Abstract
Star anise (Illicium verum Hook. f) has been used as spice and herbal medicine for many years with lacking researches on evaluating its application for improving relative organ weight, intestinal development, and quality of animal products. The experiment was conducted to investigate the effects of star anise, its essential oil and leavings on carcass traits, relative organ weight, intestinal development, and meat quality of broiler chickens. A total of 384 broilers were randomly assigned to 4 treatments with 8 replicates of 12 birds each. The 4 dietary treatments were basal diet (Control), basal diet supplemented with 5 g/kg star anise (Star anise), basal diet supplemented with 0.22 g/kg essential oil (Essential oil), and basal diet supplemented with 5 g/kg leavings (Leavings). The concentration of main active components in the experimental diets was 0.204 g trans-anethole/kg of diet. All birds were fed a starter diet (0–21 d) and a grower diet (22–42 d). Birds supplemented with star anise and essential oil had a greater (P < 0.05) final body weight (BW) than control birds and those supplemented with leavings. However, the carcass yield, half chamber rate, eviscerated rate, and percentages of breast muscle and thigh muscle in birds were similar (P > 0.05) among all treatments. Birds supplemented with star anise and essential oil had higher (P = 0.010) relative weight of thymus than those in control and leavings groups. Essential oil supplemented groups appeared to contain the highest (P < 0.05) villus height in ileum and villus height/crypt depth ratio in ileum and jejunum among all the groups. Meanwhile, among all the groups, breast muscles of essential oil–supplemented groups appeared to contain the lowest (P = 0.012) boiling loss but highest (P < 0.001) concentration of inosinic acid (inosine 5′-monophosphate, IMP). In conclusion, dietary supplementation of 5 g/kg star anise and 0.22 g/kg essential oil improved BW, relative organ weight, and intestinal development, and 0.22 g/kg essential oil can also increase the concentration of IMP but decrease the boiling loss in breast muscles of broilers; however, 5 g/kg leavings had no effect.
Key words: star anise, extractions, carcass trait, meat quality, inosinic acid
Introduction
Broiler chicken is one of most widespread farm animals with over 90 billion tons of meat per year (Food and Agriculture Organization, 2017). Owing to the high demands of broiler meats by consumers, the intensive farming which produce large quantities of meat at lowest cost possible was being popular. However, birds are more susceptible to stresses such as infectious diseases and oxidative stress under modern intensification farming systems (Hangalapura et al., 2003). Increased stress and generation of free radicals are responsible for the development of various diseases and decreases in animal production and product quality, leading to greatly reduced efficiency and economic losses (Yang et al., 2019). Owing to the limitation of in-feed antimicrobials as growth promoters, it is necessary to explore feed additives with high efficacy to improve performance and minimize infections (Ren et al., 2018). The use of natural products containing bioactive components showed a promising approach in poultry industry (Alagawany et al., 2019; Khafaga et al., 2019; Reda et al., 2019). Thus, there is an increasing interest in phytogenic feed additives.
Star anise (Illicium verum Hook.f.) has been widely used as spice and herbal medicine for many years in traditional Chinese. Its extractions contained trans-anethole (85–90%) as its main active ingredient and other compounds such as estragole and anisaldehyde (Ciftci et al., 2005; Wang et al., 2011; Ding et al., 2017). It is of note that star anise and its extractions are rich in the characteristic flavor as an aromatic plant (Wang et al., 2011). Star anise and its extracts are generally recognized as safe with antiparasitic, antibacterial, antioxidant, antifungal, and antipyretic properties (Ciftci et al., 2005; Soltan et al., 2008; Hong et al., 2012; Cho et al., 2014). The presences of abovementioned active compounds are responsible for reducing environmental stress and has been proved in vivo and in vitro. However, there are limited studies focused on the effects of dietary star anise and its extractions on relative organ weight, intestinal development, and quality of broilers' products. In view of this, the aim of this study was to evaluate parameters including the carcass traits, relative organ weight, intestinal development, and meat quality of broilers when fed diets containing star anise and its extractions.
