Mancozeb exposure disrupts endocrine function of the ovary and thyroid in Red Munia (Amandava amandava)

Mancozeb (MCZ), a dithiocarbamate fungicide, has the potential to disrupt thyroid hormone (TH) functioning in non-target organisms. THs play a crucial role in seasonal reproduction and previous studies have shown that even low levels of MCZ exposure can affect thyroid and testicular function in the Red Munia bird (Amandava amandava), a distinct seasonal breeder. This study specifically examines the impact of MCZ exposure on female Red Munia to investigate any sex-specific effects. Exposure to sublethal levels (0.5% LD50) of MCZ for 30 consecutive days during the critical transition to the breeding phase disrupts the pituitary-ovarian and pituitary-thyroid axes in Red Munia. The morphometry (number/size/immunointensity) of pituitary luteinizing hormone (LH) and thyroid-stimulating hormone (TSH) producing cells, immunoreacted with anti-human (h) LHβ/anti-chicken (c) LHβ, and anti-hTSH β respectively, was significantly altered. Plasma levels of LH (p < 0.01), follicle-stimulating hormone (p < 0.001), and TSH (p < 0.01) were significantly decreased. There was a significant increase in the number of atretic primordial and primary follicles, thinning and disorganization of the granulosa cell layers in maturing follicles, and significant decrease in plasma levels of estradiol (p < 0.001).The reduced diameter of the thyroid gland, a significant increase in empty follicles, and a decrease in plasma levels of THs (T3, p < 0.01; T4, p < 0.001), indicate disruption of thyroid function. It is not only MCZ and its residual products, but also the inert ingredients in the commercial formulation/metabolites, may have contributed to the interference with thyroid function during the transition to the breeding phase to compromise ovarian recrudescence in the Red Munia bird.