Key words

Antioxidants; Vitamin C; Ocimum sanctum; SOD; GSH-Px; Catalase; GSH; Lipid Peroxidation; Broiler Chickens.

Introduction

Poultry production suffers significant losses because of heat stress. Heat stress adversely affects broiler performance and livability. Body temperature and metabolism rate of birds are relatively high compared to mammals, which make birds vulnerable to oxidative stress under high environmental temperature, which is the major cause of sudden death syndrome [1]. Heat stress not only adversely affects production performance but also increases the incidence of infectious and metabolic diseases in poultry. This can be minimizes by the use of anti-stress compounds. Antioxidants are substances, present biologically lower concentrations and significantly delay or prevent oxidation of substances like protein, lipids, DNA and carbohydrates [2]. External sources of antioxidant are essential for the control of oxidation process, which include vitamin C & E, carotenoids, phytoflavanoids etc.

Vitamin C also commonly known as ascorbic acid is an important antioxidant. Although birds synthesize vitamin C in their body, however, its supplementation in the poultry diet has been recommended during stressful conditions [3]. Several herbal plants are found to posses anti oxidant properties and the ubiquitous herb i.e., Ocimum sanctum which belongs to Lamiaceae family is a fairly economic therapeutic agent for several pathological conditions as well as anti-stress [4] and antioxidant agent [5].

The present study was conducted to evaluate the effect of Vitamin C and Ocimum sanctum on antioxidant enzyme levels in broiler chicken under heat stress.

Materials and Methods

A forty broiler chicks of day old age were randomly divided into 4 groups comprising of 10 birds in each group with following dietary regimes.

Group I: Standard diet (Control)
Group II: Standard diet + Vitamin C (300mg/kg)
Group III: Standard diet + Ocimum sanctum (0.5%)
Group IV: Standard diet + Vitamin C (300mg/kg) + Ocimum sanctum (0.5%)

The birds were reared from day old to 6th week of age in cages under standard managemental practices during months of April & May. The temperature inside the house is ranged from 35 – 38°C. Freshly collected O. sanctum leaves were shade dried and powdered. Vitamin C and Ocimum sanctum leaf powder were supplemented as above to the standard broiler diet. The broiler starter and finisher diets were fed ad libitum to the birds. The Ocimum sanctum leaf powders were used at 0.5% level of inclusion based on the reports of [6], along with Vitamin C (300mg/kg).

Blood samples were collected at the end of 6th week from the wing vein using heparinised vacutainer for separating plasma by standard procedures of centrifugation. The levels of superoxide dismutase (SOD) activity in plasma was measured by the method of [7], glutathione peroxidase (GSH-Px) activity as per the method described by [8] and catalase activity as per the method of [9]. Reduced glutathione levels in plasma were estimated by the method of [10]. Lipid peroxidation assay was carried out according to [11]. Statistical analysis of the data was analyzed by randomized block design as per [12].

Results & Discussion

Superoxide dismutase is considered as critical antioxidative enzyme that acts as a scavenger of oxygen anion to form hydrogen peroxide and hence diminishes the toxic effects due to the free radical. This primary defense widely distributed in oxygen metabolizing cells to protect aerobic cells from deleterious actions of free radicals [13]. The mean plasma SOD values of broilers at 6 weeks of age as influenced by dietary supplementation of Vitamin C and O. sanctum, is presented in Table 1. In the present study, dietary supplementation of Vitamin C (300mg/kg), O. sanctum at 0.5% level and their combination significantly (p<0.05) enhanced plasma SOD activity when compared control group. The results of our study are in accordance with the earlier reports of [14], who observed that SOD activity significantly (P<0.05) increased with dietary supplementation of Vitamin C in summer stressed broilers. Similarly, [6] reported significant (P<0.05) increase in SOD activity with dietary supplementation of O. sanctum in broilers.

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GSH (reduced glutathione) offers protection against oxygen derived free radicals and cellular lethality following exposure to oxidative stress. Its high electron donating capacity combined with higher intracellular concentrations generate great reducing power [15]. Dietary supplementation of Vitamin C and O. sanctum and their combinations on plasma GSH levels is presented in Table 2.

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Means bearing common superscripts in column do not differ significantly (p<0.05)

The findings of increased plasma GSH (reduced glutathione) levels in the present study were in agreement with the reports of [16], they observed increases in plasma GSH enzyme levels by supplementation of O. sanctum in broilers.

Lipid peroxidation occurs as a consequence of increased oxidative stress primarily due to disruption of pro-oxidant/antioxidant balance. Increased oxidative stress has been associated with increased lipid peroxidation in many diseases [17]. In the present study, plasma malondialdehyde (MDA) levels were decreased with dietary supplementation of Vitamin C and Ocimum sanctum. This may be due to conversion of lipid peroxides to alcohol derivatives rather than MDA in the presence of higher GSH levels with Vitamin C and Ocimum sanctum.

The findings of decreased plasma malondialdehyde (MDA) levels in the present study were in agreement with the reports of [14], they observed decreased plasma malondialdehyde (MDA) levels by supplementation of Vitamin C in broilers. Similarly, [18] observed that there was significant decrease in plasma malondialdehyde (MDA) levels by supplementation of Vitamin C in broilers. [16] observed that there was significant decrease in plasma malondialdehyde (MDA) levels by supplementation of Ocimum sanctum in broilers.

Hence it is concluded that the combination of both Vitamin C and O. sanctum can combat oxidative stress caused by rapid growth rate in heat stressed broilers there by effectively enhancing the SOD, GSH-Px, catalase activities and GSH levels with concomitant decrease in lipid peroxidation levels in plasma of heat stressed broilers.