Abstract
Ruminants are generally considered to be less susceptible to the effects of mycotoxins than monogastric animals as the rumen microbiota are capable of detoxifying some of these toxins. Despite this potential degradation, mycotoxin-associated subclinical health problems are seen in dairy cows. In this research, the disappearance of several mycotoxins was determined in an in vitro rumen model and the effect of realistic concentrations of those mycotoxins on fermentation was assessed by volatile fatty acid production. In addition, two hypotheses were tested: (1) a lower rumen pH leads to a decreased degradation of mycotoxins and (2) rumen fluid of lactating cows degrade mycotoxins better than rumen fluid of non-lactating cows. Maize silage was spiked with a mixture of deoxynivalenol (DON), nivalenol (NIV), enniatin B (ENN B), mycophenolic acid (MPA), roquefortine C (ROQ-C) and zearalenone (ZEN). Fresh rumen fluid of two lactating cows (L) and two non-lactating cows (N) was added to a buffer of normal pH (6.8) and low pH (5.8), leading to four combinations (L6.8, L5.8, N6.8, N5.8), which were added to the spiked maize substrate. In this study, mycotoxins had no effect on volatile fatty acid production. However, not all mycotoxins fully disappeared during incubation. ENN B and ROQ-C disappeared only partially, whereas MPA showed almost no disappearance. The disappearance of DON, NIV, and ENN B was hampered when pH was low, especially when the inoculum of non-lactating cows was used. For ZEN, a limited transformation of ZEN to α-ZEL and β-ZEL was observed, but only at pH 6.8. In conclusion, based on the type of mycotoxin and the ruminal conditions, mycotoxins can stay intact in the rumen.
Highlights
Mycotoxins are secondary fungal metabolites that are harmful to animals and humans [1].Monogastric animals are considered to be more susceptible to the toxic effects of mycotoxins than ruminants as the rumen microbiota are capable to degrade some of those toxic molecules to less toxic metabolites [2,3,4]
One possible reason could be the higher proportion of maize silage in the ration of higher yielders [2], which is more vulnerable to contamination with multiple mycotoxins than e.g., grassland products [12,13,14]
In Belgium and the Netherlands, maize silage is given to non-lactating cows instead of grassland products as maize silage is low in calcium and potassium which diminish the incidence of milk fever at the beginning of lactation [15,16]
Summary
Mycotoxins are secondary fungal metabolites that are harmful to animals and humans [1]. The highly fermentable ration of lactating cows in combination with a higher feed intake leads to a higher rumen passage rate [17] and a higher incidence of metabolic disorders such as subacute ruminal acidosis (SARA), associated with a microbial shift in the rumen [18]. These factors can lead to an impaired detoxification of mycotoxins by the rumen microbiota so that mycotoxins can reach the postruminal parts of the gastrointestinal tract, may impair gut health and the gut barrier function and/or can be absorbed, entering systemic circulation and exerting their toxic effects on the animal. DOM-1 as a metabolite of DON and α-ZEL, β-ZEL, zearalanone (ZAN), α-zearalanol (α-ZAL) and β-zearalanol (β-ZAL) as metabolites of ZEN were monitored as these can be formed in the rumen [3,27,28,29,32,33] and analytical standards are commercially available
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