Effects on broiler production

Given the antimicrobial activity of thyme (Dorman and Deans, Reference DORMAN and DEANS2000; Rahimi et al., Reference RAHIMI, TEYMOURI ZADEH, KARIMI TORSHIZI, OMIDBAIGI and ROKNI2011), it would be expected that this plant could have positive effect on the growth of broiler chickens. The beneficial effects of thyme on broiler performance have been reported either alone or in combination with other agents (Al-Mashadani et al., 2011). Mansoub (Reference MANSOUB2011a) found that 1g/kg of thyme fed to broilers resulted in improved weight gain and feed efficiency. Zhang et al. (Reference ZHANG, YAN, KEEN and WALDROUP2005) concluded that thyme oil may be a promising alternative to antibiotic growth promoters. Further, Al-Kassie (Reference AL-KASSIE2009) demonstrated that feeding thyme oil at the rate of 100 and 200 ppm increased feed intake, body weight and feed conversion ratio (FCR) as well as dressing percentage, liver, heart, gizzard and decreased abdominal fat. Bolukbasi et al. (Reference BOLUKBASI, ERHAN and OZKAN2006) found that thyme oil (200 ppm) resulted in higher hot carcass and wing weight. In their published paper of 2011, Al-Mashadani et al. documented that live body weight increased significantly in broiler chickens fed thyme oil (300 mg) alone or in combination with anise (300mg) from 28-38 days of age. Langhout (Reference LANGHOUT2000) reported that the addition of oil improves nutrient digestion in poultry and enhanced the liver function. Al-Kassie (Reference AL-KASSIE2009) suggested that oil derived from thyme contain thymol and carvacrol which increase feed intake and weight gain in broilers. In a study using 2% thyme, El-Ghousein and Al-Beitawi (Reference EL-GHOUSEIN and AL-BEITAWI2009) found that the treatment increased body weight, live weight, dressing percentage, leg, breast, wing and total edible parts percentages, while decreasing feed intake and mortality. Zeweil (Reference ZEWEIL2003) investigated feeding thyme flowers to growing Japanese quail at the level of 1 g/kg and observed that body weight and FCR were improved. Abdel-Latif et al. (Reference ABDEL-LATIF, AHMAD and EL-KAIATY2002) found a higher dressing percentage when birds were fed thyme. Ocak et al. (Reference OCAK, ERENER, BURAK AK, SUNGU, ALTOP and OZMEN2008) reported that when broilers of mixed sex were fed 0.2% thyme from 7-35 days of age, they had improved weight gain compared to control, although feed intake, feed efficiency and carcass quality did not differ. Thyme powder (5g/kg) increased body weight gain in broiler chicks compared to control and was almost same as the antibiotic (flavophospholipol) treated birds (Toghyani et al., Reference TOGHYANI, TOHIDI, GHEISARI and TABEIDIAN2010).

Thyme may act in several ways to produce such beneficial effects. Massada (Reference MASSADA1976) concluded that thyme contained major components of essential oils which improve animal performance by increasing digestive enzyme secretion and nutrient utilisation through enhanced liver function (Langhout, Reference LANGHOUT2000; Williams and Losa, Reference WILLIAMS and LOSA2001). El-Ghousein and Al-Beitawi (Reference EL-GHOUSEIN and AL-BEITAWI2009) suggested that the antibacterial action of thyme may be involved in the improved performance of broilers. Hernandez et al. (Reference HERNANDEZ, MADRID, GARCIA, ORENGO and MEGIAS2004) found that broilers fed diets containing thyme had improved apparent total faecal digestibility and crude protein digestibility, which may be responsible for the enhanced performance of broiler chicks reported elsewhere. Similarly, Lee et al. (Reference LEE, EVERTS and KAPPERT2003a) found that thyme increased the activities of pancreatic digestive enzymes including amylase, lipase, trypsin and chymotrypsin in broilers and concluded that such enzyme stimulating effects may result in better feed utilisation and nutrient availability.

