New Advances in Postharvest Technology: An Overview for Feed Production from Postharvest Wastes and By-Products

Abstract

Globally agricultural production system generates a substantial proportion of postharvest waste that causes environmental pollution resulting in economic losses and human health-related problems. It is therefore important to make an assessment of this loss and turn it back to the consumption cycle. Processing and conversion of by-products, residues, and agricultural wastes and their reuse in the production cycle is a suitable solution for the economic use of these types of postharvest waste, especially in feeding livestock animals or in related industries. This chapter provides an overview of the assessment of the postharvest wastes that are generated in the field or on the farm at the time of harvest or processing industry. After introducing the potential use of technologies to upgrade postharvest waste for animal feed purposes and briefly discussing livestock performance, this review presents the latest and most interesting research on the use of postharvest wastes as feed.

1. Introduction

Livestock production is rapidly increasing due to population growth, changing lifestyles, and dietary habits in developed industrialized countries. It accounts for approximately 40% of the gross value of agricultural products. Projections indicate that total demand for animal products in developing countries will double by 2030 [1]. Considering this issue and with the aim of dealing with food insecurity and strengthening sustainable agriculture, it is possible to use feeding strategies and feedstuffs that are able to increase livestock productivity and have fewer environmental effects compared to conventional livestock production [2]. In addition to reducing the environmental impacts associated with animal feed production, valorizing plant by-products for feed formulation can maximize resource efficiencies and helps the competitiveness of feed manufacturers by making available of more sustainable raw materials that could reduce dependence on current raw materials [3]. Plant by-products (PBP) include a wide range of secondary residues produced from the industrial processing of plants into valuable commercial products [4]. These by-products are considered safe and widely accepted as animal feed [5]. These by-products include residues from food factories, fruit and vegetable wastes, and grain harvesting by-products. However, the use of plant waste as animal feed has limitations arising from the processes of agricultural products transformation industries, which can affect the possibility of evaluating its nutritional value. For example, its high water content, which is frequently greater than 80%, makes it more difficult and can hasten the spread of microbiological contamination [6]. On the other hand, the use of PBP in animal nutrition is limited due to restrictions such as diversity in nutrient composition and technical requirements for storage, which are necessary to stabilize the product and reduce seasonal availability of resources. Furthermore, preservation methods such as thermal processing can be expensive and diminish the environmental sustainability of PBP feed [5]. Also, the lack of efficient storage strategies is a fundamental barrier that limits the use of PBP in animal feeding, as their intrinsic instability causes quick quality deterioration and severe changes in nutritional composition [7]. This chapter provides information on some agricultural postharvest residues, their chemical composition, processing methods, nutritional value, and guidelines for including PBP in livestock diets. It also covers aspects related to the use of such post-harvest waste as a substrate for the production of value-added products. It is expected that this chapter will promote conversion of agricultural waste into valuable resources and help create opportunities for development. The recycling of these resources saves livestock feed and also reduces the environmental pollution associated with the disposal of PBP.

2. Grape pomace

Grapes are one of the most widely grown crops in the world, with an expected production of more than 79 million tons in 2018 [8]. Grape seeds have a significant amount of oil, which contains large amounts of unsaturated fatty acids, more than 80% of which include linoleic acid (Figure 1) [9].

Figure 1.

Grape plant.

Due to the presence of antioxidant substances such as flavonoids, grape pomace plays an important role in preventing the phenomenon of oxidation by removing free radicals produced from the environment under heat stress [10]. Proanthocyanidins of grape seed extract act as antioxidants in poultry feed, improve the performance of broiler chickens, and treat clinical symptoms caused by oxidative stress caused by Eimeria tenella infection [11]. Grape pomace can be used in animal nutrition, so that the use of its extract in amounts of 62 and 92 mg in the diet of broiler chickens from the age of 3 to 6 weeks prevented the lipid oxidation of the chicken carcasses during their storage in the refrigerator [12]. When grape pomace is fed to cattle as a dietary supplement, it can potentially increase the oxidative stability of beef products by increasing intestinal absorption and transfer of polyphenolic compounds to meat [13]. It has been reported that the use of grape pomace up to 10% of the ration of fattening lambs has no negative effects on the growth performance of lambs (Figures 2 and 3) [15].

Figure 2.

Grape pomace.

Figure 3.

Components of grape pomace [14].

