Background
Mycotoxins are naturally occurring toxic secondary metabolites of fungi, primarily produced by five genera, including Aspergillus, Alternaria, Claviceps, Fusarium, and Penicillium [1,2,3,4]. As of the latest research, over 500 mycotoxins have been identified, posing a significant threat to human and animal health [5]. Among the most prevalent mycotoxins found in agricultural commodities are aflatoxin B1 (AFB1), deoxynivalenol (DON), and zearalenone (ZEN) [6,7,8]. AFB1, produced mainly by Aspergillus, is the most toxic mycotoxin, exhibiting hepatotoxic, carcinogenic, mutagenic, and teratogenic properties in various animal species [9,10,11,12,13,14]. Both DON and ZEN are primarily produced by Fusarium [15,16,17]. DON, a type B trichothecene, can induce anorexia, vomiting, and intestinal and immune system disorders in multiple species by inhibiting DNA, RNA, and protein synthesis [18,19,20,21,22]. ZEN is an estrogenic mycotoxin as it competes with 17β-estradiol for estrogen receptor binding, and can induce reproductive and fertility disorders [23,24,25,26,27].
Since mycotoxins in feed can negatively affect animal health, but can also threaten human health when converted into animal products, many countries have established safety standards for these toxins in feed and feed ingredients. For example, the European Commission set the maximum levels of AFB1, DON, and ZEN at 5–20, 900, and 250 μg/kg, respectively, in feed ingredients and complete feed [28, 29]. In 2017, General Administration of Quality Supervision, Inspection and Quarantine of the People’s Republic of China released the latest version of safety standards (GB 13078–2017) for AFB1, DON, and ZEN; which are 10–20, 1,000–5,000 and 100–250 μg/kg, respectively, for feedstuffs and complete feeds [7, 30].
However, current global warming and climate change are making corn, wheat and other crops more susceptible to fungal colonization, and mycotoxin contamination [31,32,33]. Thus, it will be important to monitor mycotoxin levels in livestock feed ingredients well into the future to maintain animal health and ensure the safety of human food products. There are several climatic regions across China, especially the warm or humid conditions of the Yangtze, Yellow River basins and northeast region and their numerous rainfall events, are favorable for mold growth and mycotoxin production in crops, which is increasing crop susceptibility to fungal infection [34,35,36]. Therefore, monitoring mycotoxin concentrations in the feedstuffs and complete feeds from these and other regions across China is essential to prevent farm animal exposure to mycotoxins and to ensure feed and food safety. Thus, the current study was conducted to investigate and renew the individual and combined contamination of AFB1, DON, and ZEN in more than 23,000 feedstuffs and complete feeds collected from different regions of China during the past 4 years.
Methods
Sample collection and preparation
A total of 23,003 feed samples were collected from 2021 to 2024 from either companies or livestock farms in different regions of China. There were 17,489 feedstuff samples including 7,018 corn, 1,558 dried distillers grains with solubles (DDGS), 1,608 corn gluten meal, 968 corn germ meal, 42 corn bran, 1,734 wheat, 845 wheat flour, 340 wheat bran, 169 wheat middlings, 44 wheat germ, 2,558 peanut meal, 58 cottonseed meal, 49 soybean meal, 82 brown rice, 24 rice bran, 20 rice bran meal, 36 sorghum, 182 distiller's grains, 80 corn sugar residue, 33 sugar residue, 27 nucleotide residue, 14 cottonseed protein, along with 5,514 complete feed samples including 658 pig feed, 4,814 poultry feed and 42 ruminant feed. These feed samples were primarily collected from the provinces of Anhui, Beijing, Chongqing, Fujian, Guangdong, Guangxi, Gansu, Henan, Hebei, Hunan, Hubei, Heilongjiang, Inner Mongolia, Jiangsu, Jiangxi, Jilin, Liaoning, Ningxia, Shandong, Sichuan, Shanxi, and Zhejiang by the feed companies. Since few feed samples with insufficient quantity, 11,826, 14,812, and 8,794 samples were analyzed for AFB1, DON, and ZEN, respectively. The feed samples were stored in sealing bags at −20 °C before analysis.
