The study was published in Animal Feed Science and Technology.
The Chinese researchers found that fermented feed positively affects average daily gain (ADG) and gain: feed (G/F) ratio but has little or no effect on average daily feed intake (ADFI).
“This suggests that the improvements in performance are associated with increased nutrient availability and/or utilization.
“Fermented feed ingredients enhanced the performance of weaned and growing pigs but not of finishing pigs. We speculate this is due to finishing pigs having a more developed digestive system and stable gastrointestinal tract microbiome (Nousiainen et al., 1998; Ao et al., 2011).
“In contrast, the fermented feed additives improved performance in all stages of growth and would appear to be beneficial for weaners and growing and finishing pigs,” said the authors, based at Zhejiang University in China.
They said FF can be classified into two categories based on fermentation technology i.e. fermented liquid feed and solid-state fermented feed (Joris et al., 2015; Mukherjee et al., 2016).
“Furthermore, solid-state fermented feed can be categorized based on the intended use such as: 1) fermented feed additives which have functional features (e.g. fermented medicinal plants which improve animal immunity) (Juglchizzola et al., 2006; Ao et al., 2011; Ahmed et al., 2016); 2) fermented feed ingredients which replace the protein or energy sources, reducing the anti-nutritional factors hence improving the feed efficiency (Kim et al., 2006; Kim et al., 2010; Cho et al., 2013; Le et al., 2016).”
The team said their review involved a systematic search in PubMed and Web of Science for studies published between January 1, 2000 and December 20, 2018 to determine the effects of FF supplementation on pig growth performance.
Studies were considered eligible if they met the following inclusion criteria:
1) the breeding background was ordinary commercial pigs (e.g. Duroc × Landrace × Yorkshire);
2) the intensity of energy and protein was uniform in the control and treatment groups;
3) the studies were randomized controlled trials;
4) the FF had a specific intended use.
They included weaned piglets with an initial weight ranging 5 kg to 10 kg and a feeding period of less than 6 weeks. The initial weight of the included growing pigs ranged from 20 to 50 kg, and the initial weight of finishing pigs was greater than 65 kg.
The exclusion criteria were as follows:
1) probiotics supplementation without fermentation period for the feedstuff;
2) studies on inhibitory effects of FF on pathogenic bacteria and infective virus;
3) studies on distillers dried grains with soluble-supplements;
4) studies on fermented liquid feed and liquid feed;
5) studies lacking a control group;
6) studies on pure native pig breeds;
7) studies on FF without clear nutrition alternative target;
8) studies where pig growth was not assessed in stages.
In total, the team said they identified 1371 studies, of which 25 (with data of 2,391 pigs) were included in the meta-analysis. The studies reviewed were carried out by Chinese, and Korean researchers in the main - there was one paper from the US (Jones et al, 2010) included in the meta-analysis.
Among the 25 selected studies there were 13 on weaned pigs, three studies of both growing and finishing pigs, six studies of growing pigs, and three studies of finishing pigs. The mean initial body weight of weaned piglets, growing pigs and finishing pigs were 7.2 kg, 31.1 kg and 77.3 kg, respectively, they reported.
Underlying reasons for fermented feed effects on growth performance
The team said that fermentation improves the quality of feed ingredients - fermentation of protein source promotes protein digestibility, increases the ratio of small to large peptides and reduces anti nutritive factors such as trypsin and protein inhibitors (Feng et al., 2007; Wang et al., 2007; Hung et al., 2008; Ao et al., 2010; Wang et al., 2014; Zhang et al., 2018).
Fermentation of energy sources increases enzyme activity, short chain fatty acid levels and starch digestibility while reducing fiber, polysaccharides and anti-nutritional factors (Li et al., 2011; Liu et al., 2017; Park and Kim, 2018).
Fermented medicinal plants boost oxidation activity and have pharmacodynamics properties (Ao et al., 2011; Yan et al., 2012a; Zhao et al., 2016).
“Further, we compared the effects of the included fermented feed additives with basal diets on nutrient digestibility and blood hematology. We found that fermented feed additives supplement increased digestibility of dry matter and N and lymphocyte compared with basal diet.
“The fermentation process does however reduce dry matter and results in energy losses of about 3%; it can also increase the losses of some amino acids and vitamins (Nousiainen et al., 1998; Canibe and Jensen, 2003; Niven et al., 2006). Our analysis suggests these potential losses are more than compensated for by improvements in nutrient availability or absorption.”
The researchers said fermented feed also affects performance via three other means:
1) Gut microbes: FF depends on low pH environment, and the dominant microorganisms inhibit growth of harmful microorganisms sustaining intestinal microbial balance (Plumed-Ferrer and von Wright, 2010). For instance, the reduction of coliforms in piglet gastrointestinal tract alleviates piglet diarrhea (Kim et al., 2010);
2) Nutrition uptake ability: FF supplementation improves intestinal villus height and the ratio of villus height to crypt depth. This is closely related with nutrition uptake ability mainly due to the increased short-chain fatty acids and reduced coliforms (Wang et al., 2007);
3) Immune function: FF promotes immune functions by promoting lymphocyte proliferation and transformation, increasing serum concentration of immune globulin and cytokine release (Yan et al., 2011; Zhou et al., 2015). The positive impacts of FF on gut health, nutrition uptake ability, and immune functions promotes the ADG and G/F upregulation in FF fed pigs.
They added that the influence of FF on ADFI suggested by their analysis is questionable due to lack of related studies.
Limits of meta-analysis
The authors said their meta-analysis only explored effects of about 50 g/kg fermented feed ingredients and about 0.2 g/kg fermented feed additives supplementation on pig growth performance because of the need to control variables. However, the optimal concentration of FF was unclear.
The effects of fermented protein-sources feed and fermented energy-sources feed were not explored in weaned piglets and finishing pigs because of limitation of the number of articles, they stressed.
Source: Animal Feed Science and Technology
Title: Effects of fermented feed supplementation on pig growth performance: A meta-analysis
Authors: B. Xu, Z Li, C. Wang, J. Fu, Y. Zhang, Y. Wang, Z. Lu