The Emerging Role of Prolactin as a Biomarker for Reproduction, Health, and Welfare in Wildlife Species: Elephants as a Model.

Prolactin is a key hormone that plays significant roles in reproduction, extending far beyond its well-known function in mammalian lactation. It is vital for reproductive success across diverse taxa, including birds, fish, reptiles, and amphibians, where it regulates critical reproductive behaviors and physiological processes like parental care, pregnancy maintenance, embryonic diapause, immunity, osmoregulation, metamorphosis, and molting. Environmental cues often fine-tune its actions to ensure reproduction occurs under optimal conditions. Conversely, dysregulation of prolactin can severely impact reproduction. While hyperprolactinemia is the most common pituitary disorder affecting fertility in women and other species, including elephants, hypoprolactinemia can lead to inadequate parental care due to poor milk production or inadequate brooding. Environmental stressors such as pollution and climate change can further disrupt prolactin levels, compounding reproductive failures. Its sensitivity to social and environmental stressors has led to its increasing recognition as a valuable biomarker for animal welfare assessment. Elucidating prolactin's multifaceted functions can substantially advance our comprehension of reproductive strategies across diverse taxa. These insights could potentially inform and enhance conservation efforts for threatened species ex situ and in situ, contributing to more effective wildlife management and preservation strategies. Here, we review the role of prolactin in reproduction, health, and welfare across species, with a particular emphasis on elephants. Nearly three decades of elephant studies, facilitated by accessible blood sampling, have yielded valuable insights into its physiological roles and association with reproductive dysfunction. While many prolactin mechanisms in elephants have similarities to those observed in other species and humans, there are notable differences that warrant further study to enhance our understanding of its role in physiology and behavior and contribute to our broader knowledge of reproductive endocrinology across species.