Effects of experimental exposure to zearalenone on reproductive system morphometry, plasma estrogen levels, and oocyte quality of beef heifer

The aim of the present study was to evaluate the effects of zearalenone (ZEA) on the reproductive system morphometry, oestrogen (E2) levels and oocyte quality of beef heifers. Twenty non-pregnant purebred Nellore (Bos indicus) heifers [age, ≥18 months; initial body weight, 348 ± 30 kg (mean ± standard deviation)] were used. The animals were randomly divided into experimental group and a control group of 10 animals each. Group experimental was administered 300 ppb ZEA per os for 98 days, and the control group was administered placebo per os for 98 days. The administration of ZEA was carried out daily by adding mycotoxin to the diet. All heifers were evaluated weekly via rectal ultrasound examinations (12 weeks). Diameters of the right and left uterine horns, right and left ovaries, largest antral follicle and corpus luteum were measured. Vulva size was also measured. Blood samples were collected to estimate E2 levels. At the end of 12 weeks, the heifers were slaughtered, and the ovaries were sent to the laboratory for in vitro embryo production. A completely randomized design was adopted, and repeated measures analysis of variance (p < .05) was performed (except for oocyte quality). Vulva size (p = .0985); diameters of uterine horns (p = .0522), ovaries (p = .6955), antral follicles (p = .6355) and corpus luteum (p = .3808); and E2 levels (p = .3379) were not affected by the treatments. ZEA-contaminated diet significantly reduced (p = .05) the proportion of viable oocytes (49.4%, n = 207) compared with the control diet (59.9%, n = 222); however, the blastocyst rate did not differ between the groups (p = .9418). The results indicate that contamination of beef heifer's diet with 300 ppb ZEA affected neither morphometric parameters nor plasma oestrogen levels; however, ZEA contamination was detrimental to oocyte quality.