Journal of Food Science & Technology

ISSN: 2472-6419

Impact Factor: 1.265

VOLUME: 5 ISSUE: 1

Page No: 8-17

Effects of long-term dietary glycerol monolaurate supplementation on productivity, egg quality, intestinal mucosal morphology and serum parameters of laying hens


Affiliation

Haiying Cai1,2, Mengyun Liu2, Jing Li1, Chenggang Cai1, Minjie Zhao2,*, Fengqin Feng2,*

1 Zhejiang Key Lab for Chem & Bio Processing Technology of Farm Product, School of Biological and Chemical Engineering, Zhejiang University of Science and Technology, Hangzhou 310023, China;

2 College of Biosystems Engineering and Food Science, Zhejiang University, Hangzhou, 310058, China

Citation

Haiying Cai, Mengyun Liu, Jing Li, Chenggang Cai, Minjie Zhao, Fengqin Feng, Effects of long-term dietary glycerol monolaurate supplementation on productivity, egg quality, intestinal mucosal morphology and serum parameters of laying hens(2020)Journal of Food Science & Technology 5(1) pp:8-17

Abstract

Objective: This study evaluated the long-term effects of supplementation with a medium-chain monoglyceride, glycerol monolaurate (GML), on the productive performance, egg quality, intestinal mucosa structure and serum parameters of laying hens.

Methods: A total of 120 17-week-old Hy-Line brown laying hens were randomly distributed into 4 groups with 5 replicates and 6 hens per replicate, that were fed corn-soybean meal-based diets supplemented with 0, 0.15, 0.30 or 0.45 g/kg GML for 52 weeks.

Results: The results showed that, compared with the control group, the laying rate and average egg weight in the 0.30 g/kg GML group were significantly increased (p<0.05), and the feed conversion ratio in the 0.30 g/kg GML group was significantly decreased (p<0.05) from 58 to 69 weeks. At 58 weeks of age, eggshell thickness was significantly increased (p<0.05) in the 0.15 and 0.30 g/kg GML groups. At 69 weeks of age, eggshell thickness and eggshell strength were significantly increased (p<0.05) in all the GML groups. In the serum, the activities of aspartate transaminase and alkaline phosphatase were significantly decreased (p<0.05) in all the GML groups. The activity of glutamic-pyruvic transaminase and the total cholesterol and low-density lipoprotein-cholesterol concentrations were significantly decreased (p<0.05) while the high-density lipoprotein-cholesterol concentration was significantly increased (p<0.05) in the 0.30 and 0.45 g/kg GML groups. Regarding intestinal morphology, supplementation with 0.30 g/kg GML significantly increased (p<0.05) the villus height and crypt depth of the duodenum, the villus height of the jejunum and the villus length to crypt depth ratio of the jejunum.

Conclusion: These results suggest that GML supplementation during weeks 58-69 could improve laying performance and egg quality in laying hens, possibly because of the favorable effects of GML on the intestinal mucosa structure, lipid profiles and liver function.

Keywords: Laying Hens; Glycerol Monolaurate; Egg Quality; Intestinal Morphology; Serum Property

Introduction

Antibiotics have been extensively applied in the poultry industries to prevent disease and infections, improve growth and productivity performance, and increase efficiency of feed utilization [1]. However, an increasing number of countries have gradually restricted or banned the use of antibiotics as feed additives due to growing concerns regarding outbreaks of resistant bacteria [2], and potential damage to gut microbiota [3]. Given these concerns, alternatives to antibiotics as feed additives has been developed by feed additive researchers and manufacturers of animal nutrition, including feed enzymes, fatty acids, probiotics, prebiotics and plant extracts [4]. Medium chain fatty acids (MCFAs) have been reported to be effective as feed additives in improving serum lipid profiles, decreasing fatty deposition and regulating gut structure in laying hens and broilers [5]. Zeitz et al. [6] showed that dietary fats rich in lauric and myristic acids increased the feed conversion efficiency and breast meat percentage of broilers and attributed this to the improvements of gut health.

Glycerol monolaurate (GML), a monoglyceride of lauric acid, naturally exists in breast milk, coconut oil and palm oil [7]. The antimicrobial property of GML suggests GML has potential as an alternative to antibiotics. GML has broad antimicrobial activity, and is especially effective against Gram-positive bacteria such as Staphylococcus aureus and Bacillus, possibly through the disruption of the plasma membranes of the bacteria [8]. In addition, GML is effective in killing bacterial spores and some Staphylococcus aureus strains with antibiotic-resistant biofilms [9]. Furthermore, GML has been reported to prevent simian immunodeficiency virus (SIV) transmission and postoperative infection due to its strong antiviral properties [10]. With digestion and absorption features similar to those of MCFAs, GML has also been used to regulate animal physiological function and gut microbiota [11]. Zhang et al. reported that GML can modulate human immune system by regulating lipid dynamics in T cells and preventing cytokine production and exotoxin stimulation [12]. For the above reasons, GML has been investigated for its effects as a feed additive on the health, productivity and egg properties of chickens [13]. In addition, Yuniwarti et al. [14] found that virgin coconut oil containing lauric acid as a dietary supplement could be converted into GML in the body of broilers and increase chicken body weight.