Materials and methods
Star Anise (I. verum Hook. f) and its Extractions
Star anise (I. verum Hook. f) was purchased from a local market (Wuma market, Tai'an, China), and its essential oil was extracted using a traditional water steam distillation according to our previous studies (Ding et al., 2017). The remaining part of star anise powder which was collected after steam distillation was considered as leavings. The chemical composition of the materials was analyzed by gas-chromatographic based on Ding et al. (2017).
Birds and Experimental Design
The animal care protocol was approved by the Shandong Agricultural University Animal Care and Use Committee (Tai'an, China). The experiment was conducted using male Arbor Acres broiler chicks. A total of 384 broilers (male) were randomly assigned to 4 dietary treatments (8 cages per treatment; 12 birds per cage). The 4 treatments were basal diet (Control), basal diet supplemented with 5 g/kg star anise (Star anise), basal diet supplemented with 0.22 g/kg essential oil (Essential oil), and basal diet supplemented with 5 g/kg leavings (Leavings). To obtain a level of 0.204 g trans-anethole/kg of diet, the concentrations of effective components in diets were shown in Table 1. All birds were fed a starter diet (0–21 d) and a grower diet (22–42 d), and all diets (Table 2) were formulated to meet the National Research Council (1994). All birds were inspected daily, and mortalities were recorded.
Table 1.
Concentrations of effective components in the experimental diets1, g/kg.
| Items | Control | Star anise | Essential oil | Leavings |
|---|---|---|---|---|
| Trans-anethole | BD | 0.204 | 0.204 | BD |
| Estragole | BD | 0.003 | 0.003 | BD |
| Anisaldehyde | BD | 0.002 | 0.002 | BD |
Abbreviation: BD, below detection.
Control, basal diet; Star anise, Control +5 g/kg star anise; Essential oil, Control +0.22 g/kg essential oil; Leavings, Control +5 g/kg leavings.
Table 2.
Ingredients and nutrient compositions of experimental diets.
| Items | Starter 0 to 21 d | Grower 22 to 42 d |
|---|---|---|
| Ingredients, % | ||
| Corn | 58.40 | 63.09 |
| Soybean meal | 35.40 | 29.50 |
| Soy oil | 2.20 | 3.48 |
| Limestone | 1.62 | 1.98 |
| Calcium hydrogen phosphate | 1.28 | 0.90 |
| Sodium chloride | 0.23 | 0.23 |
| Choline chloride | 0.09 | 0.09 |
| DL-Methionine | 0.28 | 0.25 |
| Lysine | 0.10 | 0.08 |
| Premix1 | 0.40 | 0.40 |
| Chemical composition2 | ||
| Metabolizable energy, kcal/kg | 3,229 | 3,298 |
| Crude protein, % | 21.92 | 19.91 |
| Calcium, % | 1.12 | 0.93 |
| Available phosphorus, % | 0.48 | 0.35 |
| Lysine, % | 1.23 | 1.07 |
| Methionine, % | 0.49 | 0.38 |
Supplied per kilogram of diet: vitamin A, 8,050 IU; cholecalciferol, 3,000 IU; vitamin E, 30 mg; vitamin K3, 5 mg; thiamin, 2.58 mg; riboflavin, 12.5 mg; choline chloride, 800 mg; calcium pantothenate, 13 mg; niacin, 45 mg; biotin, 0.20 mg; folic acid, 1.20 mg; Mn, 100 mg; Fe, 80 mg; Zn, 58 mg; Cu, 8.8 mg; Se, 0.28 mg.
The chemical composition of the diets was determined according to AOAC (1990) methods except metabolizable energy and available phosphorus, which were calculated values. They were calculated according to “feed description and proximate composition” in Feeding standard of chicken (People's Republic of China, NY/T 33-2004).
