Physiological responses and performance of broiler chickens offered olive leaf extract under a hot humid tropical climate

Abstract

This study was designed to determine the effects of olive leaf extract (OLE) supplementation in the drinking water on growth performance, hematological parameters, plasma triiodothyronine and malondialdeyde, superoxide dismutase, and rectal temperature of broiler chickens under a hot-humid tropical climate. Two hundred and forty Arbor acre broiler chickens were used for this experiment and were allotted to four treatments comprising four replicates of 15 birds each. The birds were offered OLE per liter of water at various levels (0, 5, 10, or 15 mL) in a completely randomized design. Rectal temperature (RT), hematological indices, weight, weight gains, feed consumed, feed conversion ratio, and plasma triiodothyronine (T₃) were the parameters measured. The results obtained showed that the plasma T₃ of the birds offered 15 mL OLE was higher (P < 0.05) than those of the birds in the other treatment groups. Significant differences (P < 0.05) were observed in the feed intake (DFI), total feed intake (TFI), final weight (FW), total weight gain (TWG), and feed conversion ratio (FCR) among treatments. The DFI, TFI, FW, TWG, and FCR of broilers offered 15 mL OLE were significantly (P < 0.05) better than those offered the 10 mL and 5 mL levels. It was concluded that inclusion of 15 mL of OLE enhanced the performance of broiler chickens during the hot dry season.

DESCRIPTION OF PROBLEM

Broiler chickens are faced with the challenge of heat stress in the tropical environment. Heat stress occurs when birds have difficulty in balancing body heat production and body heat loss. At high environmental temperatures, birds rely on different mechanisms to regulate their body temperature within a zone of comfort, or thermoneutral zone [1]. Heat stress in chickens is prompted by a combination of environmental temperature and humidity that prevents the birds’ thermoregulatory process from effectively dissipating the heat produced during metabolism [2]. Severe hot dry seasons, especially between December and April in Nigeria, impose stress on birds leading to poor performance and high mortality in chickens [3]. Environmental modifications have been studied on increasing the airflow over birds to increase heat loss. Increasing ventilation rates, the use of evaporative cooling systems in enclosed houses, and lowering stocking densities have been suggested [4]. Owing to the fact that it is costly to cool poultry houses in the developing countries, efforts are concentrated mainly on nutritional modifications. Nutritional approaches usually made are the optimization of diets to cover the altered needs of stressed birds for protein and energy and to provide some additional nutrients, including the use of the antioxidants vitamin C and E in the poultry diet because of their anti-stress effects and due to their reduced synthesis during heat stress [5, 6].

In the search for natural antioxidant additives, much attention has been directed to several herbal preparations used in the diets of broiler chickens including Aloe species [7], Chinese medicinal herbs [8], cinnamon [9], Acacia nilotica [10], neem [11], garlic [12], ginger [13], tulsi [14], and turmeric [15] to enhance the performance and ameliorate the effects of stress on the animals.

Olive trees are rich in phenolic substances that have significant biological properties, the most important of which is oleuropein. Olive trees produce natural phytochemicals that have important medicinal properties [16]. For example, the leaf extract contains oleuropein, ligostroside, dimethyl oleuropein, oleoside [17, 18], flavonoids including apigenin, kaempferol, and luteolin, as well as phenolic compounds such as caffeic acid, tyrosol, and hydroxytyrosol [19]. Oleuropein, most present in the olive leaf [20], has shown beneficial and health-promoting effects which are associated with its antioxidant property [21]. Thus, this study was designed to investigate the effects of olive leaf extract (OLE) on the physiological response of broiler chickens raised during the hot dry season.

MATERIALS AND METHODS

Experimental Location and Meteorological Observations

The research was carried out at the Poultry Unit of the Research Farm of the Federal University of Agriculture, Abeokuta, Ogun State, Nigeria (latitude 7°13^΄N; longitude 3°26^΄E and altitude 76 meters above sea level) in a prevailing tropical climate with a mean annual rainfall of 1,037 mm, and annual mean temperature and relative humidity of 34°C and 82%, respectively. The average weekly ambient temperature and relative humidity during the experiment are presented in Table 1.

Experimental Birds and Management

Natural-flavored high strength OLE produced by Olive Leaf Australia (Coominya, Australia), was purchased from a reputable health food store. The extract was produced in accordance with the Australian Code of Good Manufacturing Practice (AUST. L 108980) with a guaranteed minimum oleuropein content of 4.4 mg/mL.

