An investigation of branched-chain amino acid interactions in nursery pigs and lactating sows

Abstract

Amino acids (AA) are fundamental nutrients that form the building blocks of tissues, milk proteins, enzymes, and various signaling molecules essential for supporting growth, reproduction, and lactation. Dietary protein is a costly component in swine diets; thus, a precise understanding of AA requirements is critical for enhancing production efficiency. With the increased use of feed-grade AA to reduce dietary crude protein, optimizing AA balance is essential to prevent deficiencies or imbalances that may impair performance. Among these, the branched-chain amino acids (BCAA) leucine, isoleucine, and valine play vital roles in protein synthesis and metabolism. However, their shared catabolic pathway creates a potential for antagonistic interactions, where an excess of one BCAA can accelerate the catabolism of the others, decreasing their availability and increasing their dietary requirements. This issue is especially relevant in diets containing corn co-products, which typically contain high levels of Leu relative to Ile and Val. There is sufficient evidence to suggest that interactions among Leu, Ile, and Val influence growth rates and feed intake in nursery pigs; however, these relationships remain incompletely defined, making it challenging to identify an ideal BCAA balance for diet formulation. For lactating sows, the data is equivocal, with variation in reported BCAA requirements suggesting that interactions between BCAA may impact lactation outcomes. However, more investigation is needed to determine these effects conclusively. Understanding the practical implications of BCAA interactions in swine nutrition is crucial for developing dietary strategies to promote efficient growth in nursery pigs and enhance lactation performance in sows. Therefore, the overall objective of this dissertation was to assess BCAA interactions in nursery pigs to determine optimal levels for growth and feed efficiency and to evaluate BCAA effects in lactating sows to explore their role in nutrient requirements and productivity. To accomplish these objectives, a series of experiments were conducted and are reported in three research chapters (Chapters 2, 3, and 4). Research presented in Chapter 2 utilized a central composite design (CCD) to simultaneously evaluate how Leu, Ile, and Val interact to influence growth performance in 10- to 20 kg nursery pigs. The results indicated that concurrently increasing dietary Leu and Ile reduces growth rate and feed efficiency, which is likely a consequence of increased BCAA catabolism limiting Val availability for growth. Furthermore, it was shown that increasing dietary Val can offset the adverse effects of excess Leu on feed intake, suggesting that optimizing Val levels is critical in practical diet formulation. However, given the mixed curvature of the response surfaces, a single optimal BCAA combination was not identified within practical dietary levels, underscoring the importance of considering both ingredient cost and specific production goals when formulating nursery pig diets. This study supports the use of CCD in evaluating complex nutrient interactions and provides a foundation for refining dietary BCAA balance to maximize production efficiency in nursery pigs. Building on the relationships identified in Chapter 2, the research reported in Chapter 3 examined whether similar BCAA interactions affect lactating sow performance. Across all metrics evaluated, there was no evidence to suggest that the various BCAA levels impacted lactating sow or piglet performance; however, high feed intake in this study resulted in potentially excessive intakes of all BCAA, which may have mitigated the potential negative consequences of BCAA interactions. Furthermore, increasing soybean meal (SBM) inclusion reduced sow lactation feed intake, independently of dietary BCAA balance, indicating other factors beyond BCAA, such as trypsin inhibitors, contributed to reduced sow feed intake with high SBM inclusion (Chapter 4). Collectively, the results of Chapters 3 and 4 do not support that BCAA interactions are altering sow lactation performance within practical dietary BCAA ranges. Overall, this research emphasizes the value of optimized BCAA ratios in nursery pig diets and suggests further exploration of AA metabolism in lactating sows to refine dietary AA requirements. These findings provide actionable insights for swine diet formulation, supporting production efficiency and sustainable practices.