Microbiological Quality of Maize Silage in Relation to Agricultural Practices: A Four-Year Study

Silage is a fundamental component of cattle feed, and its microbiological quality is critical for animal health and human safety. Improper ensiling conditions, such as oxygen exposure or inadequate acidification, can promote the growth of pathogens like Listeria monocytogenes, Clostridium botulinum, and Bacillus cereus. This study aimed to evaluate the microbial status of maize silages and identify pre-ensiling factors influencing its hygienic safety. Over a four-year period, 406 silage samples were collected from cattle farms across Poland. The research evaluated general hygiene indicators and screened for specific pathogens using standard culture methods, polymerase chain reaction toxotyping, and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. The impact of agricultural practices, including soil quality, organic fertilization, and microbial inoculation, was also analyzed. The analysis revealed that 32.1% of silages fell outside the reference pH range, indicating potential aerobic instability. While Salmonella and Campylobacter were not detected, Clostridium spp. were highly prevalent (81.0%), and C. perfringens was confirmed in 24.9% of samples. Listeria species occurred in 2.9% of silages, with L. innocua being the most frequent isolate. Statistical analysis showed that organic fertilization was significantly linked to specific C. perfringens toxotypes, though it did not increase the overall microbial burden. Conversely, microbial inoculation generally reduced the counts of several undesirable bacteria, although these differences were not statistically significant across all parameters. High pH values and significant contamination with Clostridium, B. cereus, and fungi remain critical challenges for silage safety. The results underscore the necessity for improved agricultural practices—specifically the minimization of soil and manure contamination during harvest—and the broader adoption of microbial inoculation to ensure the microbiological stability of fermented forage.