Sufficient information has been generated with sheep to recommend that breeding ewes should
not be exposed to more than 1 mg ZEN/d (approximately .5 mg ZEN/kg diet DM) for more than 20
d prior to ram introduction. Higher levels cause infertility in even shorter exposure periods. Rams,
or pregnant ewes, are resistant to higher dietary concentrations, but these are not well defined.
For cattle, a recommendation in the literature indicated not to exceed 5 mg ZEN/kg diet DM for
growing heifers prior to their first breeding. This recommendation seems reasonable, because
heifers fed 250 mg ZEN/d (equivalent to a dietary concentration of 15 mg ZEN/kg diet DM as
determined from observed feed intake in the study) had reduced ovulation rate. Reported effects
of ZEN on production and reproduction of mature cows were not sufficiently consistent to
suggest acceptable levels. However, cows may be more resistant to ZEN toxicosis than heifers