Chickens were housed in an environmentally controlled room with feeders and nipple drinkers. Feed and water were available ad libitum. The temperature was maintained at 33°C which was then gradually reduced to 26°C at the rate of 3°C per wk and was maintained at this temperature to the end of the experiment. Overhead light was provided continuously for the entire period of experiment.
Growth Performance and Sample Collection
Birds were fed twice daily for ad libitum intake, and feed residue in each cage was weighed daily. Birds in each cage were weighted at day 1 and day 42 of the experiment before feeding to obtain body weight (BW). These data were used to calculate average daily gain (ADG), average daily feed intake (ADFI), and feed conversion rate.
At the end of the experiment (42 d of age), 2 birds per replication (16 birds per treatment) were randomly selected and weighed after 8 h fasting. The birds were then sacrificed by jugular bleeding. One bird per replication was scaled in a hot water bath (60°C for 2 min), and the feathers were removed mechanically after bleeding. The weight of carcass (including organs) was measured after defeathering to determine the carcass yield (including organs). The organs (except the hearts, livers, stomachs, lungs, and kidneys) were removed and weighted to determine the percentage of half chamber rate. Then heads, neck, feet, and organs (except the lungs and kidneys) were removed and weighted to determine the percentage of eviscerated yield. Organs (duodenum, jejunum, ileum, liver, spleen, thymus, and bursa of Fabricius) were isolated and measured to calculate the relative organ weight and intestinal length. The breast and thigh muscles were removed and weighed to determine the percentages of breast and leg muscle. Both breast and muscle were dissected into 2 parts for 1) determining intramuscular fat and inosinic acid (inosine 5′-monophosphate, IMP) and 2) analyzing meat quality parameters including pH value, meat color, water holding capacity, and shear force.
Duodenum, jejunum, and ileum in another bird per replication were immediately isolated from the surrounding fat and tissue. Parts of the small intestine were fixed promptly in Bouin's fluid for subsequent analysis of histological examination.
Carcass Traits
Carcass yields (including organs), half chamber rates, and eviscerated rates were calculated by dividing these traits by final live weight after fasting. The percentages of breast muscle and thigh muscle were calculated as a percentage of eviscerated weight.
Relative Organ Weights and Intestinal Lengths
The weights of organs and lengths of small intestines were recorded and then calculated using the following formula:
Relative organ weight (g/kg) = organ weight (g)/live BW (kg); Relative intestinal length (cm/kg) = intestinal length (cm)/live BW (kg).
Histological Analysis
Sections of duodenum, jejunum, and ileum were dehydrated using graded alcohol concentrations as well as xylene after fixed in Bouin's fluid for 24 to 48 h and were subsequently embedded in paraffin. Meanwhile, 5 μm sections were cut on a Leica microtome (RM 2235, Germany), mounted on coated glass slides, and dried overnight at 37°C. Then the samples were dewaxed and rehydrated using xylene and graded alcohol concentrations before being stained with hematoxylin and eosin. Sections were dehydrated and cleared with xylene, then sealed in clear resin.
The measurements were performed with an optical microscope using DigiLab-C software. Six points were selected for microscopical investigation of villus height and cryptal depth on each slice. Villus height was measured from the tip of villus to the crypt opening, and the crypt depth was measured from the base of the crypt to the level of the crypt opening. The villus height/crypt depth (V/C) ratio was calculated using the following formula (Choi et al., 2011; Du et al., 2016):
The V/C ratio (μm/μm) = villus height (μm)/crypt depth (μm).
Meat Quality
The pH values of the breast and thigh muscles was determined using a pH meter (PH5+, Tenovo International Co., Ltd., Beijing, China) equipped with an insertion electrode.
The meat color parameters (L∗ = Lightness, a∗ = redness, and b∗ = yellowness) were determined by an Easy-to-use Color Reader (CR-10, KonicaMinolta, Tokyo, Japan).