The effects of grape pomace on the quality and characteristics of fatty acids in meat samples obtained from lactating lambs were investigated in the ewe’s diet. The results revealed that grape pomace incorporation did not have any negative effect on the carcasses but improved the water holding capacity [16]. Compared to diets lacking naturally occurring antioxidants, adding antioxidants such polyphenol-rich grape by-products to animal diets enhances meat quality while also preventing oxidation [17]. The appropriate use of grape pomace could increase the growth and production rate and reduce the feed conversion ratio (FCR) in Afshari fattening lambs [18]. Also, in another report, the use of grape pomace resulted in an increase in voluntary feed intake, growth rate, and a decrease in FCR in fattening lambs [19].

3. Pomegranate pomace

Pomegranate (Punica granatum L.) is a member of the Punicaceae family and an important native product of subtropical Asia (Figure 4) [20, 21].

Figure 4.

Pomegranate plant.

Pomegranate fruit has approximately 48% peel and 52% fruit (w/w), which is the edible part of fruit and consists of 78% juice and 22% seeds [22, 23]. Pomegranate is rich in vitamins A, B, C, and E, minerals potassium, and iron, which have healing properties. It is also a rich source of folic acid and antioxidants. This fruit contains a significant amount of phenolic compounds such as anthocyanins, punicalin, and various flavonols, which have antimicrobial, antibacterial, and anti-inflammatory properties and increase the immune system in vitro and in vivo [24]. Pomegranate peel contains 55.4% non-fibrous carbohydrates (NFC), 8.4% crude protein (CP), 16.7% lignin, 34.5% neutral detergent fiber (NDF), and 0.84–1.0% total condensed tannins [25]. Pomegranate pomace is a by-product of the pomegranate juice industry, which has strong antioxidant power, anti-inflammatory compounds, vitamin E, sterols, phenols, and natural estrogens [26]. Pomegranate by-products offer excellent nutritional value as ruminant feed and can be utilized efficiently to substitute grains in ruminant diets. Feeding cattle calves and a fresh pomegranate peel diet improved feed intake and plasma alpha-tocopherol amount [27]. The antioxidants in pomegranate peel prevent diseases in lambs and have been useful in improving the quality of meat [28]. Substitution of a portion of grain in the diet with dry pomegranate seed pulp had no effect on growth performance, carcass traits, and nutrient digestibility, but it reduced the cost of meat production and increased the antioxidant capacity of lambs. As the pomegranate seed pulp was increased in the diet, it caused a decrease in kidney fat and a tendency to increase the apparent digestion of crude fat [29]. In fattening lambs, it has also been shown that pomegranate pomace silage can significantly replace a part of the fodder, which will result in a reduction in production costs and saving environment from the waste pollution coming from pomegranate processing industries. In another study, dairy goats fed a diet supplemented with dry pomace pomegranate seeds at 14% instead of cereal grain with no detrimental effects on animals. Therefore, it was suggested that pomegranate seed pomace, as a cheap by-product, can be replaced in the diet as an energy source [30]. Dairy cows fed diets supplementing with concentrated pomegranate extract at 1 and 2% based on dry matter, revealed increased the antioxidant activity of milk by 15 and 17.2%, respectively, and compared to the control group [31]. As a new feed for beef cattle, the antioxidant potential and nutrients of fresh and ensiled pomegranate by-products (pomegranate peel) were investigated. The results of this experiment showed that fresh pomegranate peel caused a significant increase in feed intake and alpha-tocopherol concentration in plasma [31]. Inclusion of wet fresh pomegranate peels in diets of bull calves promoted an increase in feed intake, with a tendency to increased weight gain [27]. In contrast, Oliveira et al. [32] found that feeding a pomegranate extract to young calves for the first 70 d of life did not change the digestibility of dry matter, organic matter, or starch, but it suppressed the intake of grain and whole tract digestibility of fat and crude protein, likely because of its high tannin content.

4. Tomato pomace

Tomato (Lycopersicon esculentum) has an annual global production of 170 million tons, of which 127.5 million tons are used for fresh consumption and 42.5 million tons for industrial processing [33] (Figure 5). Asia produces 61.1% of the world’s tomatoes, whereas Europe, the Americas, and Africa provide 13.5, 13.4, and 11.8% of total tomato yield, respectively [34].

Figure 5.

Tomato plant (fruit).