Some feeding experiments with broilers did not find any differences in performance parameters in birds fed thyme at different doses or in combination with other plants in comparison with an unsupplemented control or an antibiotic treatment (Cross et al., Reference CROSS, SVOBODA, MCDEVITT and ACAMOVIC2003; Demir et al., Reference DEMIR, SARICA, OZCAN and SUICMEZ2003; Lee et al., Reference LEE, EVERTS and KAPPERT2003a; Reference LEE, EVERTS and KAPPERT2003b; Hernandez et al., Reference HERNANDEZ, MADRID, GARCIA, ORENGO and MEGIAS2004; Barreto et al., Reference BARRETO, MENTON, RACANICCI and PEREIRA2008; Demir et al., Reference DEMIR, KILINC, YILDIRIM, DINCER and ESECELI2008; Sengül et al., Reference SENGÜL, YURTSEVEN, CETIN, KOCYIGIT and SÖGÜT2008; Al-Mashadani et al., 2011; Dahal and Farran, Reference DAHAL and FARRAN2011). Lee et al. (Reference LEE, EVERTS and KAPPERT2003a) suggested that the absence of any effect of thyme on the birds’ performance may be related to the composition of the diet and environmental conditions of the experiment. If feed contains highly digestible ingredients, the profile of the gut microflora is altered due to unavailability of substrate, thereby leading to reduced antimicrobial effects of any plant extract. According to Langhout (Reference LANGHOUT2000) better results are associated with combination of essential oils with some similar active principle application. Barreto et al. (Reference BARRETO, MENTON, RACANICCI and PEREIRA2008) suggested that lack of effect of thyme may be due to the unavailability of the active ingredients which are usually not found in a pure state, but as complexes, which enhances their action on the body.

Performance of laying hens

Ali et al. (Reference ALI, HASSAN and ABD EL-GHANY2007) reported that the addition of 0.25% thyme in the diet of laying hens improved FCR and egg production, fertility and hatchability, however, yolk (weight, height, diameter, index and colour), shell (weight and thickness), egg (length, breadth and shape index), albumin (height and weight) and Haugh units did not change. Ghasemi et al. (Reference GHASEMI, ZAREI and TORKI2010) used 0.1 and 0.2% thyme in laying hens and found that egg production and egg mass, feed intake and FCR did not change in either group, however, egg weight increased in birds fed the 0.1% herbal product. In the same experiment, egg index, Haugh unit, shell thickness were unaffected by supplementation although yolk colour was higher in birds fed with 0.2% thyme. Mansoub (Reference MANSOUB2011b) noted that laying hens fed thyme powder improved egg production and quality. Radwan et al. (Reference RADWAN, HASSAN, QOTA and FAYEK2008) did not find any differences in nutrient digestibility in laying hens fed either 0.5 or 1.0% thyme, although the latter resulted in improved egg production and mass with no effect on shell weight or thickness, egg shape index, yolk colour score or Haugh unit. Orhan and Eren (Reference ORHAN and EREN2011) found that egg production, FCR, feed consumption, egg weight and egg shell breaking strength were unaffected by feeding thyme to laying hens. Slight improvements in mean egg production, weight, mass and FCR were found when Japanese quail hens were fed either 0.1 or 0.2% thyme (Zeweil, Reference ZEWEIL2003).

Antioxidant effects

Lipid peroxidation is a process of vital importance for the food processing industry. During this process, the polyunsaturated lipids are oxidized (Khan, Reference KHAN2011; Mohamed et al., Reference MOHAMED, HUSEEN and JAWAD2011) which adversely affects flavour, taste, nutritional value and the overall quality of foods (Botsoglou et al., Reference BOTSOGLOU, YANNAKOPOULOS, FLETOURIS, TSERVENI-GOUSSI and FORTOMARIS1997). Eggs contain oxidative products which are highly prone to lipid peroxidation. Therefore, there is commercial interest in the oxidative deterioration of marketed eggs, and its suppression. Usually the activity of the egg shell maintains the oxidative stability of the internal contents of the egg during storage. Some constituents, such as phosvitins appear to be effective in preventing the oxidation of yolk lipids. However, this limited protection may not prevent oxidation processes for a longer duration, therefore synthetic and natural antioxidants are recommended to prevent lipid peroxidation of polyunsaturated fatty acids (Khan, Reference KHAN2011).

