Role of neem (Azadirachta indica) feed additive in poultry nutrition, health and production: A review

Introduction

The widespread promotion of antibiotics as growth enhancers in poultry production has raised concerns regarding their potential impact on animal and human health. Some pharmaceutical companies have encouraged farmers to use antibiotics as growth promoters to achieve higher production and economic returns within a short period. However, consumption of poultry products containing antibiotic residues may expose humans to these substances and potentially contribute to serious health concerns (Kibria et al., 2009) [20] . Globally, the extent to which antibiotics are incorporated into poultry diets as growth promoters varies considerably. Of particular concern is the development and spread of antimicrobial resistance among zoonotic enteropathogens, including Salmonella, Escherichia coli, and Enterococci, in food-producing animals. These resistant microorganisms may be transmitted through the food chain and subsequently pose risks to human health. As a result, increasing research attention has been directed toward natural alternatives, including essential oils, plant extracts, herbs, and spices, as potential feed additives for livestock and poultry. Craig (1999) [11] suggested that several medicinal herbs may provide protection against pathogenic bacteria while also enhancing immune responses. Among these plants, neem (Azadirachta indica) has attracted considerable interest because of its diverse medicinal properties. Its antibacterial and hepatoprotective activities may contribute to improved growth and feed utilization in poultry. Previous investigations have demonstrated that neem preparations can influence hematological characteristics in poultry. Sadre et al. (1984) [33] and Gowda et al. (1998) [17] reported that feeding neem preparations to laying hens significantly reduced hemoglobin concentration, erythrocyte count, and packed cell volume. In addition, neem has been reported to possess immunomodulatory properties capable of stimulating cellular immune responses (Devakumar and Suktt, 1993) [13] . Therefore, the present review aims to examine the potential effects of neem as a natural feed additive in broiler production, with particular emphasis on its influence on hematological and biochemical responses, growth, feed utilization, and other productive characteristics.

Neem (Azadirachta indica)

Neem (Azadirachta indica) is a versatile and economically important tree that is particularly widespread in India. It has traditionally been utilized for numerous purposes, including food-related applications, insect control, and ethnomedicinal practices. Different parts of the neem tree have considerable potential for use in animal nutrition. In particular, neem leaves and the oil cake remaining after oil extraction can be incorporated into livestock feed. For centuries, neem leaves, bark, and seed-derived preparations have been used in traditional Indian medicine as well as in ethnoveterinary practices (Biswas et al., 2002; Subapriya et al., 2005) [7,38] . The species is indigenous to the dry regions of the Indian subcontinent, Myanmar, and China (Rojas-Sandoval et al., 2014) [32] . Neem is a medium-to large-sized tree that generally reaches a height of approximately 15-30 m and develops a broad, rounded crown measuring about 10-20 m in diameter. It is predominantly evergreen, although leaf shedding may occur during periods of prolonged dryness (Orwa et al., 2009; Puri, 1999) [28,30] . The plant possesses a deep taproot system and is dependent on mycorrhizal associations for optimal growth and nutrient acquisition.

Chemical composition of neem (Azadirachta indica) Chemical Composition of Neem (Azadirachta indica) Leaf/Leaf Meal

The chemical composition of neem leaves and neem leaf meal differs considerably among studies. Such variation may be attributed to several factors, including plant variety, geographical origin, soil fertility, stage of leaf maturity, seasonal conditions, and the methods used for harvesting, processing, and drying the leaves. These factors can influence the concentration and availability of nutrients and bioactive compounds present in neem leaves. Consequently, variations in the chemical profile of neem leaf meal should be considered when evaluating its nutritional and biological effects as a poultry feed ingredient.

