Detoxification by rumen microbes
It has long been accepted that rumen microbes can detoxify mycotoxins. However, in certain studies involving dairy cows, scientists found that the capacity for mycotoxin detoxification in the dairy cow’s rumen is lower than believed.
Heinz-Kiessling et al. (1984) showed that the efficacy of detoxification is not the same for all mycotoxins. Diacetoxyscirpenol (DAS), trichothecene mycotoxin (T-2), ochratoxin and ZEN are partially converted, whereas in this study no degradation was noticed for DON and aflatoxin B1. Other studies measured a partial degradation of DON into de-epoxy deoxynivalenol (DOM-1), which is a less toxic form (Prelusky et al., 1987 and Coté et al., 1986). Heinz-Kiessling et al. (1984) also showed that the decrease of ZEN was the result of a reduction to zearalenol, and mainly (90%) to α-zearalenol, which is 3 to 4 times more oestrogenic than the parent compound. Fumonisins are not altered in the rumen (Pfohl et al., 1999). Heinz-Kiessling proved that protozoa are invariably more active than bacteria in the detoxification process of certain trichothecens, but they are also more sensitive to these trichothecens than bacteria (Westlake et al., 1987).
Ruminal patterns studied
A German study (Keese et al., 2008) investigated the ruminal patterns influenced by the proportion of concentrate in the feed ration, with and without Fusarium toxin contamination of the diet. Feeding a TMR with 50% concentrate and a mean DON concentration of 5.3mg/kg dry matter (DM) to 13 German Holstein cows in early lactation (myco group) resulted in alterations in the ruminal fermentation patterns. Alteration of the volatile fatty acids balance was followed by a drop in pH values, which is critical for developing subacute acidosis. This could indicate a switch in the microbial community due to direct and/or indirect effects of the Fusarium infection on ruminal microbes.
Effect on cattle
Fusarium mycotoxins exert their effects via 3 primary mechanisms in dairy cattle:
- The first impact on animal health is an increase in immunodepression, described by Surai and Dvorska in 2005. In 2009, Korosteleva et al., concluded that Fusarium mycotoxins can decrease certain cellular aspects of the immune function in dairy cattle, while stimulating a primary humoral response to specific antigens.
- The second impact of Fusarium mycotoxins (mainly trichothecenes) is a reduction in the amount of nutrients available for use by the animal due to lower feed intake, and by irritation of the digestive tract and reduction in villi height (Pinton et al., 2012).
- The third impact is the direct oestrogenic effects on reproductive performance by ZEN and its metabolites (Klang et al., 1978).
To the dairy farmer, the clinical or subclinical losses in performance, the increase in incidence of disease and reduced reproductive performance are of great economic importance. Therefore, it is vital to detect and protect cows from mycotoxin contamination to avoid such economic losses.
This article has been reprinted from AFMA Matrix (January 2017). References available from the author at email: firstname.lastname@example.org.