In our preliminary study, short-term GML supplementation was found to significantly improve the body weight and physiological and biochemical parameters of broilers and laying hens (data not shown). The present work aimed to evaluate, for the first time, the long-term effects of basal diets supplemented with GML on the productive performance, egg quality, intestinal mucosa structure and serum parameters of Hy-Line Brown laying hens. The results of this study may further contribute to the broader application of GML and provide insight into its potential as an alternative of antibiotics.

Materials & Methods

2.1. Husbandry and experimental diets

The protocol was approved by the Institutional Animal Care and Use Committee of Zhejiang University (Protocol No. ZJU-BEFS-2016004), and the experiments were conducted according to the Guide for the Care and Use of Laboratory Animals published by the National Institutes of Health.

One hundred twenty Hy-Line Brown hens of 17 weeks of age were randomly assigned to 4 groups. Each treatment consisted of 5 replicates with 6 hens per replicate and was randomly distributed in the facility. Three adjacent cages (38 × 35 × 28 cm; length × width × height) with 2 birds per cage were considered as an experimental replicate. The hens were housed in cages with a light regime of 16L:8D with free water and food intake. A phase feeding program (phase I: 17 to 58 weeks of age; phase II: 59 to 69 weeks of age) was used with different diets, which were corn-soybean meal-based and formulated to meet the nutrient requirements of the National Research Council (NRC, 2012). The compositions of the diets for phase I and II are shown in Table 1. Hens in the control group were fed with the basal diet, whereas hens in other 3 experimental treatments received the basal diets supplemented with 0.15, 0.30 and 0.45 g/kg GML, respectively. GML was purchased from Hangzhou Kangyuan Food Science and Technology Co., Ltd. (Hangzhou, China).

Table 1. Ingredient composition and nutrient levels of basal diets (g/kg).

Item

Value

Phase I

Phase II

Ingredients

 

 

Corn

62.9

64.9

Soybean meal

23.85

21.78

Pebble

4.51

4.51

Limestone

3.42

3.42

Vitamin-mineral premix1

4.7

4.7

Cod-liver oil

0.03

0.03

Rapeseed oil

0.59

0.66

Calculated analysis

 

 

 ME (MJ kg-1)

11.85

11.98

 Crude protein

16.1

15.8

 Crude fat

28.6

29.1

 Lys

0.81

0.75

 Met + Cys

0.65

0.60

 Met

0.35

0.32

 Ca

3.73

3.78

 P

0.60

0.57

1 Providing, per kg diet: vitamin A (from vitamin A acetate), 9940 IU; vitamin D3, 4950 IU; vitamin E (from DL-α-tocopheryl acetate), 24 mg; vitamin B1, 2 mg; vitamin B2, 5.8 mg; vitamin B6, 3 mg; vitaminB12, 0.020 mg; biotin, 0.15 mg; Cu, 25 mg; Fe, 746 mg; Mn, 149 mg; Zn, 65 mg; Se, 0.30 mg.

Phase I: 17 - 58 weeks of age, Phase II: 59 - 69 weeks of age. ME: metabolizable energy; Ca: calcium; P: phosphorus.

 

2.2. Production performance

Egg production, egg weight, and mortality were recorded daily during the trial. The laying rate was defined as the ratio of the total number of laid eggs to the number of laying hens. Feed intake each week was determined by subtracting the weight of the remaining feed from the weight of the feed provided. The feed conversion ratio (FCR) was calculated as grams of total feed intake per gram of egg weight.

 

2.3. Egg quality

A total of 75 eggs per treatment (15 eggs from each replicate) laid on the last week of the 58th and 69th weeks, were randomly collected to determine the egg quality. The eggs were broken and separated into shell, albumen and yolk for weighing and their proportions were calculated. The egg quality parameters, including albumen height, Haugh unit, yolk color, eggshell strength and eggshell thickness, were measured with a digital egg tester (DET-6000, Nabel Co., Ltd., Japan).

 

2.4. Serum parameters

At the end of the trial, blood samples of 3 hens per replicate were collected via axillary vein after a 12 h fast. Each sample was immediately centrifuged at 3000 r min-1 for 15 min. The serum was decanted into a 1.5 mL polypropylene tube and stored at -80 ºC for the subsequent detection of serum parameters. The activities of aspartate transaminase (AST), alkaline phosphatase (ALP), glutamic-pyruvic transaminase (GPT), and gamma glutamyl transferase (GGT) and the concentrations of triglyceride, total cholesterol, high-density lipoprotein-cholesterol (HDLC), low density lipoprotein-cholesterol (LDLC), blood urea nitrogen, total protein, albumin, globulin, total bilirubin, creatinine, calcium (Ca), and phosphorus (P) in the serum were determined using commercially available kits (Jiancheng Co., Ltd., Nanjing, China) and automatic analyzers (COBASC 311, Roche Group, Switzerland).