The results of many reports have advocated the antioxidant effect of thyme extracts including its oil in both plasma and egg. According to Ali et al. (Reference ALI, HASSAN and ABD EL-GHANY2007) the addition of thyme (0.25%) increased plasma antioxidant level. In a study, Tserveni-Goussi et al. (Reference TSERVENI-GOUSSI, YANNAKOPOULOS and BOTSOGLOU1994) demonstrated that dietary thyme fed to laying hens eliminated the need for additional oxidative stabilisation. Further, Botsoglou et al. (Reference BOTSOGLOU, YANNAKOPOULOS, FLETOURIS, TSERVENI-GOUSSI and FORTOMARIS1997) discussed the effect of dietary thyme fed to hens on the oxidative stability of shell eggs stored over 60 days at a low temperature and concluded that eggs from hens fed thyme had reduced oxidation of liquid yolk, which significantly increased with exposure to light and acidity. Botsoglou et al. (Reference BOTSOGLOU, YANNAKOPOULOS, FLETOURIS, TSERVENI-GOUSSI and FORTOMARIS1997) suggested that thyme constituents pass into the yolk, where they are responsible for antioxidative activity and can prolong storage capacity. In a recent study, Orhan and Eren (Reference ORHAN and EREN2011) found that when a herbal mixture (0.5%) containing thyme was fed to the laying hens it reduced malondialdehyde in egg yolk during a 56 day storage period. Sengül et al. (Reference SENGÜL, YURTSEVEN, CETIN, KOCYIGIT and SÖGÜT2008) found that, in comparison to a control or flavomycin treated birds, antioxidant responses increased significantly in the thyme-fed birds, while total oxidant status and DNA damage were decreased in the treated group. Miura and Nakatani (Reference MIURA and NAKATANI1989) and Bolukbasi et al. (Reference BOLUKBASI, ERHAN and OZKAN2006) reported that thyme exhibited higher antioxidant activity than vitamin E. Lee et al. (Reference LEE, EVENTS and BEYNEN2004) found that antioxidant effect from egg yolk disappeared when the feeding of thyme to laying hens ceased.

It has been shown that phenolic components like carvacrol and thymol were found to be responsible for the stabilisation of thyme oil due to their antioxidant activity (Schwartz et al., Reference SCHWARTZ, ERNST and TERNES1996). According to Bolukbasi et al. (Reference BOLUKBASI, ERHAN and OZKAN2006) carvacrol and thymol may be responsible for the antioxidant effect of thyme oil. Bolukbasi et al. (Reference BOLUKBASI, ERHAN and OZKAN2006) found that thyme oil at the rate of 200 mg resulted in a significant reduction in TBARS (thiobarbituric acid reactive species). Apart from these compounds, other phenolics in thyme leaves such as caffeic acid, p-cymene-2,3-diol and biphenylic as well as flavonoid compounds have been found to exhibit antioxidant activity (Bolukbasi et al., Reference BOLUKBASI, ERHAN and OZKAN2006). Bolukbasi et al. (Reference BOLUKBASI, ERHAN and OZKAN2006) concluded that the antioxidant capacity of thyme oil exceeded that of vitamin E in leg tissue. Lee et al. (Reference LEE, EVENTS and BEYNEN2004) postulated that high antioxidant activity of thymol comes from the phenolic OH group which acts as a hydrogen donor to the peroxyle radicals produced during the first step in lipid peroxidation, thus retarding the hydroxyl peroxide formation. These authors further suggested that thymol and U-cymene-2,3-diol which are responsible for the antioxidant effect of thyme oil, could be transferred to the egg yolk after 12 days of feeding in response to 1.12 and 1.68% thyme extract in feed.

Antibacterial and immunomodulating effects

Rahimi et al. (Reference RAHIMI, TEYMOURI ZADEH, KARIMI TORSHIZI, OMIDBAIGI and ROKNI2011) reported that a 0.1% dose of thyme reduced E. coli and improved lactic acid bacterial populations in the gut of broilers. Dorman and Deans (Reference DORMAN and DEANS2000) demonstrated that the essential oils of certain plants exert an antimicrobial effect via its activity on the bacterial cell wall by breaking down coagulation protein. The breakdown of the cell wall is associated with the lipophilic characteristics of the essential oil that is accumulated in the cell membrane. Helander et al. (Reference HELANDER, ALAKOMI, LATVA-KALA, MATTILA-SANDHOLM, POL, SMID, GORRIS and VON WRIGHT1998) concluded that thymol and carvacrol in thyme exert their antibacterial action against E. coli and Salmonella spp. through penetration of these components into the Gram negative bacteria. Juven et al. (Reference JUVEN, KANNER, SCHVED and WEISSLOWICZ1994) postulated that the active ingredients of thyme bind to the amine and hydroxylamine groups of bacterial membrane protein and results in cell death (apoptosis). Further, Radwan et al. (Reference RADWAN, HASSAN, QOTA and FAYEK2008) found that 0.1% thyme fed to laying hens gave better antibody production responses compared to 100 or 200 mg/k vitamin E which is considered to be a potent immunomodulation agent (Khan et al., Reference KHAN, NAZ, NIKOUSEFAT, TUFARELLI, JAVADANI, N. and LAUDADIO2011b). Rahimi et al. (Reference RAHIMI, TEYMOURI ZADEH, KARIMI TORSHIZI, OMIDBAIGI and ROKNI2011) reported that a 0.1% dose of thyme improved antibody responses in poultry when tested after 42 days of treatment. On the other hand, Toghyani et al. (Reference TOGHYANI, TOHIDI, GHEISARI and TABEIDIAN2010) found that thyme powder (5 or 10 g/kg) in broiler diets had no effect on antibody titre against Newcastle and influenza viruses or sheep red blood cells. Several hypotheses have been presented to the absence of the effect of thyme in these cases. According to Barreto et al. (Reference BARRETO, MENTON, RACANICCI and PEREIRA2008) the mode of action of plant extracts depends upon their structure, metabolism and inclusive level. Therefore, it is difficult to precisely discern the amount of active ingredient required to exert a positive action, since we do not know what exact amount is required to elicit specific actions. Cechinel and Yunes (Reference CECHINEL and YUNES1998) concluded that the chemical composition of the plant may be different in different parts due to environmental conditions such as climate, soil and harvest time. Therefore, the challenge is to determine and to quantify the effects of different components present in the essential oil in vivo. Barreto et al. (Reference BARRETO, MENTON, RACANICCI and PEREIRA2008) reported that absence of the positive effect of thyme oil in their experiment may be due to using a smaller dose which was insufficient to produce its effect on poultry.