Tomato pomace is a by-product of tomato processing that refers to the skin (peel) and seeds of tomatoes and accounts for 10–40% of all processed tomatoes (Figure 6) [35]. Tomato pomace contains approximately 33% seeds, 27% peel, and 40% pulp, while dry pulp contains approximately 44% seeds and 56% peel and pulp [36] which average protein is 21.9% in tomato pomace and 38.7% in fat-free tomato seeds [37]. Tomato pulp is a good source of lycopene, carotene, vitamin E, vitamin C and nucleosides [38], carotenoids, lycopene, flavonoids, and soluble dietary fiber (Figure 7) [40, 41].

Figure 6.

Tomato pomace.

Figure 7.

Processing and uses of tomato pomace [39].

Tomato pomace is used as an ingredient in small ruminant diets due to its chemical composition and good animal acceptability [42]. In feeding ruminants, tomato pomace is sometimes considered as a concentrate due to the high content of nutrients and sometimes as forage because of its high content of the cell wall [43].

Recently, studies have been conducted using tomato residues in the form of silage and considering tomatoes along with other industrial residues in goat diets [44]. Silage of tomato pomace with 10% of wheat straw can be a good quality forage source for sheep when the forage is not available [45]. In a research, dietary replacing 10% of corn silage with ensiled tomato pomace had a positive effect on the vitamin content of milk, antioxidant function, and immunity in early lactating cows [46]. Ruminants fed diets containing tomato pomace showed higher nutritional intake as well as apparent digestibility, organic matter, dry matter (DM), and crude protein indices [47]. Tomato pomace, if properly preserved, can be included in a significant portion of animal rations for a longer period of time and can also be used as a protein and energy supplement in feeding ruminants [48]. Up to 15% of the diets supplied to sheep can be substituted with dried tomato pomace without having any negative impact on growth [49]. The substitution of barley grain diet with tomato and cucumber waste was studied on rumen fermentation and microbial communities in goats and found that up to 250 grams per kilogram of tomato waste can replace the barley grain diet [50]. Supplement consumption increased milk quality and fat content by 20 and 40%, respectively. This demonstrated that, despite the fact that TP decreased the body weight of breastfeeding goats, it might enhance the quality and fat content of their milk, which may be related to the TP’s own energy content and fatty acid composition [39]. In a study, supplementation of different levels of tomato pomace had no effect on the body weight of goats and sheep, carcass length, blood sugar, total protein, urea, or cholesterol [51].

Tomato pomace has also been used in poultry diets, so feeding 5% tomato pomace to chickens at the age of 1–28 days can increase body weight and production index, also increase the activity of superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px), and reduce HDL cholesterol and serum triglyceride concentrations [52]. The results of another study revealed that dietary inclusion of tomato pomace at 12% can significantly improve the immune system function, antioxidant enzymes, and digestive enzymes of Japanese quails [53]. The concentrate mixture in the feed of male buffaloes can be substituted with sun-dried tomato pomace without having any negative effects on urinary purine derivatives, DM intake, nutritional digestibility, microbial protein synthesis, or production of volatile fatty acids in the rumen [54].

5. Fodder beet pomace

Fodder beetroot belongs to the Chenopdiaceae family, which is native to the temperate region of Europe and was obtained from a cross between white and red garden beet [55] (Figure 8). Fodder beet is a plant with tuberous roots and broad leaves in some countries and is considered one of the most important winter fodder sources for feeding livestock, especially dairy cows [56].

Figure 8.

Fodder beet plant.

Fodder beet has a high digestibility, so its organic matter digestibility is reported to be 87–90%. It has been reported that the net energy of lactation is 7.9 to 8.2 MJ/kg of dry matter, which is equal to or even more than cereal grains [57]. In an experiment with the substitution of 24% beet pomace with barley in diets based on straw fodder in Merino fattening lambs, it was shown that the consumption of concentrate and daily weight gain in the control diet (100% barley) was more than the diet containing beet pomace [58]. Also, dairy cows fed alfalfa or silage grass had lower milk urea and lower urea or creatinine concentrations in their urine when fodder beet was added to their diet [59]. During storage, beets continue to decrease in quality and are prone to spoilage and decay due to high humidity and sugar. However, in some countries, beets are ensiled with other forages to preserve their nutritional value for cattle [60].

