Can milk replacer allowance affect animal performance, body development, metabolism, and skeletal muscle hypertrophy in preweaning dairy kids?

We aimed to evaluate performance, body development, metabolism, and expression of genes related to skeletal muscle hypertrophy in uncastrated male dairy kids fed with different levels of milk replacer (MR) during the preweaning period. Sixty newborn male kids, not castrated, from Saanen and Swiss Alpine breeds, with an average BW of 3.834 ± 0.612 kg, were distributed in a randomized block design. Breeds were the block factor in the model (random effect). Kids were allocated into 2 nutrition plans (n = 30 kids/treatment) categorized as follows: low nutritional plan (LNP; 1 L of MR/kid per day) or high nutritional plan (HNP; 2 L of MR/kid per day). All kids were harvested at 45 d of life. The majority of nitrogen balance variables were affected by the nutritional plan (P < 0.050). Morphometric measures and BCS (2.99 for LNP vs. 3.28 for HNP) were affected by nutritional plan (P < 0.050), except hip height, thoracic depth, and hip width. The nutritional plan affected the body components (P < 0.050), except esophagus and trachea. Animal performance and carcass traits were influenced by nutritional plan (P < 0.050), except carcass dressing (48.56% on average). Nutritional plan affected (P < 0.050) some blood profile variables as the total cholesterol (141.35 vs. 113.25 mg/dL), triglycerides (60.53 vs. 89.05 mg/dL), LDL (79.76 vs. 33.66 g/mL), and IGF-1 (17.77 vs. 38.55 ng/mL) for LNP and HNP, respectively. Hypertrophy was greater in HNP than LNP animals (P < 0.050), being represented by the proportion of sarcoplasm (39.76% vs. 31.99%). LNP had a greater mTOR abundance than HNP (P = 0.045), but AMPK was not affected by the nutritional plan. Our findings show that a higher milk replacer allowance enhances animal performance, body development, metabolic parameters, and cellular hypertrophy in preweaning dairy kids.