CHAPTER 2 Literature Review
2.8 Combating contamination of poultry feeds
2.8.1 Adsorbents
Adsorbents are compounds that are not absorbed in the gastrointestinal tract and have the ability to bind physically with mycotoxins, preventing their absorption. It is important to note that the adsorbents are not selective, so they may bind other components of the diet (Leeson et al., 1995). Phillips (1999) reported that aflatoxin binding agents should be rigorously tested, paying particular attention to their effectiveness and safety in aflatoxin-sensitive animals and their potential for interactions with critical nutrients.
Activated charcoal, hydrated sodium calcium aluminosilicates, bentonites and diatomaceous earth have been evaluated as adsorbents to ameliorate the toxic effects of AF in chickens. The occurrence of zeolites, bentonites, and diatomite deposits in Mozambique, represent a very valuable material with a wide range of uses, the importance of which is currently increasing (Cílek, 1989).
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2.8.1.1 Activated charcoalActivated charcoal is the residue from the destructive distillation of vegetable origin organic matter, and is porous, low in ash content and high in surface area (Leeson et al., 1995). A study of the toxicity of aflatoxin B1 in broiler chicks and its reduction by activated charcoal was carried out by Jindal et al. (1994). The results showed that adding 200 ppm activated charcoal to a 0.5 ppm aflatoxin B1 diet reduced the negative effect of AFB1 on body weights and feed intake. Teleb et al. (2004) also reported that addition of 0.5 % activated charcoal to a diet contaminated with 30 μg/kg AFB1 reduced mortality and improved body weight gain and efficiency of feed utilization. In contrast to these results, Denli and Okan, (2006) found that the addition of 2.5 g/kg activated charcoal to a diet containing 80 μg AFB
1/kg diet did not ameliorate the toxic effect of aflatoxin on chicken performance. Kubena et al. (1990) reported that adding 0.5% activated charcoal to the diet did not appear to have protective properties against the effects of 7.5 mg AFB1/kg of diet.
Khadem et al. (2012) evaluated the effects of yeast, zeolite and activated charcoal, alone or in combination, in aflatoxin B1 contaminated diets on the performance, biochemical traits, and organ weights of broilers by. The results showed that the combination of yeast plus charcoal and zeolite plus charcoal improved feed intake, body weight gain and feed conversion ratio.
Furthermore, the final live body weight of the chickens fed the combination of yeast plus zeolite and charcoal diet was higher compared to those of other treatment groups.
2.8.1.2 Hydrated sodium calcium aluminosilicate (HSCAS)
Hydrated sodium calcium aluminosilicate (HSCAS), a sorbent compound obtained from natural zeolite, was demonstrated to sorb aflatoxin with a high affinity (Ramos and Hernández, 1997).
Philips et al. (1988) reported that HSCAS when added to the diet of chickens at a level of 0.5 % significantly decreased the growth inhibitory effect of 7.5 mg AFB1 /kgof feed. The friable and pale appearance of livers from the chicks fed 7.5 mg AFB1 /kgof diet were not observed in chicks fed HSCAS plus7.5 mg AFB1 /kgof diet. These results indicated that the HSCAS was effective in ameliorating the negative effects of AFB1.
The efficacy of a hydrated sodium calcium aluminosilicate (0.5 % HSCAS) added to diets containing 3.5 mg/kg aflatoxin and 5.0 mg/kg diacetoxyscirpenol alone and in combination were evaluated. Kubena et al. (1993) reported that body weight gain, efficiency of feed utilization, mortality, and oral lesion scores were not significantly influenced by HSCAS in the absence of toxins, indicating that the HSCAS is inert. Kubena et al. (1993) also reported that
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the reduction in body weight gain caused by 3.5 mg AF/kg of diet was diminished by the addition of 0.5 % HSCAS to the diet. The combination of diacetoxyscirpenol and AF caused a larger reduction in body weight gains of chicks compared with those fed AF alone at all time periods. However the addition of HSCAS to the diet containing a combination of AF and diacetoxyscirpenol diminished the adverse effects on body weight gains. Chung et al. (1990) reported that 0.5 or 1 % dietary HSCAS does not impair manganese, vitamin A or riboflavin utilization, but that zinc utilization was reduced slightly as a result of HSCAS ingestion.
The liver is the main organ involved in the detoxification of AFB1, and also where most residues accumulate. Neeff et al. (2013) studied the efficacy of the HSCAS to reduce residual concentrations of AFB1 metabolites in the liver and kidney of broilers fed AFB1. The results indicated that the HSCAS was effective in reducing aflatoxin residues in liver and kidney of chicks fed 2.5 mg AFB1/kg of diet from hatch to day 21. However, the histopathology data indicated that the HSCAS did not prevent or reduce the severity of lesions associated with aflatoxicosis.
