Mycotoxins and Poultry

ABSTRACT

Mycotoxins are contaminants of many cereals and derivatives used as ingredients in poultry diets. They are considered secondary metabolites produced by fungi that develop well in tropical climates. When they are present in moderate to high concentrations in the diet, it might result in death, and when used in low doses, it may compromise production indexes, such as decrease in weight gain, poor feed conversion, decline in egg production and decrease in hatching rate. The management  and control of mycotoxins are essential to reduce their harmful effects. These are two important processes that must be thoroughly conducted, since mycotoxins may provide great economic losses in poultry business. The monitoring and using AntiMycotoxins Additives (AMA) are good examples for solutions.

1. MYCOTOXINS OF MAJOR IMPORTANCE IN POULTRY

Mycotoxins are toxic substances resulting from the secondary metabolism of several strains of fungi filamentous. They are organic compounds, with low molecular weight and they have no immunogenicity. The fungi grow and proliferate well in cereals, especially maize, wheat, sorghum, in where they generally find a highly nutritious substrate for their development. The fungal growth and mycotoxin production in cereals may occur at different stages of development, maturation, harvesting, transporting, processing or storage of grain. Therefore, the reduction of grain moisture by drying is of fundamental importance to reduce the levels of contamination (MALLMANN & DILKIN, 2007). In Table 1, mycotoxins of greatest impact on poultry production are related, in addition to the fungi that produce them and the conditions that favor the formation of such compounds.

1.1. Aflatoxins

Aflatoxins are secondary metabolites produced by fungi of the genus Aspergillus, especially A. flavus and A. parasiticus, they were discovered in the 1960s, after provoking an outbreak (Turkey X disease) with high mortality of turkeys in England (MALLMANN & DILKIN, 2007). In this outbreak, thousands of birds have died after consuming food containing peanut pie. The main fungus found in peanut meal was Aspergillus flavus, giving its name to this toxin.

In outbreaks of aflatoxicosis, one of the most important features is the poor absorption of food that is manifested by the presence of poorly digested food particles in the feces of birds. It is associated with steatorrhea or increased excretion of lipids. This can be severe with an increase of up to ten times of fat content in feces. In broilers, the steatorrhea is accompanied by a decrease in total and specific activities of pancreatic lipase, the main digestive enzyme from fat and a decrease of bile salts, necessary both for digestion and for absorption of fat, leading to hepatic steatosis (fatty liver). Mucosal pallor and legs is also observed in chickens and hens receiving feed contaminated with aflatoxins. This seems to be a deficient pigmentation result of reduced absorption, transport and decreased tissue deposition of carotenoids in the diet, and the aflatoxicosis identified as "pale bird syndrome".

The sensitivity to the toxic effects of aflatoxins varies considerably among different animal species, even among individuals within a species; the dose-response relationship may vary according to race, sex, age, immunity, diet composition, among other factors. For many species, males are more susceptible than females, whereas, in general, sensitivity is markedly higher in young than in adults (Leeson et al., 1995).

1.1.1. Effect of aflatoxin on laying hens

The presentation of the disorders caused by aflatoxin on egg production is only possible after a few days or weeks. The presence of pre-ovulatory follicles already formed, in the reproductive tract of the birds prior to consumption of mycotoxin justifies this late response. The decrease in egg production is preceded by a reduction in blood levels of proteins and lipids. Hens consuming diets containing aflatoxins 5 ppm for 4 weeks, may show a reduction in egg production from the eighth day, reaching a decrease in production of around 35%, one week after removal of the mycotoxin diet (ROSA et al., 2001).

Besides reducing the production of eggs, aflatoxicosis also induces a reduction in egg size, as well as the proportional reduction in the size of the yolk, due to the damage caused in the lipid and protein synthesis. However, the deposition of calcium in the eggshell is normal. Thus, the egg gets smaller due to the decreased egg white and yolk and the shell becomes thicker. Thus, the resistance increases and the shell can affect the hatchability for the reduction in gas exchange between the embryo and the environment.