 

2.5. Intestinal mucosa structure

At the end of the trial, 1 cm sections of the duodenum, jejunum and ileum from the medial portion were collected from laying hens, washed with physiological saline solution and fixed in 4% buffered paraformaldehyde. The tissue samples were embedded in paraffin, serially sectioned to 20 μm thickness, and then stained with hematoxylin and eosin. The villus height and crypt depth (4 hens from each replicate) were observed and measured with an optical microscope (DM4000B, LEICA Co. Ltd., Germany). The villus height to crypt depth ratio (VCR) of the duodenum, jejunum and ileum was calculated as the villus length divided by the crypt depth.

 

2.6. Statistical analysis

The data were analyzed by one-way analysis of variance (ANOVA) using SPSS 20.0 (SPSS Inc., Chicago, IL, USA). The results are expressed as the means ± standard deviations (SD). Differences among treatments were separated by the Tukey test for multiple comparisons, and probability values less than 0.05 were considered as significant.

Results

3.1. Productive performance

The effects of GML supplementation on the productive performance of laying hens are shown in Table 2. During phase I, phase II and the whole trial, no significant difference in the body weight or mortality rate was observed among the treatments. Relative to that in the control group, the laying rate in the 0.30 g/kg GML group was significantly increased (P<0.05) by 1.47%, 7.08% and 2.57% during phase I, phase II and the whole trial, respectively. The laying rate in the 0.15 g/kg GML group was increased slightly relative to that in the control group, but the difference was not significant. However, relative to that in the control group, the laying rate in the 0.45 g/kg GML group was significantly decreased (P<0.05) by 3.39% during phase II and slightly but not significantly decreased during phase I, indicating that the effect of GML on laying rate was dose-dependent. The highest average egg weight was observed in the laying hen group receiving 0.30 g/kg GML (65.36 g) and was significantly higher than that of the control group (P<0.05). In the other GML groups, dietary GML supplementation had no significant effect on average egg weight during phase I or phase II. Feed intake was slightly decreased following 0.15, 0.30 and 0.45 g/kg dietary GML supplementation in both phase I and phase II, but did not significantly differ from that of the control group. In addition, relative to the control treatment, 0.15 and 0.30 g/kg dietary GML supplementation decreased the FCR, whereas 0.45 g/kg GML slightly increased the FCR; however, a significant difference from the control value was observed only for the 0.30 g/kg GML group during phase II. These results confirmed that 0.30 g/kg dietary GML supplementation was optimal in this trial. In addition, the trends across the different levels of GML supplementation with respect to the effects of GML on the production performances were very similar between the two phases.

 

Table 2. Effects of different levels of GML supplementation on productive performance of hens

Item

Control

GML (g/kg diet)

0.15

0.30

0.45

Laying rate (%)

 

 

 

 

  Phase I

85.67 ± 0.45bc

86.53 ± 0.31ab

86.93 ± 0.35a

85.47 ± 0.32c

  Phase II

80.50 ± 0.26b

80.95 ± 0.14b

86.20 ± 0.36a

77.77 ± 0.81c

  Whole trial

84.60 ± 0.30bc

85.40 ± 0.30b

86.77 ± 0.25a

83.90 ± 0.69c

Average egg weight (g)

 

 

 

 

  Phase I

61.81 ± 0.43ab

62.37 ± 0.40a

62.33 ± 0.15a

61.30 ± 0.36b

  Phase II

64.39 ± 0.29bc

65.23 ± 0.32ab

65.36 ± 0.47a

64.03 ± 0.25c

  Whole trial

62.28 ± 0.30ab

62.97 ± 0.35a

63.04 ± 0.42a

61.89 ± 0.26b

Feed intake (g hen-1 per day)

 

 

 

 

  Phase I

106.33 ± 1.53

105.67 ± 2.08

105.69 ± 2.52

105.67 ± 1.53

  Phase II

109.33 ± 1.53

108.33 ± 2.08

109.00 ± 2.00

109.06 ± 1.04

  Whole trial

106.96 ± 1.30

106.22 ± 1.72

106.36 ± 1.58

106.36 ± 1.29

FCR (g:g)

 

 

 

 

  Phase I

2.01 ± 0.03

1.96 ± 0.04

1.95 ± 0.04

2.02 ± 0.04

  Phase II

2.11 ± 0.02ab

2.05 ± 0.04b

1.93 ± 0.04c

2.19 ± 0.03a

  Whole trial

2.03 ± 0.03ab

1.98 ± 0.04ab

1.94 ± 0.04b

2.05 ± 0.04a

Different letters in the same row indicate values significantly different (P<0.05) among the groups. Phase I: 18 - 58 weeks of age, Phase II: 59 - 69 weeks of age, the whole trial: 18 - 69 weeks of age. FCR: feed conversion ratio.

