Milk Powder Fortified with Folic Acid and Colostrum Basic Protein Promotes Linear Growth and Improves Bone Microarchitecture in Juvenile Mice Without Adverse Metabolic Effects

<b>Background:</b> The juvenile-pubertal period is a critical window for linear growth and bone mass accumulation. This study investigated the joint effects of folic acid (FA) and colostrum basic protein (CBP)-fortified milk powder on growth, bone health, and metabolic safety in juvenile mice. <b>Methods:</b> Three-week-old C57BL/6J mice (n = 120) were acclimatized for 1 week and then randomly assigned to three isocaloric diet groups for an 8-week intervention starting at 4 weeks of age: Control (AIN-93M), Milk (AIN-93M + FA/CBP-fortified milk powder), and Positive Control (AIN-93G). Body length and weight were measured twice weekly. Bone microarchitecture was assessed by micro-computed tomography, and bone remodeling was evaluated through histology and serum biomarkers. The GH-IGF-1 axis and related metabolic parameters were also assessed. <b>Results:</b> FA-CBP-fortified milk powder significantly accelerated linear growth at intervention week 2, with body length higher in the Milk group than in the Control group (<i>p</i> < 0.01). After 8 weeks, the Milk group showed improved trabecular bone mass and microarchitecture compared with Control, especially in males (<i>p</i> < 0.01). Bone remodeling was transiently elevated at intervention week 4, as indicated by higher serum osteocalcin and CTX-I, and by increased osteoclast and cartilage matrix formation versus Control (<i>p</i> < 0.05). The GH-IGF-1 axis was also temporarily activated at week 4, with elevated serum GH and IGF-1/IGFBP-3 ratio compared with Control (<i>p</i> < 0.05). These skeletal benefits occurred without excess weight gain or adverse metabolic effects compared with Control (all <i>p</i> > 0.05). <b>Conclusions:</b> FA-CBP-fortified milk significantly enhanced linear growth during puberty and improved bone mass and microstructure in early adulthood. These skeletal benefits are consistent with the transient activation of the GH-IGF-1 axis. Importantly, no adverse metabolic effects were detected from early intervention through adulthood, supporting its potential application in growth-promoting nutritional strategies.