Feed intake and efficiency

Opinion in the literature is divided regarding the influence of ginger on feed intake. Tekeli et al. (Reference TEKELI, KUTLU and CELIK2011) reported that 240 ppm of Z. officinale had a positive effect on feed consumption with respect to negative control broilers. Nasiroleslami and Torki (Reference NASIROLESLAMI and TORKI2010) showed that the addition of the essential oil of ginger did not affect feed intake or feed conversion in laying hens. Zhang et al. (Reference ZHANG, YANG, WANG, YANG, JIANG and GAI2009) did not find any significant difference in daily feed intake by feeding ginger at the rate of 5 g/kg when processed to different particle sizes (300, 149, 74, 37, and 8.4 μm) although numerically the feed intake was higher than the control. Zhao et al. (Reference ZHAO, YANG, YANG, WANG, JIANG and ZHANG2011) found that daily feed intake and feed conversion ratio (FCR) did not differ between laying hens fed ginger in the diet (5, 10, 15 and 20 g/kg), and Akbarian et al. (Reference AKBARIAN, ABOLGHASEM, AHMADI and HOSSEIN2011) found that feeding ginger at different levels (0.25, 0.5 and 0.75%) had no effect on feed intake and FCR in laying hens.

Incharoen and Yamauchi (Reference INCHAROEN and YAMAUCHI2009) fed dried fermented ginger (1 and 5%) to White Leghorn laying hens and found that feed consumption and FCR tended to increase in ginger fed groups. Likewise, the use of 2% red ginger in the ration of broiler chickens has resulted in higher feed intakes and FCRs (Herawati, Reference HERAWATI2010). Onu (Reference ONU2010) reported that the addition of ginger (0.25%) in the basal diet of broiler chicks resulted in improved FCR although feed intake did not change.

In some cases ginger has been applied via drinking water in poultry. In their report, Javed et al. (Reference JAVED, DURRANI, HAFEEZ, KHAN and AHMAD2009) reported that broiler chicks dosed with aqueous extract (15 ml/l of drinking) of a mixture of plants containing ginger improved feed intake and FCR. However, Kausar et al. (Reference KAUSAR, RIZVI and ANJUM1999) showed that a carminative mixture containing ginger at the dose rate of 2 and 4 ml/l of drinking water increased FCR.

Some researchers have combined plant products, including ginger, in trials. Moorthy et al. (Reference MOORTHY, RAVI, RAVIKUMAR, VISWANATHAN and EDWIN2009) found that feed intake did not differ at six week of age, although FCR was significantly higher in birds fed a combination of 0.2% ginger and 0.2% curry leaf powder.

The differences in these reported findings may be due to the different varieties of ginger used, their processing, dose and the duration of the experiments.

Most of the researchers attributed the better performance of the broiler birds fed ginger to an improvement in palatability and the quick digestive effect of this natural product. They further postulated that due to the effect of this natural product, the digestive tract would have been emptied earlier and feed consumption will have been promoted. Ginger has been found to increase secretion of gastrointestinal enzymes including lipase, disaccharidase and maltase (Zhang et al., Reference ZHANG, YANG, WANG, YANG, JIANG and GAI2009). According to Herawati (Reference HERAWATI2010) the improved performance may be attributed to the two types of digestive enzymes in ginger; protease and lipase, which are present as part of the plants natural protective mechanisms (Zhang et al., Reference ZHANG, YANG, WANG, YANG, JIANG and GAI2009). Zhao et al. (Reference ZHAO, YANG, YANG, WANG, JIANG and ZHANG2011) reported that ginger enhances animals’ nutrient digestion and absorption because of its positive effect on gastric secretion, enterokinesia and digestive enzyme activities.