 

Our results showed that long-term dietary GML supplementation significantly influenced the productive performance of laying hens, which is consistent with the reported effects of MCFAs as feed additives [15]. Van et al. [15] found that replacing part of the soybean oil and animal fat in the broiler diet with 0.3% capric acid and 2.7% lauric acid could improve the FCR. Moreover, MCFAs have been reported to improve productive performance and egg quality in poultry feeding, possibly through beneficial effects on digestion, adsorption, physiological regulation and gut health [16]. As one of the monoglycerides of MCFAs, GML might improve productive performance and egg quality in laying hens via similar mechanisms.

 

3.2. Egg quality

The effects of the different diets on the egg quality of laying hens were evaluated and are shown in Table 3. Albumen height and Haugh unit were increased by 0.30 g/kg dietary GML supplementation at the 58th and 69th weeks, but the differences were not significant. No effect of 0.15 or 0.45 g/kg GML supplementation was observed, and compared with the control group, the 0.45 g/kg GML group had higher values of albumen height and Haugh units at the 58th week but lower values of these variables at the 69th week. These results implied that the optimal concentration of GML might differ among different phases; therefore, in the present study, we divided the trial period into two feeding phases (phase I and II) for analysis. Different effects of feed additives among different feeding phases have also been observed in another research [17]. Compared with the control group, the yolk color was not significantly affected by dietary GML supplementation at the 58th week but was significantly (P<0.05) improved by 11.11% and 14.60% in the 0.30 and 0.45 g/kg GML groups, respectively, at the 69th week. In addition, relative to that in the control group, eggshell thickness was significantly (P<0.05) increased by 5.56% and 8.33% in the 0.15 and 0.30 g/kg GML groups, respectively, at the 58th week and by 8.33% in all three groups at the 69th week. Much greater eggshell strengths were observed at the 69th week in all the groups compared with the control group, with eggshell strength significantly (P<0.05) increasing by 5.71%, 6.49% and 6.75% in the 0.15, 0.30 and 0.45 g/kg GML groups, respectively. Regarding the egg components, compared with the control group, at the 58th week, the albumen proportion was significantly (P<0.05) increased by 4.53% in the 0.30 g/kg GML group, and the yolk proportion was significantly increased by 3.62% in 0.45 g/kg GML group. In addition, no significant change in albumen and yolk content was observed in all the groups at the 69th week. Relative to that in the control group, the eggshell proportion was significantly increased in the 0.30 and 0.45 g/kg GML groups at the 58th week and in the 0.15 g/kg GML group at the 69th week.

 

Table 3. Effects of different levels of GML supplementation on egg quality of laying hens

Item

Control

GML (g/kg diet)

0.15

0.30

0.45

Albumen height (mm)

 

 

 

 

  58 weeks of age

6.93 ± 0.5

6.54 ± 0.8

7.10 ± 0.7

7.21 ± 0.7

  69 weeks of age

7.91 ± 0.5

7.63 ± 0.8

8.02 ± 0.9

7.84 ± 0.6

Haugh units

 

 

 

 

  58 weeks of age

79.47 ± 3.83

81.41 ± 5.76

82.88 ± 4.66

83.73 ± 4.53

  69 weeks of age

85.26 ± 2.21

85.54 ± 2.32

85.34 ± 3.34

85.17 ± 2.03

Yolk color

 

 

 

 

  58 weeks of age

7.02 ± 0.48

7.00 ± 0.32

7.04 ± 0.47

7.08 ± 0.45

  69 weeks of age

6.30 ± 0.48c

6.56 ± 0.52bc

7.00 ± 0.47ab

7.22 ± 0.67a

Eggshell thickness (mm)

 

 

 

 

  58 weeks of age

0.36 ± 0.01b

0.38 ± 0.02a

0.39 ± 0.02a

0.37 ± 0.02ab

  69 weeks of age

0.36 ± 0.01b

0.39 ± 0.02a

0.39 ± 0.01a

0.39 ± 0.02a

Eggshell strength (kgf m-2)

 

 

 

 

  58 weeks of age

3.42 ± 0.43b

4.00 ± 0.46a

3.76 ± 0.42ab

3.70 ± 0.44ab

  69 weeks of age

3.85 ± 0.13b

4.07 ± 0.16a

4.10 ± 0.23a

4.11 ± 0.16a

Albumen proportion (%)

 

 

 

 

  58 weeks of age

56.79 ± 1.62b

56.04 ± 0.83b

59.36 ± 0.60a

56.87 ± 1.35b

  69 weeks of age

58.72 ± 3.32

59.60 ± 2.48

58.58 ± 1.77

58.19 ± 2.17

Yolk proportion (%)

 

 

 

 

  58 weeks of age

26.78 ± 1.09b

27.02 ± 0.79ab

27.21 ± 0.79ab

27.75 ± 0.76a

  69 weeks of age

26.69 ± 1.50

26.65 ± 1.63

26.46 ± 1.32

26.62 ± 1.62

Eggshell proportion (%)

 

 

 

 

  58 weeks of age

9.23 ± 0.22b

9.15 ± 0.24b

9.51 ± 0.30a

9.62 ± 0.27a

  69 weeks of age

8.86 ± 0.50b

9.48 ± 0.40a

9.06 ± 0.59ab

9.16 ± 0.48ab

Different letters in the same row indicate values significantly different (P<0.05) among the groups. Measured as a proportion (weight on weight) of the whole egg, expressed in percentage (%). kgf: kilogram force.

