Evaluation of branched-chain amino acid interactions in 10 to 20 kg nursery pigs using a central composite design.

ABSTRACT

Two groups of 240 pigs (PIC 337 × 1050, PIC Genus, Hendersonville, TN) were used to investigate the interactions between leucine, isoleucine, and valine on the growth performance of approximately 10 to 20 kg nursery pigs. At weaning, pigs were placed into 40 pens with three barrows and three gilts per pen and fed a common diet for 3 wk. On day 21 postweaning, pens were randomly assigned to 1 of 15 dietary treatments in a central composite design. Diets were formulated to various levels of standardized ileal digestible (SID) Leu, Ile, and Val by supplementing L-Leu, L-Ile, and L-Val. Levels of the branched-chain amino acids, expressed as ratios to SID Lys, ranged from 98% to 180%, 46% to 64%, and 51% to 78% for Leu, Ile, and Val, respectively. Diets were formulated to be iso-Lys, isonitrogenous, and isocaloric. Pig weights and feed intake were measured for the 21-d experiment to calculate average daily gain (ADG), average daily feed intake (ADFI), and feed efficiency (GF). Growth performance data were analyzed using the lm() function in R version 4.2.2 (R Core Team, 2022). The second-order polynomial model included the linear and quadratic effects of Leu, Ile, and Val, their three two-way interactions, and initial body weight. Pen was the experimental unit, and parameters were considered significant at P ≤ 0.10. A linear and quadratic effect of Val was observed for ADG and GF (P < 0.001). There was an interaction between Leu and Ile for ADG (P = 0.069) and GF (P = 0.032), where increasing Leu and decreasing Ile, and the inverse, improved ADG and GF. However, growth and efficiency were negatively impacted as Leu and Ile increased in the diet. There was an interaction between Leu and Val for ADFI (P = 0.060), where Leu negatively impacted feed intake at low levels of Val but had little impact as Val increased above NRC (2012) recommendations. In conclusion, Val linearly and quadratically impacted ADG and GF, regardless of Leu and Ile levels in the diet, while ADG and GF were reduced with high levels of Leu and Ile, which was resolved as either Leu or Ile was reduced. Furthermore, ADFI was negatively impacted by increased Leu when Val was below NRC (2012) recommendations but was not affected by Leu at higher Val levels. Together, the results of this experiment emphasize the complexity of amino acid metabolism in nursery pigs and the importance of considering potential interactions among amino acids when conducting requirement studies.

Leucine, isoleucine, and valine are known as the branched-chain amino acids (BCAA). Aside from being essential for protein synthesis, BCAA play signaling roles, stimulating pathways of muscle protein synthesis. The first two steps in the BCAA catabolic pathway are shared amongst the three amino acids; consequently, excess consumption of one BCAA may increase the catabolism of the other two, hindering growth performance. Therefore, the objective of this trial was to investigate the interactions of BCAA and their impact on the growth performance of approximately 10 to 20 kg nursery pigs. In the current trial, valine linearly and quadratically impacted average daily gain and feed efficiency, regardless of leucine and isoleucine levels in the diet, but high levels of both leucine and isoleucine negatively impacted growth and efficiency. Furthermore, increasing leucine in the diet reduced feed intake when accompanied by low levels of valine, which was resolved as valine increased. Using a central composite design allowed for the description of the complex interactions between BCAA in nursery pigs and demonstrated the utility and application of this design in swine nutrition research. Together, the results of this study highlight the importance of considering the balance of BCAA in the diet of nursery pigs.