Introduction
Newcastle Disease (ND) is an important viral disease of poultry owing to its wide distribution and high fatality rate. The disease is highly contagious and deaths can be abrupt and whole flocks can be lost (Eze et al., Reference EZE, OKWOR, OKOYE, ONAH and SHOYINKA2012; Eze and Ike, Reference EZE and IKE2015), either through 100% mortality rates or condemnation of carcasses (Miller et al., Reference MILLER, KOCH and SUAREZ2013). Outbreaks are caused by virulent strains of NDV, which has been found to be endemic in many countries.
ND was first identified almost simultaneously in England and Indonesia in 1926 (Kiril et al., Reference KIRIL, CLAUDIO and PATTI2016) and arises from a virulent strain of NDV, often termed avian paramyxovirus serotype-1 (APMV-1). NDV isolates are pathotyped into lentogenic, mesogenic and velogenic strains based on the severity of their clinical presentation (Cattoli et al., Reference CATTOLI, SUSTA, TERREGINO and BROWN2011). Usually, the clinical signs of ND vary depending on pathotype of the virus, bird age, species, environmental stress, co-infection with other organisms and immune status of the host (OIE, 2013). The Office International des Epizooties/ World Organisation for Animal Health (OIE) regards ND as a notifiable disease (in the List A Group of diseases) (Liu et al., Reference LIU, WAN, NI, WU and LIU2003).
The genome of NDV contains six genes of approximately 15.2 kb (Susta et al., Reference SUSTA, HAMAL, MILLER, CARDENAS-GARCIA, BROWN, PEDERSEN, GONGORA and AFONSO2014), that encode the same number of structural proteins arranged in the 3’ to 5’ direction; nucleoprotein (NP), phosphoprotein (P), matrix protein (M), fusion (F), haemagglutinin-neuraminidase (HN), and large RNA polymerase (L) (Miller et al., Reference MILLER, KOCH and SUAREZ2013). Coupled with a worldwide distribution, NDV has the propensity to infect a wide variety of domestic and wild avian species which makes it a major concern in poultry production (Afonso and Miller, Reference AFONSO and MILLER2013). Further classification, characterisation, clinical signs, host range, economic importance, prevention and control of NDV have been widely documented (Alexander, Reference ALEXANDER2011; OIE, 2013; Dimitrov et al., Reference DIMITROV, RAMEY, QUI, BAHL and AFONSO2016; Foreman et al., Reference FOREMAN, FRIEDMAN, CASSADY and MARKERT2017).
Current control measures include use of vaccines, which were originally formulated over 60 years ago (Garcia et al., Reference GARCIA, LOPEZ, MORALES, OLVERA, MARQUEZ, MERINO, MILLER and AFONSO2013) as well as biosecurity measures on farm (Eze et al., Reference EZE, OKWOR, OKOYE, ONAH and SHOYINKA2012). Oral, intraocular and intranasal routes are most commonly used for vaccine administration (Spradbrow, Reference SPRADBROW1994). However, vaccination has been proven to be insufficient in preventing poultry from ND, especially in the tropics, often due to the poor handling and storage.
In commercial poultry production, antimicrobial compounds are commonly included in poultry diets by farmers for promoting growth and control of diseases (Demir et al., Reference DEMIR, ŞENAY, ÖZCAN and SUIÇMEZ2005). The search for alternative to antibiotic growth promoters (AGPs) has been intensified following concerns regarding the development of resistant groups of pathogenic and opportunistic pathogens and the breakdown of the symbiosis existing between animals and desirable gut flora (Alloui et al., Reference ALLOUI, AGABOU and ALLOUI2014). Supplementing poultry feed with known quantities of prebiotics (some of which have been identified to have antibacterial, antiviral and antitumor properties) or probiotics have been known to increase their growth performance (Pourali et al., Reference POURALI, MIRGHELENJ and KERMANSHAHI2010; Abudabos et al., Reference ABUDABOS, ALYEMNI, DAFALLA and KHAN2017; Mohammed et al., Reference MOHAMMED, JACOBS, MURUGESAN and CHENG2018). The current review focuses on the possibility of using these feed additives to improve the seroconversion of vaccinated poultry against NDV.