 

Adequate eggshell strength and thickness are essential for protection against the penetration of and contamination with pathogens. Eggshell quality is influenced by many factors, such as genetics, environment, nutrition, and the health status of layer hens [18]. Our study showed that the dietary GML supplementation increased eggshell thickness, eggshell strength and eggshell proportion. Lee et al. [16] reported that a microencapsulated organic acid blend (17% fumaric acid, 13% citric acid and 10% malic acid) containing 1.2% MCFAs (capric and caprylic acids) improved egg production, eggshell strength, Haugh unit and serum Ca concentration in laying hens, indicating that the positive effects of MCFAs and GML treatment on the eggshell parameters were possibly related to improved calcium absorption. Moreover, the improvements in the egg quality of the yolk proportion and color might be attributable to changes in lipid compositions because GML was reported to promote the absorption of lipid and lipid soluble pigments, such as zeaxanthin in the diet as an effective emulsifier [19].

 

3.3. Serum parameters

The influences of different level of GML supplementation on the serum biochemical indices of laying hens were analyzed (Table 4). In the 0.15, 0.30 and 0.45 g/kg GML groups, AST activity was significantly decreased relative to that in the control group by 14.86%, 17.20% and 7.11%, respectively, and ALP activity was significantly decreased by and 16.60%, 49.35% and 28.38%, respectively. Furthermore, the GPT activity was significantly decreased compared with the control level by 34.36% and 21.00% in the 0.30 and 0.45 g/kg GML groups, respectively. In the other GML groups, the GGT activity was lower than that in the control group, but the differences were not significant. Relative to that in the control group, the total cholesterol concentration was significantly decreased by 22.70%, 44.99% and 42.74% in the 0.15, 0.30 and 0.45 g/kg GML groups, respectively. In the 0.30 and 0.45 g/kg GML groups, the LDLC concentration was significantly decreased relative to the control concentration by 30.16% and 44.44%, respectively, whereas the HDLC concentration was significantly increased by 27.39% and 35.22%, respectively. No significant effect of treatment was observed on the concentration of serum triglyceride, urea nitrogen, total protein, albumin, globulin, total bilirubin or creatinine. Ca concentration was significantly increased by 24.87% in the 0.30 g/kg GML group relative to the control group, which indicated that the positive effect of GML on Ca absorption might have accounted for the enhanced eggshell strength in laying hens. However, no significant effect of treatment was observed on P concentration.

 

Table 4. Effects of different levels of GML supplementation on serum parameters of laying hens (69 weeks of age)

Item

Control

GML (g/kg diet)

0.15

0.30

0.45

AST (IU/L)

223.32 ± 8.88a

190.14 ± 6.40c

184.90 ± 8.12c

207.44 ± 10.75b

ALP (IU/L)

672.40 ± 36.15a

560.80 ± 48.87b

340.60 ± 59.90c

481.60 ± 79.72b

GPT (IU/L)

13.62 ± 0.93a

11.84 ± 1.39ab

8.94 ± 0.91c

10.76 ± 0.73bc

GGT (IU/L)

23.00 ± 1.58

22.60 ± 2.41

22.40 ± 1.14

21.60 ± 2.30

Triglyceride (mmol/L)

12.61 ± 0.69

13.09 ± 0.59

13.20 ± 0.30

12.84 ± 0.61

Total Cholesterol (mmol/L)

4.89 ± 0.57a

3.78 ± 0.38b

2.69 ± 0.40c

2.80 ± 0.33c

LDLC (mmol/L)

0.63 ± 0.08a

0.75 ± 0.14a

0.44 ± 0.07b

0.35 ± 0.07b

HDLC (mmol/L)

2.30 ± 0.12b

2.60 ± 0.45ab

2.93 ± 0.40a

3.11 ± 0.20a

Blood urea nitrogen (mmol/L)

0.44 ± 0.11

0.42 ± 0.04

0.36 ± 0.09

0.32 ± 0.13

Total protein (g/L)

55.98 ± 3.28

55.28 ± 2.83

54.40 ± 1.28

53.10 ± 2.10

Albumin (g/L)

18.30 ± 1.16

17.04 ± 1.30

18.28 ± 1.85

18.36 ± 0.58

Globulin (g/L)

37.68 ± 3.01

38.24 ± 3.01

36.12 ± 1.59

34.74 ± 2.35

Total bilirubin (μmol/L)

0.84 ± 0.05

0.88 ± 0.08

0.92 ± 0.08

0.88 ± 0.08

Creatinine (μmol/L)

9.20 ± 0.84

9.24 ± 0.87

10.03 ± 1.02

9.80 ± 1.30

Ca (mmol/L)

5.59 ± 0.36b

6.09 ± 0.44b

6.98 ± 0.28a

6.15 ± 0.21b

P (mmol/L)

1.68 ± 0.14

1.79 ± 0.22

1.88 ± 0.31

1.63 ± 0.17

Different letters in the same row indicate values significantly different (P<0.05) among the groups. AST: aspartate transaminase; ALP: alkaline phosphatase; GPT: glutamic-pyruvic transaminase; GGT: gamma glutamyl transferase; LDLC: low-density lipoprotein cholesterol; HDLC: high density lipoprotein cholesterol.

