Chemical composition and properties of essential oils in BCS

The composition and properties of BCS are considered to be a good source of protein, crude fat, crude fibre and macro minerals. BCS contain a yellowish volatile oil (0.5-1.6%), a fixed oil (28-42%), proteins (23 to 37%), ash (4.86% to 4.41%), total carbohydrate (33 to 40%) and different phytochemicals (Ramadan, Reference RAMADAN2007; Cheikh-Rouhou et al., Reference CHEIKH-ROUHOU, BESBES, HENTATI, BLECKER, DEROANNE and ATTIA2007). The major unsaturated fatty acids are linoleic acid (50.3-49.2%), followed by oleic acid (25.0-23.7%), while the main saturated fatty acid is palmitic acid (17.2-18.4%) (Cheikh-Rouhou et al., Reference CHEIKH-ROUHOU, BESBES, HENTATI, BLECKER, DEROANNE and ATTIA2007). The active constituents of BCS include volatile oil consisting of carvone, an unsaturated ketone, terpene or d-limonene also called carvene, α-pinene, p-cymene and nigellone (Ramadan, Reference RAMADAN2007). Pharmacologically active constituents of the volatile oil are thymoquinone, dithymoquinone, thymohydroquinone and thymol (Ghosheh et al., Reference GHOSHEH, HOUDI and CROOKS1999), while selenium, DL-α-tocopherol, DL-γ-tocopherol and trans retinol are among important antioxidants present in BCS (Al-Saleh et al., Reference AL-SALEH, BILLEDO and INAM2006; Nasir et al., Reference NASIR, ABID, HAYAT and SHAKOOR2005).

BCS possess antibacterial activity against Gram positive and negative bacteria (Hanafy and Hatem, Reference HANAFY and HATEM1991), antioxidant (Mariod et al., Reference MARIOD, IBRAHIM, ISMAIL and ISMAIL2009), immune-potentiating (Al-Mufarrej, Reference AL-MUFARREJ2014, Kumar et al., Reference KUMAR, PATRA, MANDAL, SAMANTA and PRADHAN2017a) and hepato-protective (Daba and Abdel-Rehman, Reference DABA and ABDEL-REHMAN1998) activities. Essential oil of BCS can inhibit the growth of several pathogenic bacteria such as Escherichia coli, Bacillus subtilis and Streptococcus faecalis (Saxena and Vyas, Reference SAXENA and VYAS1986). The BCS extracts and their EO have a range of other activities, including effects on physio-pathologies, e.g., anti-inflammatory, anti-diarrhoeal properties, and activity in different body systems, e.g., endocrine and immune system (Gilani et al., Reference GILANI, JABEEN and KHAN2004). The availability of large number of essential nutrients and a variety of pharmacologically active substances make BCS appropriate for the use in poultry diets as an ingredient as well as a feed additive.

The main issue with published research into the use of BCS in the diets is that studies utilised different black cumin seeds or its essential oil preparations. Phytochemicals composition in BCS can vary to a great extent due to the source. For example, Al-Saleh et al. (Reference AL-SALEH, BILLEDO and INAM2006) analysed 115 samples from different sources (Ethiopia, India, Syria, Saudi Arabia and Sudan) for phytochemical composition. They reported that these varied considerably due to the sources of BCS. Thymoquinone and thymol was highest for an Ethiopian source (3.1 and 0.23 g/kg BCS, respectively) and lowest in a Sudanese source (1.3 and 0.11 g/kg BCS) with substantial sample variation. There is no information about the composition of their bioactive ingredients present in the BCS when they were used in the diets. Therefore, discrepancies in the animal responses reported among the studies can be attributed to different concentrations of active compound present in BCS.

Feed intake and growth performance

Several studies have reported that average daily weight gain (ADWG) of poultry improved with supplementation of BCS in diets (Osman, Reference OSMAN2002; El-Bagir et al., Reference EL-BAGIR, HAMA, HAMED, EL-RAHIM and BEYNEN2006; Guler et al., Reference GULER, DALKILIC, ERTAS and CIFTCI2006; Durrani et al., Reference DURRANI, CHAND, ZAKA, SULTAN, KHATTAK and DURRANI2007; Abu-Dieyeh and Abu-Darwish, Reference ABU-DIEYEH and ABU-DARWISH2008; Al-Beitawi et al., Reference AL-BEITAWI, EL-GHOUSEIN and NOFAL2009; Ashayerizadeh et al., Reference ASHAYERIZADEH, DASTAR, RAHMATNEJAD, SHARG, ASHAYERIZADEH and HOSSAINI2009; Erener et al., Reference ERENER, ALTOP, OACK, AKSOY, CANKAYA and OZTURK2010; Ismail, Reference ISMAIL2011; Khan et al., Reference KHAN, ANSARI, HAQ and ABBAS2012; Yatoo et al., Reference YATOO, SHARMA, KHAN, RASTOGI and PATHAK2012; Saleh, Reference SALEH2014; Jahan et al., Reference JAHAN, KHAIRUNNESA, AFRIN and ALI2015). Osman (Reference OSMAN2002) found that supplementing broiler chicken diets with BCS oil significantly enhanced ADWG. El-Bagir et al. (Reference EL-BAGIR, HAMA, HAMED, EL-RAHIM and BEYNEN2006) showed that dietary BCS at the concentration of 10 or 30 g/kg significantly increased the final body weight (BW) of laying hens. Guler et al. (Reference GULER, DALKILIC, ERTAS and CIFTCI2006) found that birds fed diets containing 10 g/kg and an antibiotic had the highest ADWG compared to the control. Abu-Dieyeh and Abu-Darwish (Reference ABU-DIEYEH and ABU-DARWISH2008) observed that feeding of diets containing 10 and 15 g/kg BCS diet for a period of four weeks significantly increased ADWG. Erener et al. (Reference ERENER, ALTOP, OACK, AKSOY, CANKAYA and OZTURK2010) found that BCS (10 g/kg) increased the ADWG compared to control at the age of 42 days. In research by Khan et al. (Reference KHAN, ANSARI, HAQ and ABBAS2012) at 28 and 42 days of age the BCS-fed groups (25 and 50 g/kg) had significantly greater ADWG than birds fed 12.5 g/kg BCS and the antibiotic diets. Yatoo et al. (Reference YATOO, SHARMA, KHAN, RASTOGI and PATHAK2012) showed that ADWG of all the treatment groups was higher than the control, with highest gain in the 0.5% BCS group. In a study by Durrani et al. (Reference DURRANI, CHAND, ZAKA, SULTAN, KHATTAK and DURRANI2007), BCS supplementation (20, 30 and 40 g/kg diet) increased body weight of chickens compared with the control.

