Reproductive efficiency in horse breeding has increased in the last three decades all over the world. It can be influenced by many factors but their roles are not precisely described. Feedstuffs contaminated with mycotoxins are frequently fed to animals. Zearalenone, a mycotoxin with estrogenic effect, and T-2 toxin, a cytotoxic trichothecene mycotoxin are proven to have adverse effect on female reproduction in many species, but nothing is known about their effects on the mares' reproductive function. Dexamethasone, a synthetic glucocorticoid is frequently applied in equine medicine, however limited information is available concerning its effect on spermatogenesis and semen quality in males of domestic animals. In the first experiment the effect of zearalenone was studied in mares. After an entire oestrous cycle, mares were given 7 mg purified zearalenone per os daily, beginning on day 10 of the next cycle, until subsequent ovulation. The toxin had no effect on the length of the interovulatory interval, luteal and follicular phases. It did not influence significantly peripheral plasma progesterone profiles, follicular activity and uterine oedema. In the second experiment the effect of long term administration of T-2 toxin was studied in mares. After one complete oestrous cycle (Cycle 1) each mare was given 7 mg purified T-2 toxin per os daily, beginning on day 10 after ovulation in Cycle 2. Exposure to toxin was continued for 32 to 40 days, until day 7 of Cycle 4. During this period all animals remained in good physical condition but skin lesions were observed around the mouth in 3 cases. Toxin administration had no effect on the length of the interovulatory interval, the luteal and follicular phases. It had no effect on peripheral plasma progesterone profiles and on follicular kinetics. Uterine flushing was attempted in 5 mares and yielded 3 embryos (60%) which were of normal size and morphology. In the third experiment the effect of dexamethasone sodium phosphate on spermatogenesis and semen quality was investigated in stallions. Animals were treated with 0.05 mg/bw kg dexamethasone sodium phosphate iv. once a day for 7 days. Semen was collected from the stallions before and after drug administration for a period of one complete spermatogenesis. GnRH- and hCG-stimulation tests were carried out 4 times during the study. Dexamethasone did not influence fresh and frozen-thawed semen parameters significantly. In 2 treated stallions some parameters tended to decrease after treatment, indicating different individual sensitivity to dexamethasone. Basal testosterone concentrations were decreased and LH concentrations were increased during treatment but FSH levels were not influenced. Dexamethasone increased LH and testosterone response to GnRH after treatment but hCG Induced testosterone secretion was not affected. It can be concluded that the reproductive function of mares and stallions remains within the normal physiological range after low dose exposure to zearalenone, T-2 toxin and treatment with dexamethasone at therapeutic dose. However, it should be taken into consideration that the model studies carried out and the results are only relevant for these experimental conditions. Dose, duration of treatment, type of mycotoxin and dexamethasone, age, sex, body condition, reproductive and health status of the animals may be important factors which influence the results of such toxicological studies.
|Translated title of the contribution||Effect of certain mycotoxis contaminating feedstuff (zearalenone, T-2 toxin) and dexamethasone on the reproductive function of horses. Summary report of a research program|
|Number of pages||8|
|Journal||Magyar Allatorvosok Lapja|
|Publication status||Published - Dec 1 2001|
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