Parameter

Esonu et al. (2006) [15] Ansari et al. (2012) [4] Obikaonu et al. (2012) [25]

Medicinal properties of neem (Azadirachta indica)

Neem leaves contain a variety of biologically active compounds with antimicrobial properties, as reported by Makeri et al. (2007) [22] and Valarmathy et al. (2017) [44] . In addition, neem has been associated with anti-inflammatory, antihyperglycemic, antiulcer, antimalarial, antifungal, antiviral, and antioxidant activities (Kale et al., 2003) [18] . Sodium nimbidate is one of the important bioactive constituents of neem and has been reported to exhibit antiinflammatory activity. Another important compound, nimbidin, has been associated with antiarthritic effects, reduction of blood glucose levels, and protection against gastric ulcers (Bandyopadhyay et al., 1998; Biswas et al., 2002) [5,7] . In ruminant nutrition, condensed tannins and saponins present in plant materials may also contribute to improved rumen ecology and fermentation processes (Suchitra et al., 2008) [39] .

Effect of Neem (Azadirachta indica) on Poultry Performance

Several studies have investigated the influence of neem supplementation on growth and productive performance in poultry. Wankar et al. (2008) [45] reported a significant improvement in average body weight when neem leaf powder was incorporated into broiler diets at levels of 1, 2, and 3 g/kg. In contrast, Landy et al. (2011) [21] observed a significant reduction in body weight at 42 days of age when neem leaf powder was included at 7 and 12 g/kg. This negative response may have been associated with the bitter taste of neem, which can reduce feed acceptance at higher inclusion levels. The findings of Singh et al. (2014) [37] differed from those of Landy et al. (2011) [21] , as significant improvements in body weight gain were observed when neem leaf powder was incorporated into layer diets at 1, 2, and 3 g/kg. Similarly, Shihab et al. (2017) [36] reported significant increases in body weight and feed intake in broilers receiving neem leaf powder at 2 g/kg. Birds supplemented with neem leaf powder generally exhibited improvements in body weight, weekly weight gain, and feed consumption. Durrani et al. (2008) [14] , however, reported a significant reduction in feed and water intake when neem leaf powder was administered through drinking water. These findings differed from those of Landy et al. (2011) [21] , who found no significant differences in feed intake among treatment groups when neem leaf powder was incorporated into broiler diets at 7 and 12 g/kg. Singh et al. (2014) [37] , on the other hand, observed significant differences in feed intake among treatment groups when neem leaf powder was supplied to layers at 1, 2, and 3 g/kg.

Durrani et al. (2008) [14] also reported significant improvements in the relative weights of the liver, heart, and gizzard when neem leaf powder was supplied through drinking water at 40 mL/L. Conversely, Kharde and Soujanya (2014) [19] found no significant differences in carcass characteristics, including heart, gizzard, and liver weights, when neem leaf powder was incorporated into broiler diets at 1 and 2 g/kg, either alone or in combination with garlic powder at 0.5 and 1 g/kg. Similarly, Shihab et al.

(2017) [36] observed no significant differences in the relative weights of the liver, heart, and gizzard in broilers receiving neem leaf powder at 2 g/kg.

Durrani et al. (2008) [14] further reported a significant improvement in average body weight when neem leaf powder was administered through drinking water at 50 mL/L. Comparable findings were reported by Onyimonyi et al. (2009) [27] , who observed significant improvements in body weight and body weight gain when neem leaf powder was incorporated into broiler diets at 0.5%.

