Effects of mycotoxins on reproduction and fertility

One of the most prominent toxins associated with impairment of the reproductive cycle, is zearalenone. Pigs are the most sensitive animal species, and this sensitivity is related to the metabolic conversion of zearalenone into its a-hydroxy metabolite, a-zearalenol, which has a higher estrogenic potency than does the parent molecule. Ruminants are less sensitive to zearalenone as a-zearalenol is produced in the rumen by the rumen microorganisms (Maleki-nejad et al, 2006). Intestinal absorption of this hydroxy-metabolite is assumed to be rather low and the a-zearalenol is thought to be reconverted in the liver to zearalenone and/or to a-zearalenol or other secondary metabolites with lower estrogenic potential. The fate of zeara-lenone in horses remains to be evaluated, but zearalenone affects oocyte maturation ex vivo, suggesting a role for zearalenone in fertility disorders in mares (Minervini et al., 2006).

Research on the effect of mycotoxins on reproduction has focused on females, particularly on the impairment of oocyte maturation and early embryogenesis. This focus is consistent with reports from veterinary practice that describe reduced fertility or reduced litter sizes as a consequence of mycotoxin exposure. Male reproduction and sperm quality also may be affected following exposure to mycotoxins. However, very few in vivo investigations have addressed this topic, e.g., evaluating the effects of ochratoxin A exposure on sperm quality in boars (Biro et al, 2003). The various in vitro experiments showing the susceptibility of sperma-tocytes to mycotoxins provide only limited information, as the concentrations used cannot be correlated to actual exposure levels or to mycotoxin levels in the testicles or the seminal fluid.

Experiments in rodents have shown that some mycotoxins are teratogens at high concentrations. Comparable effects in farm animals cannot be entirely excluded since the time window between exposure, in the vulnerable phase of the first trimester of pregnancy, and visible signs during delivery, is quite long. In daily practice, malformed animal neonates generally are euthanized, and records of their occurrence are very incomplete.

A mycotoxin with a distinct mechanism of action is ergovaline, the best investigated ergot alkaloid in cases of fescue (grass) intoxications. Ergovaline activates dopaminergic receptors and acts as an anti-prolactin agent. Thus, milk production following the partus is absent or delayed and can result in potentially fatal starvation of foals and calves if undiagnosed.

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