Growth performance and body weight gain

Tekeli et al. (Reference TEKELI, KUTLU and CELIK2011) stated that Z. officinale improved body weight gain in broiler chickens at the rate of 120, 240 and 360 ppm, however Zhang et al. (Reference ZHANG, YANG, WANG, YANG, JIANG and GAI2009) did not find any significant difference for average daily gain in broilers by feeding ginger at the rate of 5 g/kg. Herawati (Reference HERAWATI2010) found that the use of 2% red ginger in the ration of broiler chickens produced higher body weights. Onu (Reference ONU2010) reported that the addition of ginger (0.25%) to the basal diet of broiler chicks resulted in higher body weights. In their work, Kausar et al. (Reference KAUSAR, RIZVI and ANJUM1999) showed that carminative mixture containing ginger at the dose rate of 2 and 4 ml/l of drinking water increased body weight on the 5^th week of the experiment. Javed et al. (Reference JAVED, DURRANI, HAFEEZ, KHAN and AHMAD2009) reported that broiler chicks dosed with aqueous extract of a mixture of plants containing ginger improved body weight gain. El-Deek et al. (Reference EL-DEEK, ATTIA, MAYSA and HANNFY2002) observed that a diet containing 1 g/kg of ginger did not affect growth performance, whereas Farinu et al. (Reference FARINU, ADEMOLA, AJAYI and BABATUNDE2004) reported that supplementation of ginger at the levels of 5, 10, or 15 g/kg slightly improved growth in broilers. In contrast, Al-Homidan (Reference AL-HOMIDAN2005) observed reduced growth rate in starter broilers (1 to 4 wk) when ginger was fed at the rate of 60 g/kg body weight at the 6^th week of age (Moorthy et al., Reference MOORTHY, RAVI, RAVIKUMAR, VISWANATHAN and EDWIN2009) which may be due to the toxic effect of this compound (Zhang et al., Reference ZHANG, YANG, WANG, YANG, JIANG and GAI2009). The different results on growth performance of broilers may be ascribed to the different doses used in the experiments.

Carcass traits

In a recent study, Zhang et al. (Reference ZHANG, YANG, WANG, YANG, JIANG and GAI2009) observed that birds fed ginger produced higher carcass weights compared to untreated birds. Dressing percentage, breast weight and leg weights increased significantly in response to an aqueous extract of a plant mixture containing ginger (Javed et al., Reference JAVED, DURRANI, HAFEEZ, KHAN and AHMAD2009). Zhang et al. (Reference ZHANG, YANG, WANG, YANG, JIANG and GAI2009) suggested that improved carcass quality of broilers may be associated with the antioxidant effect of ginger which enhances protein and fat metabolism. Conversely, Moorthy et al. (Reference MOORTHY, RAVI, RAVIKUMAR, VISWANATHAN and EDWIN2009) reported no effect of ginger supplementation on carcass characteristics including New York dressed percentage, eviscerated weight, ready to cook percentage, abdominal fat pad and giblet weight. El-Deek et al. (Reference EL-DEEK, ATTIA, MAYSA and HANNFY2002) found that the dressing percentage did not differ between control and ginger treated broilers up to sixth week of age. Likewise, Onu (Reference ONU2010) affirmed that the addition of ginger (0.25%) in the basal diet of broiler chicks did not result in significant differences in carcass characteristics.

Egg production and quality

Nasiroleslami and Torki (Reference NASIROLESLAMI and TORKI2010) found that the addition of the essential oil of ginger increased egg shell weight and egg shell thickness in laying hens. However, feeding ginger essential oil did not affect egg index, yolk index and Haugh unit. However, other researchers have not always seen the same benefits. Zhao et al. (Reference ZHAO, YANG, YANG, WANG, JIANG and ZHANG2011) reported that laying hens fed with ginger at the rates of 5, 10, 15 and 20 g/kg of feed had no effect on laying rate and average egg weight, however egg mass increased significantly in supplemented groups. Akbarian et al. (Reference AKBARIAN, ABOLGHASEM, AHMADI and HOSSEIN2011) showed that feeding ginger at the rates of 0.5 and 0.75% improved egg production although egg weight did not differ between the control and treated groups. Previous work (Incharoen and Yamauchi, Reference INCHAROEN and YAMAUCHI2009) showed that White Leghorn laying hens fed dried fermented ginger (1 and 5%) showed better egg production and mass in comparison to those of control birds. However, there were no significant differences in shell breaking strength, shell thickness, shell ratio, albumin ratio, yolk ratio, yolk colour and Haugh unit among the dietary treatments.

The exact mechanism through which egg laying performance is enhanced is not known. According to Zhao et al. (Reference ZHAO, YANG, YANG, WANG, JIANG and ZHANG2011) the higher performance of the laying hens may be due to antioxidant, antimicrobial and other activities such as increased blood circulation and secretion of digestive enzymes and reduction in the oxidation of feed.

Antioxidant effects

Free radicals are constantly generated inside the body and cause oxidative damage to the cells. Therefore, neutralising entities must be present in order to alleviate such peroxidative damage. The antioxidant defence system includes natural and synthetic antioxidants and antioxidant enzymes present in the biological system (Sies, Reference SIES1991; Zhang et al., Reference ZHANG, YANG, WANG, YANG, JIANG and GAI2009). Free radicals are constantly produced in the body and certain amounts of these components are necessary for normal physiological functions. When their production exceeds normal levels however, they cause peroxidative damage to the cell membrane and organelles (Khan, Reference KHAN2011). Generally the body has three major antioxidant enzymes namely superoxide dismutase (SOD), glutathione peroxidase (GSHPx) and catalase which are involved in scavenging reactive oxygen species (Zhang et al., Reference ZHANG, YANG, WANG, YANG, JIANG and GAI2009; Zhao et al., Reference ZHAO, YANG, YANG, WANG, JIANG and ZHANG2011). Therefore, an increase in the level of these enzymes would enhance the scavenging capacity of these deleterious substances. Malondialdehyde (MDA) is the end product of lipid peroxidation, therefore, monitoring MDA is a useful indicator of the extent of lipid peroxidation in the cell (Sumida et al., Reference SUMIDA, TANAKA, KITAO and NAKADOMO1989).

