A STUDY ON THE DETERMINATION OF AFLATOXIGENIC FUNGI IN POULTRY FEEDS AND AFLATOXIN B1 IN FRESH AND BOILED BROILER LIVERS IN LIVE BIRD MARKETS IN ZARIA, NIGERIA
ABSTRACT
There is increasing concern for the contamination of poultry products with Aspergillus strains responsible for aflatoxin production. The occurrence of aflatoxigenic fungi in poultry feeds and aflatoxin B1 in fresh and boiled broiler liver samples in live bird markets in Zaria, Nigeria were examined. Feed samples were cultured for fungi on Sabouraud dextrose chloramphenicol agar to detect the presence of Aspergillus species. Aflatoxin production potential was evaluated using Czypeck dox agar. Desiccated coconut agar was used to detect fluorescence of Aspergillus spp and indirect competitive enzyme linked immunosorbent assay (cELISA) was used to determine aflatoxin residue concentrations (µg/kg) in both fresh and boiled (100°C for 90 mins) liver samples. Out of the 300 poultry feed samples tested, 234(77.9%) were contaminated with Aspergillus spp of which 126(53.8%), 48(20.5%), 27(11.5%), 15(6.4%), 9(3.9%), 5(2.1%), 3(1.3%), and 1(0.4%) were identified as A. flavus, A. fumigatus, A. parasiticus, A. niger, A. nidulans, A. terreus, A. nomius, and A. caelatus respectively. On desiccated coconut agar, Aspergillus had isolation frequency of 98(51.9%) with (P < 0.05). Samples from Dan Magaji, had isolation frequency of 28(28.6%), Zaria City 21(21.4%), Samaru 17(17.4%), Sabon Gari, 7(7.1%), Kwangila 14(14.3%) and Tudun wada 11(11.2%). The mean and standard deviation of aflatoxins in freshly tested liver concentration were 41.45 ± 29.55, 66.40 ± 22.28, 9.90 ± 6.50, 10.00 ± 1.74, 29.80 ± 17.16 and 35.25 ± 8.14 µg/kg for Zaria city, Sabon Gari, Kwangila, Samaru, Tudun wada and Dan Magaji respectively. All the liver sample of birds in live bird markets had aflatoxin B1 concentration higher than the maximum limit (4 µg/kg) set by World Health Organization and Standard Organization of Nigeria. Also, there was statistically significant (P < 0.05) difference in sample locations. Furthermore, the mean value and standard deviation of boiled liver contents were 8.2 ± 5.0, 1.8 ± 0.7, 0.6 ± 0.3, 29.0 ± 9.5, 5.2 ± 5.1, 4.5 ± 3.3 µg/kg for Samaru, Kwangila, Dan Magaji, Sabon Gari, Zaria City and Tudun wada respectively. The mean value and standard deviation of liver content before and after boiling were 15.98±15.00 and 8.22±10.52 µg/kg respectively. There was no statistical difference in the processed form of liver (P < 0.05). Aflatoxin content, were found in edible tissues both before and after heat treatment. Strict measures should be taken to monitor toxins in feed and chicken meat products.
CHAPTER ONE
INTRODUCTION
1.1 Background of the Study
The study of mycotoxins really began in 1960 with the outbreak of Turkey X disease in the U.K, linked to peanut meal imported from Brazil (Sargeant et al., 1961). Mycotoxins, the secondary metabolites from toxigenic fungi, are contaminants in foods and feeds, exerting harmful effects upon animal and human health (Zahoor-ul-Hassan et al., 2010). Mycotoxins are low-molecular weight secondary metabolites, produced by certain strains of filamentous fungi, such as Aspergillus, Penicillium and Fusarium, which invade crops in the field. Mycotoxins are structurally-diverse simple C4 compounds, for example, moniliformin, to complex substances such as the phomopsins which are filamentous fungi that vary in their chemistry and biological effects (Sudakin, 2003; Dinis et al., 2007). The most important mycotoxins in naturally contaminated food and feeds are aflatoxins (AFs), ochratoxins (O), zearalenone (ZEN), T-2 toxin, deoxynivalenol and fumonisins (Sultana and Hanif, 2009). No region of the world escapes the problem of mycotoxins and according to Lawlor and Lynch (2005) and Okoli et al. (2006b), mycotoxins are estimated to cause loss of as much as 25 % of the world’s crops each year. The mycotoxins accumulate in foods during storage under favourable conditions of ambient temperature and relative humidity for fungal growth. Mycotoxins are produced only under aerobic conditions Ratcliff (2002), where they often attack ground nut, maize, cotton seed cake, wheat, and soyabean. They are regularly implicated in toxic syndromes in animals and humans (Charoenpornsook and Kavisarasai, 2006). However, animals may have varying susceptibilities to mycotoxins, depending on physiological, genetic and environmental factors. Most mycotoxins such as aflatoxin B1, T-2 toxin and ochratoxin A inhibit protein synthesis (Charoenpornsook and Kavisarasai, 2006). The consumption of multiple doses of mycotoxin-contaminated diet may induce haematological, biochemical, physiological changes in the liver and growth depression in animals (Awad et al., 2006; Shi et al., 2006; Rezar et al., 2007; Gowda et al., 2008). Thus, the presence of mycotoxins in poultry feeds can result in significant economic losses to the poultry industries (Awad et al., 2006). Mycotoxins have been detected in various food commodities from many parts of the world and are presently considered as some of the most dangerous contaminants of food and animal feeds (Okoli, 2005; Okoli et al., 2006a; 2006b; 2007a; 2007b). Adverse effects of mycotoxins on animal health and production have been recognized in animals kept under intensive management such as poultry, swine and cattle as a consequence of the consumption of high levels of contaminated cereals and oilseeds in the diet (Charoenpornsook and Kavisarasai, 2006).
