19% TP group was significantly higher than
that in the 0.02% TP group (P < 0.05);
on the 20th day, the 0.19%TP group and 0.24%TP group was
significantly higher than the other groups (P
< 0.05). On the 30th day, the 0.19% TP group was
significantly higher than that of the CK group and the 0.02, 0.05 and 0.14% TP
groups. In addition, on the 30th day, the 0.24% TP group reached the
highest, which was 7.071 μg/g.
It
can be seen from Table 3 that on the 10th day, the egg weight, yolk
weight and eggshell weight of the 0.14% TP group were significantly lower than
that of the control group (P < 0.05);
the egg shape index of 0.05, 0.09, 0.14 and 0.24% TP groups were significantly
lower than those of control group and 0.02% TP group (P < 0.05); the eggshell thickness of all test groups was
significantly lower than the control group (P
< 0.05). There were no significant differences in egg white weight,
relative density, Haugh unit, egg shell color, egg yolk color and other egg
quality indexes of each group of eggs (P >
0.05).
It
can be seen from Table 4 that on the 20th day, the egg weight of the
0.19% TP group was significantly lower than the control group (P < 0.05); the egg yolk weight of the
0.14%TP group was significantly lower than the control group (P < 0.05); except for the 0.02% TP
group, the eggshell color of other test groups was significantly lower than
that of the control group (P < 0.05);
the relative density of the 0.24% TP group was significantly lower than that of
the 0.02 and 0.05% TP groups (P < 0.05);
in the 0.14 and 0.24% TP groups, the eggshell thickness was significantly lower
than that of the CK group (P < 0.05).
There were no significant differences in other egg quality indicators among the
groups (P > 0.05).
It
can be seen from Table 5 that on the 30th day, the egg weight in the
0.14% TP group was significantly lower than that in the control group, and the
egg yolk color in the 0.05 and 0.14% TP groups increased significantly (P < 0.05); the relative density of
the eggs in the 0.14% TP group was significantly lower than 0.05% TP group (P < 0.05); the Haugh unit of 0.24% TP
group was significantly lower than that of 0.14% TP group (P < 0.05); 0.09, 0.14, 0.19 and 0.24% TP groups eggshell
thickness is significantly lower than 0.05% TP group (P < 0.05); other egg quality indicators were not significantly
different among the groups (P > 0.05).
It
can be seen from Fig. 3 that on the 10th day, the egg production of
the 0.05 and 0.24% TP groups was significantly higher than that of the control
group, 0.14% TP, and 0.19% TP groups (P <
0.05); on the 20th day, the egg production of the 0.24% TP group
Significantly higher than the control group, 0.09% TP, 0.14% TP groups; on the
30th day, the egg production of 0.02, 0.05, 0.19, 0.24 TP group was
significantly higher than that of the control group, 0.09, 0.14% TP groups (P < 0.05).
Related studies have shown that dietary special substances
may have effect on the physiology of laying hens (Celebi 2019; Demir and Kaya
2020), and thus also may effect the quality and the nutritional components of
eggs (Wahab et al. 2019; Aydin and Bolukbasi 2020; Liu et al.
2020; Mahfuz et al. 2020). TP can improve health of the body, so it is widely used in
livestock and poultry feed. Studies have shown that EGCG can inhibit the body's
oxidative stress and inflammation, lower blood lipids and blood sugar, and
regulate gene expression and related signal pathways (Masuda et al. 2001; Khan et al. 2006; Wolfram et al.
2006; Bose et al. 2008; Tipoe et al. 2010). In addition, EGCG
stimulates the production of tumor necrosis factor (TNF-α) and interferon
(IFN-γ) by changing the immune response of macrophages, thereby increasing
the immune activity of macrophages and achieving the purpose of suppressing
tumors (Matsunaga et al. 2001).