Two hundred and forty day-old straight run broilers chicks of Abor acre strain were purchased from a reputable hatchery in Nigeria and were randomly allotted to four treatment groups of four replicates having fifteen birds each. The 4 treatment groups were daily supplied drinking water without OLE (0), with 5, 10, and 15 mL of OLE per liter of water. The birds were reared on a deep-litter floor in an open-sided poultry house. The birds were floor-brooded for three weeks on wood shavings. Additional sources of heat were provided during the brooding period. The chicks were fed ad libitum with standard starter mash for the first 28 days and thereafter with finisher mash. Diets were formulated to meet [22] nutrient recommendations for each feeding phase. Water at ambient temperature was supplied ad libitum throughout the period of the experiment.²

Data Collection

Rectal Temperature.

Rectal temperature in the birds was taken at 2 pm every day and the data were pooled together weekly. A digital thermometer was inserted through the cloaca into the rectum. Each bird was restrained lightly and calmly and the reading was taken when the thermometer beeped.

Growth Performance.

Bodyweights of the birds on a group basis in each replicate were monitored weekly throughout the duration of the experiment using a sensitive scale. Records of daily weight gain (DWG) were obtained by dividing the weekly weight gain by 7 and feed intake (FI) was taken as the difference between the feed weighed in and unconsumed feed weighed back at the end of each period. Feed conversion ratio (FCR) was calculated by dividing the feed intake by the weight gain.

Collection of Blood Samples.

Four milliliter blood samples were collected from 2 chickens per replicate each from the brachial veins over a period of 30 sec to 1 min using hypodermic syringes. Blood collection was done at the fourth and eighth weeks of the experiment. The blood was drawn into heparinized tubes to prevent coagulation. Blood samples were then analyzed for hemoglobin (Hb), packed cell volume (PCV), white blood cells (WBC), red blood cells (RBC), and heterophil, lymphocyte. Hb estimation was determined by the cyanmethaemoglobin method and PCV by the microhematocrit method [45]. RBC and WBC were determined using Neubaur's hemocytometer and Toluidine blue (0.015%) saline as diluent [46]. The blood films stained with Wright's stain [47] were studied for the differential leucocyte counts. Mean cell volume (MCV), mean corpuscular hemoglobin (MCH), and mean corpuscular hemoglobin concentration (MCHC) were calculated [48].

Plasma Malondialdehyde, Triiodothyronine Concentration, and Superoxide Dismutase Activity.

Plasma was obtained by centrifuging the heparinized blood for 15 min (3,500 rpm), and then stored at −20°C to be analyzed later. Malondialdehyde concentrations were measured by using the method of [23] while superoxide dismutase (SOD) activity was measured as described by [24]. Plasma triiodothyronine levels were assayed with immunoenzymatic ELISA kit in the Laboratory of Veterinary Medicine, Federal University of Agriculture, Abeokuta, Ogun State, Nigeria, as described by [25].

Data Analysis.

Data were analyzed by ANOVA with OLE as the independent variable in a completely randomized design. When differences among OLE were significant (P < 0.05), means were separated using Duncan's multiple range test [26].

RESULTS

Growth Performance

In Table 2, the obtained results show that there were no significant differences among the birds in all treatment groups. The daily feed intake, total feed intake, final body weight, and total weight gain of the birds offered 15 mL and 10 mL OLE were similar to but higher (P < 0.05) than those offered 5 mL or in the control. There was a gradual improvement of FCR with increasing dose of OLE with the 5 mL dose being better (P < 0.05) than the control and the 2 higher doses better than the 5 mL dose³⁴ (P < 0.05).

Haematology, Plasma Triiodothyronine, and Malondialdehyde

Table 3⁴ shows the effect of different levels of OLE on hematological parameters, plasma triiodothyronine, and malondialdeyde of broiler chickens during the hotndry season. There was no significant effect of different levels of OLE on any of the hematological parameters monitored. The birds that were offered 10, 5, and 0 mL OLE had similar plasma triiodothyronine (T₃), which was lower (P < 0.05) than the levels recorded in the birds that were offered 15 mL OLE in the drinking water.

At the starter phase, the serum malondialdehyde (MDA) level observed in the birds in the control group was higher (P < 0.05) those of the birds offered different levels of OLE. The birds offered 15 mL OLE had a lower (P < 0.05) serum MDA level when compared with the birds in the other treatment groups.

At the finisher phase, the serum MDA level observed in the birds offered 5 mL OLE was higher (P < 0.05) than those of the birds in all other treatment groups. Birds in the control group had a higher (P < 0.05) serum MDA level than those of the birds in the 10 mL and 15 mL groups. However, the birds in the 10 mL and 15 mL groups were similar in their serum MDA levels.

