Aflatoxins are toxic metabolites produced by fungi that can affect ruminant animals and their production.

Mycotoxins are a group of toxic metabolites produced by different genera of fungi that can contaminate forage and animal feed. These molecules can alter the physicochemical and nutritional properties of feed and forages fed to ruminants. For this reason, they are considered a group of pathogenic molecules of great importance on farms and during production processes in dairy and meat ruminants.

You might also be interested in Mycotoxins in forages for cows: What are their effects?

What are aflatoxins?

Aflatoxins are part of the general group of mycotoxins that affect animals. These aflatoxins are toxic secondary metabolites produced by fungi of the species Aspergillus flavus, Aspergillus parasiticus, and Penicillium puberulum. Aflatoxin production increases during the stationary phase of growth of these fungi, i.e., when their multiplication has stabilized. In addition, these fungi grow in large quantities when environmental conditions are favorable. For example, when feed or forage is stored in conditions of excessive humidity or for a long period.

The grains used in animal feed that are most frequently contaminated with aflatoxins are sorghum, cotton, corn, and wheat.  Aflatoxin-producing fungi can grow on the crops as well as during the transport and storage stages of these products. Because aflatoxins are thermostable, they remain potentially harmful even in foods that have already been processed.

Importance and classification of aflatoxins in ruminants

Aflatoxins are currently an important group of study because of their effects on ruminants and humans. Their effects have also been studied for some years in other animals such as dogs and birds, where they have a great impact.

You might also be interested in Mycotoxins in pets

Aflatoxins ingested and eliminated by ruminants are of interest for human medicine and veterinary medicine since mutagenic, carcinogenic, teratogenic, and immunosuppressive effects of these compounds have been reported.

Among all the mycotoxins described, more than 250 are recognized. Within the Aflatoxin group, classifications have also been made. Thus, they have been grouped according to the fluorescence they emit in the thin layer chromatography test when irradiated with ultraviolet light.

• B (Blue, they emit blue fluorescence): B1 and B2
• G (Green, emit green fluorescence): G1 and G2
• M (Milk, for excretion in milk): M1 and M2.

AFB1 is the most common of all and is of great importance in ruminants intended for milk production. Once AFB1 is in ruminants, it is transformed in the liver by cytochrome P450 enzymes located in the liver. Thus, it is metabolized and becomes AFM1, which is excreted in milk and urine.

Clinical effects of aflatoxins in ruminants

The effects of aflatoxins in ruminants can be classified depending on the dose and time of exposure to aflatoxins, since, according to this, different signs can be observed.

Acute effects

Acute effects of aflatoxin exposure in ruminants include a wide range of clinical signs. Among the most notorious are depression, incoordination (ataxia), dyspnea, anemia, epistaxis, and melena. In addition, these signs are exacerbated when there are stressful conditions for the animals such as mobilization, recent calving, extreme weather conditions, among others.

In calves, nervous signs such as convulsions, blindness, walking in circles, ataxia, spasms, and tremors have been observed. In more severe cases, pregnant cows exposed to high doses of aflatoxins may present abortions.

Doses of 4 mg/kg in cattle are reported to cause liver failure and subsequent death.

Subacute effects

Subacute effects have another wide range of clinical signs observed during examination and abnormalities in laboratory tests. The most prominent are related to changes in mucosal and skin coloration, due to jaundice and bruising. Also, ascites and rectal prolapse can be observed in animals, produced by inflammatory processes of the intestine (hemorrhagic enteritis). Among the laboratory findings, hypoprothrombinemia stands out, which predisposes to the presentation of subcutaneous hemorrhages.

Finally, photosensitization has been observed in ruminants, which favors lesions around the eyes, nostrils, and tongue.

Chronic effects

This is the most common form presented in animals, but at the same time, it is difficult to detect. Animals may present anorexia, low milk production, bristly hair, anemia, jaundice, ascites, and depression. At necropsy, animals have been diagnosed with neoplastic liver lesions, such as benign hepatomas, bile duct carcinoma, and hepatocellular carcinoma.

On the other hand, the role of aflatoxins eliminated in milk in cows that chronically consume them should be highlighted. AFB1, once consumed, is metabolized by ruminants at the hepatic level. Aflatoxin M, which has been shown to have adverse effects, is then eliminated in milk. AFM1 can cause immunosuppression in both calves and humans consuming the milk. The effect of aflatoxins on RNA and DNA synthesis has been studied, which alters many cellular processes in exposed animals and humans.

For this reason, the regulatory bodies of each country must establish maximum permissible limits for these aflatoxins in milk. The International Agency for Research on Cancer (IARC) classifies AFM1 in Group 1 of carcinogenic agents for humans and animals.

What are mycotoxin binders?

Mycotoxins present in animal food products are a concern for the livestock industry. Therefore, the animal science and veterinary fields have focused their efforts on the development of mycotoxin binders.

These binders aim to reduce excretion elimination in products such as goat milk. Silicoglycidol has demonstrated the ability to significantly reduce milk excretion of aflatoxin M1 in goats, without causing significant effects on production.

Mycotoxin binders prevent Aflatoxin B1 from being absorbed by ruminants in the intestine and thus from being metabolized in the liver. This prevents its metabolism to Aflatoxin M1 and its elimination in milk. The mycotoxin binder Silicoglycidol has a high adsorption efficiency for these mycotoxins, which prevents their elimination in milk.

Use of mycotoxin binders in animals

The effect of Silicoglycidol was evaluated in 18 goats randomly distributed in three groups: negative control group, positive control group, and a group treated with Silicoglycidol. Table 1 summarizes the distribution and treatments of each group.

Table 1. Group of goats exposed to Aflatoxin and treated with Silicoglycidol.

The results indicated that goats exposed to AFB1 and treated with Silicoglycidol eliminated 26.27% less AFM1 compared to exposed and untreated goats. This is a remarkable reduction in the elimination of Aflatoxin M1 in milk, which was evaluated during the 28 days of the study. The study was conducted at the University of Cordoba (Spain). On the other hand, Silicoglycidol had no change in milk production, milk composition, or blood parameters.

You may also be interested in: Capacity of Silicogycidol molecule to reduce the excretion of aflatoxin M1 in goat milk

Conclusions

Aflatoxins are an important group of toxic metabolites produced by fungi that affect ruminants. They are produced by fungi mainly Aspergillus and are classified B, G, and M. The most important is aflatoxin B1 which is transformed to Aflatoxin M1 in the liver of ruminants and eliminated in milk.

The effects of aflatoxins can be classified by their dose and time of exposure into acute, subacute, and chronic. Accordingly, the variety of signs observed in ruminants is wide and makes diagnosis difficult.

Recent studies are focused on the development of molecules with mycotoxin binding capacity to prevent mycotoxin absorption and elimination. Therefore, studies have been carried out in goats to evaluate the efficacy of a mycotoxin binder called Silicoglycidol. This molecule has shown excellent results in goats and birds exposed to food contaminated with aflatoxins.

Finally, the effect of aflatoxins in ruminants is also considerable in public health, due to their effect on animal and human health.