Extraction and quantified of AFB1, DON and ZEN
The extraction and quantified of AFB1, DON, and ZEN from the feed samples collected between 2021 and 2024 were performed as previously described [7, 35,36,37,38,39]. Briefly, 5 g of the mashed feed samples were mixed with a 25-mL solution of ethanol:water (50:50, v/v), blended using a commercial blender at high speed for 3 min, centrifuged at 4,200 r/min for 10 min, filtrated and collected the filtrate. The quantification of AFB1, DON, and ZEN were performed with commercially available test kits purchased from TRUTHERS Biotechnology Co., Ltd. (Tianjin, China) according to their operating instructions. Specially, the quantum dot fluorescence immunochromatographic assay were used to detection. The mycotoxins in the sample bind to the specific antibodies labeled with quantum dots, inhibiting the binding between the antibodies and the mycotoxin-BSA conjugate on the detection line (T line), resulting in changes in the fluorescence value of the T line. The content of mycotoxins is calculated by the high and low fluorescence value signals of the T line. The limit of detection (LOD) for AFB1, DON and ZEN set at 1.0 μg/kg, 100 μg/kg and 10 μg/kg, respectively.
Statistical analysis
All the data were analyzed by Microsoft Excel 2019 (Microsoft Corporation, Redmond, USA) and expressed as means, median, maximum, or percentages.
Results
Contamination of AFB1 in feeds
A total of 11,826 feed samples, including 8,442 feedstuffs and 3,384 complete feeds, were collected between 2021 to 2024 for analysis of AFB1 (Table 1). AFB1 was detected in 20.0%–100% of feedstuff and complete feeds, with the average levels ranging from 1.2 to 728.7 μg/kg. The highest median concentration of AFB1 was 770 μg/kg in wheat bran from the 2024 harvest, followed by 390 μg/kg in complete pig feed and 185.2 μg/kg in corn sugar residue from the 2024 harvest. The maximum levels of AFB1 were 4,490 μg/kg in DDGS harvested in 2024, followed by 2,380 μg/kg in wheat and 1,720 μg/kg in corn harvested in 2024. Among all the analyzed feedstuff samples, 819 raw feed ingredient samples (accounting for 9.7%) were contaminated with AFB1 at concentrations exceeding China’s safety standard. Notably, 74 samples of complete pig feed and 43 samples of complete poultry feed, which account for 2.2% and 1.3% of all the analyzed complete feed samples, were contaminated with AFB1 at levels exceeding the Chinese safety standard concentrations.
Contamination of DON in feeds
In total, 14,812 feed samples, including 11,527 feedstuff and 3,285 complete feeds, were collected between 2021 to 2024 for analysis of DON (Table 2). DON was detected in 33.3%–100% of feedstuff and complete feeds, with the average levels ranging from 106 to 8,634.8 μg/kg. The highest median concentration of DON was 9,762 μg/kg in corn bran from the 2021 harvest, followed by 7,177 μg/kg and 4,840 μg/kg in corn germ meal from the 2023 and 2022 harvests. The maximum levels of DON were 84,000 μg/kg in wheat flour harvested in 2023, followed by 53,860 μg/kg in corn harvested in 2023 and 34,800 μg/kg in corn germ meal harvested in 2022. Among all the analyzed feedstuff samples, 316 raw feed ingredient samples (accounting for 2.7%) were contaminated with DON at concentrations over 5,000 μg/kg. Notably, the content of DON in corn germ meal and DDGS harvested between 2021 to 2024 exceeded the standard by 9.1%–69.5% and 2.6%–21.2%. Additionally, 24 samples of complete pig feed, 7 samples of complete poultry feed, and 4 samples of complete ruminant feed were contaminated with DON at levels exceeding the Chinese safety standard concentrations, which accounted for 4.6%, 0.3% and 13.3% of complete feeds samples of the same category analyzed, respectively.
