Dietary Protein Levels Affect Neonatal Pig Growth and Mesenchymal Stem Cell Behavior

Growth rate is highest during neonatal development and exerts lifelong effects on animal performance. Despite this, our knowledge of the nutritional requirements needed to support this rapid growth is limited. Our previous work has demonstrated that alterations in the activity and differentiation potential of mesenchymal stem cells (MSC) can dramatically impact bone growth and development. With increasing interest in and evidence of cross-talk between muscle and bone, we examined the impact of dietary protein levels on the growth of neonatal pigs and the activity of their MSC. Thirty 1-d-old (24 ± 6 h) piglets were individually housed and fed with milk replacers that were 25% deficient (D), adequate (A), or 25%in excess (E) of protein requirements based on sow milk composition and an extrapolation of the NRC requirements for older pigs. The starting weights of the pigs in each group were 1.47±0.1 kg for the D and 1.46 ±0.1 kg for the A and E groups. Body weight and feed intake were recorded daily for the 17d study. Blood was collected on d11 and d17 for serum urea nitrogen (SUN) determination. Humeri were collected for the isolation of MSC analysis and radial/ulna bones were collected for physical measurement and bone mineral determination. Final body weight and ADG were significantly higher in the E than the D group (5.60±0.27kg vs 4.75±0.27kg and 0.27±0.01kg/d vs 0.21±0.01kg/d). This increased growth rate, coupled with equal feed intake across treatment groups, led to improved G:F in the E than the D group (P<0.05). SUN level increased with increasing dietary protein levels at both d11 and d17 (P<0.05). Radial/ulna bone volume was significantly greater in the E and A groups than in the D group characterized by increased radius cross sectional area (E: 39.94±1.87mm²; A: 39.21±1.97mm², D: 33.21±1.87mm²). The E group had significantly higher bone weight (19.05±0.76g vs 15.82±0.75g) but lower bone ash ratio than D group (%) (35.6±0.4 vs 37.9±0.4). No significant difference for dry bone and bone ash weight was found among groups. In vivo MSC proliferation rate (%), as determined by BrdU labelling, was significantly higher in the E than the D group (19.9±2.9 vs 11.4 ±2.9). These findings suggested that dietary protein levels in excess of what is currently considered required during the neonatal period allows for improved growth and feed efficiency. Additionally, early dietary protein deficiency alters neonatal bone development, potentially via alterations in MSC activity.