Aflatoxins produced by the toxigenic fungi, mainly Aspergillus flavus and Aspergillus parasiticus, constitute one of the major health hazard groups of naturally-occurring toxicants, both for man and animals. There are six forms of aflatoxins: B1, B2, G1, and G2 are found in plant-based food, while M1 (metabolite of B1) and M2 are found in foods of animal origin. Aflatoxin B1 is the most harmful form due to its direct link to human liver cancer (Leslie et al., 2008; USAID, 2012). The order of potency for both acute and chronic toxicity of aflatoxins is AfB1 > AfG1 > AfB2 > AfG2 (Santacroce et al., 2008). Among the four major groups of aflatoxins; namely B1, B2, G1 and G2; aflatoxin B1 (AFB1) is the most toxic and it is a known carcinogen. Acute or chronic aflatoxicosis in domestic birds results in decreased meat/egg production, immunosuppression and hepatotoxicosis (Verma et al., 2004; Khan et al., 2010). Human exposure to aflatoxins may result from consumption of plant-derived foods that are contaminated with the toxins, and the carry-over of aflatoxins and their metabolites in animal products such as meat and eggs (CAST, 2003).
Aflatoxin is one of the numerous naturally-occurring mycotoxins that are found in soils and foods. Aflatoxins have been found in soil as well as in grains, nuts, dairy products, tea, spices and cocoa, as well as animal and fish feeds (Waliyar et al., 2008).
1.2 Statement of the Research Problem
Mycotoxins that occur in food and/or feedstuffs have great significance in the health of humans and livestock (Tola and Kebede, 2016). The growth of this heterologous group of fungi in feed and the generation of secondary metabolites of mycotoxins have adverse effects on the poultry industry and human health as well (Monson et al., 2015; Oliveira et al., 2015).
Exposure of Pregnant women to aflatoxin may cause increased maternal mortality and low birth weight. Infants exposed to aflatoxin-contaminated foods may be more susceptible to stunting growth and malnutrition (Shuaibu et al., 2010). Aflatoxins impair livestock growth, reproduction, immune functioning and ability to metabolize vaccines (Makun et al., 2012).
The economic impact of reduced animal productivity, increased incidence of disease due to immunosuppression, damage to vital organs and interference with reproductive capacity is many times greater than the impact caused by death due to mycotoxin poisoning (Akande et al., 2006). It has been pointed out that aflatoxin contamination of feeds of food-producing animals can result in residues of ingested aflatoxins or its metabolites in meat, milk and egg (Gizachew et al., 2016).
It has been estimated that more than 5 million people in developing countries world-wide are at risk of chronic exposure to aflatoxins through contaminated food (Shepard, 2005; Strosnider et al., 2006). Animals exposed to aflatoxins show a variety of symptoms, depending on the animal species. However, in all animals, aflatoxins may cause liver damage, decreased reproductive performance, reduced milk or egg production, embryonic death, teratogenicity, tumors and suppressed immune function, even when low levels are consumed (Akande et al., 2006). Aflatoxins are both acutely and chronically toxic in animals and humans (Pimpukdee et al., 2004).
Aflatoxin B1 is known to be the most toxic metabolite, especially in sensitive species such as poultry (Hussein and Brasel, 2001). Beside direct losses related to mortality, feed conversion and growth rate, recovering birds remain poor. Indeed, air sacculitis is a major reason for carcass condemnation at slaughter inspection (Kunkle, 2003; Lupo et al., 2010). It is proven that aflatoxin leads to reduced egg production as well as their quality in laying hens (Rizzi et al., 2003).
Poultry feeds in live bird markets is at risk of unsafe aflatoxin accumulation which can negatively affect human health, food security and economic trade (Williams et al., 2004). Their toxicity depends on different factors including its concentration, the duration of exposure, the species, sex, age, and health status of animals (Jewers, 1990).