Effect of Neem (Azadirachta indica) on Hematobiochemical Parameters of Poultry

Neem supplementation has also been investigated for its effects on hematological and biochemical parameters in poultry. Alam et al. (2015) [3] reported no significant differences in hematological indices, including red blood cell (RBC) count, hemoglobin (Hb), packed cell volume (PCV), and erythrocyte sedimentation rate (ESR), when neem leaf powder was added to broiler diets at 1, 2, and 3 g/kg. Nevertheless, neem supplementation was associated with improvements in body weight and feed conversion efficiency, indicating its potential role in enhancing productive performance without adversely affecting major hematological parameters. These observations were consistent with the findings of Bonsu et al. (2012) [9] , who reported that inclusion of neem leaves in broiler diets improved productive characteristics, blood parameters, carcass characteristics, and sensory attributes of meat. Nodu et al. (2016) [24] observed no significant differences in most hematological and serum biochemical parameters of broiler chickens administered graded levels of Azadirachta indica leaf extract. However, significant differences were observed in total protein and alkaline phosphatase (ALP). Total protein values ranged from 54 to 59 µ/L, whereas ALP values ranged from 249 to 337 µ/L. These findings were comparable with those reported by Trincha et al. (2012) [42] . Obikaonu et al. (2012) [25] reported significant reductions in cholesterol, glucose, alanine aminotransferase (ALT), and aspartate aminotransferase (AST) concentrations when neem leaf powder was incorporated into broiler diets at 2.5%, 5%, 7.5%, and 10%. However, no significant differences were detected in total protein, calcium, or sodium concentrations. Similarly, Shihab et al. (2017) [36] reported significant improvements in total protein, cholesterol, triglycerides, albumin, globulin, and calcium concentrations in broilers supplemented with neem leaf powder at 2 g/kg. The reduction in cholesterol concentration associated with increasing dietary neem leaf meal was consistent with observations reported by Ogbuewu et al. (2008) [26] in rabbits. Upadhyay (1990) [43] likewise reported reduced blood cholesterol concentrations in broilers and rats fed neem leaf meal. Sharma et al. (2002) [35] reported that the inclusion of neem seed at concentrations of 25%, 50%, and 75% in broiler diets improved productive performance. Similarly, Sarag et al. (2001) [34] observed increased body weight and improved feed conversion efficiency when neem oil was incorporated into broiler diets at a concentration of 0.25%. Chakravarty and Prasad (1991) [10] also reported substantial increases in body weight following the inclusion of neem leaves in broiler diets. Obikaonu et al. (2011) [25] suggested that dietary neem leaves can influence both hematological and serum biochemical characteristics in broilers. Their findings indicated a significant increase in blood glucose and a significant reduction in cholesterol concentration (p < 0.05). Increasing the dietary concentration of neem leaf was also associated with a reduction in liver enzyme levels, suggesting a possible hepatoprotective effect. Tollba et al. (2009) [41] reported that inclusion of neem leaves in broiler diets improved feed conversion efficiency, feed consumption, body weight, mortality-related outcomes, carcass characteristics, and the development of lymphoid organs, including the bursa of Fabricius and thymus. The treatment was also associated with increases in total protein, albumin, globulin, and triglyceride concentrations, whereas cholesterol and fat-related parameters were comparatively reduced. Oyagbemi et al. (2012) [29] investigated the potential of neem at a 10% inclusion level against coccidial infection and demonstrated its possible role in enhancing immunity against both clinical and subclinical infections. Lonkar et al. also reported that inclusion of neem seed in broiler diets was associated with a reduction in blood cholesterol levels. Tipu et al. (2006) [40] described several medicinal properties of neem, including antibacterial, antioxidant, and antiprotozoal activities, supporting its potential application as a natural feed additive. Deore et al. (2005) [12] investigated the incorporation of neem oil into broiler diets and reported effects on productive performance at inclusion levels below 5%. Alam et al. (2014) [2] evaluated the effects of a polyherbal preparation containing neem and other plant extracts (NNTT extract) on hematological parameters in broilers. No significant changes were observed in total leukocyte count (TLC), PCV, Hb, or ESR between the treated and control groups. The authors suggested that the plant-based preparation did not produce either harmful or substantial beneficial effects on these hematological indices. Similar findings were reported by Bishnu et al. (2009) [6] . Rahaman et al., however, observed significant differences (p < 0.05) in ESR and PCV between control and treated groups.

Hemoglobin concentration also differed significantly between the groups on day 42. Following treatment with a combination of neem leaf and ginger extracts, ESR decreased, whereas other hematological parameters increased. These findings were consistent with those of Biu et al. (2009) [8] and Akbari et al. (2008) [1] , who reported a significant increase (p < 0.05) in hemoglobin concentration in neem-supplemented groups compared with controls. Furthermore, dietary supplementation with neem alone or in combination with turmeric and vitamin E significantly increased PCV values (p < 0.05) compared with the control group, which was consistent with the findings of Nayaka et al. (2013) [23] .

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