| Summary: | Purpose: Maternal effects, a class of phenotypic effects on offspring unrelated to genotype, are known to impact phenotype plasticity and offspring fitness, including potential effects of maternal glucocorticoids. The prenatal effects of maternal glucocorticoids have been well documented in a variety of species, but post-natal effects are less well studied, particularly in thecontext of lactation. Methods: We altered maternal stress hormones via ACTH challenges in lactating elephant seals to determine if prolonged maternal stress hormone elevation resulted in transfer of cortisolduring suckling. We then evaluated whether maternal cortisol transfer altered pup phenotype and development by measuring metabolic hormones, metabolites, and oxidative stress markers near the end of lactation. We resampled pups 2 weeks after weaning to examine the persistence of these effects after this important life-history transition. Findings: Milk cortisol concentrations were higher in the ACTH mothers, although milk cortisol concentrations were physiologically relevant in control females. Offspring cortisol and thyroid hormones were affected by maternal cortisol transfer and these effects persisted after weaning. Maternal treatment with ACTH, likely via elevated milk cortisol, increased oxidative stress and damage in suckling pups, but reduced oxidative damage and protein catabolism during fasting after weaning. Conclusion: These findings provide evidence for phenotypic changes in offspring resulting from transfer of maternal cortisol during suckling that alter development and oxidative stress systems. Transfer of maternal glucocorticoids and resulting effects may be enhanced in capital breeding mammals with high rates of milk fat transfer.
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