Greater ADWG by BCS may be attributed to better absorption of nutrients from the intestine (Kumar et al., Reference KUMAR, PATRA, MANDAL, SAMANTA and PRADHAN2017a). Addition of BCS in feeds may increase bile flow rate, which may increase emulsification and activate the pancreatic lipases aiding in fat digestion and absorption of fat soluble vitamins (Crossland, Reference CROSSLAND1980). In BCS EO, the main active constituent thymoquinone (approximately 60%) and other components (carvone, anethole, carvacrol and 4-terpineol) may serve as antibacterial agents and antioxidants, and as stimulants of digestive enzymes in the intestinal mucosa and pancreas (Abu-Dieyeh and Abu-Darwish, Reference ABU-DIEYEH and ABU-DARWISH2008). This could improve the digestion of dietary nutrients and feed efficiency, thus increasing the growth rate. Mandour et al. (Reference MANDOUR, ASHRY and HEDAYA1998) reported that low doses of BCS increased thyroxin concentration, thereby increasing the metabolic rate. The improved performance of BCS may be due to active ingredient contents of BCS. Indeed, many biological activities of the BCS have been attributed to the high content of active components and antioxidants like the thymoquinone, thymol, carvacrol and p-cymene (Gilani et al., Reference GILANI, JABEEN and KHAN2004). Another possible reason for the positive effect of BCS on ADWG and feed conversion ratio (FCR) in broiler chickens may be related to the antimicrobial effects of BCS. Different investigations have reported that BCS had antimicrobial activity in the gut (El-Kamali et al., Reference EL-KAMALI, AHMED, MOHAMED, YAHIA, ELTAYEB and ALI1998; Kumar et al., Reference KUMAR, PATRA, MANDAL, SAMANTA and PRADHAN2017a). Therefore, improved performance of BCS may be attributed to combined effects of all these active ingredients functioning in a positive manner (Guler et al., Reference GULER, ERTAS, KIZIL, DALKILIC and CIFTCI2007; Abu-Dieyeh and Abu-Darwish, Reference ABU-DIEYEH and ABU-DARWISH2008).

Supplementation of BCS in poultry diets significantly increased average daily feed intake (ADFI) in many studies (Osman and El-Barody, Reference OSMAN and EL-BARODY1999; Abbas and Ahmed, Reference ABBAS and AHMED2010; Erener et al., Reference ERENER, ALTOP, OACK, AKSOY, CANKAYA and OZTURK2010; Ismail, Reference ISMAIL2011; Yatoo et al., Reference YATOO, SHARMA, KHAN, RASTOGI and PATHAK2012; Abou-El-Soud, Reference ABOU-EL-SOUD2000); whereas other researchers found that supplementation of BCS in the poultry diet decreased the ADFI (Osman, Reference OSMAN2002; Szczerbińska et al., Reference SZCZERBIŃSKA, TARASEWICZ, SULIK, KOPCZYŃSKA and PYKA.2012; Çetin et al., Reference ÇETIN, YURTSEVEN, ÔENGÜL and SÖGÜT2008; Shewita and Taha, Reference SHEWITA and TAHA2011). Many of researchers showed that supplementation of BCS did not influence the ADFI (Denli et al., Reference DENLI, OKAN and ULUOCAK2004; Guler et al., Reference GULER, DALKILIC, ERTAS and CIFTCI2006; Ashayerizadeh et al., Reference ASHAYERIZADEH, DASTAR, RAHMATNEJAD, SHARG, ASHAYERIZADEH and HOSSAINI2009; Al-Mufarrej, Reference AL-MUFARREJ2014; Saleh, Reference SALEH2014; Ghasemi et al., Reference GHASEMI, KASANI and TAHERPOUR2014; Khalaji et al., Reference KHALAJI, ZAGHARI, HATAMI, HEDARI-DASTJERDI, LOTFI and NAZARIAN2011), hence the evidence for any effect on intakes is conflicting.

Osman and El-Barody (Reference OSMAN and EL-BARODY1999) reported that powdered BCS (2, 4, 5, 8, and 10 g/kg in the diet) increased ADFI in broiler chickens. Erener et al. (Reference ERENER, ALTOP, OACK, AKSOY, CANKAYA and OZTURK2010) determined that both BCS (10 g/kg) and BCS extract (1 g/kg) increased ADFI compared to the control diet, but ADFI did not differ significantly between BCS and BCS extract. Yatoo et al. (Reference YATOO, SHARMA, KHAN, RASTOGI and PATHAK2012) found that the ADFI of experimental birds during starter phase (0 to 3 weeks), finisher phase (4-6 weeks) and overall experimental period (to six weeks of age) was higher in treatment group (1% BCS) than the control group. Abou-El-Soud (Reference ABOU-EL-SOUD2000) showed that the total ADFI was highest in Japanese quail chick fed diet supplemented with 2% whole crushed BCS compared to those fed diet supplemented with 0, 1% whole BCS, BCS meal and BCS oil.