 

The cholesterol profile was significantly improved in laying hens receiving GML supplementation in this study, which is consistent with the effects of MCFAs [22]. MCFAs and medium-chain triglycerides have been reported to enhance the capacity to transport excess cholesterol and to lower serum cholesterol levels [23]. Shokrollahi et al. [22] showed that dietary MCFAs (caproic acid < 3%, caprylic acid = 30%, capric acid = 56%, lauric acid = 10%, other fatty acids < 0.03%) significantly decreased LDLC and total cholesterol level, and increased the level of HDLC. Additionally, Zeng et al. [24] reported that dietary MCTs significantly prevented abdominal fat accumulation in high fat diet-fed mice without affecting serum total triglyceride concentration. These reports suggest that GML might play important roles in the modulation of lipid metabolism by regulating cholesterol metabolism, a possibility that requires further investigation.

 

3.4. Intestinal mucosa structure

The effects of the different levels of GML supplementation on the intestinal mucosa structure of laying hens are shown in Table 5 and Figure 1. Relative to the values in the control group, the villus height and crypt depth of the duodenum were significantly increased by 17.74% and 10.55%, respectively, in the 0.15 g/kg GML group and by 17.63% and 11.27%, respectively, in the 0.30 g/kg GML group. The villus height of the jejunum was significantly increased by 3.06% in 0.15 the g/kg GML group, and the VCR of the jejunum was significantly increased by 21.08%, 9.48% and 7.52% in the 0.15, 0.30 and 0.45 g/kg GML groups, respectively.

 

Table 5. Effects of different levels of GML supplementation on intestinal mucosa structure of laying hens (69 weeks of age)

Intestine

Item

Control

GML (g/kg diet)

0.15

0.30

0.45

Duodenum

Villus length (μm)

166.37 ± 4.34c

195.89 ± 5.78a

183.93 ± 9.09b

159.78 ± 4.55c

Crypt depth (μm)

28.93 ± 1.06b

34.03 ± 1.36a

32.19 ± 1.64a

28.68 ± 0.74b

VCR (μm:μm)

5.75 ± 0.16

5.76 ± 0.13

5.72 ± 0.12

5.57 ± 0.09

Jejunum

Villus length (μm)

139.42 ± 7.30b

169.96 ± 6.68a

143.68 ± 4.18b

150.25 ± 8.94b

Crypt depth (μm)

22.80 ± 1.39

22.95 ± 0.56

21.45 ± 0.79

22.82 ± 1.14

VCR (μm:μm)

6.12 ± 0.06c

7.41 ± 0.34a

6.70 ± 0.24b

6.58 ± 0.15b

Ileum

Villus length (μm)

127.85 ± 5.38

120.11 ± 13.66

123.84 ± 9.22

123.59 ± 5.83

Crypt depth (μm)

28.42 ± 0.72

28.35 ± 0.62

27.25 ± 0.70

28.22 ± 0.82

VCR (μm:μm)

4.50 ± 0.27

4.23 ± 0.41

4.54 ± 0.31

4.38 ± 0.28

Different letters in the same row indicate values significantly different (P<0.05) among the groups.

 

https://www.sdrpjournals.com/articles/images/10589/1.png

Figure 1. Intestinal morphology (duodenum, jejunum and ileum) of laying hens fed diet with 0, 0.15, 0.30 or 0.45 g/kg GML supplementation.

Villus height and crypt depth are important indices of intestinal digestion and absorption capacity, which are mainly determined by the rates of enterocyte regeneration and apoptosis [25]. Hanczakowska et al. [26] reported that dietary MCFA (2 g/kg capric acid) significantly increased the villus height and crypt depth of piglets by 31.33% and 20.71%, respectively. The improvement to the intestinal epithelial cell structure of laying hens due to GML supplementation in this study is consistent with a previous study of dietary MCFAs supplementation [26], which confirms that GML and MCFAs improve productive performance by influencing digestion and adsorption via a similar mechanism. As medium-chain glycerides can be directly consumed as energy sources for enterocytes [5], dietary GML supplementation could stimulate enterocyte renewal and differentiation, thereby increasing the villus height and crypt depth. Moreover, the in vivo antibacterial effects of GML could contribute to improving intestinal health of animals by regulating the gut microbiota and inhibiting bacterial toxin production and inflammation reactions [11]. The potent anti-inflammatory action of GML could reduce the release of macrophages and the excess production of pro-inflammatory cytokines, which cause tissue damage and increase energy expenditure by interfering with adenosine triphosphate (ATP) synthesis and producing intensive stress proteins nonessential for growth [27]. Moreover, unlike the parameters in the upper digestive tract (duodenum and jejunum), the villus height, crypt depth and VCR of ileum were not significantly influenced by GML supplementation, suggesting selective effects of GML on metabolite and gut microbiota modulation, which is consistent with previous study [28].

