Mapiye, C., Dugan, M. E. R., Turner, T. D., Rolland, D. C., Basarab, J. A., Baron, V. S., McAllister, T. A., Block, H. C., Uttaro, B. and Aalhus, J. L. 2013. Short Communication: Erythrocytes assayed early ante mortem can predict adipose tissue and muscle trans-18:1 isomeric profiles of steers fed red clover silage supplemented with flaxseed. Can. J. Anim. Sci. 93: 149-153. Steers were fed a red clover silage-based diet with or without flaxseed to evaluate over time the effects of flaxseed supplementation on erythrocytes (ERC) trans(t)18:1 isomers composition and their relationships to adipose tissue and muscle t18:1 profiles at slaughter. Concentrations of most ERC t18:1 isomers in steers fed flaxseed increased (P<0.01) markedly in the first 2 mo and increased gradually thereafter. Strong (P<0.01) correlations of t9-, t10- and t11-18:1 isomers were observed from month 2 to 6 between ERC and beef tissues collected at slaughter from steers fed flaxseed. Findings suggest that ERC sampled as early as 2 mo into the feeding period can be indicative of variation in beef t18:1 isomeric profile at a later slaughter date when feeding red clover silage with flaxseed.