The increasing ADFI can be a result of a more palatable diet, since it has been shown that the flavour can stimulate or depress ADFI in birds. Indeed, BCS, as an aromatic plant, has been widely used as digestive and appetite stimulant. BCS stimulates the activity of digestive system, improving diet palatability, enhancing appetite of poultry and increasing the amount of feed intake able to be processed (Gilani et al., Reference GILANI, JABEEN and KHAN2004).

In contrast to above studies, Osman (Reference OSMAN2002) found that supplementing broiler chick diet with BCS oil significantly decreased ADFI. Broiler chicks fed diet having 1 and 2% BCS showed a significant decrease in ADFI (Abbas and Ahmed, Reference ABBAS and AHMED2010). In agreement, Szczerbińska et al. (Reference SZCZERBIŃSKA, TARASEWICZ, SULIK, KOPCZYŃSKA and PYKA.2012) reported significantly lower ADFI (38.2 versus 40.3 g) in quail receiving feed supplemented with 5.0% BCS (but not at 2.5% BCS in the diet, which had ADFI of 42.6 g) when compared to the unsupplemented control group. Durrani et al. (Reference DURRANI, CHAND, ZAKA, SULTAN, KHATTAK and DURRANI2007) found that the group receiving 2 to 4% BCS in the diet had a significant effect on reducing feed intake. Shewita and Taha (Reference SHEWITA and TAHA2011) observed the lowest ADFI in the chicken diet supplemented with 4 g/kg BCS compared with a diet with higher concentrations of BCS (6, 8, and 10 g/kg). To support this, Çetin et al. (Reference ÇETIN, YURTSEVEN, ÔENGÜL and SÖGÜT2008) reported a linearly decreasing feed intake with increasing percentage of BCS extract in the feed ration of partridges.

However, not all trials have shown any feed intake effects, for example Denli et al. (Reference DENLI, OKAN and ULUOCAK2004) reported that supplementation with BCS extract did not significantly affect the ADFI of quail. Guler et al. (Reference GULER, DALKILIC, ERTAS and CIFTCI2006) fed BCS at four different doses (0.5%, 1.0%, 2.0% and 3.0% of diets) compared against avilamycin at 10 mg/kg, and BCS did not influence ADFI at 21 and 42 days of age. Ashayerizadeh et al. (Reference ASHAYERIZADEH, DASTAR, RAHMATNEJAD, SHARG, ASHAYERIZADEH and HOSSAINI2009) did not find any significant effect on ADFI after addition of BCS (1g/kg) in the broiler diet. Trials by Ghasemi et al. (Reference GHASEMI, KASANI and TAHERPOUR2014) showed that ADFI were unaffected with addition of 0.5, 1.0 and 2.0% BCS to the diets, and Khalaji et al. (Reference KHALAJI, ZAGHARI, HATAMI, HEDARI-DASTJERDI, LOTFI and NAZARIAN2011) observed no effect on ADFI after addition of 1% BCS for entire growing periods.

The effects of BCS on FCR are contradictory among studies, although supplementation significantly improved FCR in many trials (Guler et al., Reference GULER, DALKILIC, ERTAS and CIFTCI2006; Durrani et al., Reference DURRANI, CHAND, ZAKA, SULTAN, KHATTAK and DURRANI2007; Abu-Dieyeh and Abu-Darwish, Reference ABU-DIEYEH and ABU-DARWISH2008; Ashayerizadeh et al., Reference ASHAYERIZADEH, DASTAR, RAHMATNEJAD, SHARG, ASHAYERIZADEH and HOSSAINI2009; Erener et al., Reference ERENER, ALTOP, OACK, AKSOY, CANKAYA and OZTURK2010; Toghyani et al., Reference TOGHYANI, GEISARI, GHALAMKARI and MOHAMMADREZAEI2010; Yatoo et al., Reference YATOO, SHARMA, KHAN, RASTOGI and PATHAK2012; Saleh, Reference SALEH2014; Jahan et al., Reference JAHAN, KHAIRUNNESA, AFRIN and ALI2015; Ghasemi et al., Reference GHASEMI, KASANI and TAHERPOUR2014; Jahan et al., Reference JAHAN, KHAIRUNNESA, AFRIN and ALI2015). The increased body weight and feed efficiency observed in poultry fed the BCS supplemented diets may be related to the various properties of BCS and its chemical components (Guler et al., Reference GULER, DALKILIC, ERTAS and CIFTCI2006; Al-Beitawi and El-Ghousein, Reference AL-BEITAWI and EL-GHOUSEIN2008; Abu-Dieyeh and Abu-Darwish, Reference ABU-DIEYEH and ABU-DARWISH2008). Guler et al. (Reference GULER, DALKILIC, ERTAS and CIFTCI2006) found that from 1 to 42 days of age, FCR were improved significantly by supplementation with 1% BCS by approximately 5% compared to the control group. Abu-Dieyeh and Abu-Darwish (Reference ABU-DIEYEH and ABU-DARWISH2008) observed that broilers fed 1 and 1.5% of BCS had lower FCR than other treatments, and the best feed efficiency was achieved by broilers given 1.5% BCS in their diet. Erener et al. (Reference ERENER, ALTOP, OACK, AKSOY, CANKAYA and OZTURK2010) reported that birds fed BCS (10 g/kg) in the diet improved FCR compared to those on BCS extract (1 g/kg) or control diets.

In the studies of Nasir and Grashorn (Reference NASIR and GRASHORN2010) and Abbas and Ahmed (Reference ABBAS and AHMED2010), the authors noticed a beneficial trend of BCS supplementation on FCR, mirrored by another trial where broiler chicks fed diets containing 1 and 2% BCS showed a non-significant effect on FCR (Abbas and Ahmed, Reference ABBAS and AHMED2010). Nasir and Grashorn (Reference NASIR and GRASHORN2010) did not find consistent effects on FCR in broiler chickens on diets containing 1% BCS. The lack of effect of the supplements might relate to the composition of basal diets and management and husbandry conditions.