6. Olive pomace

Olive (Olea europaea L.) is a small tree of the Oleaceae family, which is widely cultivated in the Mediterranean region. After extracting oil from olives, that is used in food preparation [61], a significant amount of olive pomace is obtained, which includes the peel, fruit, core, fleshy part of the fruit, and the shell of the wooden core (about 25% of the weight of the olive product) (Figure 9) [62].

Figure 9.

Olive plant.

Olive pomace, that is obtained by extracting oil from olive fruit, has a lot of fat and moisture, so with the drying process, its moisture content decreases [63]. Olive pomace also has chemical properties in terms of nutrition, with a high percentage of cellulose, hemicellulose, and lignin. It is also a good source of fatty acids, minerals, and phenolic compounds [64] (Figure 10). Despite having positive impacts, using olive waste as animal feed is not commercially viable because of concerns with digestion, taste, and safety [65].

Figure 10.

Olive pomace.

Non-starch polysaccharides (NSP) are among the anti-nutritional factors found in olives that negatively affect the digestion and absorption of other nutrients. Soluble non-starch polysaccharides increase the viscosity of the contents of the gastrointestinal tract and reduce the digestibility of nutrients, while insoluble NSPs limit enzyme access to the substrate by trapping nutrients [66]. Olive pomace is less used by ruminants due to its high lignin, low crude protein, and poor digestibility compared to forage. However, inclusion of olive pomace to the diet had a positive effect on the production and fat percentage of cow and sheep milk [67]. Several studies have been carried out on the solid-state fermentation of olive pomace using fungal strains, which allows its use as a feed additive for ruminants (cows, sheep, goats, and camels) and poultry [68, 69].

Studies have shown that the use of olive pomace in the diet of laying hens increased egg weight and shell weight, but had no effect on other functional parameters and egg quality characteristics [70, 71]. In a research study, olive pulp was used at 2.5, 5, 7.5, and 10% in preliminary and final diets of broilers, and the results showed a significant reduction in feed intake and conversion rate, which could be due to the presence of inhibitory substances in olive pulp [72]. Because of their antibacterial effect against pathogenic intestinal bacteria, phenolic compounds derived from olive leaves may be useful to broilers [73]. Additionally, broilers’ digestive enzymes that alter nutrient digestibility can be stimulated or inhibited by phenolic substances [74].

7. Apple pomace

Apple (Malus domestica Borkh) is one of the earliest known fruits and is commonly grown in temperate climates [75] (Figure 11). Apple pomace is a heterogeneous mixture consisting of skin, core, seed, calyx, stem, and soft tissue.

Figure 11.

Apple plant (fruit).

Apple pomace is rich in pectin, fermentable carbohydrates, minerals, and crude fiber, which increases its use for animal feed [76]. It also contains large amounts of sugar and is rich in various sources of carbon [77] (Figure 12).

Figure 12.

Apple pomace.

Aside from its antioxidant characteristics, apple pomace also contains antibacterial, antiviral, and anti-inflammatory capabilities [78, 79]. Figure 13 shows apple processing and apple pulp production. When fermented apple pomace is added to sheep diets, meat oxidation was decreased during storage without altering other aspects of meat quality [81]. Apple pomace dietary supplement improved milk production, apparent digestibility of crude protein and neutral detergent fiber, decreased rumen pH, and improved milk quality and serum biochemical parameters in Guanzhong dairy goats [82]. Feeding fermented apple pomace with basic rations to dairy cows leads to an average increase in milk production (1.90–1.89 kg per cow per day), milk fat, milk protein, and milk solid content, with a decrease in the incidence of disease in cows [83].

Figure 13.

Processing of apple and generation of apple pomace [80].

Moreover, the alfalfa forage in the ration of fattening lambs was replaced with ensiled apple pomace in proportions of 20, 40, and 60% and result of the experiment revealed that a diet containing 20% apple pomace silage increased the daily feed intake and increased the body weight of the lambs [84]. In another experiment, replacing of alfalfa in the diet of Arabian sheep with 30% dry apple pomace improved the activity of rumen microbes in digestion and fermentation of diet nutrients by reducing the duration of rumination and chewing time [85]. The reason for this was the probability of the cell wall and the size of the smaller particles in the diet containing apple pomace. In other words, it has been discovered that increasing the amount of cell wall in the diet or the size of the forage particles increases chewing activity [86]. However, apple pomace has disadvantages. The main concern of apple pomace is related to the environmental pollution caused by its waste accumulation, and it is not considered as a high-quality feed for animals due to its low protein content [87].

