Mycotoxin absorbents in dairy cattle

Ingestion of mycotoxins by animals causes damage to the production system and can still be transferred to animal products, including milk. Due to its carcinogenic and genotoxic potential, the intake of mycotoxins, especially aflatoxins, is relevant to human health. The use of mycotoxin-absorbing agents has gained attention in dairy cattle nutrition. Therefore, it aimed to conduct a literature review on the use of mycotoxin absorbers in the dairy cattle diet. Mycotoxin absorbing agents can be of organic or inorganic origin, the inorganic ones being the most studied. Inorganic and organic agents have been shown to be effective in reducing the transfer of aflatoxin M1 to milk. However, the inclusion of mixed agents (organic and inorganic) is promising as a potential for mycotoxin absorption. In general, organic, inorganic and mixed absorbents showed positive results in improving the antioxidant and inflammatory status in the liver.


Introduction
Mycotoxins are a group of toxic compounds produced by filamentous fungi in growing forages or stored rations. These when ingested can reduce food consumption, health and the productive and reproductive performance of domestic and human animals (OGUNADE et al. 2016).
Among mycotoxins, aflatoxin B1 (AFB1) is the most problematic in dairy cows, as its metabolite, aflatoxin M1 (AFM1) can be transferred to milk (DIAZ et al., 2004). Thus, it may impact the health of consumers of milk and its derivatives.
Many approaches have been employed to reduce the risk of ingestion of aflatoxin by cattle and the resulting aflatoxicosis. Ozonation and ammonization can minimize the production and effects of toxins in corn and cottonseed meal (CAST, 2003). However, these approaches are expensive and time-consuming (KUTZ et al., 2009), so they are not normally used on dairy farms. Recently, a new approach to research is the use of mycotoxin absorbers. It consists of compounds of great molecular weight capable of reducing the bioavailability of mycotoxin in the gastrointestinal tract.
Therefore, it aimed to conduct a literature review on the use of mycotoxin absorbing agents for dairy cattle.
as hydroxy-AFB1 and aflatoxin M1 (GALVANO et al., 1996;EFSA, 2004;UPADHAYA et al., 2010). Thus, aflatoxin M1 (AFM1) represents a safety risk in milk and dairy products (IARC, 2002;WU, 2010). The maximum amount of AFM1 in milk allowed by the United States Food and Drug Administration (FDA, 2000) is 0.5 μg / kg of milk and by the National Health Surveillance Agency of Brazil (ANVISA, 2011) is 0.5 μg / kg of milk. While the maximum concentration of AFM1 in milk allowed by the European Commission is 0.05 μg / kg (EFSA, 2004).
In this context, there is a need to add substances that promote the inhibition and / or inactivation of mycotoxins contained in the animals' diets. Thus, the use of mycotoxin-absorbing additives seems to be an alternative to circumvent the problems arising from the contamination of mycotoxins in the feed of farm animals.

Main mycotoxin absorbers
Mycotoxin absorbing agents are compounds of high molecular weight that bind to the mycotoxins present in contaminated foods, limiting their bioavailability after ingestion. Mycotoxins can bind to absorbent agents through different types of interactions: hydrophobic bonds, hydrogen bonds, electrostatic attraction or repulsion and coordination bonds (DI GREGORIO et al., 2014).
It is important that the mycotoxin complex and absorbent agent (mycotoxin + absorbent) are stable throughout the digestive tract. Thus, its stability at variable pH and the physical-chemical properties of the toxins is one of the crucial parameters to be evaluated to avoid the desorption of the toxin in the gastric tract (AVANTAGGIATO et al., 2005;HUWIG et al., 2001;KABAK et al., 2006). In general, the absorbent agents most used in animal nutrition can be divided into two groups: inorganic and organic compounds.

Inorganic absorbers Aluminosilicates
Aluminosilicates are the most abundant group of rock-forming minerals and the basic structure of silicate clay minerals consists of the association of aluminum tetrahedral and octahedral silica sheets, both having hydroxyl and oxygen groups (DI GREGORIO et al., 2014).
Within this group, there are two main subclasses: phyllosilicates and tectosilicates. Philosilicates include bentonites, montmorillonites, smectites, kaolinites and illites. They can absorb substances on their surface or within their interlaminar space. On the other hand, silicate ceilings are formed by zeolites, which provide a large specific bonding surface, as well as size, shape and charge selectivity (HUWIG et al., 2001).  Hydrated calcium and sodium aluminum silicate (ACSH) ACSH has been shown to act as an enterosorbent that binds strongly and selectively to aflatoxins in the animals' gastrointestinal tract, decreasing their bioavailability and toxicity (HARPER et al., 2010;NEEFF et al., 2013;PHILLIPS et al., 2008).
Evidence suggests that aflatoxins can react at various locations in the ACSH particles, especially in the interim region, but also at the edges and basal surfaces (KOLOSOVA and STROKA, 2011). Furthermore, another form of AFB1 sorption by ACSH surfaces may involve the interaction or chelation of AFB1 with cations (especially Ca) or with various metals (DI GREGORIO et al., 2014).

