## 3 Results and Discussion
### Identification and Quantification of Aflatoxin M1  
All 23 commercial CM samples analyzed contained detectable AFM1 levels, with an average concentration of 1.64 \(\upmu\)g/L. Notably, 73.91% of the CM exceeded the maximum permissible limits established by Mexican regulations (0.5 \(\upmu\)g/L) and European regulations (0.05 \(\upmu\)g/L) [28,45]. Sample B exhibited the highest concentration at 7.62 \(\upmu\)g/L, significantly surpassing the concentrations found in the other CM samples. This particular CM originated from a nationally distributed milk brand processed in Durango, Mexico, a region characterized by a semi-arid climate, with low rainfall (less than 500 mm) and extreme temperatures [52]. In conjunction with suboptimal agricultural and storage practices, these climatic conditions may facilitate the proliferation of aflatoxin-producing fungi such as Aspergillus spp. in crops utilized as dairy cattle feed, including maize and sorghum [53,54]. Furthermore, the application of silage in dairy operations presents additional risks if storage conditions are not meticulously controlled, thereby heightening the likelihood of aflatoxin formation [55]. Inadequate storage infrastructure in regions supplying feed ingredients may also contribute to heightened AFM1 levels [56], as evidenced by the findings in sample B.  
Mycotoxin contamination may occur at various stages of animal feed production, encompassing pre-harvest, drying, and storage processes [57]. Insufficient agricultural practices, inadequate management, and adverse environmental conditions contribute to the formation of mycotoxins, which can disseminate throughout fungal colonies, contaminating spores, hyphae, and the surrounding substrate [58,59]. Consuming these contaminated foods remains the primary route of exposure to mycotoxins in dairy cattle, particularly in semi-arid regions [59,60,61].  
The remaining 26.8% of CM, which included A, I, J, L, M, and O, remained compliant with legal limits, demonstrating an average AFM1 concentration of 0.18 \(\upmu\)g/L (Figure 2). The present study's findings align with prior research conducted across various regions. [PERSON] et al. (2021) identified fluctuations in AFM1 levels in raw milk obtained from distinct locations within Greece, indicating that geographical factors and management practices may significantly affect contamination levels [18]. Similarly, [PERSON] and [PERSON] (2023) substantiated the efficacy of analytical methods for detecting AFM1 in dairy products in Slovakia, emphasizing the necessity of reliable techniques for monitoring this mycotoxin [19]. Furthermore, the research conducted by [PERSON] et al. (2023) in Hungary highlighted the urgent need for continuous monitoring to assess exposure to AFM1 among the general population [20]. In Mexico, there are limited studies evaluating the incidence of AFM1 in milk intended for human consumption. The most recent report documented a concentration of 0.03 \(\upmu\)g/L in CM, which remains well within national legal thresholds [22,28]. The presence of AFM1 in milk primarily reflects the contamination of dairy cattle feed with AFB1, which is commonly found in cereals, oilseeds, flours, and by-products utilized in feed formulation. Seasonal factors may also impact the concentration of AFM1 in milk [62,63]. Elevated levels have been reported during the autumn-winter period compared to the spring-summer period [64]. This trend correlates with a decreased availability of fresh forage and an increased reliance on dry stored feed, which is more susceptible to fungal contamination under moisture conditions and inadequate storage [64]. Given that the CM samples in this study were collected during the winter, the heightened AFM1 concentrations observed in 80% of the CM may be partially attributed to this seasonal vulnerability.