2.8.1.3 Bentonite
Bentonite clay carries a uniquely strong negative ionic charge which causes it to “magnetically”
attract any substance with a positive ionic charge such as bacteria, toxins, and metals (Hedayati et al. 2014). Magandane (2013) reported that Mozambique has a bentonite mine, in Maputo province, Boane District. The bentonite has been mined since 1967 in this place, but its economic and social significance for the country is negligible. The products are supplied to a number of customers throughout South Africa, Zimbabwe and Mozambique but only 25 % is utilized in local industry, mainly for drilling construction and small foundry industries (MIMOC, 2011). Bentonites are efficient at sequestering aflatoxin; they decrease the bioavailability of the toxin in the gastrointestinal tracts of birds when they are incorporated in the diet (Magnoli et al., 2007).
Santurio et al. (1999) reported that the addition of 5.0 g sodium bentonite /kg of feed into chicken diet containing 3 mg AF/kg feed improved body weights at 42 d of age by 31.3 %, increased food intake by 23.8 % and improved productive efficiency by 40.1 %. In addition, liver, heart, pancreas and crop weights and biochemical variables were not affected by dietary sodium bentonite. Chickens fed sodium bentonite alone had similar performance to those feed the control diet containing no aflatoxin.
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Pasha et al. (2008) also reported that chickens fed sodium bentonite at a level of 0.5 % had significantly higher body weight compared with those fed the control diet. Kermashani et al.
(2009) observed that chickens fed AFB1 showed sign of aggression, pale colored combs and skin, fluffy feathers, and retarded growth rate at week 3 and later. However, chickens fed sodium bentonite (0.5 or 1 %) alone or and sodium bentonite plus AFB1 had a normal appearance.
Rosa et al. (2001) observed that natural sodium bentonite (0.3 %) from southern Argentina was effective on reducing the bioavailability and the toxic effects of AF (5mg AFB1/kg diet) in growing broilers chicks from 30 to 52 day of age. No differences on body weight gain were observed between birds fed the control diet and those fed AF plus sodium bentonite, suggesting that sodium bentonite ameliorated the negative effects of AF. Indresh et al. (2013) also reported that the addition of 0.75 or 1.0 % bentonite into an AF (0.5 ppm) diet prevented the reduction in body weight, feed intake, and poor feed conversion ratio of the birds fed the AF contaminated diet.
Exposure of chickens to aflatoxin leads to reduce the immunity. Manafi (2012) reported that addition of high grade sodium bentonite to diets containing AF significantly improved antibody titers against ND and IBD vaccine compared to the AF control diet. Indresh et al. (2013) observed that serum antibody titres against (ND) and (IBD) vaccination that were significantly depressed in chicks fed AF diet were restored with the inclusion of 1 % bentonite in the AF diet.
Even though all bentonites samples contained predominantly smectites their aflatoxin adsorption capacities differed substantially. Therefore, it is important to assess the properties of the clays to assure effectiveness before they are introduced in animal feed (Velazquez, 2011).
2.8.1.4 Diatomaceous earth
Diatomaceous earth (DE) is a natural occurring siliceous sedimentary mineral formed from microscopic skeletal remain of unicellular algae-like plants called diatoms. The typical chemical composition of oven-dried diatomaceous earth is 86 % silica, 5 % sodium, 3 % magnesium and 2 % iron oxide (Mordirsanei et al., 2008).
The efficacy of DE to reduce the negative effects of AFB1 in chickenswas evaluated. Modirsane et al. (2008) reported that dietary inclusion of DE (30 g/kg-1) alone did not affect body weight gain or serum biochemical values. The addition of DE (30 g/kg-1) into the aflatoxin (1 mg/ kg-1)
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diet, improved feed intake, body weight gain, and feed conversion ratio compared to birds fed AF alone. In contrast, Denli and Okay (2006) found that the addition of 2.5 g/kg diatomite to diets containing 0, 40 or 80 μg AFB
1/kg feed, failed to prevent the harmful effects of AFB1. The contrasting results could be due to the different concentrations of AFB
1 usedor to the different source of clay used.
Diatomaceous earth has also been reported as having the ability to reduce the incidence of gastro-intestinal parasites. Bennett et al. (2011) observed that DE has the potential to control internal (Capillaria spp, Eimeria spp. and Heterakis) and external parasites (e.g. Ornithonyssus sylviarum).