Embryo mortality with eggs intoxicated with aflatoxins happens because these substances, after being biotransformed in the liver, have as one of the major metabolites, aflatoxin M₁, which is eliminated from the body through the yolk. Moreover, aflatoxin B₁ and aflatoxicol can also be found in the yolk, from 24 hours after ingestion of aflatoxins.

Aflatoxin B₁ can contaminate both the yolk and the egg white. Trucksses et al. (1983) found aflatoxicol and aflatoxins B₁ and M₁ in eggs 24 hours after consumption of contaminated feed. Therefore, it must be noted that while the rate of posture is affected only 8 days after onset of intoxication, hatchability begins to be affected 24 hours after consumption. Aflatoxins can enter the egg at any stage of its development. For an oocyte to develop into a mature egg, it takes 7 to 8 days and 24 hours more to complete the process of formation of the egg, and then, this is the necessary time since the contamination until the detection of aflatoxins in the egg.

Considering aflatoxicosis in breeders, the highest rates of embryonic mortality happen in the final third of incubation. This is due the products of biotransformation of aflatoxins are concentrated in the yolk, which is used by the embryo as an energy source during this period of the incubation process, causing the contamination. 

Fernandes (2004) assessed the performance of broilers chicks of matrices with increasing levels of aflatoxins and noted that chicks intoxicated from breeders had lower quality, resulting in lower body weight at 7 days old. Furthermore, chicks from broilers fed with diets containing 750 ppb had a mortality rate higher than those originated from matrices that did not ingest aflatoxins.

1.1.2. Effect of aflatoxin on the production of turkeys

Throughout the past few years, Brazil has achieved significant increases in production and export of meat and poultry products. In this context, it has great importance to turkey production. Turkeys are more susceptible to the effects of aflatoxin than broilers, without identifying the real impact of these mycotoxins in the development of these birds.

A study conducted by Rauber (2006) showed that during the first 42 days, turkeys present sensitivity to aflatoxin intoxication about 4 to 6 times higher than chickens. In this study, turkeys were fed diets containing 0 to 1000 ppb aflatoxin (divided into seven treatments). The treatment that received the highest dose showed a weight gain of about 38% lower than the control group (Table 2). Another important finding is related to mortality, which was 37%, while the control group there was no mortality. The evolution of weight gain in animals intoxicated in the treatments was inversely proportional to the dose of aflatoxins in the diet (R = - 0.84 and P = 0.00; Weight 42kg = 2298.94- 0.87*ppb aflatoxin). Comparatively, broilers fed 3000 ppb aflatoxin for 42 days showed a 27% reduction in weight gain (Giacomini et al., 2006).

1.1.3. Effect of aflatoxin on the performance of different strains of broiler chickens

Some studies (Giacomini et al., 2006, Mallmann et al., 2006) show that there are degrees of sensitivity among individual animals of the same species and same gender regarding aflatoxin intoxication. Mariani (1998) proved the difference in susceptibility of broilers to aflatoxin as the age of these birds, indicating that younger birds have more damage in their development compared to older birds. An experiment was conducted at LAMIC which found that there are differences in performance between the three main strains of broiler chickens reared in Brazil when they are fed with feed contaminated with aflatoxins (Table 3).

The Y strain, from the 14th day, following up to 42 days presents relative decrease in weight, significantly higher than at least one of the other strains used in this experiment. Besides the differences in losses, another important factor is the coefficient of variation (CV) of the weights of birds in the intoxicated animals, and the lineage X had the highest CV among the lines evaluated in all periods. This result indicates that lots of birds of this strain are more unequal when they are fed diets containing aflatoxins.

1.2. Cyclopiazonic acid

Besides producing aflatoxins, some strains of Aspergillus flavus also produce cyclopiazonic acid (CPA). This mycotoxin has been associated with some clinical signs shown by birds in the first time of aflatoxicosis described (Turkey X disease). Despite this, analysis of samples that episode showed the presence of this mycotoxin (Kuilman-WAHLS, 2002). The CPA occurs naturally in corn and peanuts, and its presence is usually associated with the presence of aflatoxins (Vaamonde, 2003).