Antimicrobial effects of phytochemicals may have more impact when the diet contains less digestible ingredients and there is more threat of colonisation of pathogenic bacteria in the intestinal tracts. Usually, it may be expected that any performance enhancing effects of feed additives become more apparent when birds receive less digestible diets and/or are kept in poor sanitary, environmental and management conditions. It is known that well-nourished healthy chickens do not respond to antibiotic supplements, when they are housed under clean and disinfected conditions (Lee et al., Reference LEE, EVERTS, KAPPERT, FREHNER, LOSA and BEYNEN2003). In experiments with good management and environment conditions, feed efficiency of the birds was at their maximum, leaving no or very little room for improvement by BCS inclusion.

Negative effects on feed efficiency by BCS have been noted in some studies (Al-Beitawi and El-Ghousein, Reference AL-BEITAWI and EL-GHOUSEIN2008; Majeed et al., Reference MAJEED, ABDELATI, ELBAGIR, ALHAIDARY, MOHAMED and BEYNEN2010). Majeed et al. (Reference MAJEED, ABDELATI, ELBAGIR, ALHAIDARY, MOHAMED and BEYNEN2010) noticed that for the entire feeding period of seven weeks the diet with 0.25% BCS increased the FCR by 3.7%; whereas Al-Beitawi and El-Ghousein (Reference AL-BEITAWI and EL-GHOUSEIN2008) found that dietary BCS at high inclusion levels diminished feed efficiency in broiler chickens. The FCR for the control diet was 2.10 and, for the diets with increasing doses of BCS (1.5 to 3%) was 2.06, 2.22, 2.11 and 2.16, respectively. It was concluded that dietary BCS may deteriorate feed efficiency in broiler chickens in a dose-dependent relationship.

Nutrient utilisation

Utilisation of nutrients may increase due to supplementation of BCS, as Yatoo et al. (Reference YATOO, SHARMA, KHAN, RASTOGI and PATHAK2012), Saleh (Reference SALEH2014) and Kumar et al. (Reference KUMAR, PATRA, MANDAL, SAMANTA and PRADHAN2017a) reported improvements. Yatoo et al. (Reference YATOO, SHARMA, KHAN, RASTOGI and PATHAK2012) reported higher dry matter (DM) digestion compared with the control when the diet was supplemented with 1% BCS or 0.5% each of fenugreek and BCS in combination. Saleh (Reference SALEH2014) reported that digestion of DM and crude protein (CP) increased significantly when birds were fed diets with BCS oil at 1 ml/kg compared with a control and avilamycin diet, while crude fat digestion was not affected. Kumar et al. (Reference KUMAR, PATRA, MANDAL, SAMANTA and PRADHAN2017a) found that nutrient utilisation of CP, ether extract (EE) and non-starch carbohydrate increased in broiler chickens due to supplementation of BCS at 0.5 to 2% in the diets.

These benefits may be attributed to enhanced enzymes activity caused by the essential oils in BCS. The choleric of BCS may increase bile flow (Mahfouz and EL-Dakhakhny, Reference MAHFOUZ and EL-DAKHAKHNY1960) and activate pancreatic lipase that aids in fat digestion and fat-soluble vitamin absorption (Crossland, Reference CROSSLAND1980). Any stimulating effect of essential oils on digestive system (Wenk, Reference WENK2003) can result in better utilisation of nutrients and performance of birds. BCS possesses antibacterial and antifungal properties (Hanafy and Hatem, Reference HANAFY and HATEM1991), which can result in increased nutrient availability for the bird. It has been well documented that AGP-increased nutrient digestibility perhaps due to their effects on the intestinal microbiota (Bedford, Reference BEDFORD2000). Extracts from spices and herbs may stimulate digestive secretions and enzymatic activity, thus exerting beneficial actions within the digestive tracts (Platel and Srinivasan, Reference PLATEL and SRINIVASAN2004).

Intestinal morphology

There is limited study investigating the effect of BCS on intestinal morphology. Adding BCS did not exert significant effect on villous height, crypt depth and their interrelation (Kumar et al., Reference KUMAR, PATRA, MANDAL, SAMANTA and PRADHAN2017a). However, Boka et al. (Reference BOKA, MAHDAV, SAMIE and JAHANIAN2014) found an enhancement of villus height to crypt depth ratio after dietary supplementation with at least 2% BCS. Small intestinal histomorphology including villus height, crypt depth and their ratio are one of important indicators of gut health in broiler chickens. Increased villus height and villus height to crypt ratio are directly correlated with an increased epithelial turnover (Fan et al., Reference FAN, CROOM, CHRISTENSEN, BLACK, BIRD, DANIEL, MCBRIDE and EISEN1997) and longer villi are associated with activated cell mitosis (Samanya et al., 2002), while shortening of villus and deeper crypts lead to poor nutrient absorption, increased secretion in gastrointestinal tract and reduced performance. Medicinal plants with antibacterial activity can decrease the harmful bacteria in the intestinal wall and cause a reduction in the production of toxic compounds and damage to intestinal epithelial cells such as shorter villi and deeper crypts, improving intestinal morphology. Giannenas et al. (Reference GIANNENAS, TONTIS, TSALIE, CHRONIS, DOUKAS and KYRIAZAKIS2010) reported a shorter villus and a deeper crypt when the counts of pathogenic bacteria increase in the gastrointestinal tract, which result in fewer absorptive and more secretory cells.