The water-holding capacity was reported as drip loss and boiling loss using procedure described by Yang et al. (2010) and were calculated using the following formula:
Drip loss (%) = [(initial weight–final weight)/initial weight] × 100%;
Boiling loss (%) = [(raw weight–cooked weight)/raw weight] × 100%
Shear force was determined using a texture analyzer (C-LM3B, Tenovo International Co., Ltd., Beijing, China) and was expressed in N. It was measured perpendicular to the axis of muscle fibers in 6 replicates for each treatment.
The intramuscular fat of muscles was analyzed by the official methods of Association of Official Analytical Chemists (AOAC, 1990), expressed as a percentage of fresh muscle weight.
Concentration of IMP
The flavor trait was analyzed by determining IMP concentration in the preprocessing of breast muscle according to the procedure described by Zhang et al. (2008). The obtained solution was filtered through a 0.45-nm membrane filter before being used for a high-performance liquid chromatography (Waters 515, Milford, MA) analysis. The mixture of 8% methanol and 92% phosphoric acid solution of 0.5% concentration (V/V) was applied as mobile phase. The flow rate was 1.0 mL/min. Detection was performed at a wavelength of 254 nm with the column (250 mm × 4.6 mm) maintained at a constant temperature (30°C).
Statistical Analyses
This experiment was designed as a complete random design, and cages were considered as experimental unit. All the parameters were analyzed by the general linear model procedure followed by Duncan's multiple ranges test of SAS software (version 8.2, SAS Institute Inc., Cary, NC). The level of significant difference was set at P < 0.05.
Results
Growth Performance
All birds performed healthy, and no mortality was detected throughout the entire experimental period. Birds supplemented with star anise and essential oil had a greater BW at day 42 (P < 0.05) than control birds and those supplemented with leavings. Additionally, birds supplemented with essential oil also had greater ADG and ADFI during the entire experimental period (P < 0.05) compared with those in the Control and Leavings (Table 3).
Table 3.
Effects of star anise, essential oil, and leavings on growth performance of broilers.1
| Items | Control | Star anise | Essential oil | Leavings | SEM | P-value |
|---|---|---|---|---|---|---|
| Final body weight, g | 2,451.4c | 2,505.9a,b | 2,541.3a | 2,455.2b,c | 17.528 | 0.004 |
| Average daily gain, g/d | 57.5b | 58.7a,b | 59.6a | 57.5b | 0.543 | 0.032 |
| Average daily feed intake, g/d | 102.2b | 104.7a,b | 106.2a | 101.9b | 0.966 | 0.014 |
| Feed:gain, g:g | 1.779 | 1.783 | 1.782 | 1.771 | 0.021 | 0.974 |
a-cMeans within a row with different letters differ significantly (P < 0.05).
Data are means for 8 replicates per treatment.
Carcass Traits
Supplementation of essential oil significantly increased (P < 0.05) the carcass weight and thigh muscle weight and tended to increase (0.05 < P < 0.1) the half chamber weight and eviscerated weight of birds compared with the Control (Table 4). However, there was no observed significant (P > 0.05) differences of the carcass yield (including organs), half chamber rate, eviscerated rate, and percentages of breast and thigh muscle in birds among all treatments.
Table 4.
Effects of star anise, essential oil, and leavings on carcass traits of broilers.1
| Items | Control | Star anise | Essential oil | Leavings | SEM | P-value |
|---|---|---|---|---|---|---|
| Live weight, g | 2,425.6b | 2,480.5a | 2,485.9a | 2,429.6b | 19.033 | 0.026 |
| Carcass weight (including organs), g | 2,255.8b | 2,309.3a | 2,319.3a | 2,257.1b | 18.332 | 0.005 |
| Half chamber weight, g | 2,105.4 | 2,150.6 | 2,155.3 | 2,116.2 | 19.567 | 0.056 |
| Eviscerated weight, g | 1,688.2 | 1,733.9 | 1,752.6 | 1,698.3 | 25.116 | 0.093 |
| Breast muscle weight, g | 479.3 | 491.9 | 494.7 | 482.7 | 13.959 | 0.703 |
| Thigh muscle weight, g | 364.7b | 376.6a,b | 382.4a | 364.1b | 7.656 | 0.042 |
| Carcass yield (including organs), % | 93.00 | 93.10 | 93.30 | 92.90 | 0.239 | 0.667 |
| Half chamber rate, % | 86.80 | 86.70 | 86.70 | 87.10 | 0.482 | 0.931 |
| Eviscerated rate, % | 69.60 | 69.90 | 70.50 | 69.90 | 0.942 | 0.914 |
| Brest muscle rate, % | 28.39 | 28.37 | 28.23 | 28.42 | 0.630 | 0.997 |
| Thigh muscle rate, % | 21.60 | 21.72 | 21.82 | 21.44 | 0.520 | 0.959 |
a-bMeans within a row with different letters differ significantly (P < 0.05).
