Endocrine and reproductive function in ewes exposed to the organochlorine pesticides lindane or pentachlorophenol

The effects of lindane (LIN, gamma-hexachlorocyclohexane) and pentachloroph enol (PCP) on reproduction and general endocrine function were examined in breeding ewes as a model for wild and domestic ungulates, which may be expo sed to low levels of pesticides that are potential endocrine-disrupting che micals. Ewes (n = 13/group) were fed either a control untreated diet (CON), or a diet treated with LIN (1 mg/kg/d) or PCP (7 mg/kg/d) during the 5 wk prior to mating and throughout pregnancy and lactation. Mating response, ov ulation rate, follicle and corpus luteum size, gestation length, pregnancy rate, lambing rate, and lamb birth weight were recorded. After weaning, 6 e wes from each group were bled at 15-min intervals for 8 h during the day an d night and for 1 h before and 5 h after iv administration of gonadotropin- releasing hormone, thyroid-stimulating hormone (TSH), and adrenocorticotrop in, to measure serum concentrations of luteinizing hormone, follicle-stimul ating hormone, thyroxine (T4), and cortisol. Ewes were then killed and endo crine tissues examined histologically. Pregnancy rate as a result of mating s taking place at the synchronized estrus was significantly decreased by th e lindane treatment However, PCP and lindane did not markedly affect any ot her aspect of reproductive function studied. In PCP-treated ewes, serum con centrations of T4 were significantly reduced compared to control ewes durin g the day and night; however, the T4 response to TSH was not altered by PCP treatment. No other measured endocrine parameters were consistently affect ed by lindane or PCP. Thyroid follicle size was significantly increased in the LIN and PCP ewes compared to the control ewes. Low serum concentrations of T4 in the PCP ewes may have resulted in increased TSH secretion and inc reased thyroid follicle size. In conclusion, although pesticide treatments had no serious adverse effects on reproductive function in breeding ewes, P CP reduced T4 concentration, which in the long term could influence reprodu ctive and general performance.