Prebiotics
Cummings and MacFarlane (Reference CUMMINGS and MACFARLANE2002) defined prebiotics as feed ingredients that selectively stimulate the growth and activities of the beneficial microflora in the gut, such as Lactobacillus and Bifidobacteria spp., leading to an improved health. They were redefined by Roberfroid (Reference ROBERFROID2007) as ingredients that specifically change activity and/or composition in the microflora of the gastrointestinal tract which confers benefits to the host wellbeing and health. According to the revised definition, Roberfroid (Reference ROBERFROID2007) stated that only galacto-oligosaccharide and inulin meet the criteria to be called prebiotics. However, until now fructo-oligosaccharides (FOS), galacto-oligosaccharides (GOS) and inulin obtained from plants are the best-known sources of prebiotics (Dwivedi et al., Reference DWIVEDI, SAHRAWAT, PUPPALA and ORTIZ2014).
In general, prebiotics are nutritional ingredients that are non-digestible by the host which are then selectively fermented in the intestine to improve the growth and activity of the resident beneficial organisms. A literature search from 2003 to 2014 by Dwivedi et al. (Reference DWIVEDI, SAHRAWAT, PUPPALA and ORTIZ2014) revealed the presence of prebiotic carbohydrates in a large number of foods with vegetables and root and tuber crops being the dominant source. Fructans have been identified recently as polysaccharide and oligosaccharide prebiotic consisting of fructan units which has, at the reducing end, a single D-glucosyl unit (Shalini et al., Reference SHALINI, ABINAYA, SARANYA and ANTONY2017).
These nutritional ingredients are fermented by the normal gut microflora (such as Lactobacillus and Streptococcus spp.) to produce hydrogen peroxide and lactic acid as end products (Khan et al., Reference KHAN, CHAND and ALI2016a). The production of lactic acid lowers the pH of the gut which inhibits the growth of harmful microorganisms (Khan et al., Reference KHAN, NAZ, DHAMA, KATHRIK, TIWARI, ABDELRAHMAN, ALHIDARY and ZAHOOR2016b). Talebi et al. (Reference TALEBI, AMANI, POURMAHMOD, SAGHAEI and REZAIE2015) found that supplementation of poultry feed with commercial FOS increased ND humoral immune response significantly.
Spice and herb derivates
Spices and their derivatives are generally added to food to improve their taste and flavour, although they have been exploited for medicinal use for millennia (Rivlin, Reference RIVLIN2001). In animals, the use of spices has been more of prophylactic purpose to improve growth and feed utilisation (Simon, Reference SIMON2005).
So far, a number of herbs, spices and their essential oils have been evaluated by different researchers (Eze et al., Reference EZE, OKWOR, OKOYE, ONAH and SHOYINKA2012; Saleh et al., Reference SALEH, EBEID and ABUDABOS2018) for their antibacterial, antifungal, antiviral, antioxidant and antitumor properties in poultry (Akthar et al., Reference AKTHAR, DEGAGA and AZAM2014). A study carried out by Waheed et al. (Reference WAHEED, HASNAIN, AHMAD, TARAR, YAQEEN and ALI2017), showed that treatment with extracts including fenugreek and black cumin seed increased NDV titre significantly following vaccination. A similar result was reported by Abou-Elkhair et al. (Reference ABOU-ELKHAIR, AHMED and SELIM2014) using a combination of black pepper (Piper nigrum), tumeric (Curcuma longa), and coriander seeds (Coriandrum sativum).
