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Introduction
The pig requires that the diets use in their feeding were strictly balanced in nutrients for obtaining an optimums developing in these animals. In fact, the food is the most important supply which allows measuring the profitability of the production system: the conversion in meat depends on the type and food quality (Atsbeha et al. 2020).
The pig feeding represents between 70 and 80 % of the changeable costs in a production (Lezcano et al. 2015). The nutrition of breeds and improvements lines of pigs is mainly supported in the use of concentrate foods, based on soybean and cereals. The fast growing of population, the climatic conditions and the production of biofuel and, more recently, the appearance of new diseases as COVID-19 had caused that the conventional raw matters increased their price in the world (Caicedo et al. 2021).
The use of alternative foods for pigs has market at present, with the purpose of reducing the maintenance cost of these animals (Castro y Martínez 2015 and Lezcano et al. 2017). The agricultural wastes are considered an economic source of nutrients for pigs. However, for their efficient use in the animals’ diet they should be processed, due to in natural state have secondary metabolites which can affect the availability and use of nutrients.
For the use of these agricultural resources for a long time it can resort to the fermentation technique, knew as silage with agricultural resources (Lezcano et al. 2017).The production of silage with local resources, as taro, sweet potato, banana, sugar cane, cassava, "chontaduro", potato and carrot, among others, is a good option for pigs feeding (Lezcano et al. 2017).
The importance of fermentation has been researched from thousands of years. At present, this biotechnological process has been taken to a great scale because their significant interest in the food industry for humans and animals, in the pharmaceutical and biochemical industry, among others (Bhargay et al. 2008, Borras and Torres 2016 and Soccol et al. 2017).
The literature reports that trough fermentation the growth of enzyme producer microorganisms and unicellular protein (UCP) can guarantee (Nasseri et al. 2011 and Borras et al. 2017). In some researchers has been showed that the lactic acid bacteria (LAB) developed in this medium allows the phenolic compounds release, which generates antioxidant activity and, in consequence improves the animal’s health (Caicedo et al. 2020a).
For the previous mentioned, the objective of this study was to assess the results of the use of agricultural by-product silage in the different pig categories.
Solid state fermentation (SSF)
The solid state fermentation consists on the development of microorganisms with the capacity of absorbing or maintaining the water in the substrate with the presence or absence of soluble nutrients, however, is important that the microorganisms were in mediums with diffusing nutrients in the semisolid interface (Borrás-Sandoval et al. 2017 and Sadh et al. 2018). The SSF is an aerobic process in which live pure or mixed microorganisms in a substrate rich in nitrogen for the formation of enzymes, organic acids and microbial protein, under conditions of temperature, pH and humidity, however, there is not free water. The SSF is a protein and energetic source of low economic value with respect to the balanced foods (Borras and Torres 2016).
Liquid state fermentation (LSF)
In the liquid state fermentation (LSF) or submerged, the substrate is liquefied or lie down in water. It is mainly use in industrial processes due to its high yield, low cost and low contamination (Sadh et al. 2018). Sagar (2019) state that the LSF is a biological conversion technique of complex substrates to simples ones, where take part microorganisms (fungi, yeasts and bacteria) that during the fermentative process release additional compounds, named secondary metabolites, as antibiotics, enzymes and growing factors, and also fermentation products as carbon dioxide and alcohol.
The LSF is a biotechnological process in which the agricultural products are used for their processing. It constitutes a feasible alternative for animal feeding which make possible the use of this resource for a long time (Caicedo et al. 2019a and Saavedra et al. 2020). This biotechnological process allows an appropriate control of the lactic acid, pH and ammoniac to achieve a fermented product with good nutritional, microbiological and organoleptic characteristics, without danger of transmitting diseases to the animals (Wang et al. 2016).
Products and by-products from the agro-industry for obtaining inocula destined to SSF and LSF production of agricultural recourses
Natural yogurt. Is the coagulated product which is obtained by means of the lactic fermentation of milk or by the mixture of dairy products through Lactobacillus bulgaricus and Streptococos themophilus. It didn’t have fruit, sugar and sweetener. Each species of bacteria stimulates the growing of the other one and its metabolism, which give it a creamy texture and a slightly acid taste to the final product. The yogurt constitutes a highly nutritive food, which control the intestinal flora, restore the hepatic functions and is of rapid digestibility (Vera 2011).
Sugar cane juice and filter cake mud. The sugar cane juice is obtained from the sugar cane milling. It has high sugars content, depending of the variety, maturity and quality of the sugar cane. The sugar cane juice has soluble solids, as sucrose, glucose and fructose. It also has non sugars compounds, as wax, fats, organic acids, pectin and colorings. The microorganisms that are found during the sugar cane juice fermentation constitute the yeasts Saccharomyces cerevisiae, Crytococcus laurentii, Candida utilis, C. guilliermondii and Phodotorula mucilaginosa (Armijos 2016).