Conclusion

The abuse of antibiotics in poultry feed has caused a series of problems, including antibiotic residues in meat and egg products, disorders of human gut microbiota, contamination of the environment, and the development and spread of antibiotic-resistant bacteria, which calls for research and development on natural alternatives to antibiotics. GML is generally recognized as safe by the USA Food and Drug Administration and has been widely used as a food additive for its emulsifying and antimicrobial properties. Analysis of serum plasma parameters and intestinal mucosa morphology in this study supported the view that GML is a safe and advantageous substitute for traditional antimicrobial drugs in the poultry industry. In addition, dietary GML supplementation was proven to be useful for improving productive performance and egg quality in laying hens. These improvements are possibly the results of the improved intestinal mucosa structure and serum physiological and biochemical parameters,. Collectively, these results suggested that GML has promise as an alternative to conventional antimicrobials in laying hens to improve weight gain and feed conversion. Furthermore, these results suggest that GML has potential as a functional feed additive to increase laying performance and egg quality, possibly through its beneficial effects on the intestinal structure, lipid profiles and liver function.

Acknowledgement

This work was supported by the National Natural Science Foundation of China  (No. 31972079), the Natural Science Foundation of Zhejiang Province of China (No. LY18C200006), the Basic Research Project of Education Department of Zhejiang Province (No. Y201737161), the Technology and Achievement Transformation Project of Hangzhou, China (NO. 20161631E01), and the Zhejiang University New Rural Development Research Institute Agricultural Technology Promotion Fund (NO. 2017006).


Competing interests

We certify that there is no conflict of interest with any financial organization regarding the material discussed in the manuscript.

Author's contributions

Conception and design: H. Cai, M. Zhao, F. Feng. Acquisition of data: H. Cai, M. Liu, J. Li, M. Zhao. Analysis and interpretation of data: H. Cai, C. Cai, M. Zhao. Manuscript drafting and revising: H. Cai, C. Cai, M. Zhao.

References

  1. Ronquillo MG, Hernandez JCA. Antibiotic and synthetic growth promoters in animal diets: Review of impact and analytical methods. Food Control 2017;72:255-67.

    View Article           
  2. Founou LL, Amoako DG, Founou RC, Essack SY. Antibiotic Resistance in Food Animals in Africa: A Systematic Review and Meta-Analysis. Microb Drug Resist 2018;24:648-65. PMid:29683779

    View Article      PubMed/NCBI     
  3. Dudek-Wicher RK, Junka A, Bartoszewicz M. The influence of antibiotics and dietary components on gut microbiota. Prz Gastroenterol 2018;13:85-92. PMid:30002765

    View Article      PubMed/NCBI     
  4. Swiatkiewicz S, Swiatkiewicz M, Arczewska-Wlosek A, Jozefiak D. Chitosan and its oligosaccharide derivatives (chito-oligosaccharides) as feed supplements in poultry and swine nutrition. J Anim Physiol Anim Nutr (Berl) 2015;99:1-12. PMid:25041091

    View Article      PubMed/NCBI     
  5. Zentek J, Buchheit-Renko S, Ferrara F, et al. Nutritional and physiological role of medium-chain triglycerides and medium-chain fatty acids in piglets. Anim Health Res Rev 2011;12:83-93. PMid:21676342

    View Article      PubMed/NCBI     
  6. Zeitz J, Fennhoff J, Kluge H, Stangl G, Eder K. Effects of dietary fats rich in lauric and myristic acid on performance, intestinal morphology, gut microbes, and meat quality in broilers. Poultry Sci 2015;94:2404-13. PMid:26240391

    View Article      PubMed/NCBI     
  7. Witcher KJ, Novick RP, Schlievert PM. Modulation of immune cell proliferation by glycerol monolaurate. Clin Diagn Lab Immun 1996;3:10-13.

    View Article           
  8. Cai H, Yu L, Li Y, Zhang H, Feng F. Antimicrobial mechanism analysis of an oil in water microemulsion by dna microarray-mediated transcriptional profiling of Escherichia coli. J Food Safety 2014;34:176-83.

