Incidence of Aspergillus fumigatus and potentiality of gliotoxin production in animal feed and silage intended to dairy cattle feed

Abstract

Fungal invasion of raw materials and the consequent formation of mycotoxins are considered a potential risk factor for food quality. In previous studies carried out by our research group showed the presence of the main toxicogenic fungi (Aspergillus, Penicillium and Fusarium) and its associated mycotoxins (aflatoxin, zearalenone and fumonisins) in poultry, pig and rabbit feeds (Dalcero et al., 1997, 1998, 2002; Magnoli et al., 1998, 1999, 2002). This pollution reduces the nutritional value of foods and can affect animal health with serious economic losses in meat and milk products. Fungal species such as A. fumigatus have adapted to ensiling conditions and hence are the most frequent contaminants on ensilaged feed. In previous studies showed the A. fumigatus prevalence respect to the other toxigenic species present in silage and finished food destined to bovine consume subjected to intensive breeding (Cavaglieri et al., 2005). The gliotoxin is a potent inmunosupresor with genotoxic, citotoxic and apoptotic effects (Upperman et al., 2003). In Argentina there are no data about contamination with A. fumigatus and their toxins into silage and finished foods destined to consumption of dairy cattle feed. The aim of this study was to evaluate the incidence of A. fumigatus and its capacity to produce gliotoxin in food destined to dairy cattle feed. The isolation and identification of the contaminant mycobiota was carried out according to the keys proposed by Pitt and Hocking, (1997) and Klich (2002). For the determination of the capacity to produce gliotoxin by A. fumigatus strains isolated from silage, finished foods followed the methodology described by Dos Santos et al., (2002) and Boudra and Morgavi (2005). In general, silage samples contained counts that ranged from 1.75 x 105 to 9.35 x 107 CFU/g, showing a high degree of fungal contamination. The total count of finished food samples showed levels between ND at 2.85 x 107 CFU/g. The total fungal count in analyzed silage and finished food exceeded the levels proposed as a quality limit, which establish that it should not exceed 1 x 104 CFU/g for all ingredients and supplies destined to animal feed (GMP, 2005). The mycological survey showed the presence of 9 genera of filamentous fungi and yeasts. Six species of Aspergillus were identified. The isolation frequency of A. fumigatus was higher in the finished food (40%) than in corn silage (20%).Other species were isolated at frequencies lower than 8.6% from both assayed food samples. It should be noted that unlike the silage, A. parasiticus and A. terreus were not detected in the compound food. Twenty one and 44% of the A. fumigatus strains isolated from silage and finished food, respectively were gliotoxin producers. This mycotoxin is reported as the most toxic metabolite produced by A. fumigatus and, if found in feed, the amount produced by some strains is sufficient to pose an animal health risk.