ISSUE FOCUS FEED & ADDITIVE MAGAZINE February 2024 41 IMPROVING PRE-ABSORPTIVE NUTRIENT UPTAKE The key element to address in the pre-absorptive phase of nutrient utilization is to ensure that feed digestibility is maximized so that nutrients are unlocked and the pig can extract maximum value from its feed. Digestibility can be maximized via two main mechanisms, 1) ensuring fiber, protein and starch are fully utilized and 2) removing bacterial cell debris (such as peptidoglycans) from the intestinal surface so that the digested nutrients are available for absorption. Post-weaning piglet diets can include a range of plant-based ingredients containing many different types of non-starch polysaccharides (NSPs) contributing indigestible components such as arabinoxylans, glucans, mannans and galactans and impacting diet viscosity and digestibility of nutrients. The endogenous enzymes in the pig are unable to fully digest these NSP components. The use of targeted exogenous carbohydrases such as xylanases, β-glucanases, β-mannanases, and amylases have been shown to improve the net energy of the diet by cleaving NSP fractions into more readily fermentable components (Kiare et. al., 2013) and thereby facilitating more flexibility in the choice and sourcing of feed ingredients for pigs. Improving fiber digestion through use of exogenous enzymes has also been shown to modulate the microbial ecology and stimulate fermentation which can improve gastrointestinal health through the stimulatory effects of short chain fatty acids, especially butyrate (Kerr and Shurson, 2013; Zhao et. al., 2019). In addition to maximizing net energy extraction, ensuring full utilization of the amino acids in the diet, is also essential to enable the piglet to achieve its genetic potential. Decreasing the undigestible crude protein content of feed and avoiding protein fermentation in the hindgut are important aspects of supporting growth and resilience. While protein sources such as soybean meal, peas and sunflower meal are effective ingredients for supplying amino acids, they also contain significant amounts of cell wall materials consisting of xyloglucans and pectins. These compounds can contribute to an increased viscosity of the digesta preventing effective amino acid utilization and need a combination of enzymes to assist in their breakdown. Supplementing piglet diets with a mixture of enzymes including beta-glucanases and endo-pectinases resulted in an increase in daily weight gain of up to 7% (Schurz and Richter, 2002). Furthermore, Blanco-Perez et al. (2021) have identified that pectins can have indirect and direct beneficial effects on immune modulation and therefore pectin release from raw materials through enzyme use may have positive health benefits for the pig. When bacteria die, the resulting cell wall debris, which is rich in peptidoglycans, can impair nutrient absorption from the intestinal surface (van Immerseel et al., 2020). Peptidoglycans can be cleaved by muramidase, resulting in formation of muramyl dipeptide (MDP). The MDP can be recognized by epithelial cell receptors (NOD-2) and the NOD-2 receptors play a crucial role in supporting barrier protection and surveillance of the cell wall (Constans, 2005). Consequently, with a proper functioning cell wall, absorption of nutrients can be maximized. A meta-analysis of the effect of including muramidase in piglet diets for 42 days showed that average daily gain was improved by 7% and feed conversion efficiency by 6% (DSM, 2020). OPTIMIZING POST-ABSORPTIVE NUTRIENT UTILIZATION Supporting resilience from the post-absorptive perspective requires the most effective transfer of nutrients to productive purposes such as lean muscle deposition, with limited diversion of nutrients to maintenance and unproductive inflammatory responses. Strategies to reduce the inflammatory processes, such as developing immune competency and gut functionality should be continued in this phase. As carbohydrates supply approximately 60-70% of the net energy needs of the piglet, a major contributor to resilience is centered on fiber nutrition and its optimized use. In addition to the use of enzymes to assist with release of nutrients as required in the pre-absorptive phase, use of carbohydrases also play
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