ISSUE FOCUS 40 FEED & ADDITIVE MAGAZINE February 2024 daily gain and/or backfat deposition. Animals with high RFI use more nutrients for a given level of performance than animals that have a low RFI. Low RFI animals are therefore more efficient at extracting and/or utilizing nutrients, and methods to optimize this efficiency are an integral aspect of supporting resilience. Another key component in understanding the role of resilience in piglets is the degree to which the challenge impacts the pig, and the length of time needed for the pig to recover from the challenge. The recovery period can be considered as the resilience period. The level of recovery in performance is related to the health, immune competency and gut functionality of the piglets and is why getting these aspects right is so important. The particularly important role of the immune system in resilience has been shown in a number of publications, such as a paper by Sauerwein (2005), that have measured the relationship between haptoglobin (an acute phase protein that reflects sub-clinical inflammation) level and performance. As haptoglobin blood level increases, average daily gain decreases. It is important to recognise that the immune system requires a different suite and supply of these nutrients, especially amino acids, to what is needed for lean muscle growth and that feeding diets to support lean muscle accretion may not adequately supply the correct proportion of nutrients to support immune optimisation. For example, the amino acids phenylalanine, tryptophan and threonine are needed in much higher proportion for acute phase protein synthesis than skeletal muscle deposition (Klasing and Iseri, 2013). Similarly, when animals are challenged with unsanitary conditions (requiring an upregulated immune response), the requirement ratio between tryptophan and lysine is altered with pigs in unsanitary conditions requiring more tryptophan to maintain acceptable performance (Le Floc’h, 2009) and in addition overall nitrogen digestibility is decreased in unsanitary conditions (Noorman, 2002). Decreasing nitrogen digestibility and nitrogen retention efficiency can lead to increases in protein substrate availability in the hindgut for pathogen growth, further challenging the immune system of the pig. Therefore, the key aspects to supporting resilience in pigs is to ensure: 1. the optimal extraction of nutrients from the feed (optimum nutrient digestive efficiency – the pre-absorptive component), and 2. the appropriate allocation of nutrients to maintenance and production (the post-absorptive component). These concepts are outlined in Figure 1. Figure 1. Mechanisms for Supporting Resilience
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