Data are means for 8 replicates per treatment.
Relative Organ Weights and Intestinal Lengths
Birds supplemented with star anise and essential oil had higher (P = 0.010) relative weight of thymus than those in Control and Leavings. However, the relative weights and lengths of duodenum, jejunum, and ileum and the relative weights of liver and bursa of Fabricius in birds were similar (P > 0.05) among all treatments (Table 5). Birds fed star anise and essential oil showed increased (P = 0.020) relative weight of spleen as compared with those in Control and Leavings.
Table 5.
Effects of star anise, essential oil, and leavings on relative organ weights and intestinal lengths of broilers.1
| Items | Control | Star anise | Essential oil | Leavings | SEM | P-value |
|---|---|---|---|---|---|---|
| Relative weight, g/kg BW | ||||||
| Duodenum | 5.465 | 5.305 | 5.339 | 5.227 | 1.034 | 0.987 |
| Jejunum | 11.190 | 11.608 | 10.910 | 10.579 | 1.582 | 0.769 |
| Ileum | 7.905 | 7.996 | 7.949 | 7.964 | 1.357 | 1.000 |
| Liver | 17.42 | 17.50 | 17.62 | 17.43 | 0.771 | 0.975 |
| Spleen | 1.152c | 1.232a,b | 1.259a | 1.160b,c | 0.057 | 0.020 |
| Thymus | 5.111b | 5.360a | 5.347a | 5.088b | 0.142 | 0.010 |
| Bursa of Fabricius | 0.657 | 0.659 | 0.638 | 0.647 | 0.033 | 0.738 |
| Relative length, cm/kg BW | ||||||
| Duodenum | 14.961 | 14.727 | 14.660 | 14.511 | 1.719 | 0.980 |
| Jejunum | 33.913 | 32.956 | 33.396 | 33.755 | 5.064 | 0.991 |
| Ileum | 33.546 | 33.497 | 33.707 | 34.351 | 4.780 | 0.991 |
a-cMeans within a row with different letters differ significantly (P < 0.05).
Data are means for 8 replicates per treatment.
Intestinal Histology
Birds supplemented with star anise and essential oil had higher (P < 0.05) villus height and V/C ratio in jejunum than those in Control and Leavings (Table 6). Among all the groups, essential oil-supplemented groups appeared to contain the highest (P < 0.05) villus height in ileum and V/C ratio in ileum and jejunum. In contrast, the crypt depth in duodenum of birds was lowest (P = 0.002) among all the groups.
Table 6.
Effects of star anise, essential oil, and leavings on intestinal histology in broilers.1
| Items | Control | Star anise | Essential oil | Leavings | SEM | P-value |
|---|---|---|---|---|---|---|
| Villus height, μm | ||||||
| Duodenum | 1,122.5 | 1,125.7 | 1,111.9 | 1,116.2 | 41.330 | 0.964 |
| Jejunum | 1,053.2c | 1,110.5b | 1,155.2a | 1,049.4c | 26.411 | <0.001 |
| Ileum | 879.7b | 882.8b | 947.5a | 882.3b | 35.110 | 0.049 |
| Crypt depth, μm | ||||||
| Duodenum | 202.0a | 197.6a | 181.5b | 193.7a | 5.607 | 0.002 |
| Jejunum | 157.8 | 154.0 | 158.8 | 157.5 | 5.512 | 0.637 |
| Ileum | 136.5 | 137.0 | 141.1 | 138.6 | 7.279 | 0.803 |
| Villus height/Crypt depth ratio, μm/μm | ||||||
| Duodenum | 5.569b | 5.706b | 6.128a | 5.776b | 0.247 | 0.042 |
| Jejunum | 6.678b | 7.184a | 7.296a | 6.662b | 0.299 | 0.019 |
| Ileum | 6.452b | 6.447b | 6.730a | 6.398b | 0.136 | 0.019 |
a-cMeans within a row with different letters differ significantly (P < 0.05).