Contamination of ZEN in feeds
A total of 8,794 feed samples, including 6,153 feedstuffs and 2,641 complete feeds, were collected between 2021 and 2024 for analysis of ZEN (Table 3). ZEN was detected in 85.0%–100% of feedstuff and complete feeds, with the average levels ranging from 18.1 to 3,341.6 μg/kg. The highest median concentration of ZEN was 2,566.4 μg/kg in corn gluten meal from the 2024 harvest, followed by 1,824.7 μg/kg in corn bran from the 2021 harvest and 1,424.4 μg/kg in distiller’s grains from the 2024 harvest. The maximum levels of ZEN were 30,154 μg/kg in corn gluten meal harvested in 2022, followed by 10,958 μg/kg in corn harvested in 2022 and 10,345.1 μg/kg in corn gluten meal harvested in 2024. A total of 965 raw feed ingredient samples, which account for 15.7% of all the analyzed feedstuff samples, were contaminated with ZEN at concentrations over the Chinese safety standard concentrations. Additionally, 149 samples of complete pig feed and 82 samples of complete poultry feed, which account for 5.6% and 3.1% of all the analyzed complete feed samples, were contaminated with ZEN at levels exceeding the Chinese safety standard concentrations.
Co-contamination of AFB1, DON and ZEN in feeds
The co-contamination of AFB1, DON, and ZEN in feed samples between 2021–2024 was presented in Table 4. More than 70.0% of analyzed feed ingredient samples had a combined contamination rate of 60.0%–100% for AFB1 + DON, AFB1 + ZEN, DON + ZEN, and AFB1 + DON + ZEN. Notably, except for the complete pig feed collected from 2022, the co-contamination ranges of AFB1 + DON, AFB1 + ZEN, DON + ZEN, along with AFB1 + DON + ZEN in most complete feeds were 61.5%–100%, 76.7%–100%, 66.7%–100%, and 58.3%–100%, respectively.
Discussion
Mycotoxins have been reported to reduce animal performance, threaten human and animal health, as well as bring huge economic loss to the feed and food industry [4]. Thus, it will be important to monitor mycotoxin levels in livestock feed ingredients well into the future to maintain animal health and ensure the safety of human food products. Considering the widespread contamination, the present study was carried out to investigate the individual and combined contamination of the most prevalent and toxic mycotoxins, AFB1, DON, and ZEN in feedstuffs and complete feeds harvested between 2021 and 2024. In general, the analyzed mycotoxins displayed a considerably high occurrence in the analyzed feed samples harvested between 2021 and 2024, ranging from 20.0% to 100%, 33.3% to 100%, and 85.0% to 100% for AFB1, DON, and ZEN, respectively. Additionally, the LOD of the AFB1, DON, and ZEN are relatively high, which might underestimation of the actual exposure risk of these mycotoxins. These results indicated that the mycotoxin contamination of raw materials and complete feeds in China is quite serious.
The average concentration of AFB1 (1.2–728.7 μg/kg) determined in the present study was higher than previously reported concentrations (1.2–27.4 μg/kg) from samples harvested between 2016–2020 [7, 37]. Notably, 9.7% of all the analyzed raw feedstuff samples, especially corn, corn gluten meal, corn germ meal, and peanut meal, with AFB1 exceeded the Chinese safety standard concentration, which is much higher than the previously reported 0.9% of analyzed feedstuff samples with AFB1 exceeded the Chinese safety standard concentration [7, 30, 37]. Furthermore, there were 31.6% and 1.4% of the analyzed complete pig feed and poultry feed respectively contained AFB1, especially in complete pig feeds harvested in 2024, whereas the excess rate was as high as 85.5%. These results are much higher than the previous reports that 1.5% and 1.2% of all the analyzed final products for pig and poultry contained AFB1 over the limitation of Chinese safety standards [7]. The most toxic AFB1 is a frequent contaminant of various commodities, primarily cereals, nuts, and spices, and represents a highly toxic mycotoxin [9, 40, 41], therefore, it is necessary to persist in supervising the levels of AFB1 in the raw feed ingredients and its final products in the future. Additionally, since the safety limitation of AFB1 in European Commission (5–20 μg/kg) is lower than China (10–20 μg/kg), which might restrict the export of these Chinese feedstuffs [28,29,30].
