Effect of lindane on clutch size and level of egg yolk protein in domestic duck.

Lindane (gamma-hexachlorocyclohexane) was administered to laying ducks (Anas platyrhynchos domesticus) in 3 doses viz. (1) 20 mg/kg body weight daily, (2) 20 mg/kg body weight thrice weekly and (3) 20 mg/kg body weight twice weekly for 8 weeks. Egg laying was immediately stopped for 3 weeks in the first 2 groups and when resumed it became highly irregular with clutch size drastically reduced (1 against 7 of control ducks). The initial delay was absent in the 3rd group and reduction in clutch size was also marginal (5 against 7). Laying frequencies were 8.3%, 11.7% and 40% in Groups 1, 2 and 3 birds respectively against 50% frequency of the normal ducks. Hepatic, plasma and ovarian vitellogenin levels were substantially reduced in the first 2 groups. At the same time liver RNA level was markedly reduced. Ovary of such birds lack mature vitellogenic follicles and the thecal layer of moderately differentiated oocytes became highly atrophic. Stilbestrol (50 mg/kg body wt--single injection) administration to lindane fed pauci-layer ducks restored egg laying within 24 h, with return of a normal level of plasma vitellogenin and hepatic RNA. The results suggest that lindane induced estradiol insufficiency causes inhibition of hepatic RNA and yolk protein synthesis, thereby preventing transformation of moderately differentiated oocytes to mature vitellogenic follicles, delaying ovulation and thus drastically reducing clutch size.