Onion (Allium cepa) belongs to the family Liliaceae and, according to FAO (2006), it is the second most important vegetable crop in the world after the tomato in terms of the size of the surface area dedicated to its cultivation. The genus Allium has over 550 species but only a few are useful as food and drugs (Goodarzi et al., Reference GOODARZI, LANDY and NANEKRANI2013). The onion bulb contains numerous sulphur compounds and most of its parts contain phytonutrients with proven antiviral, antibacterial, antiparasitic and antifungal properties as well as immunomodulation properties (Goodarzi et al., Reference GOODARZI, LANDY and NANEKRANI2013). The components of onions are water 89.1%; carbohydrate 9.3%; protein 1.1%; fat 0.1%; minerals and certain vitamins (Galdon et al., Reference GALDON, RODRIGUEZ, RODRIGUEZ and ROMERO2008). Onions contain non-nutritive health-promoting compounds (Lee et al., Reference LEE, LEE, CHOI, LEE, OHNISI-KAMEYAMA, KOZUKUE, LEVIN and FRIEDMAN2008) such as non-structural and soluble carbohydrates, mainly fructo-oligosaccharides (FOS), monosaccharides (Jaime et al., Reference JAIME, MARTÍN-CABREJAS, MOLLÁ, LÓPEZ-ANDRÉU and ESTEBAN2001) and polyphenols (Roldán-Marín et al., Reference ROLDÁN-MARÍN, SÁNCHEZ-MORENO, LLORÍA, ANCOS and CANO2009) which have shown appreciable anti-NDV properties (Talebi et al., Reference TALEBI, AMANI, POURMAHMOD, SAGHAEI and REZAIE2015; Chen et al., Reference CHEN, JIANG, LI, WANG, WANG and LI2016). These non-digestible carbohydrates are prebiotics and have been found to be of interest to human health (Galdon et al., Reference GALDON, RODRIGUEZ, RODRIGUEZ and ROMERO2008) as well as in animal production (Aditya et al., Reference ADITYA, AHAMMED, JANG and OHH2017; Rahman et al., Reference RAHMAN, KHAN, CHAND, SADIQUE and KHAN2017).
Onions have high content of dietary fibres especially FOS and fructans (Jaime et al., Reference JAIME, MARTÍN-CABREJAS, MOLLÁ, LÓPEZ-ANDRÉU and ESTEBAN2001) but these differ in chain length distribution from those from other sources, like chicory (Roldán-Marín et al., Reference ROLDÁN-MARÍN, SÁNCHEZ-MORENO, LLORÍA, ANCOS and CANO2009). Fructofuranosylnystose, kestose and nystose have been found to be the main FOS source in onion bulbs (Jaime et al., Reference JAIME, MARTÍN-CABREJAS, MOLLÁ, LÓPEZ-ANDRÉU and ESTEBAN2001). Substantive research into FOS has identified their health benefit as non-digestible dietary fibres (Benkeblia and Shiomi, Reference BENKEBLIA and SHIOMI2006).
Rahman et al. (Reference RAHMAN, KHAN, CHAND, SADIQUE and KHAN2017) showed that supplementation of poultry feed with 1.5, 2 and 2.5 g/kg of onion powder significantly increased feed conversion, weight gain, reduction in E. coli population and increase in Lactobacillus and Streptococcus spp.. Aditya et al. (Reference ADITYA, AHAMMED, JANG and OHH2017) recorded better weight gain and lower redness of meat when 7.5 g/kg was supplemented in poultry diets. However, when Goodarzi et al. (Reference GOODARZI, LANDY and NANEKRANI2013) supplemented the feed of poultry with 30 g/kg of fresh onion bulb they found it did not induce any significant anti-NDV effect on the antibody titre.
Garlic (Allium sativum) is extensively used globally and its therapeutic properties have been extensively explored in traditional medicine for the control of infectious and non-infectious diseases (Lukanov et al., Reference LUKANOV, GENCHEV and RIBARSKI2015). Block (Reference BLOCK1985) reported the widespread and frequent use of garlic in ancient times by Egyptians, Babylonians, Vikings, Greeks, Hindus and Chinese against ailments including flatulence, intestinal disorders, worms, skin diseases, and respiratory infections.
Garlic is bulbous and reaches a height of 1.2 m. garlic has two subspecies namely softneck and hardneck garlic (Bayan et al., Reference BAYAN, KOULIVAND and GORJI2014). Like onions, it is a member of the Lillaceae family (Iciek et al., Reference ICIEK, KWIECIEŃ and WŁODEK2009). A large number of garlic supplements are available commercially either as garlic oil, dehydrated garlic powder, aged garlic extract (AGE) or garlic oil macerate (Amagase et al., Reference AMAGASE, PETESCH, MATSUURA, KASUGA and ITAKURA2001).
