The effects of zearalenone on reproduction in swine. I. The relationship between ingested zearalenone dose and anestrus in non-pregnant, sexually mature gilts.

Ninety-nine sexually mature, non-pregnant gilts were checked for estrus daily with a mature boar and then allocated at estrus (D O) to receive 2 kg/d of a diet containing 0, 1, 5 or 10 ppm purified zearalenone between D 5 and 20 of the estrous cycle during two seasons of the year (winter and summer). None of the gilts exhibited any visual signs of "hyperestrogenism" and there was no effect of season on interestrous interval (P>0.05). A significant effect of zearalenone dose on inter-estrous interval was detected (P<0.001). Gilts receiving 0 or 1 ppm had similar inter-estrous intervals (21.0+/-0.3 and 21.5+/-0.8 d, respectively) whereas gilts receiving 5 and 10 ppm had extended cycles (29.2+/-2.9 and 32.7+/-3.3 d, respectively). Plasma progesterone concentrations at D 19 to 21 were higher in gilts with extended cycles (P<0.001) and corpora lutea (CL) were present at laparotomy. Some 86% of these retained CL underwent spontaneous regression resulting in the onset of estrus within the next 30 d. Fecal zearalenone concentrations rose during ingestion of contaminated diets and declined to pretreatment values within 2 d (1 ppm) to 8 d (10 ppm) of the cessation of treatment. These data show that feeding zearalenone at concentrations of 5 to 10 ppm from D 5 to 20 of the estrous cycle causes luteal maintenance and extended inter-estrous intervals. Spontaneous regression of these CL usually occurs within 30 d after zearalenone is removed from the diet. Fecal zearalenone analysis does not appear to be an effective method for determining prior exposure to zearalenone when carried out more than a few days following the last ingestion of zearalenone.