Overall assessment of fermented feed for pigs: a series of meta-analyses

As an alternative to antimicrobial growth promoters, fermented feed (FF) has been continuously developed for two decades; however, its effects on feed, performance, digestibility, and meat quality of pigs have yet to be systematically and comprehensively evaluated. This study aimed to (i) quantitatively evaluate the effects of fermentation on nutritional components of feed stuffs; (ii) quantitatively evaluate the effects of FF on pig growth performance, digestibility, and meat quality; and (iii) explore the dose-effect relationship. From PubMed and Web of Science (searched range from January 1, 2000 to April 4, 2019), we collected 3,271 articles, of which 30 articles (3,562 pigs) were included in our meta-analysis. Our analysis revealed that fermentation significantly increased the CP content in feed (P < 0.05). For weaned piglets and growing pigs, FF significantly improved ADG, G:F, DM digestibility, N digestibility, and energy digestibility (P < 0.05). However, compared with the basal diet, FF had no significant effects on growth performance and nutrient digestibility in finishing pigs (P > 0.05). In the subgroup analyses, fermented ingredients increased the growth performance of weaned piglets and growing pigs, and fermented additives promoted the growth of pigs at all stages. The dose-effect analysis confirmed that the optimal doses of fermented ingredients and additives were 8% and 0.15%, respectively. Furthermore, FF had beneficial impacts on meat quality through increased lightness, redness, marbling and flavor and reduced drip loss (P < 0.05). In conclusions, FF improved growth performance and meat quality primarily due to its positive effects on nutritive value and utilization.