A Comparison of Effects of Zearalenone and Estradiol Benzoate on Reproductive Function during the Estrous Cycle in Gilts2

Effects of estradiol benzoate (EB) and zearalenone (Z) on luteal maintenance and plasma hormone concentrations were studied in 45 gilts. Gilts were allocated to receive either 20 mg Z, 2 mg EB or no treatment (C) on d 1 to 5 (T1), 6 to 10 (T2) or 11 to 15 (T3) of an estrous cycle (five per treatment). Onset of estrus was designated as d 0 of the estrous cycle. Zearalenone was added to the daily ration and EB was administered via an intramuscular injection. Blood samples were collected every 10 min over a 4-h period on the first 2 d prior to onset of treatment; the first, third and fifth days of treatment; and the first two and the fifth day after the end of the treatment periods. Gilts receiving EB and Z during T2 and T3 had longer (P<.05) inter-estrous intervals than C gilts. The range in inter-estrous intervals for Z and EB treatments was 28 to 74 and 27 to 63 d, respectively. Mean plasma progesterone concentrations were elevated (P<.05) during T2 and T3 in EB and Z-treated gilts when compared with C females. Estradiol benzoate treatment during T2 and T3 reduced (P<.05) mean plasma luteinizing hormone (LH) concentrations more than C or Z treatments. Mean plasma concentrations of 13, 14-dihydro-, 15-keto-prostaglandin F2α(PGFM) during T3 were higher (P<.05) in C and Z gilts on d 13 and 15 post-estrus when compared with EB gilts. These results indicated that 2 mg EB or 20 mg Z from d 6 to 10 or 11 to 15 of the estrous cycle extended the inter-estrous interval in swine. Estradiol benzoate during the same periods decreased mean plasma LH concentrations while Z did not. Additionally, EB treatment during T3 prevented the increase in PGFM concentrations of d 13 and 15 observed in both C and Z gilts.