Melatonin and Lactation in Ruminants Dairy Animals: A Systematic Review and Meta-Analysis of Preclinical Studies

Melatonin is present in breast milk with a diurnal pattern, potentially supporting early circadian rhythm development. This systematic review and meta-analysis aimed to evaluate the effects of exogenous melatonin supplementation, compared with no treatment or placebo, on milk yield, milk composition, somatic cell count, colostrum composition, and neonatal growth outcomes in lactating ruminant livestock.

A systematic search of PubMed, Scopus, Web of Science, and Google Scholar was conducted up to March 15, 2026. All continuous outcomes were pooled as standardized mean differences (SMD) to account for variability in measurement scales across studies.

We identified 25 eligible studies in lactating animals. Melatonin supplementation did not significantly alter milk yield across species (SMD = 0.49). Significant improvements were observed in milk fat (SMD = 0.77) and protein content (SMD = 0.39), particularly in cows. Melatonin also significantly reduced somatic cell count (SMD = -1.98). Other components such as lactose, total solids, and solid not fats showed no significant change. Neonatal outcomes, including birth weight, weight at weaning, and daily gain, showed no significant improvement. Colostrum analysis showed a small increase in lactose content but no consistent effects on fat, protein, or IgG. However, most pooled analyses demonstrated substantial heterogeneity (I² frequently > 90%).

Exogenous melatonin shows potential for improving milk quality and mammary health in ruminant dairy animals, but its impact on milk yield and neonatal development remains unclear. These preclinical findings are hypothesis‑generating, and carefully designed clinical studies would be required before considering melatonin use in lactating women.