Table 4: Effects of different concentrations of TP on egg
quality on the 20th day
Egg quality index |
CK |
0.02% TP |
0.05% TP |
0.09% TP |
0.14% TP |
0.19% TP |
0.24% TP |
Egg weight (g) |
54.295a
± 0.769 |
50.764ab
± 1.067 |
52.174ab
± 0.993 |
51.462ab
± 1.028 |
51.559ab
± 1.389 |
50.165b
± 1.080 |
52.397ab
± 1.136 |
Egg yolk weight (g) |
16.950a
± 0.304 |
16.125ab
± 0.365 |
15.900ab
± 0.224 |
15.990ab
± 0.240 |
15.671b
± 0.412 |
16.195ab
± 0.532 |
16.337ab
± 0.391 |
Egg white weight (g) |
29.931
± 0.841 |
27.289
± 0.795 |
28.705
± 0.712 |
28.257
± 0.798 |
29.853
± 1.232 |
27.481
± 0.824 |
28.800
± 1.137 |
Eggshell weight (g) |
6.674
± 0.233 |
6.600
± 0.176 |
6.859
± 0.154 |
6.599
± 0.149 |
6.720
± 0.225 |
6.414
± 0.137 |
6.686
± 0.277 |
Eggshell color |
55.260a
± 1.689 |
51.340ab
± 1.336 |
46.907b
± 1.748 |
49.973b
± 1.196 |
49.893b
± 0.989 |
50.087b
± 1.676 |
49.807b
± 2.181 |
Egg Shape Index |
1.374
± 0.015 |
1.395
± 0.016 |
1.391
± 0.016 |
1.365
± 0.016 |
1.382
± 0.014 |
1.381
± 0.012 |
1.376
± 0.010 |
Relative density (g/mL) |
1.084ab
± 0.003 |
1.090a
± 0.002 |
1.090a
± 0.002 |
1.089ab
± 0.002 |
1.085ab
± 0.002 |
1.087ab
± 0.002 |
1.082b
± 0.003 |
Yolk color |
7.300
± 0.213 |
7.333
± 0.159 |
7.143
± 0.143 |
7.400
± 0.254 |
7.267
± 0.228 |
7.267
± 0.206 |
7.000
± 0.138 |
Haugh unit |
82.640
± 3.410 |
83.572
± 2.988 |
81.247
± 1.994 |
82.374
± 3.446 |
85.288
± 1.402 |
83.431
± 1.960 |
83.646
± 2.362 |
Eggshell thickness (mm) |
0.371a
± 0.007 |
0.364ab
± 0.007 |
0.362ab
± 0.006 |
0.365ab
± 0.007 |
0.341bc
± 0.006 |
0.356ab
± 0.007 |
0.333c
± 0.011 |
Table 5: Effects of different concentrations of TP on egg
quality on the 30th day
Egg quality index |
CK |
0.02%TP |
0.05%TP |
0.09%TP |
0.14%TP |
0.19%TP |
0.24%TP |
Egg weight (g) |
54.058a
± 0.882 |
51.419ab
± 1.272 |
52.170ab
± 0.821 |
50.788ab
± 1.174 |
49.913b
± 1.008 |
51.717ab
± 1.217 |
51.608ab
± 0.608 |
Egg yolk weight (g) |
17.141
± 0.219 |
16.332
± 0.359 |
16.304
± 0.401 |
16.163
± 0.341 |
16.026
± 0.319 |
16.267
± 0.395 |
16.131
± 0.361 |
Egg white weight (g) |
30.598
± 0.872 |
27.786
± 0.916 |
28.245
± 0.384 |
27.901
± 0.998 |
27.828
± 1.003 |
27.981
± 0.967 |
28.552
± 1.110 |
Eggshell weight (g) |
30.598
± 0.872 |
27.786
± 0.916 |
28.245
± 0.384 |
27.901
± 0.998 |
27.828
± 1.003 |
27.981
± 0.967 |
28.552
± 1.110 |
Eggshell color |
51.260
± 1.721 |
49.467
± 1.811 |
48.547
± 1.865 |
51.247
± 1.295 |
50.680
± 1.799 |
50.073
± 1.678 |
48.414
± 1.565 |
Egg Shape Index |
1.381
± 0.020 |
1.399
± 0.011 |
1.387
± 0.013 |
1.376
± 0.016 |
1.373
± 0.013 |
1.383
± 0.013 |
1.367
± 0.013 |
Relative density (g/mL) |
1.081ab
± 0.001 |
1.085ab
± 0.002 |
1.086a
± 0.002 |
1.082ab
± 0.001 |
1.080b
± 0.002 |
1.081ab
± 0.002 |
1.081ab
± 0.002 |
Yolk color |
6.933c
± 0.153 |
7.286abc
± 0.163 |
7.867a
± 0.192 |
7.333abc
± 0.187 |
7.600ab
± 0.254 |
7.067bc
± 0.228 |
7.091bc
± 0.211 |
Haugh unit |
70.898ab
± 2.460 |
69.974ab
± 2.180 |
73.249ab
± 2.108 |
73.062ab
± 2.199 |
74.646a
± 1.865 |
69.715ab
± 3.229 |
66.692b
± 2.678 |
Eggshell thickness (mm) |
0.349abc
± 0.006 |
0.363ab
± 0.008 |
0.370a
± 0.007 |
0.335c
± 0.005 |
0.329c
± 0.007 |
0.343bc
± 0.009 |
0.345bc
± 0.010 |
Fig. 3: Effect
of adding different content of TP in diet on egg production
Compared
with EGCG, C occupies a smaller proportion in TP, and its antioxidant and
anti-inflammatory activities have been confirmed in some studies (Moraeset al. 2014). However, there is no report
on the analysis of TP composition in eggs by adding TP to the diet. In this
experiment, Gallus domestiaus was
used as the experimental animal to study the effect of dietary supplementation
of TP on the content of EGCG and C in eggs. The results showed that the content
of EGCG in egg yolk increased with the increase of TP.