8. Fruit and vegetable waste

In recent years, the use of agricultural by-products in feeding animals has proven to be a successful solution for reducing feed costs, reducing environmental pollution, and ensuring the quick and inexpensive return of these materials to the nature cycle [88]. Nutrition is thought to be the most important determinant of increasing animal output. However, in agriculturally dependent nations, poor nutrition and pricey feedstuffs, particularly concentrate feed, are the main obstacles [89]. Dry citrus pomace is the best nutritional citrus product for livestock, and it is prepared for feeding all year round. Fresh citrus pomace has a moisture content of 85–88%, so adding moisture-absorbing materials in ensiling it can increase the quality of silage production [90]. The chemical and physical composition of citrus by-products is different depending on the type of fruit and the type of processing in the processing factories [91]. Vitamins, polyphenols (particularly anthocyanins), dietary fiber, and important unsaturated fatty acids are among the bioactive components found in fruit pulp [92]. Citrus pomace, tomato pomace, apple pomace, sugarcane pomace, and pistachio peel are among the by-products of agricultural transformation industries that are used as potential sources for animal feed [93]. Fruit and vegetable waste (FVW), waste from the food industry, vegetable industry, and general markets can be added to animal feed without adverse effects due to the presence of nutrients, minerals, fiber, vitamins, and bioactive compounds [94]. Considering that the cost of animal feed is increasing due to the increase in the cost of fertilizer and unsuitable climate for agriculture, therefore, food waste is an alternative source of feed ingredients. It can reduce feed and disposal costs and reduce environmental pollution [95]. Fruit and vegetable processing industries produce a large amount of waste, which is an excellent source of nutrients for livestock [7]. The use of FVW as an animal feed material has the potential to assist meet the increasing demand for animal protein as the world’s population grows through 2050 [54]. In addition, transferring FVW to livestock feed can help sustain livestock production and reduce competition for land and water use [96]. In order to grow livestock populations and combat the feed crisis while lowering environmental risks and addressing the problems provided by diverse biophysical elements, the interaction between waste management and sustainable livestock feed production can be crucial [97]. Dairy cows’ diets supplemented with 18% fruit and vegetable residues as part of the concentrate resulted in milk with a higher percentage of beneficial fatty acids without reducing daily milk production [98]. A mixture of waste juices from various fruits and vegetables, such as carrots, apples, mangoes, avocados, and oranges, can make up to 20 percent of a broiler’s diet [99]. The main limitation of using agricultural waste and products from transformation industries as animal feed is the abundance of secondary compounds such as saponins, tannins, and essential oils in these products, which can limit the widespread use of these co-products in animal feed [100].

Carrot (Ducus carota) is one of the root vegetables that are damaged during harvest or discarded due to low quality, which can be a good feed for ruminants. Carrot pomace spoils very quickly due to high water activity. Drying carrot pomace is considered a suitable solution for maximizing the use of abundant nutrient sources in carrot pomace as well as increasing its shelf life. Carrot pomace is rich in insoluble fiber such as lignocellulose, which is a combination of pectin polysaccharides, hemicellulose, and cellulose, and these components have favorable physiological properties. Carrot pomace based on dry matter contains 2.7% crude protein, 24% insoluble fiber in neutral detergent, 15% insoluble fiber in acidic detergent, and 4.9% phenolic compounds, as well as carotenoids and soluble sugars such as sucrose, fructose, and xylose, which can be used in animal feeding [101].

Potato peel is one of the agricultural wastes that can be utilized as an alternative feed for animals due to its natural sources of energy and fiber with low protein levels [102]. Potato peel as a by-product of the food industry is a completely cheap, valuable, and cost-effective raw material for the production of economically important materials, added value, and product extraction, including biopolymers, natural antioxidants, dietary fiber, and natural food additives [103]. Potato peel contains polyphenols and various phenolic acids that are responsible for its antioxidant activities. Moreover, chemical composition of this by-product consists of 25% starch, 30% non-starch polysaccharide, 20% acid-soluble and acid-insoluble lignin, 18% protein, 6% ash, and 1% fat in dry form [104, 105]. When potato peel with high starch concentrations was fed, milk fat content was higher in dairy cows. It seems that the slow breakdown of starch from potato peels in the rumen can increase the higher transport of precursors of milk fat synthesis in the udder [106]. Also, starch, as one of the side products of potatoes, is the most abundant source of energy for the most livestock [107].

