Effects of paraformic acid supplementation, as an antibiotic replacement, on growth performance, intestinal morphology and gut microbiota of nursery pigs

A total of 150 crossbred male pigs [21±1 days old; 8.85±0.15 Kg body weight (BW)] were randomly assigned to five dietary treatments with five replicates per treatment and six pigs per pen to evaluate the effect of paraformic acid (PFA), as a substitute to antibiotics, on growth performance, intestinal morphology, and gut microbiota of nursery pigs. The treatments were: 1) NC: nutrient adequate control diet; 2) PFA1: similar to NC plus 0.30% PFA; 3) PFA2: similar to NC plus 0.60% PFA; 4) PFA3: similar to NC plus 1.0 % PFA; and 5) PC: similar to NC plus 0.15% of chlortetracycline. Pigs were fed the same nutritional profile during the two-phase feeding regime [Phase 1 (P1; d 0–14), and phase 2 (P2; d 15–30)]. Initial BW, and BW and feed disappearance at the end of each phase were recorded to calculate average daily feed intake (ADFI), average daily gain (ADG), and feed to gain ratio (F: G) per phase. Fecal score was determined at the end of P1, while the intestinal morphology and microbiota analysis were performed at the end of P2. Pigs fed PFA2 had higher ADG than those fed NC in P1. A quadratic response was found in the overall Phase 1 and Phase 2 (P1&amp;2) with the highest ADG in pigs fed PFA2 (<italic>p </italic>&lt; 0.05). Pigs fed PC had the highest ADFI during P2 and overall P1&amp;2 (<italic>p </italic>&lt; 0.05). The PFA2 group had the lowest F:G ratio among treatments in P1 and P2, with a quadratic response in the overall P1&amp;2 (<italic>p </italic>&lt; 0.05). Pig fed PFA1, PFA2, PFA3 and PC showed better fecal consistency than NC (<italic>p </italic>&lt; 0.05). No differences were found in intestinal morphology among treatments. PFA groups supplementation modulated the relative abundance of <italic>Lactobacillus</italic> and <italic>Streptococcus</italic> in jejunum. In the cecum, PFA2 had a higher relative abundance of  <italic>Prevotella</italic> when compared to NC, but lower than PC. In addition, pigs fed NC diet had higher abundance of <italic>Treponema</italic> and <italic>Methanobrevibacter </italic>than other treatments. In conclusion, the supplementation of 0.6% PFA improved growth performance and modulated gut microbiota in nursery pigs.