Zhang et al. (Reference ZHANG, YANG, WANG, YANG, JIANG and GAI2009) showed that supplementation of ginger at the rate of 5 g/kg significantly increased the activities of SOD and GSHPx and reduced MDA in broilers at the age of 21 and 42 days. The reduced level of MDA indicated that the addition of ginger alleviated the lipid peroxidative damage to the cell. According to these authors, the antioxidant effect of ginger increased linearly with decreasing the size of the ginger particle from 300 to 37 μm. It appears that the effect of the particle size on improving the antioxidant status is likely due to an alteration to the availability of the effective compounds in ginger. However, very low particle size (8 μm) may negate antioxidant activity due to mechanical damage and exposure to ambient air, thereby reducing the usefulness of the effective compounds in the ginger. Zhao et al. (Reference ZHAO, YANG, YANG, WANG, JIANG and ZHANG2011) reported that supplementation of ginger in laying hens improved serum and egg yolk enzymatic antioxidant activity measured at 35 and 70 days of laying period. Moreover, it has been reported that feeding ginger at the rate of 0.5 and 0.75% significantly increased the activities of GSHPx and reduced MDA concentration in plasma (Akbarian et al., Reference AKBARIAN, ABOLGHASEM, AHMADI and HOSSEIN2011).

Although increased levels of these antioxidant enzymes and a reduction in MDA concentration may be due to the presence of ginger in the feed, the mechanism involved is not yet known. Literature has shown that polyphenolic flavonoids in the plants are some of the major sources of the antioxidant compounds (Huang and Frankel, Reference HUANG and FRANKEL1997; Singh et al., Reference SINGH, MARIMUTHU, DE-HELUANI and CATALAN2005). The potential active ingredients in ginger are gingerols, shogaols, gingerdiol, gingerdione and some related phenolic ketone derivatives (Kikuzaki and Nakatani, Reference KIKUZAKI and NAKATANI1996; Fuhrman et al., Reference FUHRMAN, ROSENBLAT, HAYEK, COLEMAN and AVIRAM2000; Zhang et al., Reference ZHANG, YANG, WANG, YANG, JIANG and GAI2009; Zhao et al., Reference ZHAO, YANG, YANG, WANG, JIANG and ZHANG2011). Some studies have also shown that raw ginger plant materials and single constituents like [6]- gingerol have the ability to protect against lipid peroxidation (Aeschbach et al., Reference AESCHBACH, LOLIGER, SCOTT, MURCIA, BUTLER, HALLIWELL and ARUOMA1994; Kuo et al., Reference KUO, YEH and PAN1999). Furthermore, Zhao et al. (Reference ZHAO, YANG, YANG, WANG, JIANG and ZHANG2011) reported that ginger contains several compounds such as gingerol, shogaols, gingerdiol, gingerdione, and some relating phenolic ketone derivatives that possess antioxidant activities. They concluded that the enhanced serum antioxidants may be partially attributed to the slowing of the process of oxidation of the feed by ginger powder.

Blood biochemistry

Saeid et al. (Reference SAEID, ARKAN and AL-BADDY2010) found that serum glucose, total cholesterol, LDL-cholesterol and VLDL-cholesterol decreased significantly in broilers fed with 0.4 and 0.6% aqueous ginger extract, however, HDL-cholesterol concentration increased in these birds. Onu (Reference ONU2010) reported that supplementation of ginger (0.25%) in the basal diet of broiler chicks did not result in any significance difference in terms of total protein, albumin, globulin, urea and creatine. Recently, Rehman et al. (Reference REHMAN, DURRANI, CHAND, KHAN and FAWAD UR REHMAN2011) studied the effect of dosing broilers (10 ml/l of drinking water) with an aqueous extract of a mixture of medicinal plants (garlic, berberine and aloe vera) along with ginger, which resulted in a significant decrease in serum glucose, ALT (alanine aminotransferase), AST (aspartate aminotransferase) and ALP (alkaline phosphatase) concentration, however, serum protein increased significantly in the treated group. In the same experiment, the cholesterol profile including total cholesterol, triglyceride, LDL, VLDL decreased significantly in the treated group, while HDL cholesterol concentration increased. Zhang et al. (Reference ZHANG, YANG, WANG, YANG, JIANG and GAI2009) found that total protein concentration was higher at 21 day and 42 days of sampling in broilers treated with ginger powder but cholesterol concentration was reduced at these intervals. Kausar et al. (Reference KAUSAR, RIZVI and ANJUM1999) reported that carminative mixture containing ginger at the dose rate of 2 and 4 ml/L of drinking water did not affect serum albumin, globulin and total protein in broilers. Al-Homidan (Reference AL-HOMIDAN2005) observed reduced total protein and globulin in the plasma of broiler chicks due to dietary supplementation of 60 g/kg which may be due to a toxic effect of the ginger. Farinu et al. (Reference FARINU, ADEMOLA, AJAYI and BABATUNDE2004) reported that supplementation of ginger at the rate of 5, 10 and 15 g/kg did not affect total protein and albumin in the serum of broiler chickens. The discrepancies in these results may be due to the difference in doses used as well as experimental conditions.