Another study was conducted on adult rams to determine the chemical composition, nutrient digestibility, and mineral content of potato compared to alfalfa as a forage in ruminants. The findings revealed that potato had much higher mineral, DM, and NDF digestibility than alfalfa. It can be stated that potato leaves are a nutritious alternative to other types of forages for ruminants because of their high nutritional value [108]. In one study, a significant increase in milk production was observed after supplementation with 6 kg of potato waste per day [109].

9. Waste and by-products of grain post-harvest

Plant residues are a post-harvest by-product, and the quantity harvested is directly related to all the factors that normally affect crop yield. Rice bran is a rice processing by-product which accounts for tons of food waste per year. In comparison with other grains, rice bran is rich in terms of nutrient density, amino acid, and fatty acid characteristics, including 74% unsaturated fatty acids and tocopherol content. Both protein and fat in rice bran have relatively high biological values [110]. Rice bran can be used up to 10% without any adverse effect on laying performance, digestive organs, and egg quality [111]. The use of fine-grain straw has also become common in the diet of dairy cows. There are three primary reasons why straw should be included in diets provided to dry and lactating dairy cows or dairy heifers [112]: 1) to reduce the density of nutrients (primarily energy) in the diet. For dairy heifer diets, straw is usually added to the diet to dilute the energy content. 2) For “drying” wet diets. Straw can be added to diets formulated with wet ingredients to increase the amount of dry matter in the ration and make it more suitable for dairy cows. 3) Changing the ratio of cation to anion in the diet of dry cows. Straws are often low in potassium, and low-potassium forages can help prevent milk fever in dairy cows [112].

Grain processing techniques are classified into two groups: physical and chemical processing. Physical processing, includes rolling, crimping, and grinding, breaks the outer tissues of the grain and provides access to rumen microorganisms and digestive enzymes. Chemical treatment with alkalis, for example, sodium hydroxide or ammonia, has a similar effect to rolling or crushing on access to rumen microbes and digestive enzymes [113]. Attempts have been made to replace concentrate feed in traditional animal diets with fermented wheat straw, especially to reduce the cost of animal feed. The use of wheat straw as an additive causes the least decomposition of dry matter compared to other additives [114]. Using symbiotic lignocellulose-decomposing bacteria from termite guts to process agricultural by-products can improve their nutritional value by degrading lignin, a component resistant to rumen fermentation, and boosting plant cell wall digestibility [115]. For 6 weeks, lignocellulosic biomass from wheat straw (LBWS) and palm leaf (Phoenix dactylifera) (LBDL) were incubated with lignocellulose-degrading bacteria isolated from termite gut, which altered their chemical composition and boosted nutrient digestibility [116]. Barley straw has a better nutritional value than wheat straw, with an average of 90.9% dry matter, 3.8% crude protein, and 6 mega joules of metabolizable energy per kilogram of dry matter. However, it is high in lignocellulose and low in calcium and phosphorus. Ruminant animals can be fed with barley straw because rumen microorganisms can ferment the cell walls [117]. In addition to the physical and biological methods used in straw processing, chemicals can be used to break the interpolymeric bonds in the cell wall to release carbohydrates (such as hemicelluloses) that are readily fermented by ruminal microorganisms. The use of alkaline substances such as NaOH, KOH, Ca(OH)₂, wood ash, or urea is mainly associated with improved digestibility and may improve the value of low-quality feeds [118, 119, 120] Corn residue has been used for decades for grazing, bedding, or harvesting as supplemental feed for beef and dairy cattle [121]. Corn processing methods that economically increase digestibility and acceptability without adversely affecting rumen pH or disrupting digestive function include: (1) particle size reduction, which results in dry rolled or dry ground grain with or without moisture addition (tempering); 2) ensiling with inherent moisture before the grain has dried in the field to create high-moisture maize, or reconstituting maize before ensiling and/or feeding.; 3) steaming flaking [122] and microwave irradiation [118, 123, 124]. Sugarcane bagasse is a fibrous residue from the process of extracting water from sugarcane stalks that is available in large quantities and can be used as an alternative source of forage for ruminant feed. Due to the conversion of agricultural and industrial waste into animal feed, sugarcane bagasse is regarded as a tool for achieving value-added and ecologically responsible activities [125]. The effect of sugarcane bagasse on beef cattle has been investigated with the aim of maximizing their performance, and it was reported that sugarcane bagasse can be used as an exclusive source of forage for beef cattle [126]. However, it has low nutritional value and high indigestible fiber content as dry matter (DM), such as ether extract (0.31%), protein (2.67%), hemicellulose (51.5%), cellulose (54.61%), and lignin (14.29%), which leads to low digestibility (26.7%) and consequently poor animal performance [127]. The results of several studies have shown that the pistachio by-product has a high nutritional value and has good potential to be used in ruminant diets [128]. The pistachio by-product is high in non-fiber carbohydrates (36.40–9.4%), neutral detergent fiber (30.9%), and crude protein (11.4%) [129]. Feeding 21% pistachio by-products and palm waste silage to lambs increases their lean meat yield compared with control [130].

