Nutritive value and occurrence of mycotoxins in various forage silages sampled at different levels in dairy farm silos

Abstract

Context Consumers require nutritious and safe animal products, particularly milk and meat. Forage silage is a major source of feed for dairy cattle. However, inappropriate silo preparation and management can affect silage nutritional quality and may lead to fungal growth and mycotoxin production. Aims We aimed to determine the nutritional quality of different forage silages in dairy farms from four regions in northern Tunisia where silage production is a common practice, and to screen for the presence and concentration of 23 mycotoxins. Methods Six different forage silage types from 27 silos were sampled 100 days after ensiling. Samples were taken from upper, middle and lower sections of the silo. The pH and nutritional values of the silages were determined. The QuEChER method was used to extract mycotoxins, and they were identified and quantified through liquid or gas chromatography with tandem mass spectrometry. Key results Silage pH ranged from 4.4 to 7.8, and dry matter content of forage biomass from 15% to 47%. Values of pH of silage samples varied among the silo levels (P = 0.001), whereas nutrient contents of silage biomass were similar among the three levels. Only five Fusarium mycotoxins (deoxynivalenol, two enniatins, beauvercin, HT-2 toxin) were detected at different concentrations depending on the silo level. Oat, oat + triticale and oat + sulla silages were the most heavily contaminated with mycotoxins. Biomass in the upper silo level was the most co-contaminated. Conclusions High pH (>4) and dry matter content (>30%) indicate low quality silages; therefore, the silages were generally of low quality. Although the evaluated silages were contaminated with five of the targeted mycotoxins, their concentrations were so low that they do not represent a risk to the health of dairy cattle. Implications Forage biomass should have a dry matter content of 20–30% on the day of silo filling. It is important to sample silage from the upper, middle and lower sections of the silo to screen for mycotoxins. In future studies, the transfer of detected mycotoxins to milk should be determined.