It has been shown that garlic powder contains FOS and allicin (allyl 2-propenethiosulphinate or diallylthiosulphinate) (Amagase et al., Reference AMAGASE, PETESCH, MATSUURA, KASUGA and ITAKURA2001) as its main bioactive components. Alliin is found in intact garlic which is also rich in vitamin C, riboflavin, thiamine, niacin, potassium and selenium (USDA, 2014). Alliinase enzyme is activated following the chopping or crushing of garlic, converting non-proteinogenic amino acid alliin to allicin (Bayan et al., Reference BAYAN, KOULIVAND and GORJI2014) which gives freshly chopped garlic its characteristic taste and smell. Hence, allicin is regarded as a defence molecule produced by garlic upon tissue damage (Borlinghaus et al., Reference BORLINGHAUS, ALBRECHT, GRUHLKE, NWACHUKWU and SLUSARENKO2014), and Ankri and Mirelman (Reference ANKRI and MIRELMAN1999) reported that, in its pure form, allicin has demonstrated antiviral and antimicrobial activity. This has been exploited in various AGP replacement supplement products for animals.
A number of published trials have explored different dietary levels of garlic supplementation to enhance growth characteristics and FCR in chickens (Gbenda et al., Reference GBENDA, ADEBISI, FAJEMISIN and ADETUNJI2009; Fayed et al., Reference FAYED, RAZEK and JEHAN2011). However, Pourali et al. (Reference POURALI, MIRGHELENJ and KERMANSHAHI2010) reported that feeding garlic powder had no significant effect on the antibody against NDV serum level. Eid and Iraqi (Reference EID and IRAQI2014) carried out supplementation experiment using 160 Hubbard chicks. The result showed that chicks supplemented with garlic powder had higher antibody titres against NDV. Navidshad et al. (Reference NAVIDSHAD, DARABIGHENE and MALECKY2016) reported that 10 g/kg of garlic supplement in the feed of White Leghorn was able to increase anti-NDV antibody production. An increase in mean HI titre of 4.0 was recorded in cobb broiler chicken following vaccination and supplementation of poultry feed with garlic extract compared to a mean HI titre increase of 3.4 in the vaccinated but not supplemented group and a reduction in mean HI titre in the non-vaccinated and untreated (control) group (Hassan et al., Reference HASSAN, ELBAYOUMI, MEKKY, SEDEEK, RABIE and GIRH2013). Hence, an increase in mean HI titre of 0.6 in the chicken was attributed to the garlic extract. These findings cast doubt on an earlier study that reported a significant difference in NDV antibody levels between vaccinated and unvaccinated chickens whose feed were supplemented with garlic of which the researchers suggested that the difference may not have resulted from the feed (Jafari et al., Reference JAFARI, JALAI, GHORBANPOOR and SARAEI2008). However, Safdar et al. (Reference SAFDAR, MUHAMMAD and NAZ2016) in another study reported that garlic had no effect on anti-NDV-HI antibody.
Probiotics
The word ‘probiotic’ is a Greek derivative meaning, ‘for life’. It was Lilly and Stillwell (Reference LILLY and STILLWELL1965) who first used the word ‘probiotic’ to mean substances secreted by one organism (a protozoa) that enhanced the growth of another. This definition placed probiotics as the opposite of antibiotics. Fuller (Reference FULLER1989) modified this definition to ‘a live microbial feed supplement which beneficially affects the host animal by improving its intestinal microbial balance’. Salminen (Reference SALMINEN1996) expanded the definition as ‘a live microbial culture or cultured dairy product which beneficially influences the health and nutrition of the host’, which included the nutrition of the host rather than the initial focus on health.
The intestinal flora is made up of a complex interrelationship comprising different populations of microorganisms - both indigenous to the host and derived from the external milieu. Commercial probiotics may be presented as powders or pastes. The benefits of feeding probiotics can only be achieved if the minimum viable microbial count is administered with 106 CFU ml-1 being reported as the minimum microbial count required for efficacy (Boylston et al., Reference BOYLSTON, VINDEROLA, GHODDUSI and REINHEIMER2004).
