Stallion sperm membranes comprise of a high proportion of poly-unsaturated fatty acids, making stallion spermatozoa especially vulnerable to peroxidative damage from reactive oxygen species generated as a by-product of cell metabolism. Membrane Lipid Replacement therapy with glycerophospholipid (GPL) mixtures has been shown to reduce oxidative damage in vitro and in vivo. The aims of this study were to test the effects of a commercial preparation of GPL, NTFactor® Lipids, on stallion spermatozoa under oxidative stress. When oxidative damage was induced by the addition of arachidonic acid to stallion spermatozoa, the subsequent addition of GPL reduced the percentage of 4-hydroxynonenal (4-HNE; a key end product of lipid peroxidation) positive cells (32.9±2.7 vs 20.9±2.3%; P≤0.05) and increased the concentration of 4-HNE within the spent media (0.026±0.003 vs 0.039±0.004 μg/mL; P≤0.001), suggesting that oxidized lipids had been replaced by exogenous GPL. Lipid replacement improved several motility parameters (total motility, 2.0±1.0 vs 68.8±2.9%; progressive motility, 0±0 vs 19.3±2.6%; straight line velocity, 9.5±2.1 vs 50.9±4.1 μm/s; curvilinear velocity, 40.8±10 vs 160.7±7.8 μm/s; average path velocity 13.4±2.9 vs 81.9±5.9 μm/s; P≤0.001), sperm viability (13.5±2.9 vs 80.2±1.6%; P≤0.001) and reduced mitochondrial ROS generation (98.2±0.6 vs 74.8±6.1%; P≤0.001). Supplementation with GPL during 17 oC in vitro sperm storage over 72 h improved sperm viability (66.4±2.6 vs 78.1±2.9%; P≤0.01) and total motility (53±5.6 vs 66.3±3.5%; P≤0.05). It is concluded that incubation of stallion spermatozoa with sub-mm-sized GPL micelles results in the incorporation of exogenous GPL into sperm membranes, diminishing lipid peroxidation and improving sperm quality in vitro.