Effects of Enzymes or Fermented Feed on Nitrogen Balance, Meat Quality, Intestinal Microbiota Profile and Barrier Functions of Landrace × Rongchang Pigs Fed with a Diversified Low-Protein Diet

Reducing the dependence on traditional protein sources, and decreasing feeding costs and nitrogen emissions, are important tasks in livestock production. A 5 × 5 Latin square nitrogen balance trial (five castrated male pigs) and an animal growth experiment with 120 Landrace × Rongchang pigs were performed and randomly divided into five diets: a normal crude protein level diet (CON); LP diet; diversified LP containing broken rice, rapeseed meal, and DDGS (DLP); DLP + 0.05% cellulase (DLP + CE); and DLP + 20% fermented feed (FDLP). The CON group showed higher nitrogen intake, urinary nitrogen, and total nitrogen excretion than the other four groups (p < 0.05). The fecal nitrogen was decreased with the LP, DLP + CE, and FDLP groups compared to the CON group (p < 0.05). The mRNA expression of jejunal fatty acid transport protein 1 was upregulated in the LP, DLP + CE, and FDLP groups compared to the CON and DLP groups (p < 0.05). The DLP + CE group showed a higher intramuscular fat content in pigs than the CON and DLP groups (p < 0.05). In the LD muscle, the FDLP and DLP + CE groups upregulated fatty acid synthase expression compared to the LP and DLP groups (p < 0.05). Colonic mRNA expression of zonula occludens-1 and claudin-1 was upregulated in the FDLP group compared to the CON and DLP groups (p < 0.05). These results suggest that the supplementation of cellulase and fermented feed in DLP diets improved nitrogen utilization and intestinal health without compromising growth performance or meat quality in Landrace × Rongchang pigs.