71 EFFECTS OF A CONTROLLED DIETARY EXPOSITION TO ZERALENONE ON SELECTED REPRODUCTIVE PARAMETERS IN DAIRY COWS

Abstract

Whole plant corn silage is an important component of dairy cow nutrition. Growing conditions in a moderate climate, as are present in large parts of Europe and North America, are often beneficial for mould contaminations to occur. Very commonly, varieties of Fusarium spp. grow on the corn plant producing the non-steroidal estrogenic mycotoxin zearalenone (ZEN). Numerous studies have shown that ZEN massively interacts with the porcine reproductive system. Nevertheless, only a few studies have assessed the possible effects on dairy cows, most publications being field studies following accidental exposure. Therefore, it was aim of the present study to assess the effects of a controlled dietary exposition on selected reproductive parameters in dairy cows. The chosen exposure concentration was within the range of the ‘Commision Recommendation on the presence of deoxynivalenol, zearalenone, ochratoxin A, T-2 and HT-2 and fumonisins in products intended for animal feeding’ of the European Union. Corn plants were artificially inoculated with Fusarium spp. and the silage obtained from the whole plant was analysed to determine to which degree the silage contained ZEN. Thirty Holstein Friesian cows and heifers (aged between 2 years 3 months and 5 years at calving) were allocated to 3 groups with 10 animals each: control (CTL), uncontaminated silage; ZEN 50, silage with 0.25 mg of ZEN/day; and ZEN 100, silage with 0.5 mg of ZEN/day. The contaminated rations were distributed by automated feeding stations to ensure an equal uptake. Feeding began 7 days post-parturition. Blood samples were obtained twice weekly for 12 weeks and were analyzed regarding the progesterone level via radioimmunoassay. At the same time, the oestrous cycle was monitored by ultrasonography. Furthermore, the size of the corpus luteum (CL) was measured 7 ± 2 days after the third ovulation. Simultaneously, the luteal blood flow was documented via Doppler ultrasonography. The peripheral blood progesterone level (x_geom. ± CV; CTL: 9.3 ± 1.7; ZEN 50: 8.5 ± 1.6; ZEN100: 7.1 ± 1.5) did not differ among groups. Furthermore, it was not possible to detect differences in luteal blood flow, size of the CL (mean ± SD; CTL: 6.4 ± 1.7 cm²; ZEN50: 5.9 ± 1.3 cm²; ZEN 100: 5.0 ± 1.0 cm²) or the ratio of luteal size and size of the area supplied with blood (CTL: 0.1 ± 0.1; ZEN 50: 0.1 ± 0.0; ZEN 100: 0.1 ± 0.1). Although the mean length of the oestrous cycles (n = 60; distributed among groups) did not differ among groups (CTL: 24.0 ± 1.7 days; ZEN 50: 27.2 ± 1.6 days; ZEN 100: 27.7 ± 1.4 days), it was possible to detect an interaction between the age of the animal and the treatment regarding the cycle length in tendency (P < 0.07) by two-way ANOVA. The results of the present study indicate that, independent of the age of the animal, exposure to ZEN even within recommended dosages might result in an endocrine disruption in dairy cows. A larger sample size would contribute to the verification of these findings. Further analyses regarding the peripheral level of 17β-estradiol as well as molecular examinations are under progress.