Data are means for 8 replicates per treatment.
Meat Quality
No significant differences of pH, meat color, shear force, and intramuscular fat were detected on breast and thigh muscle among the treatments in broilers (Table 7). However, birds fed essential oil showed lowest (P < 0.05) boiling loss in breast muscle and drip loss in thigh muscle among all the groups.
Table 7.
Effects of star anise, essential oil, and leavings on pH, meat color, water-holding capacity, shear force, and intramuscular fat of broilers.1
| Items | Control | Star anise | Essential oil | Leavings | SEM | P-value |
|---|---|---|---|---|---|---|
| Brest muscle | ||||||
| pH 45 min | 6.30 | 6.44 | 6.33 | 6.42 | 0.048 | 0.148 |
| pH 24 h | 5.88 | 5.85 | 5.85 | 5.88 | 0.080 | 0.981 |
| pH 48 h | 7.07 | 7.12 | 7.13 | 7.10 | 0.118 | 0.983 |
| Meat color | ||||||
| L∗ | 47.0 | 47.0 | 47.2 | 46.9 | 0.948 | 0.994 |
| a∗ | 0.7 | 0.7 | 0.7 | 0.6 | 0.063 | 0.979 |
| b∗ | 7.6 | 7.6 | 7.5 | 7.7 | 0.438 | 0.984 |
| Drip, % | 6.279a | 6.275a | 5.866b | 6.294a | 0.096 | 0.012 |
| Boiling, % | 21.02 | 20.96 | 20.86 | 20.77 | 0.426 | 0.976 |
| Shear force, N | 13.13 | 13.11 | 12.69 | 13.06 | 0.515 | 0.921 |
| Intramuscular fat, % | 2.655 | 2.670 | 2.525 | 2.584 | 0.102 | 0.731 |
| Thigh muscle | ||||||
| pH 45 min | 6.57 | 6.62 | 6.52 | 6.52 | 0.071 | 0.694 |
| pH 24 h | 6.15 | 6.18 | 6.18 | 6.18 | 0.127 | 0.998 |
| pH 48 h | 7.33 | 7.30 | 7.33 | 7.33 | 0.123 | 0.997 |
| Meat color | ||||||
| L∗ | 51.7 | 51.7 | 52.4 | 52.2 | 1.357 | 0.975 |
| a∗ | 3.9 | 3.4 | 3.4 | 3.6 | 0.289 | 0.600 |
| b∗ | 8.6 | 8.5 | 8.5 | 8.6 | 0.477 | 0.996 |
| Drip, % | 7.879a | 7.817a | 7.253b | 7.849a | 0.129 | 0.007 |
| Boiling, % | 12.69 | 12.38 | 12.45 | 12.70 | 0.374 | 0.900 |
| Shear force, N | 8.94 | 8.96 | 8.67 | 8.91 | 0.133 | 0.402 |
| Intramuscular fat, % | 2.724 | 2.744 | 2.726 | 2.744 | 0.116 | 0.999 |
a-bMeans within a row with different letters differ significantly (P < 0.05).
L∗, Lightness; a∗, Redness; b∗, Yellowness.
Data are means for 8 replicates per treatment.
Concentration of IMP
Birds supplemented with essential oil obtained highest (P < 0.001) concentration of IMP among all the groups (Figure 1). However, supplementation of star anise and its leavings has no significant effects (P > 0.05) on the concentration of IMP in birds as compared with those in Control.