The exact mechanisms through which blood metabolites are altered are not known. It was postulated that (E)-8 beta, 17-epoxyllabed-12-ene-15, 16-dial, a compound isolated from ginger, interferes with cholesterol biosynthesis in liver homogenates of hypercholesterolaemic mice causing its reduction (Tanabe et al., Reference TANABE, CHEN, SAITO and KANO1993). Srinivasan and Sambaiah (Reference SRINIVASAN and SAMBAIAH1991) reported that feeding rats with ginger significantly elevated the activity of hepatic cholesterol 7-alpha-hydroxylase which is a rate limiting enzyme in the biosynthesis of bile acids and stimulates the conversion of cholesterol to bile acids leading to the excretion of cholesterol from the body.

Toxicological effects

Studies concerning the toxicological effects of using ginger as a feed supplement in poultry feed are rare. However, Herawati (Reference HERAWATI2010) reported that broilers fed diets containing 0.5, 1.0 and 1.5% red ginger showed oedema, necrosis and inflammation in muscles. Ginger contains atsiri sescuiterpen oil which is potentially toxic in animals. All phytobiotics have toxic characteristics and the intensity of their toxicity is determined by the dose and duration of the feeding period (Herawati, Reference HERAWATI2010). Feeding such substances at higher doses causes symptoms of congestion, oedema, inflammation and necrosis (Ganiswarna, Reference GANISWARNA1995).

Other effects

The surface of the gastrointestinal tract in chickens responds very quickly to alterations in nutrient intake (Dou et al., Reference DOU, GREGERSEN, ZHAO, ZHUANG and GREGERSEEN2002). The histology of the intestinal villi and epithelial cells on the apical surface is commonly affected by dietary feed components (Yamauchi et al., Reference YAMAUCHI, BUWJOOM, KOGE and EBASHI2006). It has been suggested that longer villi absorb a greater amount of available nutrients due to an increased surface area (Caspary, Reference CASPARY1992). Greater villi height and more mitosis in the gut indicate that the function of intestinal villi is stimulated as a result of enhanced absorption (Langhout et al., Reference LANGHOUT, SCHUTTE, VAN LEEUWEN, WIEBENGA and TAMMINGA1999; Yasar and Forbes, Reference YASAR and FORBES1999). Incharoen and Yamauchi (Reference INCHAROEN and YAMAUCHI2009) showed that the villus height, surface area, cell area and cell mitosis in the intestinal segment had higher values in ginger-fed laying hens compared to the control birds. Moreover, they also found an increased number of filamentous bacteria which have been found to have strong immunomodulating effects due to high levels of IgA in the intestine and may have protective roles against infection with Salmonella enteritidis and Escherichia coli O103 (Garland et al., Reference GARLAND, LEE and DICKSON1982; Heczko et al., Reference HECZKO, ABE and FINLAY2000). Kausar et al. (Reference KAUSAR, RIZVI and ANJUM1999) reported that carminative mixture containing ginger at the dose rate of 4 ml/l of drinking water increased means titre in primary and secondary responses against Newcastle disease, suggesting immunomodulating effects of ginger. Sudrashan et al. (Reference SUDRASHAN, FAIROZE, WILDFRED and SHEKAR2010) reported that essential oil isolated from ginger resulted in a significant reduction in the bacterial counts of Staphylococcus, E. coli and Salmonella when applied as a decontaminating agent in the ratio of 1:150, 1:250 and 1:500 to chicken meat. Zhao et al. (Reference ZHAO, YANG, YANG, WANG, JIANG and ZHANG2011) found that ginger reduced the oxidation of stored feed which may be partially responsible for the improved laying performance and for the serum and egg yolk antioxidant contents.