Background:Branched chain amino acids (BCAAs) are important substrates for milk protein synthesis in the mammary gland,and are tightly related to lipid metabolism.No study has been performed examining the role of BCAAs with high fat diets on milk fat synthesis.This study was designed to investigate the effect of dietary BCAAs on growth performance of piglets,progeny body weight,and milk fat composition in sows fed a high fat diet.Four diets (CON =control diet;HF =high fat diet with 8％ soybean oil;HF-MB=HF plus 0.39％ BCAAs;HF-HB=HF plus 0.78％ BCAAs) were fed to sows from late gestation to weaning.Results:Compared to HF,BCAAs (HF-MB and HF-HB) increased the litter weight (P ＜ 0.05) and overall litter weight gain (P ＜ 0.05) at weaning and increased colostrum fat content by 27.3-35.8％ (P ＜ 0.01).Fatty acid profiles between the two doses of BCAAs were similar.Compared with HF,HF-MB tended to decrease the percentage of C18∶3n3 (P=0.063) and increased the percentage of C18∶1 n9c (P =0.03).In addition,BCAAs in HF-MB increased the concentration of total fatty acid by 22.1％ in colostrum (P =0.03) but decreased that in serum at parturition by 53.2％ (P =0.027).The fatty acids in colostrum that increased with BCAAs were C15∶0,C17∶0,C20∶3n6,C20∶4n6,C20∶5n3 and C22∶6n3 (P =0.00～0.04).Colostrum fatty acids of C20∶0,C21∶0,C22∶0,C16∶1,C20∶1,C18∶1 n9c also tended to be increased (0.05 ＜ P＜ 0.1) with BCAAs.The change in sow serum fatty acid profile due to BCAAs was different from that in colostrum.Conclusions:BCAAs in high fat diet of sows altered the fatty acid composition in colostrum and enhanced litter growth.Our study indicated that BCAAs supplementation can enhance mammary fatty acid uptake and mammary fat synthesis and that supplemental BCAAs and fat in late gestation and lactation diets for sows can improve reproductive performance.