Effects of dietary methionine and lysine supplementation on nutrients digestion, serum parameters and mRNA expression of related amino acid sensing and transporting genes in growing goats

Sufficient amino acid is necessary to the growth of animals. The experiment investigated the effects of dietary unprotected methionine (Met) and lysine (Lys) sources on nutrient digestion, nitrogen utilization and mRNA expression of related genes in growing goats fed a maize stover-based diet. Twenty Liuyang black weather goats were used and assigned randomly to 4 dietary treatments: (1) the control (basal) diet (NS:), (2) control diet with a supplementation of unprotected DL-Met (SM), (3) control diet with a supplementation of unprotected L-Lys-HCI (SL), (4) control diet with a supplementation of unprotected DL-Met and L-Lys-HCI (SML). The experiment showed that there were no differences of DMI (dry matter intake), fecal output, apparent digestibility, energy balance and N balance (P >  0.05). Adding Lys decreased serum threonine, isoleucine, phenylalanine, total amino acids (P <  0.05) comparing with NS, SM and SML (P < 0.05). SL and SML reduced serum Met and arginine compared with NS and SM (P <0.05). Compared to NS, SM and SL, SML lowered serum leucine (P = 0.057). SM, SL and SML had lessen: total cholesterol (TC) and SLC38A2 mRNA expression in jejunum compared to NS (P < 0.05). SM had the lowest mRNA expression of SLC7A7 in jejunum, SLC7A9 in ileum, SLC7A1 in cecum (P <  0.10). NS had the lowest mRNA expression of EIF4B in the duodenum (P =  0.057). Overall, adding a small amount of free Met and Lys did not affect apparent digestibility but changed serum AAs profile and tended to influence protein synthesis resulted from expression changes of related AAs transporters in the specific intestine tract and mTOR pathway. Our findings provided valuable information for improving animal production through amino acid nutrition regulation.