Adverse Effects, Transformation and Channeling of Aflatoxins Into Food Raw Materials in Livestock

Abstract

Aflatoxins are wide-spread harmful carcinogenic secondary metabolites produced by Aspergillus species, which cause serious feed and food contaminations and affect farm animals deleteriously with acute or chronic manifestations of mycotoxicoses. On farm, both pre-harvest and post-harvest strategies are applied to minimize the risk of aflatoxin contaminations in feeds. The great economic losses attributable to mycotoxin contaminations have initiated a plethora of research projects to develop new, effective technologies to prevent the highly toxic effects of these secondary metabolites on domestic animals and also to block the carry-over of these mycotoxins to humans through the food chain. Among other areas, this review summarizes the latest findings on the effects of silage production technologies and silage microbiota on aflatoxins, and it also discusses the current applications of probiotic organisms and microbial products in feeding technologies. After ingesting contaminated foodstuffs, aflatoxins are metabolized and biotransformed differently in various animals depending on their inherent and acquired physiological properties. These mycotoxins may cause primary aflatoxicoses with versatile, species-specific adverse effects, which are also dependent on the susceptibility of individual animals within a species, and will be a function of the dose and duration of aflatoxin exposures. The transfer of these undesired compounds from contaminated feed into food of animal origin and the aflatoxin residues present in foods become an additional risk to human health, leading to secondary aflatoxicoses. Considering the biological transformation of aflatoxins in livestock, this review summarizes (i) the metabolism of aflatoxins in different animal species, (ii) the deleterious effects of the mycotoxins and their derivatives on the animals, and (iii) the major risks to animal health in terms of the symptoms and consequences of acute or chronic aflatoxicoses, animal welfare and productivity. Furthermore, we traced the transformation and channeling of Aspergillus-derived mycotoxins into food raw materials, particularly in the case of aflatoxin contaminated milk, which represents the major route of human exposure among animal-derived foods. The early and reliable detection of aflatoxins in feed, forage and primary commodities is an increasingly important issue and, therefore, the newly developed, easy-to-use qualitative and quantitative aflatoxin analytical methods are also summarized in the review.

Keywords: Aspergillus; aflatoxin; livestock; mitigation strategies; storage conditions.

FIGURE 1

Chemical structures of aflatoxins most frequently found in animal husbandry.

FIGURE 2

Factors influencing the aflatoxin content of grains during storage.

FIGURE 3

Microbial products for mycotoxin mitigation in animal husbandry and their applications. Red arrows represent potential carry-over of mycotoxins or toxigenic Aspergilli. Blue arrows represent applications of microbes and microbe-derived products. (1) Fermentation and animal feed supplement industries; (2) crop production; (3) preparation and storage of silage and other feedstuffs; (4) livestock; (5) product; (i) pre-harvest biocontrol; (ii) antagonism in silage and feed; (iii) host gut microbiota and immune modulation, probiotic effect; (iv) enterosorption; (v) bioadsorption from product (milk). [Stock image credits: Freepik, macrovector, and vectorpocket].

FIGURE 4

The major metabolic pathways of AFB₁. The aflatoxin derivatives presented here include aflatoxin B₁ (AFB₁), aflatoxin M₁ (AFM₁), aflatoxin Q₁ (AFQ₁), aflatoxin P₁ (AFP₁), AFB₁-8,9-epoxide (AFBO), AFB₁-8,9-dihydrodiol (AFB₁-dhd) and aflatoxicol (AFL). Some enzymes taking part in the biotransformation and detoxification of aflatoxins are also indicated including cytochrome P450 (CYP450), glutathione-S-transferase (GST), microsomal epoxide hydrolase (mEH), and aflatoxin-aldehyde reductase (AFAR).