    View Article           
  9. Patrick M, Schlievert PM, Kilgore SH, Kaus GM, Ho TD, Ellermeier CD. Glycerol monolaurate (GML) and a nonaqueous five-percent GML gel kill Bacillus and Clostridium spores. mSphere 2018;3:1-9. PMid:30463926

    View Article      PubMed/NCBI     
  10. Li Q, Estes JD, Schlievert PM, et al. Glycerol monolaurate prevents mucosal SIV transmission. Nature 2009;458:1034-38. PMid:19262509

    View Article      PubMed/NCBI     
  11. Jiang Z, Zhao M, Zhang H, et al. Antimicrobial emulsifier - glycerol monolaurate induces metabolic syndrome, gut microbiota dysbiosis and systemic low-grade inflammation in low-fat diet fed mice. Mol Nutr Food Res 2018:1700547. PMid:29131494

    View Article      PubMed/NCBI     
  12. Zhang MS, Sandouk A, Houtman JC. Glycerol monolaurate (GML) inhibits human T cell signaling and function by disrupting lipid dynamics. Sci Rep 2016;6:30225. PMid:27456316

    View Article      PubMed/NCBI     
  13. Zhao M, Cai H, Liu M, et al. Dietary glycerol monolaurate supplementation for the modification of functional properties of egg white protein. J Sci Food Agr 2019;99:3852-59. PMid:30680726

    View Article      PubMed/NCBI     
  14. Yuniwarti E, Asmara W, Artama W, Tabbu C. Virgin coconut oil increases the productivity of broiler chicken post avian influenza vaccination. Anim Prod 2013;14:192-98.

  15. Van Der Hoeven-Hangoor E, Van Der Vossen J, Schuren F, et al. Ileal microbiota composition of broilers fed various commercial diet compositions. Poultry Sci 2013;92:2713-23. PMid:24046419

    View Article      PubMed/NCBI     
  16. Lee SI, Kim HS, Kim I. Microencapsulated organic acid blend with MCFAs can be used as analternative to antibiotics for laying hens. Turk J Vet Anim Sci 2015;39:520-27.

    View Article           
  17. Wang J, Wang X, Li J, et al. Effects of dietary coconut oil as a medium-chain fatty acid source on performance, carcass composition and serum lipids in male broilers. Asian Austral J Anim 2015;28:223-30. PMid:25557818

    View Article      PubMed/NCBI     
  18. Nedomová Š, Severa L, Buchar J. Influence of hen egg shape on eggshell compressive strength. Int Agrophys 2009;23:249-56.

  19. Projan SJ, Brown-Skrobot S, Schlievert PM, Vandenesch F, Novick RP. Glycerol monolaurate inhibits the production of beta-lactamase, toxic shock toxin-1, and other staphylococcal exoproteins by interfering with signal transduction. J Bacteriol 1994;176:4204-09. PMid:8021206

    View Article      PubMed/NCBI     
  20. Schiefer HB. Mycotoxicoses of domestic animals and their diagnosis. Can J Physiol Pharm 1990;68:987-90. PMid:2200592

    View Article      PubMed/NCBI     
  21. Mirbod M, Mahdavi AH, Samie AH, Mehri M. Effects of Curcuma longa rhizome powder on egg quality, performance and some physiological indices of laying hens fed different levels of metabolizable energy. J Sci Food Agr 2017;97:1286-94. PMid:27328772

    View Article      PubMed/NCBI     
  22. Shokrollahi B, Yavari Z, Kordestani A. Effects of dietary medium-chain fatty acids on performance, carcass characteristics, and some serum parameters of broiler chickens. Brit Poultry Sci 2014;55:662-67. PMid:25166886

    View Article      PubMed/NCBI     
  23. Zhou SM, Wang YQ, Jacoby JJ, et al. Effects of medium-and long-chain triacylglycerols on lipid metabolism and gut microbiota composition in C57BL/6J mice. J Agric Food Chem 2017;65:6599-607. PMid:28704610

    View Article      PubMed/NCBI     
  24. Zeng Z, Zhang S, Wang H, Piao X. Essential oil and aromatic plants as feed additives in non-ruminant nutrition: a review. J Anim Sci Biotechnol 2015;6:10-19. PMid:25774291

    View Article      PubMed/NCBI     
  25. Günther C, Neumann H, Neurath MF, Becker C. Apoptosis, necrosis and necroptosis: cell death regulation in the intestinal epithelium. Gut 2012;62:1062-71. PMid:22689519

    View Article      PubMed/NCBI     
  26. Hanczakowska E, Szewczyk A, Okoń K. Effects of dietary caprylic and capric acids on piglet performance and mucosal epithelium structure of the ileum. J Anim Feed Sci 2011;20:556-65.

    View Article           
  27. Bannerjee K, Camacho-Hubner C, Babinska K, et al. Anti-inflammatory and growth-stimulating effects precede nutritional restitution during enteral feeding in Crohn disease. J Pediatr Gastroenterol Nutr 2004;38:270-75. PMid:15076624

    View Article      PubMed/NCBI     
  28. Zentek J, Buchheit-Renko S, Manner K, Pieper R, Vahjen W. Intestinal concentrations of free and encapsulated dietary medium-chain fatty acids and effects on gastric microbial ecology and bacterial metabolic products in the digestive tract of piglets. Arch Anim Nutr 2012;66:14-26. PMid:22397093

    View Article      PubMed/NCBI     

Journal Recent Articles