Hypocholesterolemic and antilipidimic effects

El-Ghousein and Al-Beitawi (Reference EL-GHOUSEIN and AL-BEITAWI2009) and Abdulkarimi et al. (Reference ABDULKARIMI, DANESHYAR and AGHAZADEH2011) postulated that hypocholesterolemic and antilipidimic effects of thyme may be due to the action of thymol and carvacrol on HMG-CoA reductase, the rate limiting enzyme of cholesterol, which reduced fat absorption from the gut or the lipid catabolism for gluconeogensis. A number of studies have documented the antilipidimic and hypocholesterolaenic effects of thyme in poultry. Ali et al. (Reference ALI, HASSAN and ABD EL-GHANY2007) reported decreased LDL, HDL, total cholesterol, triglyceride and total lipids in blood in laying hens fed 0.25% thyme. Furthermore, Al-Kassie (Reference AL-KASSIE2009) demonstrated that feeding thyme oil at the rate of 100 and 200 ppm decreased body fat and plasma cholesterol level. El-Ghousein and Al-Beitawi (Reference EL-GHOUSEIN and AL-BEITAWI2009) found that adding 2% thyme, as a whole plant, to broiler feed reduced triglyceride and cholesterol. Recently, Al-Mashadani et al. (2011) found that blood cholesterol decreased significantly in response to thyme oil alone or in combination with aniseed. Dahal and Farran (Reference DAHAL and FARRAN2011) found that LDL cholesterol was significantly reduced when broiler birds were fed 2.0% thyme. Case et al. (1995) reported that feeding thyme at a level of 150 ppm reduced in Leghorn birds, the cholesterol level by 9% in 21 days. Mansoub (Reference MANSOUB2011a; Reference MANSOUB2011b) found that 1g/kg thyme fed to the broilers resulted in improved cholesterol profiles in the blood and tissue of broiler chickens. Rahimi et al. (Reference RAHIMI, TEYMOURI ZADEH, KARIMI TORSHIZI, OMIDBAIGI and ROKNI2011) stated that 0.1% dose of thyme decreased cholesterol, triglyceride, LDL cholesterol and increased HDL cholesterol compared to the control birds. Moreover, Toghyani et al. (Reference TOGHYANI, TOHIDI, GHEISARI and TABEIDIAN2010) reported increased HDL cholesterol at the level of 10 g/kg thyme in feed.

Some of authors failed to find any beneficial effects of thyme on lowering the cholesterol level in birds. For example, in the experiment of Radwan et al. (Reference RADWAN, HASSAN, QOTA and FAYEK2008) the plasma total cholesterol, HDL and LDH cholesterol did not change by feeding 0.5 or 1.0% thyme to laying hens. Ghasemi et al. (Reference GHASEMI, ZAREI and TORKI2010) reported no change in the cholesterol profile when laying hens were fed either 0.1 or 0.2% thyme and garlic mixture. Similarly, Sengul et al. (2008) found no effects of thyme water extract or oil on the blood cholesterol level. The exact cause of such results is difficult to trace in the available literature, however, difference in experimental conditions, dose and duration, and processing technique of medicinal plants, have been cited as some of the plausible explanation (Khan et al., Reference KHAN, NAZ, NIKOUSEFAT, TUFARELLI, JAVADANI, N. and LAUDADIO2011b).