Growth and Clinical Variables in Nitrogen-Restricted Piglets Fed an Adjusted Essential Amino Acid Mix: Effects of Partially Intact Protein-Based Diets

Background: Current recommendations for protein levels in infant formula are intended to ensure that growth matches or exceeds growth of breastfed infants, but may provide a surplus of amino acids (AAs). Recent infant studies with AA-based formulas support specific adjustment of the essential amino acid (EAA) composition allowing for potential lowering of total protein levels. With the use of a combination of intact protein and free EAAs, we designed a formula that meets these adjusted EAA requirements for infants. Objective: Our objective was to test whether this adjusted formula is safe and supports growth in a protein-restricted piglet model, and whether it shows better growth than an isonitrogenous formula based on free AAs. Methods: Term piglets (Landrace x Yorkshire x Duroc, n = 72) were fed 1 of 4 isoenergetic formulas containing 70% intact protein and 30% of an EAA mixture or a complete AA-based control for 20 d: standard formula (ST-100), ST-100 with 25% reduction in proteinaceous nitrogen (ST-75), ST-75 with an adjusted EAA composition (O-75), or a diet as O-75, given as a complete AA-based diet (O-75AA). Results: After an initial adaptation period, ST-75 and O-75 pigs showed similar growth rates, both lower than ST-100 pigs (similar to 25 compared with 31 g . kg(-1) . d(-1), respectively). The O-75AA pigs showed further reduced growth rate (15 g . kg(-1) . d(-1)) and fat proportion (both P