Plasma levels of β-hydroxy-β-methylbutyrate (HMB) and leucine in neonatal pigs fed low-protein (LP) diets supplemented with HMB (31) or leucine (Leu) (66) or a high-protein (HP) diet (31, 66). A: plasma HMB from study 1. HMB4, HMB40, and HMB80, 4, 40, and 80 μmol HMB·kg body wt−1·day−1. B: plasma leucine from study 1. C: plasma leucine from study 2. Statistical analyses were performed with 1-way ANOVA followed by Tukey’s test. Values are means ± SE; n = 7–10 pigs. Means with different letters differ at P < 0.05.