Intestinal microbes

Supplementation of BCS in diets may reduce pathogenic microorganisms in the gut due to antibacterial effects of compounds in its essential oils (Khan et al., Reference KHAN, ANSARI, HAQ and ABBAS2012; Boka et al., Reference BOKA, MAHDAV, SAMIE and JAHANIAN2014). The caecal coliform and E. coli population decreased in BCS (1.25, 2.5 or 5.0%) and antibiotic supplemented groups (Khan et al., Reference KHAN, ANSARI, HAQ and ABBAS2012). However, no effect of BCS on caecal Lactobacillus population was noted (Khan et al., Reference KHAN, ANSARI, HAQ and ABBAS2012; Kumar et al., Reference KUMAR, PATRA, MANDAL, SAMANTA and PRADHAN2017a). Boka et al. (Reference BOKA, MAHDAV, SAMIE and JAHANIAN2014) reported that all dietary BCS levels (1%, 2% and 3% of diet) decreased the numbers of ileal E. coli count. Contrary to the results observed above, Khalaji et al. (Reference KHALAJI, ZAGHARI, HATAMI, HEDARI-DASTJERDI, LOTFI and NAZARIAN2011) and Ismail (Reference ISMAIL2011) did not find any effect of BCS (10 g/kg) and BCS extract (1 g/kg) on caecal Lactobacillus, coliform, and E. coli populations in broiler chickens. A decreasing tendency of caecal E. coli count was noted after BCS supplementation (Kumar et al., Reference KUMAR, PATRA, MANDAL, SAMANTA and PRADHAN2017a). Low caecal coliform populations in the gut of broiler chickens fed BCS may be explained by antibacterial activity against different pathogenic bacteria (El-Kamali et al., Reference EL-KAMALI, AHMED, MOHAMED, YAHIA, ELTAYEB and ALI1998; Durrani et al., Reference DURRANI, CHAND, ZAKA, SULTAN, KHATTAK and DURRANI2007). A variety of different bioactive components such as thymoquionone, thymodihydroquinone, carvone, carvene are present in BCS, and these constituents possess antibacterial activity (Patra, Reference PATRA2012; Hanafy and Hatem, Reference HANAFY and HATEM1991) and are well known for their pharmacological effects (Gilani et al., Reference GILANI, JABEEN and KHAN2004).

Immunity

Immuno-potentiative activity of BCS has been noted in different studies. Kumar et al. (Reference KUMAR, PATRA, MANDAL, SAMANTA and PRADHAN2017a) noted that BCS (5, 10 and 20 g/kg diet) quadratically increased antibody titre against Newcastle disease virus (NDV) at 35 days of age, but no significant effect was seen in the antibody titre at 28 days of age. In this study, broiler chickens were vaccinated against NDV with live B1 strain and LaSota strain vaccines at five and 18 days of age, respectively. In another study on chickens vaccinated against NDV and infectious bronchitis diseases at seven and 21 days of age, and against infectious bursal disease virus (IBDV) at 14 days of age, antibody titre against NDV and IBDV was significantly enhanced by BCS at 42 days of age (Al-Beitawi et al., Reference AL-BEITAWI, EL-GHOUSEIN and NOFAL2009). Including BCS at the level of 40 g/kg increased antibody production against NDV (vaccinated at seven and 21 days of age) and IBDV (vaccinated at the age of 11 and 18 days) in broiler chickens (Durrani et al., Reference DURRANI, CHAND, ZAKA, SULTAN, KHATTAK and DURRANI2007). Al-Mufarrej (Reference AL-MUFARREJ2014) noticed that NDV titre (vaccinated at one day of age) did not differ among the different doses of BCS (7, 14, 21 or 28 g/kg diet) at 21, 28, 35 and 42 days of age, but they were improved compared to the control group. However, Toghyani et al. (Reference TOGHYANI, GEISARI, GHALAMKARI and MOHAMMADREZAEI2010) reported that incorporation of BCS (2 and 4 g/kg) in poultry diets failed to induce any significant impact on antibody titres against influenza and NDV virus at 18 and 28 days of age, although lymphoid organ ratio (bursa and thymus) increased with BCS levels. Shewita and Taha (Reference SHEWITA and TAHA2011) did not observe any effect of BCS (2 to 10 g/kg) on antibody titre against NDV at the age of 14, 24 and 34 days in chickens vaccinated at 14, 26 and 35 days of age, but the weight of bursa and thymus increased considerably by 80 to 95%. In later studies, non-significant effects on antibody titres by BCS supplementation were considered due to the use of low doses and presence of low concentrations of active principles in BCS.

Weights of immune organs were found to alter due to BCS supplementation in some studies. Spleen and weight tended to decrease linearly with increasing levels of BCS, while weights of bursa increased linearly (Kumar et al., Reference KUMAR, PATRA, MANDAL and DEBNATH2017b). Toghyani et al. (Reference TOGHYANI, GEISARI, GHALAMKARI and MOHAMMADREZAEI2010) noted that the lymphoid organ weight increased when broilers were fed diets supplemented with BCS at 2 and 4 g/kg diet. Al-Mufarrej (Reference AL-MUFARREJ2014) showed that dietary supplement of BCS at the level of 10 or 14 g/kg enhanced immune responsiveness in broiler chickens, but at 21 days the bursa showed no significant difference between all groups and the controls. At 35 days of age, the bursa showed no significant difference between all groups post-vaccination. Similarly, there was no significant difference between spleen weight ratio with body weight for other groups at 21 and 35 days of age. El-Deek et al. (Reference EL-DEEK, HAMDY, ATTIA and KHALIFAH2009) reported no significant difference in lymphoid organs as an indication of immune response due to feeding different dietary concentrations of BCS, whether in the spleen or bursa. Hermes et al. (Reference HERMES, ATTIA, IBRAHIM and EL-NESR2011) found that addition of BCS oil, BCS meal to broiler chickens diets significantly increased liver, spleen and thymus gland. Yatoo et al. (Reference YATOO, SHARMA, KHAN, RASTOGI and PATHAK2012) found variable response on the weight of immunological organs but did not differ significantly. It should be noted that the weight of lymphoid organs may be altered by several pathological conditions, including mycotoxin contamination in feeds (Cazaban et al., Reference CAZABAN, MASFERRER, PASCUAL, ESPADAMALA, COSTA and GARDIN2015).