The filter cake mud is also a waste from the sugar cane, resulting of the fabrication process of the brown sugar leaf and the natural sugar. It is rich in phosphorus, nitrogen, calcium and organic matter, with minimum amount of potassium (Lagos-Burbano and Castro-Rincón 2019).
Whey. It is a by-product which obtained from the separation of the casein and dairy fat during the cheese production. It has at about 55 % of the nutrients present in the milk. Among their components are highlighted the lactose, proteins of high biological value (lactoglobulins and albumins), lipids, minerals and vitamins. The beneficial microorganisms Lactobacillus acidophilus, L. casie, L. reuteri and Bifidobacterium are found in the whey (Guerrero-Haber et al. 2011 and Poveda 2013). According to Haberkorn (2018), this by-product of the dairy industry is considered a prebiotic and probiotic of excellent quality, improves the metabolic functioning of the animal, in addition to providing texture, color and taste of the food. This waste has great potential to be used in pig feeding due to its high nutritional value and high palatability.
Microorganisms used in the production processes of SSF and LSF from agricultural resources
Homofermentative and heterofermentative bacteria. They are classified as homofermentative and heterofermentative and are essential to form a consistent and successful fermentation. They are used as probiotics by suppressing the growth of pathogenic microorganisms (Ramírez-López and Vélez-Ruiz 2016). They constitute the lactic acid bacteria (LAB), are anaerobic, non-motile, lack cytochromes and do not reduce the nitrate to nitrite. Being acid tolerant, they are at pH as low as 2-3 and as high as 9.6. However, the optimum pH is 4-4.5, so they are resistant in environments where organic acids are produced, unlike other bacteria that are susceptible to this medium.
Mainly, the LAB feed on sugars such as glucose and lactose, vitamins, amino acids, among others (García et al. 2020). The homofermentative bacteria only produce lactic acid, while heterofermentative the lactic acid and other products, such as acetic acid and ethanol. The group of homofermentative bacteria is made up of Lactococcus, Pedioccocus, Enterococcus, Vagococcus and Streptococcus, while the group of heterofermentative bacteria includes Oenococcus, Weicella, Carnobacterium, Lactosphaera, Leuconostoc and some Lactobacillus (Ramírez et al. 2011).
Yeasts. They are the organisms most used in fermentation techniques, due to their great capacity to produce unicellular protein (UCP). They can reach protein values higher than foods traditionally intake for animal feeding, such as fishmeal, soybean, and cereals (Reyes-Sánchez et al. 2018). Yeasts produce organic acids, pentoses and methyl pentose, sugar alcohols, polysaccharides and even i-inositol for protein synthesis (Moyano 2014). Among the main fermentative yeasts are Pichia guilliermondii LEV, Saccharomyces cerevisiae, Candida albicans, C. tropicalis, C. krusei, C. parsilosisis, C. pintolopessi and C. lipolytica.
Filamentous fungi. The micellar structure of the fungi allows them to have a capacity for adherence and penetration on substrates. It also represents advantages for carbon synthesis, since they have complete organisms for the absorption of polysaccharides. Fungi grow at room temperature, easily adapt to substrates, have the capacity to degrade lignosaccharides, and are organisms with the potential to produce enzymes and biomass (Rodríguez et al. 2017). Fungi used in fermentation processes include the genera Trichoderma, Alternaria and, in some cases, Penicillium and Aspergillus and Pleurotus trametes (De Oliveira et al. 2018).
Chemical characteristics of SSF and LSF from agricultural resources used in pig feeding
For the preparation of SSF and LSF, local raw materials are used that have low costs and are available throughout the year. Energetic agricultural wastes combined with water, molasses, whey, vinasse, and sources of inoculums of yeasts, lactic bacteria, and filamentous fungi are used as substrates for the production of SSF and LSF, since they stabilize the pH, reduce or eliminate secondary metabolites, produce microbial protein and preserve food for a long time (Rendón et al. 2013, Lezcano et al. 2014, Caicedo et al. 2015 and García et al. 2020).
The pH is one of the most important factors to take into account in the SSF and LSF processes and is closely related to the final quality of the food. The initial inoculation with preservative microorganisms produces acidity in the medium to inhibit the growth of putrefactive and pathogenic microorganisms that alter the nutritional value of the food (García et al. 2015). Caicedo et al. (2016) evaluated the safety effect of the LSF of taro tubers and reported pH values between 3.8 and 4, 96 h post-processing, as a result of the rapid acidification of the medium. These authors also reported the absence of putrefactive and pathogenic microorganisms, such as molds, coliforms, Salmonella spp, and Escherichia coli.
