Characterization and schematic modeling of the evolution of weaning age in piglets and its physiological, nutritional and productive implications: a review.

Modern intensive swine production systems have progressively reduced weaning age from conventional weaning ages of around 30 days to 21 days or less, aiming to improve sow reproductive efficiency and increase production flow. Although this strategy has enhanced productivity, it has also created a mismatch between the piglet's chronological age and biological maturity, particularly at gastrointestinal, metabolic, endocrine, and immune levels. This review provides an integrated analysis of the evolution of early weaning and its physiological, nutritional, and productive implications within a systemic framework. Current literature suggests that early weaning disrupts intestinal and metabolic maturation, contributing to enzymatic immaturity, structural alterations of the intestinal epithelium, microbiota dysbiosis, activation of the hypothalamic-pituitary-adrenal axis, and early negative energy balance. These changes reduce feed intake, impair average daily gain, increase inter-animal variability, and elevate susceptibility to post-weaning disorders. Although nutritional interventions, including specialized diets and functional additives, have partially mitigated these effects, they have also increased system complexity and dependence on technological inputs. From a General Systems Theory perspective, early weaning can be understood as an emergent property of intensive production systems, with implications for productivity, animal health, welfare, and sustainability. Collectively, the reviewed evidence highlights the importance of aligning weaning management with physiological maturity and supports integrative strategies such as precision nutrition, tailored transition diets and omics-based tools to improve post-weaning adaptation.