The aim of the study was to investigate the effects of dietary BCAA supplementation on growth performance, N balance, and whole-body protein turnover in piglets from 8 to 21 kg. Twenty-eight individually caged Large White × Landrace barrows were randomly assigned to 1 of 4 dietary groups (n = 7). All 4 diets were fortified with Lys, Met, Thr and Trp to satisfy the SID AA requirements recommended by NRC (2012). Diet PC was a positive control diet (19.5% CP); diet NC was a reduced-CP negative control diet (16.7% CP); diets T1 and T2 were reduced-CP diets to which 0.17% Ile, 0.16% Val, and 0.24% Leu or 2-fold dose of each BCAA were added, respectively. Nitrogen balance was determined over 5 subsequent days at the beginning of the 3rd week of the experiment. Whole-body protein turnover was determined by using the end product method after a single oral dose of ¹⁵N-glycine. All data were analyzed using the One-way ANOVA and Duncan's procedures. The results showed that NC group had decreased ADG, ADFI and absolute N retention compared with the PC group, which were restored in T1 and T2 groups (P < 0.05). Total N excretions (g/d) were reduced (P < 0.05) in NC, T1 and T2 groups compared with PC group. There was no difference between PC and NC groups for protein synthesis, whereas T1 and T2 groups had higher (P < 0.05) protein synthesis than NC group. No difference in protein degradation were detected among 4 groups. There was no difference between T1 and T2 groups except for a higher N excretions in T2 group. These results indicate dietary BCAA supplementation improves growth performance and dietary N utilization for protein accretion in piglets. Table 1. Effect of dietary BCAA supplementation on growth performance in piglets

Item	PC	NC	T1	T1	SEM	P-value
ADFI, g/d	714a	558b	707a	721a	20	<0.01
ADG, g/d	422a	322b	449a	452a	15	<0.01
G:F	0.59ab	0.58b	0.64a	0.63a	0.01	0.03
N excretion, g/d	6.14a	3.74c	3.59c	4.83b	0.23	<0.01
N retention, g/d	12.95a	8.72b	11.48a	12.15a	0.45	<0.01
Protein synthesis, g of N/(kg0.75·d)	36.29ab	26.21b	37.82a	36.52a	2.30	0.05
Protein degradation, g of N/(kg0.75·d)	34.44	24.81	36.15	34.71	1.84	0.14

^a,bWithin a row, means without a common superscript letter differ (P < 0.05).