Caicedo et al. (2015) also studied the chemical composition of four LSF variants of taro tubers, preserved between 0 and 180 d with natural yogurt, whey and molasses. There was not affectation in the nutritional composition of the fermented food and the contents of DM, CP, CF, NFE, ashes and GE were similar to those reported in taro tubers in their natural state. Likewise, with LSF of sweet potato tubers, treated with Saccharomyces cream and concentrated vinasse, Lezcano et al. (2015) obtained a chemical composition similar to the natural raw matter. In other researches carried out by García et al. (2020) with LSF of cassava, sweet potato or banana (40 %) and both, sugar cane B molasses (20 %), concentrated vinasse (10 %) and Saccharomyces cerevisiae yeast cream (30 %), when evaluating them at the 0 and 168 h, a slight reduction in DM was observed in all the fermentations with respect to the raw matter in natural state. This was attributed to the production of carbon dioxide, a co-product of fermentation in the silos. However, they achieved linear increases as a function of fermentation time for CP and true protein, caused by the increase in the colony-forming units (CFU) of lactic acid bacteria and yeast, respectively.
In foods processed by SSF for pigs, there has been showed an increase in DM contents, due to the inclusion of drying material such as wheat and rice powder (Caicedo et al. 2019b), CP associated with the unicellular protein of the medium (Gunawan et al. 2015, Caicedo et al. 2019c and Caicedo et al. 2020b) and ashes due to the inclusion of mineral salts, phosphates and carbonates in the different formulations (Fonseca-López et al. 2018).
The production of SSF and LSF of agricultural origin constitutes a novel and easy to apply process on a small, medium and large scale, for its use in the pig production system in its different production stages (Lezcano et al. 2014, García et al. al. 2015 and Caicedo et al. 2019c). In general, it has been possible to verify that alternative foods processed by LSF and SSF have a good nutritional composition and constitute a source of nutrients at a lower cost compared to conventional foods. The chemical characteristics of agricultural resources fermented by LSF and SSF used in pig’s diet are shown in table 1.
Table 1 Chemical characteristics of fermented agricultural resources and used in pigs feeding
| Agricultural resource | Used technique | Inoculum source | Nutrients | References | ||||||
|---|---|---|---|---|---|---|---|---|---|---|
| DM, % | CP, % | CF, % | SE, % | NFE, % | Ashes, % | GE, kJ g DM-1 | ||||
| Cassava root ( |
SSF | - | 42 | 0.95 | 1.05 | 0.42 | - | 0.85 | - |
Loc |
| "Chontaduro" fruit ( |
SSF | Natural yogurt | 39.60 | 6.89 | 3.76 | 11.10 | 73.60 | 4.69 | 19.49 |
Caicedo |
| Orito banana fruit ( |
LSF | Natural yogurt | 21.18 | 7.88 | 0.65 | 1.60 | 80.28 | 2.61 | - |
Caicedo |
| Cassava root ( |
LSF | Natural yogurt | 32.9 | 0.91 | 3.54 | 0.50 | 91.43 | 3.58 | 15.06 |
Reina-Rivas |
Digestibility in commercial pigs fed with SSF and LSF from agricultural resources
Digestibility studies are very important to assess the nutritional potential of foods for their efficient use by animals. The inclusion of SSF and LSF in pigs diet in permissible limits does not has rejections, and do not affect the digestibility values of the main nutrients studied with these animals (Araujo et al. 2016 and Caicedo et al. 2019b). In fact, the by-products processed by these biotechnologies have greater digestibility compared to foods in their natural state. This is due to the incorporation and colonization of beneficial microorganisms that takes place in the gastrointestinal tract (GIT) of pigs (Rendón et al. 2013). These microorganisms compete with the pathogenic flora and synthesize different enzymes and vitamins that help to improve the use of nutrients in foods.
Studies concerning nutrient digestibility in commercial pigs fed with fermented agricultural by-products are scarce to date. They focus on growing pigs. However, existing reports show high percentages of inclusion in the diet, which shows that in improved pigs it is feasible to use alternative fermented foods as a partial substitute for conventional food.
Araujo et al. (2016) included 25 % LSF of cassava treated with natural yogurt in the diet of growing pigs and obtained high use rates of DM (90.01 %), CP (66.43 %) and GE (91.48 %). In another study, Da Rocha (2016) incorporated 100 % of cassava root LSF in growing pigs and achieved good use of DM (86.87 %) and GE (90.56 %).