The main clinical signs include decreased by CPA in weight gain, vomiting, and neurologic signs (opisthotonus, hyperesthesia, and seizure) and is usually fatal. Lesions include degeneration and necrosis of the liver, hemorrhagic lesions in the myocardium, proventriculus, gizzard and spleen (Kuilman-Wahls, 2002). Among the injuries mentioned above, the most significant is the presence of erosions in the gizzard of birds contaminated.

The main group of trichothecene mycotoxins includes the T-2 toxin, deoxynivalenol (DON or vomitoxin) and diacetoxyscirpenol (DAS). They are produced by fungi of various genera, mainly Fusarium (Leeson et al., 1995).

Chronic contamination involving T- 2 toxin or DAS induced reduction in feed intake and weight gain, oral lesions, tissue necrosis lymphoid, haematopoietic and oral mucosa, with possible nervous disorders (abnormal position of the wings, decreased reflexes), abnormal feathering and thinning of the eggshells. Particularly  in layers, oral lesions occur in approximately 50% of the lots where these birds are fed a diet containing 2 ppm of T- 2 toxin. However, the T-2 toxin is highly toxic to chicken macrophages, inhibiting their phagocytic capacity. This toxin also induces the formation of peroxides from lipids, with the consequent decrease in the concentration of vitamin E in poultry.

Other birds like turkeys and geese are more sensitive to T-2 toxin than broilers. In geese, contamination from 0.1 mg/kg body weight causes decrease in egg production, in addition rates of egg hatchability and decrease by 50% when it was administered 300 mg/kg bodyweight.

Mycotoxins T-2 and DAS induced oral lesions in broiler chickens when present at levels from 1 ppm in the diet. The birds have reduced food consumption, growth retardation, changes in blood parameters and neurotoxicity.

Feed contaminated with DAS causes a decrease in egg production, coinciding with a decrease in feed consumption and the appearance of oral lesions. This result is more evident in lighter lines and persists for up to two weeks after the ingestion of the toxin. This suggests that a period of nutritional supplementation is required for the recovery of the bird. The decrease in food consumption may be related to oral lesions caused by the toxin. These lesions are found in both males and females and their presence is quickly detected by the birds, causing an increase in the period of feed intake by breeder hens (Brake et al., 2002).

The effects of trichothecenes on broilers and breeder hens include sudden refusal of food, weight loss and oral lesions, decrease in egg production, and diminished quality of the shell, with an increase in the percentage of embryonic mortality and decreased hatchability (YEGANI et al., 2006). For the chicks, the intake of trichothecenes also can lead to decreased fertility and a decrease in testis volume (Brake et al., 1999).

Oral lesions caused by the contamination with DAS become necrosis of the tip of the tongue, especially in commercial breeders and laying hens, and can rarely be found in broilers. However, the lesions found in cases of contamination by T-2 toxin, commonly are erosion and/or ulcers of the palate and the commissure of the beak of birds contaminated. These lesions can be evidenced in both breeder hens and in broilers. However, similar studies performed with DON, have clarified that with the exception of a transient decrease in hemoglobin, or a very slight effect on egg quality, there is significant evidence that this toxin affects the performance of birds. They are able to tolerate relatively high concentrations of DON in the diet and a little less than the T-2 toxin and DAS. The DON levels normally found in contaminated feed (0.35 to 8.0 ppm), no indications of any health problem perceived with chickens. DON concentrations above 82.8 ppm were administered to hens for 27 days without any effect on performance and without clinical lesions in birds. Other authors have described injuries and very minor reduction in quality of eggs in birds fed 18 ppm of DON in the diet.

Trichothecenes generally do not induce an increase in mortality in birds other than chickens, requiring levels of several hundred parts per million to result in significant mortality. Similarly, in outbreaks of mycotoxicosis attributed to T- 2 toxin that affected domestic ducks, geese, horses and pigs, mortality was observed only in geese, which suggests a great sensitivity of these birds.

