Abstract Background: Early-life diseases in dairy animals are main causes of economic loss in livestock production. Oxidative stress (OS) and thyroid hormones are important inter-related components in the normal physiology of this critical period of life. However, limited information regarding their physiology in goat kids is available. This study was conducted to investigate the age-related changes of thyroid hormones, some serum oxidative biomarkers and trace elements in healthy Saanen goat kids. Methods: Nineteen newborn healthy Saanen goat kids (14 females and five males) were studied longitudinally from birth until three months of age. Blood sampling was performed 24–48 h after birth and was repeated on 10 ± 2, 28 ± 2, 56 ± 2 and 84 ± 2 days of age. The serum levels of thyroid hormones, malondialdehyde (MDA), reduced glutathione (GSH), total antioxidant capacity (TAC), selenium (Se), manganese (Mn) and molybdenum (Mo) were measured. Results: Age-related changes were observed for all measured variables except for MDA (p < 0.05). A decreasing trend was detected throughout the study in thyroid hormones, T3: T4 ratio and Mn (p < 0.01). Some factors decreased from birth to day 10 (Se) or day 28 (TAC and GSH) and followed by an increasing trend that extended to day 84 (p < 0.01). There were significant correlations between thyroid hormones and TAC, as well as Mn levels (p < 0.05). Conclusions: These results imply that specific age-related reference values are essential for proper interpretation of the serum level of thyroid hormones and Mn in Saanen goat kids during the first three months of life. In addition, given the high level of thyroid hormones particularly during the first days of life, and their relationship with oxidative biomarkers and trace elements, improving the antioxidant system in this critical period is essential.

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