In more recent studies on digestibility, Caicedo et al. (2019c, 2019d) achieved good use of nutrients in commercial growing pigs, by including in the diet 40 % of SSF from orito banana, DM (91.33 %), CP (92.20 %), CF (70.07 %), NFE (91.23 % ), GE (90.27 %) and peach fruit DM (90.23 %), CP (92.24 %), CF (75.06 %), NFE (91.24 %) and GE (90.38 %). They concluded that it is feasible to partially replace the conventional food (corn and soybean) by alternative fermented food without affecting the use of the main nutrients.
The high values of use of fermented agricultural residues are associated with the bioavailability of nutrients and with the intestinal health of pigs.
Productive indicators in commercial pigs fed with SSF and LSF from agricultural resources
In the productive indicators of pigs (food intake, weight gain, feed conversion, final weight and carcass yield) directly influenced the type of nutrient and their availability (Recinos et al. 2017). According to Nazef et al. (2008), the probiotics in the foods produced by SSF and LSF provide a eubiotic environment in the GIT of animals. Marín et al. (2007), when using biopreparations in pigs diet, obtained high indexes of weight increase and weight gain, low diarrhea incidences and, in consequence, high productivity. The probiotics reduce the intestinal pH, which inhibit the growth of pathogen microorganisms as Escherichia coli, Salmonella spp y Clostridium spp. The benefit microbiota located in the small intestine guarantees the optimum absorption of nutrients (Giang et al. 2011).
The studies of productive performance in commercial pigs fed with SSF and LSF from agricultural resources refers satisfactory results. In growing and fattening pigs has been taken into account researchers which showed useful results with inclusion in the diet of 50 % LSF of cassava (Almaguel et al. 2011), 40 % SSF of cassava roots and corn kernel wastes (Cabrera et al. 2012), without affecting the DM intake, weigh gain, feed conversion and final weight of pigs with respect to the animals which exclusively received a control diet (corn, soybean).
It has been also informed studies of substitution of raw matters in the diet of commercial pigs. In growing pigs fed with LSF of cassava roots, Lezcano et al. (2014) successfully replace 100 % of corn in the diet, without showing affectation in weight gain and final weight of the treated animals.
In other studies, with post-weaning pigs, Caicedo and Flores (2020) included in the diet 2 and 4 % LSF of orito banana and LSF of taro (Caicedo et al. 2020c) and obtained better DM intake with respect to the control diet. This increase was due to the sensorial characteristics of the fermented foods. In rearing pigs there are scientific evidences which has successfully included SSF of tuber with taro foliage (30 %) (Caicedo et al. 2020d) and SSF of cassava roots (50 %) (Dias and Dos Santos 2021) without negative effect on DM intake and in the final weight of animals during the experimentation.
The productive results of the pigs fed with ferments are successful so the used diets fulfill with the nutritional requirements in each category (Sakomura and Rostagno 2007 and Rostagno et al. 2011). The fermented foods also have functional properties that improve the immunity, the intestinal health and the use of nutrients in the animals. The results of the productive indexes of pigs fed with agricultural silages are showed in table 2.
Table 2 Productive indicators in pigs fed with silages from agricultural resources
| Ensiled agricultural resource and inoculum source | Used technique | Category | Inclusion level or corn substitution, % | Indicators | References | ||||
|---|---|---|---|---|---|---|---|---|---|
| Initial weight, kg | DM intake, kg | Weight gain day, kg | Feed conversion kg/kg | Final weight, kg | |||||
| Sweet potato tubers ( |
LSF | Growing-fattening | Corn substitution (66) | 30.83 | - | 0.544 | 3.76 | 104.7 |
Lezcano |
| Orito banana fruit ( natural yogurt) | SSF | Growing | Inclusion (40) | 24.93 | 1.51 | 0.85 | 1.78 | 60.62 |
Caicedo |
| Cassava root (natural yogurt) | LSF | Growing-fattening | Inclusion (40) | 25.50 | 2.454 | 0.89 | 2.75 | 100.52 |
Reina-Rivas |
Conclusions
The use of silage from agricultural resources as alternative food for pigs is a relatively a new field and emerged as an option to improve the nutritional value of the raw matters of easily decomposition and to make good use of them for a long time. The results of researchers with silages, in terms of the chemical composition, digestibility and productive performance in pigs are satisfactory. In several researchers has been achieve high inclusion levels of corn (20 to 50 %) or with the hole replacement in the diet (100 %), which allow to reduce imports of conventional raw matters (corn and soybean). The by-products sources most researched to produce SSF and LSF as pig’s food constitutes the energy foods (cassava, sweet potato, taro, orito banana, "chontaduro”, potato, banana and sugar cane). These have been treated with whey, natural yogurt, Saccharomyces cream, concentrated vinasse and molasses. The future researchers with SSF and LSF of agricultural wastes for their use in pig’s production have great potential in the determination and use of the fibrous fraction, energies, minerals, amino acids and antioxidants for their incorporation in tables of local raw matters.