The study carried out by Al-Sultan et al. (Reference AL-SULTAN, ABDEL-RAHEEM, EL-GHAREEB and MOHAMED2016) showed that poultry that were supplemented with probiotics had a higher antibody response to ND vaccine compared to those whose feed were supplemented with organic acids or prebiotics as well as the control. They observed a reduction in mortality by 6.66% compared to the control. Similar effects, with higher anti-NDV antibody titre as a result of feed supplementation with probiotics have been reported (Chughtai et al., Reference CHUGHTAI, KHAN, HUSSAIN and IQBAL2015). However, a recent report by Shirisha et al. (Reference SHIRISHA, KRISHNADAIDA RAJU, REDDY and REDDY2017) suggested that there was no significant influence on anti-NDV antibody titre with probiotic supplement.
saccharomyces cerevisiae
Saccharomyces cerevisiae is single-celled yeast capable of rapid division (Hartwell, Reference HARTWELL1974). S. cerevisiae can be used as a feed supplement as it possesses potential probiotic potentials (Thornton, Reference THORNTON2010). S. cerevisiae has been used as a vehicle for vaccines in veterinary field to protect the host against viral diseases (Arnold et al., Reference ARNOLD, DURAIRAJ, MUNDT, SCHULZE, BREUNIG and BEHRENS2012). Various parts of the yeast, such as mannan-oligosaccharides (MOS) from the cell wall, have been shown to assist with NDV protection.
Chen et al. (Reference CHEN, JIANG, LI, WANG, WANG and LI2016) assessed the effect of dietary supplementation with β-glucan (BG) and MOS from S. cerevisiae on broiler chicken's production and health, under the challenge of naturally feed-borne Aspergillus fumigatus. The result showed that supplemented broilers had lower mortality rate and higher antibody titres of NDV compared to the control groups. This confirmed the results of an earlier study (Oliveira et al., Reference OLIVEIRA, FIGUEIREDO-LIMA, FILHO, MARQUES and MORAES2009) which reported the ability of S. cerevisiae to improve the anti-NDV antibody titre of test broilers.
saccharomyces boulardii
Saccharomyces boulardii was first isolated from litchi fruit by Henri Boulard in 1920s (Rajput et al., Reference RAJPUT, LI, XIN, WU, JUAN, CUI, YU and LI2013a) and has been used hitherto for promoting gut health and preventing diarrheal diseases. The use of S. boulardii can be preferred over S. cerevisiae because it remains longer in the gut than the latter (Liu et al., Reference LIU, KONG, ZHANG, JAYAKODY, KIM, XIA, KWAK, SUNG, SOHN, WALUKIEWICZ, RAO and JIN2016). S. boulardii is a natural antioxidant source (Rajput et al., Reference RAJPUT, LI, XU, HUANG, ZHI, YU and LI2013b) and its oral administration has the potential to improve enzymatic activity and antioxidation functions, hence, providing transient protection to the intestinal mucosa throughout its duration of stay (Kotowska et al., Reference KOTOWSKA, ALBRECHT and SZAJEWSKA2005).
Manafi et al. (Reference MANAFI, HEDAYATI and MIRZAIE2018) reported that the inclusion of a commercial preparation of S. boulardii in the feed of broilers improved antibody titres against NDV. According to this trial, the best immune result was obtained when the probiotic was used at a concentration of 100 g/ton, whereby the anti-NDV titre (log2) increased by 0.5 from 5.00 to 5.50.
Conclusions
The role of antibiotic alternatives, including pre- and pro-biotics, herb and spice extracts and live yeasts, in the control of virally transmitted Newcastle disease is not yet very clear. However, initial research work on various compounds and organisms indicate there are benefits, when measured as increases in titre levels following vaccination. This is important, especially in areas where vaccination efficacy is poorer due to limitations in handling and storage. More work is needed in this direction to elucidate their mode of action and effective doses and regimens for such specialist ingredients in the control of ND in poultry.
