Reproductive performance of mares fed dietary zearalenone

Authors: VANCE, CARRIE - Mississippi State University; KING, E. HEATH - Mississippi State University; BOWERS, SUSAN - Mississippi State University; RYAN, PETER - Mississippi State University; WALTERS, KEVIN - Mississippi State University; Shappell, Nancy

Submitted to: Frontiers in Veterinary Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/8/2019
Publication Date: 11/26/2019
Citation: Vance, C.K., King, E., Bowers, S.D., Ryan, P.L., Walters, K., Shappell, N.W. 2019. Reproductive performance of mares fed dietary zearalenone. Frontiers in Veterinary Science. 6:423. https://doi.org/doi: 10.3389/fvets.2019.00423.
DOI: https://doi.org/10.3389/fvets.2019.00423

Interpretive Summary: The toxicity of the estrogenic mycotoxin zearalenone, a common forage contaminant, and its effects on reproduction in mares is uncertain, and the few reports on its effects have ranged widely in their conclusions from no-effect to severely disrupting estrous cycles and even being fatal. Here we studied the in vivo effect of chronic feeding of zearalenone to mares during their estrous cycle and examined a multitude of clinical parameters as well as zearalenone’s impact on reproductive hormones and pregnancy. Our results provide strong evidence that the effects of zearalenone on horse reproduction are minor at the concentrations found at normal feed stuff contamination levels. Furthermore there was not a decrease in the rates of mares becoming pregnant if exposed to zearalenone, even for as long as 120 days. These results aid in determining guidance to feed contamination tolerances for commercial horse breeders.

Technical Abstract: It is known that zearalenone (ZON) interacts directly with estrogen receptors, and its in vivo effects on reproduction have been well documented in several species. In contrast, reports of ZON’s impact on horse reproduction are conflicting and inconclusive, some studies confounded by the presence of mycotoxins such as deoxynivalenol in the feed. This study assesses the effect of chronic consumption of zearalenone on reproduction in cycling mares fed >95% pure ZON (0, 2 or 8 mg/da; n=7 mares/treatment) for three estrous cycles, followed by artificial insemination, through 16 days of pregnancy. Animals were on ZON treatment for between 70 and 121 days (average 84) depending on individual cycle patterns. ZON-induced changes in serum concentration of estradiol (E2) and progesterone (P4), and total estrogenicity were measured using RIAs and the E-screen assay, respectively. Effects on reproductive physiology and pregnancy were monitored by ultrasound and clinical parameters. No significant changes were found in reproductive hormone levels of E2, or P4 for mares on ZON treatments compared to controls, although there was a significant (P < 0.01) increase in P4 levels across Cycle number in High ZON (8 mg/da) treated mares. There was also an increasing trend in the interovulatory interval in the High ZON treatment group. The overall estrogenicity was similar across treatments and over time, not differing from controls or between ZON treatment groups. Adverse uterine and ovarian effects were also not observed, but pregnancy rates were mixed with only 4 of 7 mares on Low ZON becoming pregnant, and only 3 maintaining pregnancy and fetal heartbeat by Day 30, compared to 5 of 6 control mares and all 7 mares on High ZON. Because reproductive efficiency and hormone concentrations are highly variable across individuals, this study did not demonstrate that ZON at 2 or 8 mg/da was detrimental to mares’ reproduction. Yet, inferring that ZON treatments were completely without effect is also not appropriate, as the absence of measurable significant differences could be attributed to the limited sample size. Most importantly, there were no extreme signs of toxicology, in contrast to previous reports when ZON was fed at these “doses”.