Figure 1.
Concentration of IMP in breast muscle among the Control, Star anise, Essential oil, and Leavings group. a-bMeans within a row with different letters differ significantly (P < 0.05). Abbreviation: IMP, inosine 5′-monophosphate.
Discussion
Growth Performance
The general trend in poultry industry is to provide a more safe feed to enhance the physiological and productive indicators (Elnesr et al., 2019). Our preliminary study have found that broilers supplemented with star anise essential oil at the rate of 200 mg/kg of diet had a greater BW at day 21 and day 42 compared with those without supplementation (Ding et al., 2017). Meanwhile, addition of star anise oil could quadratically enhance ADFI of laying hens from day 1 to day 28 (Yu et al., 2018). Similar in those studies, our results demonstrated that the in-feed star anise and essential oil possessed abilities to increase the final BW by approximately 2.26 and 2.49%, respectively, as compared with the control group. Besides, the addition of essential oil to the diets improved ADG and ADFI by approximately 3.72 and 3.91%, respectively, as compared with the control group. This phenomenon may because of the enhanced palatability contributed by aromatic flavor of essential oil and the improved gut health by its bioactive compounds with antioxidant, antimicrobial, and antiinflammation properties (Amad et al., 2011; Reisinger et al., 2011).
Carcass Traits
The addition of essential oil to the diets improved the carcass weight (including organs) and thigh muscle weight by approximately 4.02 and 6.27% respectively, as compared with the control group. Which were consistent with the results of the final BW. However, there was no significant difference in the examined percentages of carcass characteristics among all treatments. The results of carcass traits revealed that essential oil improved carcass weight (including organs) without altering percentages of relevant carcass characteristics. This may be explained that carcass traits increased as similar rate as BW growth during bird development. Additionally, no changes on percentage of carcass traits of broilers after supplementing essential oil were also detected in previous studies (Soltan et al., 2008; Hong et al., 2012).
Development of Organs and Intestines
The health of organs and intestines is important for predicting health status of broilers. The present results showed that the relative weight of spleen and thymus were 1.09-fold and 1.05-fold higher, respectively, in birds supplemented with 200 mg/kg star anise oil of diet relative to those of the control birds. In contrast, similar results by Cho et al. (2014) and Amad et al. (2011) did not observe any differences in relative organ weights in broilers fed essential oil derived from thyme and star anise. The different compositions and concentrations of the bioactive compounds in essential oil may explain the inconsistency. Additionally, supplementation with essential oil could affect intestinal morphology by increasing villus height and V/C ratio. Similar results were reported by Reisinger et al. (2011), revealing qualitative increases in villus height of ileum in broilers after feeding a mixture of oregano, anise, and citrus peel. Hong et al. (2012) also demonstrated that villus height in duodenum was higher in broilers fed with essential oil extracted from oregano, anise, and citrus peel. However, the mechanisms about the effects of bioactive compounds on improving intestinal morphology were not fully understood. The improvement of intestinal morphology by star anise and its essential oil may be because of antimicrobial and antioxidant properties of bioactive compounds. Numerous previous studies have demonstrated that the essential oil extracted from herbs have ability to inhibit growth of pathogenic bacteria such as Clostridium perfringens, Escherichia coli, and so on (Wang et al., 2011; Hong et al., 2012; Cho et al., 2014).
Meat Quality
Muscle pH is one of the most important postslaughtering parameters for meat quality. The low pH is associated with the accumulation of lactic acid by anaerobic respiration which could influence water-holding capacity (Zhang et al., 2008; Qi et al., 2010).
Meat color is a critical parameter affecting the decision of deboned and skinless raw meat products in market by consumers (Zhang et al., 2008; Qi et al., 2010). It could be altered by many factors such as age, species, and muscle protein such as myoglobin and intramuscular fat. In this study, we did not observe any changes on muscle pH and color in broilers among all the treatments. Which were consistent with the similar observation by Hong et al. (2012) and Cho et al. (2014).