Bentonites (montmorillonites)
In the case of bentonites, they are characterized by being phyllosilicate clays with layers of crystalline microstructure of variable composition. They are often called smectites because clay is the dominant mineral. In general, the degree of effectiveness of bentonite absorption depends on the amount of montmorillonite and interchangeable cations in its composition (KOLOSOVA and STROKA, 2011).
Montmorillonite is composed of layers of octahedral aluminum and tetrahedral silicon coordinated with oxygen atoms. The large surface area and high cation exchange capacity of the smectite group make them capable of adsorbing organic substances through the penetration of cations and polar molecules. Bentonites have shown great efficacy in the absorption of mycotoxins, specifically aflatoxins (KONG et al., 2014;MAGNOLI et al., 2011) and other mycotoxins (ZEN, OTA and FBs) in several studies (RAMOS et al., 1996a, b;AVANTAGGIATO et al., 2005;MIAZZO et al., 2005;WANG et al., 2012).

Zeolites
The zeolite tectosilicates consist of a set of tetrahedra of SiO4 and AlO4 joined in several regular arrangements through shared oxygen atoms to form a three-dimensional structure similar to a cage. The partial replacement of Si 4+ by Al 3+ results in an excess of negative charge that is compensated by alkaline and alkaline earth cations, such as sodium, calcium and potassium ions (DAKOVIC et al., 2003;HUWIG et al., 2001).
Studies have shown that natural zeoliteclinoptilolite can adsorb aflatoxins and other mycotoxins, such as fumonisins (DAKOVIC et al., 2010). However, modified zeolites are more effective than natural ones in relation to the absorption of fumonisins (BAGLIERI et al., 2013).

Organic adsorbents Yeast cell wall (YCW)
YCW consists mainly of proteins, lipids and polysaccharides, such as glucans and mannans, being the two main constituents of the last fraction. YCW exhibits a wide variety of mycotoxin absorption loci, as well as different binding mechanisms such as hydrogen bonds, ionic or hydrophobic interactions (RINGOT et al., 2007).
Studies suggest that PCL has a broader spectrum of mycotoxin sorption, such as ZEN, OTA and FBs (FRUHAUF et al., 2012;PFOHL-LESZKOWICZ, et al., 2015;SHETTY and JESPERSEN, 2006), including DON, being the βglucan fraction of YCW was directly correlated with the binding process (FAUCET-MARQUIS et al., 2014). The Saccharomyce cerevisiae mannans have also been shown to be effective in binding DON at different pH values (CAVRET et al., 2010).

Activated carbon (AC)
AC is an insoluble powder produced by the pyrolysis of several organic compounds, followed by its chemical or physical activation in order to develop a highly porous structure. In vitro data suggest potential affinity for several mycotoxins, however, the in vitro efficacy of AC in relation to some mycotoxins has not been confirmed in vivo (AVANTAGGIATO et al., 2005).
Generally, the adsorption properties of AC depend on the source materials, surface area and pore size distribution (KOLOSOVA and STROKA, 2011). However, AC is nonspecific, therefore, the essential nutrients for the development of animals such as vitamins and minerals (VEKIRU et al., 2007) are also adsorbed.

Mycotoxin absorbers used in dairy cattle
Systematically, in Table 2, there follows a compilation of experimental data on the effects of the use of mycotoxin absorbing agents in diets for dairy cattle.   Toxin (60 μg AFB1 / kg of food) Toxin + 2 g of YCAL / kg of food ↓ absorption of AFB1 and ↑ the elimination of AFB1 and AFM1 in the sheep's feces. There was no effect on the transfer of milk in AFM1.

Final considerations
The main mycotoxin absorbing agents can be of organic and inorganic origin. Inorganic are basically clay minerals (aluminosilicates) consisting mainly of silica and aluminum that can be divided into two subclasses: phyllosilicates and tectosilicates. In the group of organic absorbents there is activated carbon and derivatives of yeast cell wall, where the latter is the most used.
Absorbents based on aluminosilicate clays are more efficient in reducing the transfer of AFM1 to milk. Inorganic absorbents are found mainly in patented formulas such as NovasilPlus products, SolisMos and others. However, there are few studies with the use of organic absorbents in dairy cattle. Absorbent agents are mainly the basis of yeast cell wall. Apparently, the results have been shown to be effective in reducing the transfer of AFM1 in milk, despite the few studies carried out.
However, studies conducted with the union of organic and inorganic absorbing agents have shown promise. As is the case with the products Toxy-Nil, Unike Plus and Astra-Bem 20 that were efficient in reducing the concentration of AFM1 in milk.
In general, in some studies, organic, inorganic and mixed (organic + inorganic) absorbents. They have shown positive results in improving the antioxidant and inflammatory status in the liver.
Therefore, there are absorbents effective in reducing AFM1 in milk. It is enough to establish whether the formulation of mixtures of aluminosilicate clays with yeast cell wall veins are more efficient as absorbents than solely inorganic or organic. Additionally, additives composed of minerals and enzymes such as Mycofix deserve attention, since it promoted an increase in the digestibility of DM and NDF, it also reduced the activity of liver transaminases due to the high doses of mycotoxins.