Blood biochemical profile

Concentrations of glucose in blood were not affected by BCS in many studies (Al-Beitawi et al., Reference AL-BEITAWI, EL-GHOUSEIN and NOFAL2009; Ghasemi et al., Reference GHASEMI, KASANI and TAHERPOUR2014; Khalaji et al., Reference KHALAJI, ZAGHARI, HATAMI, HEDARI-DASTJERDI, LOTFI and NAZARIAN2011; Kumar et al., Reference KUMAR, PATRA, MANDAL, SAMANTA and PRADHAN2017a); whereas El-Kaiaty et al. (Reference EL-KAIATY, SOLIMAN and HASSAN2002) reported decreased serum glucose concentrations in layers by 16% and Yatoo et al. (Reference YATOO, SHARMA, KHAN, RASTOGI and PATHAK2012) found a significant reduction in blood glucose when using 1% BCS in broiler diets. Khalaji et al. (Reference KHALAJI, ZAGHARI, HATAMI, HEDARI-DASTJERDI, LOTFI and NAZARIAN2011) did not observe any significant effect of 1% BCS supplementation on serum glucose level.

The concentration of total protein tended to be higher in the BCS fed groups than in the control, which increased linearly with higher doses of BCS (Kumar et al., Reference KUMAR, PATRA, MANDAL, SAMANTA and PRADHAN2017a). Increased serum total protein with BCS supplementation was noted by Yatoo et al. (Reference YATOO, SHARMA, KHAN, RASTOGI and PATHAK2012), Khan et al. (Reference KHAN, ANSARI, HAQ and ABBAS2012), Al-Beitawi et al. (2008) and Saleh (Reference SALEH2014).

Yatoo et al. (Reference YATOO, SHARMA, KHAN, RASTOGI and PATHAK2012) reported a significantly higher serum total protein and albumin with 1% BCS supplementation as compared to a control diet, and Khan et al. (Reference KHAN, ANSARI, HAQ and ABBAS2012) found an increase in total protein value than the 1.25% antibiotic or non-supplemented diet groups. The same results were seen by Tollba and Hassan (Reference TOLLBA and HASSAN2003) and Hassan et al. (Reference HASSAN, ABO TALEB, WAKWAK and YOUSEF2007), who found high serum total protein, albumin and globulin in birds fed diets with high levels of BCS. Saleh (Reference SALEH2014) found that total protein and albumin concentrations (but not globulin concentration) and albumin to globulin ratio increased through feeding BCS oil (1 ml/kg) compared with a control diet or one containing avilamycin. As serum protein depends on the availability of dietary protein, BCS diets contained protein that was more available to the birds (Kumar et al., Reference KUMAR, PATRA, MANDAL, SAMANTA and PRADHAN2017a).

The increase in total protein and albumin may be due to an immuno-stimulating effect of BCS. El-Ghammry et al. (Reference EL-GHAMMRY, EL-MALLAH and EL-YAMNY2002) found a contrasting result, whereby incorporation of 4 g/kg BCS in feed did not influence plasma total protein, albumin as well as globulin. Hermes et al. (Reference HERMES, ATTIA, IBRAHIM and EL-NESR2011) observed slightly increased total plasma protein as well as albumin and globulin compared to control group, but differences failed to be significant.

Decreasing trends in serum total cholesterol were observed in many studies (Yatoo et al., Reference YATOO, SHARMA, KHAN, RASTOGI and PATHAK2012; Hermes et al., Reference HERMES, ATTIA, IBRAHIM and EL-NESR2011; El-Bagir et al., Reference EL-BAGIR, HAMA, HAMED, EL-RAHIM and BEYNEN2006; AL-Beitawi et al., 2008). Concentrations of cholesterol tended to be lower for BCS compared with control, which decreased linearly with increasing doses (5, 10, and 20 g/kg) of BCS (Kumar et al., Reference KUMAR, PATRA, MANDAL, SAMANTA and PRADHAN2017a). Yatoo et al. (Reference YATOO, SHARMA, KHAN, RASTOGI and PATHAK2012) reported that the serum total cholesterol was lower in birds fed 1% BCS in feed than in an unsupplemented group. Hermes et al. (Reference HERMES, ATTIA, IBRAHIM and EL-NESR2011) revealed that plasma content of cholesterol was reduced by feeding different forms and levels of BCS. In hens, El-Bagir et al. (Reference EL-BAGIR, HAMA, HAMED, EL-RAHIM and BEYNEN2006) observed that addition of 1 or 3% BCS in the diets of 68 weeks old layers resulted in a dose dependent decrease of serum total cholesterol. Ghasemi et al. (Reference GHASEMI, KASANI and TAHERPOUR2014) reported that broiler chickens fed BCS had lower plasma cholesterol concentration than those fed the control diet. Al-Beitawi et al. (2008) ran a 49 days trial using 0, 1.5, 2.0, 2.5 and 3.0% crushed or uncrushed BCS, 3.0% crushed and uncrushed BCS, and found that it reduced plasma total cholesterol. Conversely, Khalaji et al. (Reference KHALAJI, ZAGHARI, HATAMI, HEDARI-DASTJERDI, LOTFI and NAZARIAN2011) reported that 1% BCS in broiler diets did not affect the serum plasma cholesterol. Saleh (Reference SALEH2014) evaluated the effects of avilamycin at a dose of 0.001% against BCS oil at 1 ml/kg in feed and reported that plasma total cholesterol concentration was higher in BCS than in control and antibiotic groups.