Water-holding capacity measured by drip loss and boiling loss is an important parameter reflecting the juiciness and tenderness of meat products (Yang et al., 2010). Overall, the data demonstrated significant reduction in drip loss of both breast and thigh muscles when birds supplemented with essential oil. Lower drip loss indicated a higher water-holding capacity and improved muscle juiciness. A similar increase on water holding capacity were also detected by Hong et al. (2012), showing that the tenderness and juiciness of breast and thigh muscles were improved in birds fed essential oil compared with those in control and antibiotic groups. A possible explanation for improved overall acceptance may be related to the functional properties of the bioactive compounds, but the mechanism is not clear.
Shear force value is an index for describing meat tenderness. It was inversely related to the tenderness (Qi et al., 2010) and was affected by the histological properties of myofibers (Zhang et al., 2008). Besides, the content of intramuscular fat plays an important role in meat quality (flavor and juiciness) of chickens (Qi et al., 2010). However, there were no significant differences among treatments in shear force and intramuscular fat of breast and thigh muscle.
Concentration of IMP
Inosine 5′-monophosphate is a dietary nucleotide that plays an important role in meat flavor that affecting consumers' acceptances (Zhang et al., 2008). The results of this study indicated that the variation of IMP concentration of breast muscle in birds fed with essential oil were 1.27-, 1.29- and 1.41-fold higher respectively, as compared with those in Control, Star anise, and Leavings. However, supplementation of star anise and its leavings have no contributions to improve the concentration of IMP in birds compared with those in Control. The increased concentration of IMP in breast muscle of broilers by essential oil may be related to its licorice flavor (Wang et al., 2011). Meanwhile, essential oil was rich in several effective compounds such as trans-anethole, anisaldehyde, and estragole (Ciftci et al., 2005; Wang et al., 2011; Ding et al., 2017), which may be responsible for the increased concentration of IMP in the breast muscle.
An interesting finding of this study was that essential oils extracted from star anise may have potential as in-feed additives to improve growth performance, relative organ weight, carcass traits, intestinal development, and meat quality. Compared with essential oils, star anise and its leavings showed less improvements on most of those parameters. As the same substance in different forms, star anise and essential oil show effects in different degrees. Additionally, it appeared that essential oil increased the ability of star anise in this experiment especially in villus height and crypt depth of small intestines, drip loss of muscle, and concentration of IMP. This may be because of the higher purity and better absorption of bioactive compounds in essential oils compared with star anise and leavings in broilers. Star anise has shown numerous pharmacological benefits including antiparasitic, antibacterial, antioxidant, antifungal, and antipyretic (Ciftci et al., 2005; Soltan et al., 2008; Hong et al., 2012; Cho et al., 2014) because of bioactive compounds such as trans-anethole, estragole, and anisaldehyde (Ciftci et al., 2005; Wang et al., 2011; Ding et al., 2017). This may also explain the no effects of leavings on those parameters because little bioactive compounds remained after extraction. In conclusion, the isolation of the essential oil from star anise may have potential.
Conclusions
Supplementation of star anise and essential oil at the levels of 5 g/kg and 0.22 g/kg of diet respectively have potentials for increasing final BW and relative weight of spleen and thymus. However, only dietary essential oil supplementation was detected to change the ADG, ADFI, villus height and crypt depth of small intestines, drip loss of muscles, and concentration of IMP in broilers as compared with other groups, indicating essential oils extracted from star anise have more benefits on meat quality and morphology compared with star anise, whereas leavings had no effect on all of those parameters.
Acknowledgments
This work was supported by the Special Fund for Agro-scientific Research in the Public Interest of China (Grand No. 201403047) and Major Innovative Projects in Shandong Province of research and application of environment-friendly feed and the critical technologies for pigs and poultry without antibiotic (2019JZZY020609).
Conflict of Interest Statement: The authors did not provide any conflict of interest statement.
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