The average levels of DON in feeds ranged from 106 to 8,634.8 μg/kg in this study, which is relatively higher than the previously reported range of 364.5–4,381.5 μg/kg in the feeds collected in China between 2013 and 2020 [7, 34, 37]. The maximum value of DON in feedstuffs in the current study is 84,000 μg/kg, which is at least 39 times higher than the values in all the reported areas [42]. There are 2.7% of the analyzed raw feed ingredients with DON exceeded China’s safety standard, especially as much as corn (9.1%–69.5%) and DDGS (2.6%–21.2%), which are much higher than the previously reported in 2013–2020 [7, 37]. Although only 4.6% of the complete pig feed samples exceeded the Chinese safety standard concentration, 0.3% of the complete poultry feed samples and 13.3% of the complete ruminant feed samples contaminated DON over the limitation of Chinese safety standard. These divergences could be attributed to the fact that the analyzed feed samples were randomly collected from different regions, and weather varies in these areas during the harvest period [7, 34, 35, 37, 43]. Taken together, these findings remind us that we need to be cognizant of the potential for contamination of feed ingredients, especially corn, DDGS, corn gluten meal, and corn germ meal, which were relatively severely contaminated by DON. In addition, since the safety limitation of DON in European Commission (900 μg/kg) is lower than China (1,000–5,000 μg/kg), which might restrict the export of these Chinese feedstuffs [28,29,30].
The occurrence of ZEN (85.0%–100%) in the analyzed feeds in this study was lower than previously study (96.9%–100%) from harvests in 2018–2020, but it was higher than feed samples (50.0%–100%) collected from 2013 to 2017 [7, 34, 35]. Meanwhile, in the current study, the average concentration of ZEN (18.1–3341.6 μg/kg) was relatively higher than previously reported results (48.1–326.8 μg/kg and 0–729.2 μg/kg) from harvests between 2013 and 2020 [7, 34, 35]. These differences might be due to the number of feed samples, different sampling areas, and different weather conditions during harvest. Notably, 15.7% of analyzed feedstuff samples, mainly including corn and its by-products, as well as 8.7% of analyzed complete feed samples (complete pig feed and complete poultry feed), were contaminated with ZEN at concentrations that exceeded the Chinese safety standards. These findings were much higher than previously reported, where 0.5% and 1.9% of all the analyzed feedstuffs and complete feed samples, respectively, were shown to be contaminated with ZEN exceeding the regulatory limits [7].
The co-occurrence and interaction between two or more mycotoxins were regularly found, and results suggested that co-contaminates can exhibit stronger toxic effects on animals when compared to each mycotoxin [44,45,46,47]. It is worth noting that the co-contamination of AFB1, DON, and ZEN, can exert additive and synergistic toxic effects on animal health and production [48]. In the present study, the co-contamination of mycotoxins in all analyzed feeds harvested in 2021–2024 was quietly universal, with more than 20% of feedstuff samples and 15.2% of complete feeds containing 2 or more mycotoxins. Notably, DDGS, corn gluten meal, corm germ meal, distiller’s grains, complete pig feed, and complete poultry feed were more than 70% co-contaminated with AFB1, DON, and ZEN. These results were similar to previous studies that mycotoxin contamination is a widespread issue in the livestock and poultry industry [48,49,50,51,52]. The present feed safety regulations do not consider the potential toxicity of co-contamination of mycotoxins and their combined toxicity on animal health and production may be underestimated. Therefore, the combined toxicity of these mycotoxins warrants further study, which might further reduce thresholds of the regulatory limits for mycotoxins. Although how to set the regulatory limits for mycotoxins under their co-contamination is very complicate, it still might be very important to consider it when new regulatory frameworks for mycotoxins are plan in the future.
Conclusion
In summary, the mycotoxin survey of 23,003 samples collected from different areas of China from 2021 to 2024 indicated that mycotoxins are ubiquitously present in feeds. Generally, 9.7%, 2.7%, and 15.7% of analyzed raw feed ingredients collected between 2021 and 2024 were contaminated with AFB1, DON, and ZEN by exceeding the Chinese safety standards, respectively. Meanwhile, 3.4%, 1.1% and 8.7% of analyzed complete feeds exceeded China’s safety standards for AFB1, DON and ZEN, respectively. Moreover, it is worth noting that co-occurrence ≥ 2 mycotoxins were quite common in all analyzed feed samples. The co-contamination rates of the three mycotoxins (AFB1, DON and ZEN) in more than 70% of analyzed feed samples were 60.0%–100%. Taken together, these results remind us that, 1) the serious situation of mycotoxin contamination in feed requires strict supervision, 2) it is desperately necessary to constant monitoring and continue research effort on the prevention and mitigation of co-contamination of mycotoxin due to a considerable number of feed samples containing more than one mycotoxin, and 3) suitable and targeted strategies controlling mycotoxin occurrence and toxicity need to be researched and applied.