Several studies including Hermes et al. (Reference HERMES, ATTIA, IBRAHIM and EL-NESR2011), El-Bagir et al. (Reference EL-BAGIR, HAMA, HAMED, EL-RAHIM and BEYNEN2006), Al-Beitawi et al. (2008; Reference AL-BEITAWI, EL-GHOUSEIN and NOFAL2009), Akhtar et al. (Reference AKHTAR, NASIR and ABID2003) and Ghasemi et al. (Reference GHASEMI, KASANI and TAHERPOUR2014) reported that BCS supplementations resulted in a reduction in plasma triglyceride. However, Khalaji et al. (Reference KHALAJI, ZAGHARI, HATAMI, HEDARI-DASTJERDI, LOTFI and NAZARIAN2011) and Kumar et al. (Reference KUMAR, PATRA, MANDAL, SAMANTA and PRADHAN2017a) did not observe any effect of BCS supplementation on these concentrations.

The decrease in serum cholesterol concentrations might be due to enhanced bile production (El-Dakhakhny et al., Reference EL-DAKHAKHNY, MAHADY and HALIM2000). Brunton (Reference BRUNTON1999) suggested that reduction in serum cholesterol may be attributed to the lowering effect of thymoquinone and unsaturated fatty acids on the synthesis of cholesterol by hepatocytes or the fractional reabsorption from the small intestine. Moreover, BCS contain an appreciable amount of sterols, especially β-sitosterol that has the ability to inhibit the absorption of dietary cholesterol (Khan et al., Reference KHAN, ANSARI, HAQ and ABBAS2012). These compounds may stimulate the cholesterol excretion into the intestine being oxidised by bile acids (Tollba and Hassan, Reference TOLLBA and HASSAN2003). This decrease in serum cholesterol levels of broilers fed BCS diets probably suggests a general decrease in lipid mobilisation.

Carcass characteristics

Supplementation with BCS increased slaughter weight, thigh weight, breast weight, edible internal organs and abdominal fat in many studies (Guler et al., Reference GULER, DALKILIC, ERTAS and CIFTCI2006; Ashayerizadeh et al., Reference ASHAYERIZADEH, DASTAR, RAHMATNEJAD, SHARG, ASHAYERIZADEH and HOSSAINI2009; Erener et al., Reference ERENER, ALTOP, OACK, AKSOY, CANKAYA and OZTURK2010; Saleh, Reference SALEH2014; Kumar et al., Reference KUMAR, PATRA, MANDAL and DEBNATH2017b). Guler et al. (Reference GULER, DALKILIC, ERTAS and CIFTCI2006) observed significant effects of 1.0% BCS and antibiotic in the diets on liver, abdominal fat, thigh, breast, wings and neck weights. Erener et al. (Reference ERENER, ALTOP, OACK, AKSOY, CANKAYA and OZTURK2010) reported that dietary BCS increased the carcass weight. No significant effects for dietary BCS and BCS extract was observed on the dressing percentage, edible organ, and abdominal fat. Meanwhile, Saleh (Reference SALEH2014) observed that breast muscle weight was increased significantly but liver weight was not affected by feeding BCS, compared with control and avilamycin-fed birds. However, Ghasemi et al. (Reference GHASEMI, KASANI and TAHERPOUR2014) revealed that carcass percentage, internal organs weight and abdominal fat pad were not influenced by the BCS.

El-Ghammry et al. (Reference EL-GHAMMRY, EL-MALLAH and EL-YAMNY2002) reported a decrease in dressing percentage. Durrani et al. (Reference DURRANI, CHAND, ZAKA, SULTAN, KHATTAK and DURRANI2007) reported that no significant differences in most carcass traits, with the exception of liver, heart and intestine weight. The most significant differences were seen in abdominal fat percentage for the lypolytic effect of BCS meal. Abaza et al. (Reference ABAZA, SHEHATA, SHOIEB and HASSAN2008) revealed that adding 0.1% BCS oil to the diets of chicken decreased the percent of abdominal fat. This could be beneficial to divert the energy of the fat for useful physiological activities. Majeed et al. (Reference MAJEED, ABDELATI, ELBAGIR, ALHAIDARY, MOHAMED and BEYNEN2010) reported that the final weight of breast, thigh and drumstick were not affected by the composition of the diet. Al-Beitawi and El-Ghousein (Reference AL-BEITAWI and EL-GHOUSEIN2008) assumed that supplementation of diets with different levels of crushed or uncrushed BCS did not affect any carcass characteristic parameters.

In contrast, Abbas and Ahmed (Reference ABBAS and AHMED2010) found that birds fed on diet supplemented with 1% BCS resulted in a significant reduction in dressing percentage when compared to those fed a control or 2% supplemented diets. Khan et al. (Reference KHAN, ANSARI, HAQ and ABBAS2012) did not find variation in dressing percentage on day 28 and 42 between BCS supplementation and antibiotic groups. Jahan et al. (Reference JAHAN, KHAIRUNNESA, AFRIN and ALI2015) reported that there was no significant difference for the average body weight, dressing yield, thigh meat, wing meat, heart, gizzard and liver, but differences were found within breast meat, drumstick meat, abdominal fat and skin of broiler chickens at 1.5% level of BCS meal in the diet. Ismail (Reference ISMAIL2011) did not see any significant effects of dietary BCS or BCS extract on the dressing percentage, edible inner organs, abdominal fat, full gut weight, and gut length, and Khalaji et al. (Reference KHALAJI, ZAGHARI, HATAMI, HEDARI-DASTJERDI, LOTFI and NAZARIAN2011) found increased relative weight of gizzard by addition of BCS to the diet, but other carcass traits were not affected.

The difference in body weights between BCS and control diets were reflected in the dressed bird weights at slaughter. As a result of discrepancies in feed intake, the amount of metabolisable energy and protein ingested by the birds could explain the differences observed in carcass yields (Ismail, Reference ISMAIL2011). The increase in breast weight indicated that BCS may have an effect on protein utilisation. The greater ash percentage of the meat in the same study might be due to enhanced availability of minerals by birds fed diets containing BCS (Hermes et al., Reference HERMES, FATEN, ATTIA, IBRAHIM and EL-NESR2009).

