Reproductive performance of mares fed dietary zearalenone

Authors: VANCE, CARRIE - Mississippi State University; KING, E. HEATH - Mississippi State University; BOWERS, SUSAN - Louisana 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., King, E., Bowers, S., Ryan, P., Walters, K., Shappell, N.W. 2019. Reproductive performance of mares fed dietary zearalenone. Frontiers in Veterinary Science. 6:423.

Interpretive Summary: Zearalonone (ZON) is a mycotoxin found in foodstuffs that affects reproductive cycling and pregnancy in livestock species. The conflicting information on horse susceptibility to ZON prompts a thorough assessment of the effects of this mycotoxin on reproductive efficiency in mares, especially over long periods and across numerous estrous cycles, as well as pregnancy rates. At present, there are no regulatory standards for zearalenone in feedstuffs in the United States, but European guidance limits ZON to 2 ppm = 2 mg/kg in cereal products. The objective of this study was to examine effects of ZON exposure in cycling mares fed ZON at a Low and High doses, and over the course of three estrous cycles and into pregnancy; thus testing reproductive responses to ZON at the European regulatory limit and at a 4-fold higher dose nearing that reported as having severe negative effects upon chronic exposure. Chronic exposure of mares to ZON at 2–8 mg/da resulted in no statistical effect on examined hormone profiles, and no obvious toxicological effects, though the potential for a decrease in the number of foals produced/mare is not clear. These data will provide the feed industry and regulatory agencies in vivo data for both chronic and dose-dependent zearalenone effects on horse reproduction, an important first step in developing feeding guidelines and tolerance limits for zearalenone in the US. Our next assessment will be to investigate the multivariate biochemical response to ZON toxicity using NIR spectroscopy and Aquaphotomics to assess coordinated changes in serum parameters that may have been undetectable in singe compound analyses.

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.”