Background:Maternal nutrition during gestation affects fetal development, which has long-term programming effects on offspring postnatal growth performance. With a critical role in protein and lipid metabolism, essential fatty acids can influence the development of muscle and adipose tissue. The experiment investigated the effects of late gestation supplements (77 d prepartum), either rich in saturated and monounsaturated fatty acids (CON;155 g/cow/d EnerGII) or polyunsaturated fatty acids (PUFA;80 g/cow/d Strata and 80 g/cow/d Prequel), on cow performance and subsequent calf growth performance as well as mRNA expression in longissimus muscle (LM) and subcutaneous adipose tissue at birth and weaning. Results:There was no difference (P≥0.34) in cow body weight (BW) or body condition score from pre-supplementation through weaning. Relative concentrations of C18:3n-3 and C20:4n-6 decreased (P≤0.05) to a greater extent from mid-supplementation to calving for PUFA compared with CON cows. Cow plasma C20:0, C20:5n-3, and C22:6n-3 were increased (P≤0.01) in PUFA during supplementation period. At birth, PUFA steers had greater (P=0.01) plasma C20:5n-3. No differences (P≥0.33) were detected in steer birth BW or dam milk production, however, CON steers tended (P=0.06) to have greater pre-weaning average daily gain and had greater (P=0.05) weaning BW compared with PUFA. For mRNA expression in steers:MYH7 and C/EBPβin LM increased (P≤0.04) to a greater extent from birth to weaning for PUFA compared with CON;MYF5 in LM and C/EBPβin adipose tissue tended (P≤0.08) to decrease more from birth to weaning for CON compared with PUFA;SCD in PUFA adipose tissue tended (P=0.08) to decrease to a greater extent from birth to weaning than CON. In addition, maternal PUFA supplementation tended (P=0.08) to decrease MYOG mRNA expression in LM and decreased (P=0.02) ZFP423 in adipose tissue during the pre-weaning stage. (Continued from previous page) Conclusions:Late gestation PUFA supplementation decreased pre-weaning growth performance of the subsequent steer progeny compared with CON supplementation, which could have been a result of downregulated mRNA expression of myogenic genes during pre-weaning period.