Superoxide Dismutase (SOD)

Table 4 shows the effect of different levels of OLE on the SOD of broiler chickens. At the starter phase during the hot dry season, the plasma SOD of birds offered 15 mL OLE was similar to that of birds offered 10 mL OLE but higher (P < 0.05) than those of birds offered 5 mL OLE and the control group.

At the finisher phase, the plasma SOD value observed in the birds in the 5 mL and 15 mL groups was similar to but higher (P <0.05) than those of control and 10 mL groups, while the plasma SOD in the control and 10 mL groups had a similar value.

Rectal Temperature

Table 5 shows the effect of different levels of OLE on rectal temperature of broiler chickens at different weeks. OLE had no effect (P > 0.05) on rectal temperature.

DISCUSSION

The present study has revealed that addition of OLE improved the performance of broiler chickens as indicated in the final body weights, body weight gains, and feed conversion ratios. This suggests that the phytochemical in the extract ameliorated the effect of thermal stress as the benefits derived from olive leaves have been linked to the presence of polyphenols, particularly oleuropein [27]. The present results further corroborate the existing knowledge on the positive effects of olive leaf extract. OLE has been shown to possess a wide range of pharmacological activities including antioxidant [28], anti-inflammatory [30], anticancer [31], and anti-atherogenic [32] properties. In particular, it has been reported that oleuropein exerts potent antioxidant activity such as inhibition of low density lipoprotein (LDL) oxidation and free radical scavenging [28].

The improved performance of the birds offered OLE at doses of 10 and 15 mL per liter of water in the present study is in agreement with the findings of [29] who reported that dietary olive leaves significantly enhanced the performance of Mandarah chicks and their oxidative status and immunity response.

Contrary to our findings, [33] reported that there was no significant difference in the performance of broiler chickens fed different doses of OLE. The lack of difference in their findings may be a result of the probably favorable climatological conditions under which the study was carried out. The observation in the present study suggests that the beneficial effects of OLE are expressed under a high ambient temperature. This corroborates the findings of [34] who reported that broiler chickens subjected to heat stress in a hot humid climate responded favorably to vitamin C supplementation. In the hot climate of Nigeria, vitamin C supplementation also improved the body weight of broiler chickens [35]. There is however a paucity of data on the effect OLE on chickens during thermal stress.

Hematological characteristics of livestock suggest their physiological disposition to the plane of nutrition [36]. The hematological parameters obtained from this study across the treatment groups were within the normal range of values reported by [37]. Thus, this observation suggests that the addition of OLE was not deleterious to the health of the birds used in this study.

Chronic stress has been generally associated with a suppression of thyroid axis function. [38] reported that there is a suppressed secretion of thyroid-stimulating hormone and decreased conversion of the relatively inactive T₄ to more biologically active T₃ during stress. The concentrations of plasma T₃ recorded in this study were within the normal values of 0.5 to 4.0 ng/mL in poultry as reported by [41]. The higher level of T₃ observed in the birds offered 15 mL OLE in the present study suggests that addition of OLE improved the ability of the birds to respond to harsh weather conditions as it has been shown that exposure to chronic stress induces a reduction of thyroid hormone levels in mice [39]. There is a dearth of reports on chickens related to T₃ reduction in stress situations [40], especially relating to the use OLE.

Malondialdehyde level endogenously reflects lipid peroxidation, which is the sequel of diminished antioxidant protection as reactive oxygen species (ROS) levels increase while SOD is a major antioxidant enzyme that protects cells and organisms from the damaging effects of superoxide anion [42]. The antioxidant effect of OLE has been reported [27, 43]. The improved MDA observed in the present study is in agreement with the observation of [43] who indicated that olive leaf extract significantly increased plasma SOD activity and decreased thiobarbituric acid reactive substances. The higher levels of SOD observed in the present study may reflect a significant improvement in health and oxidative status of the chickens. The lower concentration of MDA in the birds offered 10 and 15 mL OLE in the present study may be attributed to the ability of OLE to confer adequate antioxidant protection against lipid peroxidation on the birds during thermal stress. The bioactive compound in OLE may have also enhanced the ability of the birds to cope with thermal stress during the hot dry season. This result is in line with the findings of [44] who reported that aqueous neem (Azadirachta indica) root and leaves reduced blood glucose level in rats. OLE-induced increase in SOD may be considered as a protective mechanism against oxidative stress by stimulating the biosynthesis and secretion of the antioxidant enzyme [49] thereby resulting into more nutrients being diverted to growth and fewer to the immune system because the birds are healthier

CONCLUSION

1. The present study has shown that 15 mL OLE per liter of water alleviated the adverse effect of thermal stress and improved performance of broiler chickens under a hot humid climate.

REFERENCES AND NOTES