Chemical composition and antioxidant properties of meat

In thigh and breast muscle, concentrations of DM, CP and EE were greater in birds fed BCS diets than in the control group and were highest at 10 g BCS/kg diet (Kumar et al., Reference KUMAR, PATRA, MANDAL and DEBNATH2017b). Al-Beitawi and El-Ghousein (Reference AL-BEITAWI and EL-GHOUSEIN2008) noted a high percentage of DM and CP in breast meat of chickens fed a diet containing 15 g /kg BCS in the diet, but high concentrations did not affect this. However, concentrations of DM and CP in leg meat were not changed by BCS in the same study. In general, high concentrations of BCS (20 to 30 g BCS/kg) increased crude fat content in both breast and leg meat of chickens (Al-Beitawi and El-Ghousein, Reference AL-BEITAWI and EL-GHOUSEIN2008). The increases in concentrations of CP and EE in muscle may be attributed to intake of greater amounts of digestible CP and EE, due to increased feed intake and digestion (Durrani et al., Reference DURRANI, CHAND, ZAKA, SULTAN, KHATTAK and DURRANI2007; Kumar et al., Reference KUMAR, PATRA, MANDAL, SAMANTA and PRADHAN2017a). Moreover, BCS or its EO may influence the activity of thyroid gland increasing hormone concentrations in the blood, which is involved in protein synthesis and energy metabolism (Hermes et al., Reference HERMES, ATTIA, IBRAHIM and EL-NESR2011).

Improvements of nutritional quality of meats by dietary interventions especially using plant bioactive compounds and vegetable oils have been attempted in different studies (Patra, Reference PATRA2014; Mandal et al., Reference MANDAL, ROY and PATRA2014a). Poultry meat has many desirable nutritional characteristics such as relatively high concentrations of poly unsaturated fatty acids (PUFA) and low lipid content (Mandal et al., Reference MANDAL, GHOSH and PATRA2014b). Fatty acid composition and anti-oxidant substances in diets are factors that influence fatty acid composition in the muscles (Crespo and Esteve-Garcia, Reference CRESPO and ESTEVE-GARCIA2001; Ertas et al., Reference ERTAS, GULER, CIFTCI, DALKILIC and SIMSEK2005). There is limited information on the effect of BCS or its oil on antioxidant status in chickens, but supplementation has resulted in improved ferric reducing antioxidant power (FRAP) in blood serum, thigh and breast meat (Kumar et al., Reference KUMAR, PATRA, MANDAL and DEBNATH2017b). Guler et al. (Reference GULER, ERTAS, KIZIL, DALKILIC and CIFTCI2007) included BCS at four different doses (5, 10, 20 and 30 g/kg) of BCS in the diets and reported that malondialdehyde (MDA) concentrations (an indicator of lipid peroxidation) in breast meat were decreased by including BCS in the diets (10, 20 and 30 g/kg, but not at 5 g/kg). In this study, inclusion of BCS in diets decreased MDA concentrations in serum (10 to 30 g/kg, but not at 5 g/kg), liver (5 to 30 g/kg) and heart (10 to 30 g/kg, but not at 5 g/kg). Rahman and Kim (Reference RAHMAN and KIM2016) noted that feeding of BCS (10 and 20 g/kg of the diet) to broiler chickens decreased MDA concentrations by 24% and 28% compared with the control group and increased the antioxidant activities (glutathione peroxidase and superoxide dismutase) in thigh muscle.

Kumar et al. (Reference KUMAR, PATRA, MANDAL and DEBNATH2017b) studied lipid peroxidation status in breast and thigh meat kept at 4°C for 1 day and 7 days. The authors noted that lipid peroxide values in thigh and breast meat were not influenced, although FRAP activity was higher in meat from chicken fed BCS. However, after EE concentration in meat (which was greater for the BCS groups) was taken into account, peroxide values in breast meat, but not in thigh meat, tended to decrease in the BCS groups compared with the control. Tuluce et al. (Reference TULUCE, OZKOL, SOGUT and CELIK2009) reported that BCS decreased lipid peroxidation in tissues due to superoxide anion scavenger activity. Guler et al. (Reference GULER, ERTAS, KIZIL, DALKILIC and CIFTCI2007) suggested that these effects might be due to antioxidant constituents like thymoquinone, carvacrol, anethole and 4-terepinol. Mariod et al. (Reference MARIOD, IBRAHIM, ISMAIL and ISMAIL2009) investigated the antioxidant activity and phenolic content of phenolic rich fractions obtained from BCS cake. Methanolic extracts of BCS showed that phenolic compounds such as syringic acid, hydroxybenzoic and pcumaric acids possess significant antioxidant properties under in vitro analysis. Bassim and Imaizumi (1998) investigated the antioxidant activity of BCS, and found that BCS ethanolic extracts applied to the corn oil prevented oxidative damage of triglycerides.

There is not much information on the effect of BCS of fatty acid profiles in meat. In one study, supplementation of BCS increased the concentrations of PUFA and some unsaturated fatty acids (Kumar et al., Reference KUMAR, PATRA, MANDAL and DEBNATH2017b). Changes in body fat deposition in muscles may be related to different rates of lipid synthesis or lipid oxidation (Crespo and Esteve-Garcia, Reference CRESPO and ESTEVE-GARCIA2001). PUFA are the most sensitive fractions to oxidation processes and lipid oxidation in meat and are one of the reasons for quality degradation during storage. Enrichment of unsaturated fatty acids in meat could be attributed to attenuation of fatty acid oxidation in tissue. The antioxidant properties of BCS may block lipid peroxidation of tissue lipids, especially PUFA, enhancing higher concentration in meat. Phytoadditives containing antioxidant properties could modify the fatty acid profiles in meat. For instance, total PUFA significantly increased in broiler chickens supplemented with cinnamon oil essential oils (Ciftci et al., Reference CIFTCI, DALKILIC, CERCI, GULER, ERTAS and ARSLAN2009).