Dose-Dependent Effects of Replacing Soybean Meal with Cottonseed Protein: Key to Optimizing Gut Health in Weaned Piglets

This study aims to systematically assess the comprehensive, dose-dependent effects of substituting soybean meal with cottonseed protein at various ratios on weaned piglets. In total, 28-day-old weaned piglets (Duroc × Landrace × Large White crossbred; n = 45) were selected and then randomly categorized into three groups: 100% soybean meal (CON), 50% soybean meal +50% cottonseed protein (CSP50), and 100% CSP (CSP100) groups. After a 7-day adaptation period, the experiment continued for an additional 28 days. The results showed no significant differences among groups in growth performance, organ indices, most carcass traits, or meat quality indicators. The CSP50 group showed significantly reduced levels of diamine oxidase (DAO) and D-lactate and increased complexity of the colonic microbial network, with improved abundance of beneficial bacterial genera such as g_Blautia and g_Eubacterium. The CSP100 group showed elevated intestinal permeability, a decreased villus height, a villus-to-crypt ratio, specific digestive enzymes, a reduced Firmicutes/Bacteroidetes (F/B) ratio and abundant inflammation-associated bacteria, including g_Streptococcus. Furthermore, correlation analysis suggested that specific gut microorganisms and metabolic pathways may be potentially related to average daily gain (ADG), average daily feed intake (ADFI), the feed conversion ratio (F/G), DAO, and D-lactic acid. These findings suggest that dietary inclusion of 50% cottonseed protein (CSP50) is associated with sustained growth performance and enhanced gut health in weaned piglets, concurrent with shifts in the composition and predicted function of the gut microbiota.