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Glycine as a Metabolic Regulator of Reproductive Function in Livestock: From Gametes to Early Embryos
State Key Laboratory of Animal Nutrition and Feeding, College of Animal Science and Technology, China Agricultural University, No. 2 Yuanmingyuan West Road, Haidian District, Beijing 100193, China
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Author to whom correspondence should be addressed.
Animals 2026, 16(13), 1967; https://doi.org/10.3390/ani16131967 (registering DOI)
Submission received: 26 May 2026
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Revised: 18 June 2026
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Accepted: 23 June 2026
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Published: 25 June 2026
(This article belongs to the Section Animal Reproduction)
Simple Summary
Glycine is a simple amino acid that performs many essential jobs in the animal body. Although its roles in maintaining general health are well known, its importance for animal fertility is often overlooked. Poor oocyte quality, reduced sperm function, and early embryonic death are major causes of reproductive failure in pigs, cattle, sheep, and poultry, leading to substantial economic losses in livestock farming. This review summarizes current evidence on how glycine may influence reproductive cells and early embryos. Available studies suggest that glycine can help maintain redox balance, mitochondrial function, osmotic stability, and metabolic signaling, especially in in vitro culture or preservation systems. However, much of the current evidence comes from laboratory models, and responses may differ among species, doses, and experimental conditions. Further in vivo studies are needed before glycine-based nutritional or culture strategies can be reliably applied to improve livestock reproductive performance.
Abstract
Reproductive inefficiency associated with impaired oocyte competence and embryonic loss remains a major limitation in livestock production. Although glycine is classified as a non-essential amino acid, its endogenous synthesis is often insufficient to meet increased metabolic demands during gestation and early embryonic development. This suggests that glycine has a conditionally essential role in reproductive physiology. However, the mechanisms through which glycine integrates metabolic and signaling processes to regulate reproductive outcomes are not fully understood. This review summarizes the recent advances in understanding glycine’s role in animal reproduction, emphasizing its function as a metabolic regulator rather than merely a structural component. Glycine contributes to reproductive processes by maintaining redox homeostasis, supporting mitochondrial function and stabilizing cellular environments as part of its osmolyte function during critical developmental stages. Additionally, glycine participates in one-carbon metabolism, influencing nucleotide synthesis and epigenetic regulation. Furthermore, emerging evidence suggests that glycine may modulate key signaling pathways, including the AMP-activated protein kinase (AMPK)-mechanistic target of rapamycin complex 1 (mTORC1) pathway. Consistent with these mechanistic roles, glycine supplementation has been associated with improvements in oocyte maturation and embryonic development, particularly in vitro. These findings highlight the potential of glycine as a dietary or culture medium supplement to enhance reproductive performance in livestock. However, most current evidence is derived from in vitro systems, and the translation of these findings into livestock production strategies requires validation through well-designed in vivo studies.
