Effects of replacing soybean meal with enzymolysis-fermentation compound protein feed on growth performance, apparent digestibility of nutrients, carcass traits, and meat quality in growing-finishing pigs

Addressing the shortage of high-quality protein resources, this study was conducted to investigate the effects of replacing soybean meal (SBM) with different levels of enzymolysis-fermentation compound protein feed (EFCP) in the diets of growing-finishing pigs, focusing on growth performance, nutrients digestibility, carcass traits, and meat quality. Sixty DLY (Duroc × Landrace × Yorkshire) pigs with an initial body weight of 42.76 ± 2.05 kg were assigned to 5 dietary treatments in a 2 × 2 + 1 factorial design. These dietary treatments included a corn-soybean meal diet (CON), untreated compound protein feed (UCP) substitution 50% (U50) and 100% SBM (U100) diets, and EFCP substitution 50% (EF50) and 100% SBM (EF100) diets. Each treatment had 6 pens (replicates) with 2 pigs per pen, and the experiment lasted 58 d, divided into phase I (1–28 d) and phase II (29–58 d). Following phase I, only the CON, U50, and EF50 groups were continued for phase II, each with 5 replicate pens. On d 59, a total of 15 pigs (1 pig/pen, 5 pens/treatment) were euthanized. During phase I, the EF50 group had a higher average daily gain (ADG) in pigs (P < 0.05) compared to the CON group, whereas the U50 group did not have a significant difference. As the substitution ratio of UCP and EFCP increased in phase I, there was a noticeable reduction in the final body weight and ADG (P < 0.05), along with an increase in the feed-to-gain ratio (F/G) (P < 0.05). In phase II, there were no significant differences in growth performance among the treatment groups, but EF50 increased the apparent digestibility of several nutrients (including dry matter, crude protein, crude fiber, acid detergent fiber, ash, gross energy) compared to U50. The EF50 group also exhibited significantly higher serum levels of neuropeptide Y and ghrelin compared to the CON and U50 groups (P < 0.05). Moreover, the EF50 group had higher carcass weight and carcass length than those in the CON and U50 groups (P < 0.05), with no significant difference in meat quality. The study findings suggest that replacing 50% SBM with EFCP during the growing-finishing period can improve the growth performance, nutrient digestibility, and carcass traits of pigs without compromising meat quality. This research offers valuable insights into the modification of unconventional plant protein meals and developing alternatives to SBM.