The Effect of Dietary Amino Acid Balance on Nitrogen and Lysine Utilization in Lactating Sows
Decreasing dietary crude protein (CP) concentration and increasing crystalline amino acid (CAA) supplementation, in order to maintain constant daily intakes of Lys and other key amino acids (AA), improves dietary AA balance. The effect of improved dietary AA balance on lactation performance, nitrogen (N) and AA utilization efficiency, and AA fates must be determined for precise lactating sow diet formulation and to meet specific production objectives. Performance, N balance, mammary biopsy, and isotope tracer studies were conducted to determine the effects of improving dietary AA balance on sow and litter lactation performance, N and Lys utilization efficiencies for milk production, mRNA abundance of mammary AA (Lys) transporters, and the partitioning of dietary AA between maternal and milk protein pools. Litter growth rates and milk protein production increased with improved AA balance, at the expense of maternal N retention, particularly in peak lactation. At identical Lys intakes, there was minimal improvement in Lys utilization efficiency for milk production with improved dietary AA balance, and there were no corresponding changes in the expression of mRNA for several Lys transporters within the mammary gland. Whole-body protein turnover and tissue-specific fractional rates of protein synthesis were not influenced by dietary AA balance. Feeding lactating sows reduced CP diets with increased inclusion of CAA, to improve AA balance and to meet the requirements of limiting AA, is a feasible way to improve the utilization of N and AA for milk protein production and decrease N losses to the environment, without negatively impacting sow and litter lactation performance. Amino acid and N requirements differ from those estimated by the NRC (2012) model and among genotypes and parity of sows. The utilization efficiencies of N and AA may change across a lactation period. All of these factors should be considered when planning future research and formulating lactating sow diets.