On
the 30th day, the content of EGCG in egg yolk of 0.24% TP group was
significantly higher than that of control group and other experimental groups.
On the 30th day, the content of EGCG in egg yolk of 0.24% TP group
was the highest, reaching 19.171 μg/g. On the 10th, 20th
and 30th day, the content of C in yolk of 0.24% TP group was
significantly higher than that of control group and 0.02, 0.05, 0.09 and 0.14%
TP groups. On the 30th day, the C content in yolk of 0.24% TP group
was the highest, reaching 7.071 μg/g.
Comprehensive analysis suggests that the content of EGCG and C in egg yolk
increases with the increase of dietary TP. Adding a higher concentration of TP
can significantly increase the enrichment of EGCG and C in egg yolk. The
results of this study provide a theoretical and practical basis for the
development of TP rich functional eggs.
Egg
weight is an important indicator for evaluating egg grade. Egg weight is
affected by the type of layer, the composition of the diet, the age of the
layer, the breeding environment and other conditions. Wang xiaohong and other
studies have shown that dietary supplementation of 400 mg/kg TP can
significantly reduce the average egg weight in the first 4 weeks of the test
period (Wang et al. 2017). Other
studies have shown that dietary supplementation of catechins can increase the
fertilization rate and hatchability of quail and prolong the shelf life of
eggs, but it reduces egg weight and egg shell quality (Kara et al. 2016). The results of this test
show that during the entire test period, compared with the control group, the
egg weight of each test group has a tendency to decrease, which is basically
consistent with the above research results. The analysis may be due to the
anti-nutrients factors such as phenolic acid and caffeine contained in TP that
can destroy or hinder the digestion and absorption of certain nutrients in
laying hens; or catechins inhibit the intestinal absorption of fat and the
activity of fat synthase, affect the formation of egg yolk lipids, thereby
reducing egg weight (Yamane et al.
1999; Kojlma and Yoshida 2008).
The
color of egg yolk is also an important sensory index
for evaluating egg quality, it mainly depends on the type and quantity
of carotenoids obtained by the laying hens from the diet. In this experiment,
on the 10th day, the egg yolk color of each test group was higher
than that of the control group. On the 30th day, compared with the
control group, the egg yolk color of the 0.05 and 0.14% TP groups were
significantly increased by 13.47 and 9.62%, respectively. The results indicate
that adding TP to the diet of laying hens can improve the color of egg yolk,
and the specific mechanism remains to be further studied.
The
thickness of the eggshell is generally 0.3~0.4 mm. If the eggshell is too thin,
it will affect the storage, transportation and sales of the egg; if the
eggshell is too thick, the hatching rate of the laying hen will be reduced (Zhao
et al. 2017). During the experiment,
the eggshell thickness of each experimental group was 0.3~0.4 mm. On the 10th
day, the eggshell thickness of each test group was significantly lower than
that of the control group. On the 20th day, the eggshell thickness
of the 0.14% TP group and 0.24% TP group was significantly lower than that of
the control group. The analysis may be due to the caffeine contained in TP. Studies
have shown that the intake of caffeine in the body will lead to the decrease of
calcium absorption and loss of calcium in the digestive tract, and reduce bone
mineral density (Tsuang et al. 2006),
which will reduce the thickness of the eggshell and affect the quality of the
eggshell.
Egg
production is one of the important economic traits of laying hens. Studies have
shown that when the Roman layer is 30 weeks old, adding 6000 mg/kg of green tea
powder and 1000 mg/kg of TP to the diet can significantly increase the egg
production rate of the layer (Xiao 2010). Because
TP has anti-oxidant and antibacterial properties, scavenge free
radicals, and improve the intestinal microbial environment. It can improve
absorption and utilization of nutrients in the diet, thereby increasing feed
conversion rate and egg production. The results of this test showed that during
the entire test period, the egg production of the 0.24% TP group was
significantly higher than that of the control group, and the egg production of
other test groups also tended to be higher than that of the control group. The
experimental results are similar to the above result, which is, adding higher
concentration of TP can improve the egg production of laying hens.
Adding a certain amount of TP to
the diet can significantly increase the content of EGCG and C in the yolk,
which has a certain impact on the egg weight, yolk color, and eggshell
thickness. Adding high concentrations of TP can increase egg production.
We acknowledge the financial
supports of Tianjin Enterprise Technology Commissioner Project (19JCTPJC59500);
the Major Special Scientific and Technological Project and Engineering Project
of Tianjin (18ZXBFNC00310) and the 131 Innovative Talent Team Building
Project of Tianjin (20180318).
LA Li designed this study; ZZ Fan, MR Qin, ZM Zhang, KY Zhang and Q Wang conducted the
experiments; ZZ Fan, CN Wu,
YQ
Zhang and SQ Mao
analyzed the main data; ZZ Fan and LA Li wrote the manuscript.
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