Increased dietary protein rather than fiber supports key metabolic and intestinal tissue functions in pigs, without...

The postweaning period in pigs is a critical window where nutritional interventions are implemented to prevent postweaning diarrhea (PWD) and antibiotic use. One common strategy is feeding low-protein diets immediately following weaning. This intervention may reduce protein fermentation and pathogen proliferation, therefore decreasing the incidence of postweaning diarrhea. These effects may also be mitigated by providing dietary fiber. However, studies examining the role of protein and fiber on gastrointestinal microbiota and metabolism are complicated by the presence of other substrates, including polyphenols and antinutritional factors in complex ingredients. In this study, semipurified diets formulated to meet nutrient requirements were fed to 40 weaned pigs (n = 10/diet) to examine the effects of high protein (HP), high fiber (HF), or both (HFHP) compared with a control (CON) diet with industry-standard crude protein and fiber content. Critical alterations in host metabolism and cecal transcriptome were identified in response to the CON diet. Diets with lower protein levels (CON and HF) induced alteration in transcripts from the serine synthesis pathways and integrated stress response in cecal tissue alongside systemic increases in metabolic pathways related to lysine degradation. High protein diets did not induce increases in gastrointestinal pathogen abundance. These results challenge the practice of feeding low-protein diets postweaning, by demonstrating a detrimental effect on intestinal cell function and muscle accretion. This suggests that with careful ingredient selection, increased dietary protein postweaning could improve pig health and growth compared with a standard diet.NEW & NOTEWORTHY Although low-protein diets are commonly used for weaned pigs and are thought to decrease diarrhea incidence, this study showed that low-protein diets may induce muscle catabolism and intestinal epithelial stress response. Eventhough high-protein diets increased protein fermentation by gut microbes, no increase in diarrhea was detected. Protein fermentation was mitigated by fiber while still supporting growth and intestinal epithelial cell function, suggesting new strategies for feeding weaned pigs with careful ingredient selection.