| Summary: | Lipopolysaccharide (LPS) from gram-negative bacteria was found to be involved in the decrease in laying performance in goose flocks with high stocking density during summer months. LPS injection delayed the increase in the laying rate and altered hierarchical follicle morphology. While there is evidence that LPS exerts suppressive effects on goose reproduction, the time course effects of LPS on the hypothalamus-pituitary-ovary (HPG) axis remain elusive. In this study, we investigated the expression of genes in the HPG axis and the plasma gonadotrophin hormone concentrations in breeding geese at 0, 6, 12, 24, and 36 h after intravenous injection with LPS. The results showed that LPS treatment enhanced and suppressed expression of hypothalamic gonadotropin-inhibiting hormone (<i>GnIH</i>) and gonadotrophin-releasing hormone (<i>GnRH</i>) mRNA, respectively, and similar effects were observed on the mRNA expression of their receptors, <i>GnIHR</i> and <i>GnRHR</i>, in the pituitary. LPS treatment transiently increased follicle <i>FSHβ</i> mRNA expression at 12 h and exerted no significant effect on <i>LHβ</i> mRNA expression in the pituitary. Regardless of the expression of <i>FSHβ</i> and <i>LHβ</i>, plasma follicle stimulating hormone (FSH) and luteinizing hormone (LH) concentrations were significantly increased during 24–36 h after LPS treatment. In the ovary, <i>StAR</i> and <i>Cyp11a1</i> were mainly expressed in the granulosa layer (GL) of hierarchical follicles, while <i>Cyp17a1</i> and <i>Cyp19a1</i> were mainly expressed in white follicles (WFs) and yellowish follicles (YFs), and to a lesser extent in the theca layer (TL). After LPS treatment, the mRNA levels of <i>Cyp11a1</i> in the GLs, <i>Cyp17a1</i> in the WFs and TL, and <i>Cyp19a1</i> in the WFs, YFs, and TL were significantly decreased. However, LPS treatment transiently upregulated <i>StAR</i> expression at 12 h. These results indicate that the exposure of laying geese to LPS may impair the HPG axis and disturb ovarian steroidogenesis. Our research provides new insights into reproductive dysfunction caused by LPS and the immune challenge in birds.
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