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Failure of Progesterone to Counteract Zearalenone Toxicoses
During Early Pregnancy in Gilts

M.L. Green, and M.A. Diekman
Department of Animal Sciences

Corn raised in the Midwest is frequently invaded by the fungus Fusarium roseum. Under the proper environmental conditions this fungus produces the mycotoxin zearalenone. Previous research at Purdue has demonstrated that zearalenone fed to sows during early pregnancy causes death of embryos and retention of corpora lutea resulting in pseudopregnancy. The embryonic death was not mediated by a change in the secretory patterns of hormones controlling reproduction. However, serum concentrations of progesterone, a hormone produced by corpora lutea of he ovary that is needed to maintain pregnancy, were suppressed 2-3 weeks postbreeding in gilts that ingested zearalenone. We propose that the ingestion of zearalenone by a pregnant gilt during early pregnancy leads to an altered estrogen: progesterone ratio. The altered hormone ratio leads to an unfavorable uterine environment for embryonic development. The objective of the following study was to determine if exogenous progesterone is an effective therapeutic measure to counteract zearalenone toxicoses in pregnant gilts.

Materials and Methods

Forty November born, nulliparous crossbred gilts (Hampshire X Chester White X Duroc) were vaccinated against parvovirus, leptospirosis and erysipelas. Three weeks after vaccination gilts were transported to an open-fronted gestation building and exposed daily to sexually mature boars for 30 minutes in early morning and late evening. Gilts in standing estrus were moved to a breeding area and mated to two fertile boars 12 hours apart. The first sixteen gilts observed in estrus were assigned randomly as they were bred to a 2 x 2 factorial arrangement of treatments in a randomized complete block design. Treatment combinations were as follows:

Zearalenone was dissolved in ethanol (22 mg/ml) and an appropriate volume was placed on 500 g of a corn-soybean diet in plastic bags. The ethanol was allowed to evaporate overnight and the bags were sealed. Feed for P and C gilts was treated in a similar manner except ethanol was placed on the samples. Gilts consumed their respective diets from day 4-15 postmating. An additional 2 kg of the base diet was provided each day after the treated sample had been ingested. Progesterone (50 mg/ml) and its carrier (.15 ethanol, .15 benzyl alcohol, .70 propylene glycol) were administered via an intramuscular injection on days 3 through 15 postmating.

All gilts were bled by jugular venipuncture daily from days 3 through 15 of gestation, on alternate days from days 17 through 31 and then twice weekly until the end of the experiment. The experiment was replicated in November using April born gilts. Z and ZP gilts were laparotomized on day 48 ± 2.9 postmating and P and C gilts were slaughtered on day 52 ± 3.6 to assess fetal development.

Results

Mean serum concentrations of progesterone in P gilts were greater on day 7-8, 10-15, 17 and 19 than in C gilts. Serum concentrations of progesterone in ZP gilts were greater on day 8, 10 and 12 than in C gilts. However, serum concentrations of progesterone were lower in ZP gilts than C gilts on day 19-31 postmating. Serum concentrations of progesterone were lower in Z gilts than C gilts on day 15, 17 and 19 postmating.

Z and ZP gilts had no viable fetuses 48 ± 2.9 days postmating, whereas 80% of the P and C gilts were pregnant. All Z gilts were pseudopregnant and characterized by turgid uteri and functional corpora lutea. Corpora lutea of pregnancy had regressed by day 35 postmating in 7 of 8 ZP gilts. All fetal parameters were similar between P and C gilts (Table 1).

Table 1. Fetal data on day 48 ± 2.9 postmatingfor the progesterone-treated and control gilts.

Conclusion

These data demonstrate that elevated serum concentrations of progesterone failed to counteract zearalenone toxicoses during early pregnancy in gilts. It appears that alteration of the estrogen:progesterone ratio in the uterus is not a critical factor in zearalenone toxicosis during early pregnancy. Future experiments will be directed towards binding the toxin during the digestive process and thus preventing its absorption in the blood of pregnant swine.

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