Fumonisins are produced by fungi of the genera Alternaria and Fusarium, mainly by F. moniliforme. Fumonisins with highest occurrence and toxicological significance are FB₁ and FB₂ (MALLMANN & DILKIN, 2007). Contamination levels in maize from different parts of the world are normally below 5 ppm, and about a third of the samples are contaminated. The analysis carried out in the last 14 years at the Laboratório de Análises Micotoxicológicas (LAMIC) found that 75% of corn samples and 72% of feed samples were contaminated with fumonisins.

Some studies indicate that toxic levels of fumonisins are above 80 ppm. Other researchers have performed experiments with extremely high doses of fumonisin (61 to 546 ppm) and found adverse effects of this toxin on performance of broilers. However, studies conducted by LAMIC using FB₁ obtained from field fungi, showed that doses below 50 ppm fumonisin B₁ already impacting negatively on the weight of broilers up to 21 days of age, representing a 4% reduction in body weight . Levels of 100 ppm led to losses of up to 12% in weight gain after 21 days. In the field, these losses may be higher since in experimental conditions. The effect of mycotoxins is usually mitigated by the elimination of stress factors.

Another important factor to be considered in regard to fumonisins, is the fact that its fungi produce a number of other toxic compounds. These substances may be present in poultry feed and determine loss of performance even more significant.

In birds contaminated by fumonisins, clinical signs generally include less weight gain, mortality, diarrhea, ascites, and pale hiericardite, edema and renal congestion, ulceration in the oral mucosa in turkeys, an increase in relative liver weight, proventriculus and gizzard.

Fumonisin contamination can be monitored through blood parameters. There is change in the relationship between circulating levels of sphingosine and sphinganine, which are precursors of sphingolipids, when contamined with this toxin.

Based on the in vivo experiments, conducted by LAMIC and SAMITEC Institute (Santa Maria, Brazil) and also the occurrence of mycotoxins evident in recent years (over 168,000 samples of raw materials and feed), was established a recommendation regarding the safety limits of mycotoxins for poultry production. These limits are shown in Table 4.

The management and control of mycotoxins involve a process that has a number of critical activities. Start by defining a monitoring program that involves the definition of the sampling process. Is the analysis and control and ends in making a decision. This should consider the safe use of diet in which the risk of contaminated by mycotoxins can be minimized and that the cost be exactly quantified, allowing the maximization of the productivity (MALLMANN & DILKIN, 2007).

Since mycotoxins are formed, the fungal growth inhibition does not imply the decrease of it. A widely used method for controlling mycotoxicoses is the use of Antimicotoxin Additives (AMA) in order to reduce the absorption/inactivation of mycotoxins in the gastrointestinal tract of birds.

Experiments conducted from 2005 to April 2011 by LAMIC in conjunction with SAMITEC Institute, evaluated 74 AMA for birds, of which only 47% shown to be effective (http://www.lamic.ufsm.br/aam/index.html). Despite the fact that most products do not fulfill the requirements for use as AMA, is still the uncertainty of how and when to use a effective product. This response is achieved through constant monitoring of the production of feed mills. In general, it is assumed that all diets for the pre-initial should have in their formulation to include an AAM; diets prepared for the other phases should take into account the risk factor Mycotoxins (MRI) for inclusion or not the AMA. This index (MRI) takes into account the interaction between the average contamination of samples and mean prevalence of each mycotoxin in these samples, which serves as a reference for making decisions regarding the use of AMA.

The presence of mycotoxins in poultry diets can determine the losses in poultry production system. From the harvest of grain, the effects of fungal contamination and mycotoxicological can be perceived, and its effects can reflect on the production of chickens.

The control depends on the implementation of appropriate policies within the agricultural management, production systems and storage, which are the root of the problem. Research in these areas should be developed, reflecting better results in economic and productive livestock, but also for the improvement of health food for human consumption.

The use of Antimicotoxines Additives in diets contaminated with mycotoxins for birds, is of strategic importance, since once the toxin is formed, detoxification processes often become expensive and impractical. Therefore, the use of such additives is still the best option. The considerable presence of mycotoxins in key components of the diet requires the adoption of a continuous program of control. It is necessary to accurately identify existing contamination, making it essential to implement the monitoring of raw materials and feed for birds.

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