10. Food waste

Food waste can be used to replace some of the grains and vegetable protein sources used in animal feed, reducing food competition between humans and animals [131]. Food waste continues to be a global problem with negative environmental, economic, and social consequences [132]. Recently, FAO [34] defined food waste using two indicators: 1) Food that is lost through production or the supply chain before it reaches the retail level 2) Food that is then thrown out by consumers or retailers [133]. As “up-cyclers,” livestock may turn inedible items into high-quality protein in the form of meat, eggs, and milk, decreasing food loss and waste [134].

The use of food waste in feeding animals has the potential to increase food security, reduce the environmental effects of the agro-food system, and reduce the costs of producing animal products [135]. Figure 14 illustrates the significance of food waste and food loss as ecosystem services connected with animal production.

Figure 14.

Food waste is generated in food processing plants, restaurants, household, and food markets [136].

Some food waste can be used directly as livestock feed, while others must be processed further. Food waste, which primarily consists of rice, pasta, and vegetables, comprises a high percentage of volatile substances and a high moisture level of 74–90%. It is mainly composed of degradable carbohydrates (41–62%), fats (13–30%), and proteins (15–25%) [137, 138]. In different feeding experiments, the proportion of food waste used in diets varied from 10–100%. Animal weight increase and/or feed efficiency responses differed according to animal species and physiological stage, period of experimental feeding, and type of food waste [134].

A variety of technologies for processing food waste have been documented, which can be divided into three groups: Wet-based, dry-based, and ensiling/fermentation treatments. Wet-based methods usually involve a simple heating step to sterilize the raw material, making it safe for animals. Wet-based feed products are high in moisture content (70–80%) with a relatively short storage life. For example, García et al. [6] sorted food waste out of municipal solid waste and heated it to 65–80°C for 10–60 min and then analyzed for nutrients, microbes, and toxins as potential feed. Westendorf et al. [139] heated food waste and food processing by-products at 100°C for 4 h to be used in pig feeding trials. Dry-based treatment combined with heating (sterilization) can produce long shelf life feeds (80–95% DM) that are easier to handle. Paek et al. [140] processed household food waste by rinsing, grinding, dewatering, and vacuum dehydration. Kim and Kim [141] described conversion of residential and restaurant food waste to dry feed by shredding and dewatering, heat-sterilizing, further dewatering, and drying. The ensiling/fermentation operation usually involves a heating sterilization process followed by the addition of prescribed microbial/yeast agents [134]. Procedures and conditions of ensiling/fermentation varied depending on individual studies. For example, Moon et al. [142] ground household food waste, heated it to 140°C, then aerobically fermented it for 24 h at 30–40°C with a probiotic microbial mix containing yeast, lactic acid bacteria, and E. coli. In another study, Kwak and Kang [143] aerobically fermented ground restaurant food waste with a microbial culture and poultry litter at 55–60°C for 4 h, then vacuum-dried it. Ensiling/fermentation treatment helps prolong the storage of the end product. For instance, Murray Martinez et al. [144] reported that feed produced from cafeteria food waste after fermentation was stable for up to 30 days. The primary or industrial processing of food intended for human and animal use has produced a significant amount of wastes that, despite their potential to cause pollution, have nutritional value and can be used to create monogastric meals [145].

11. Animal waste as a source of protein

Animal by-products from slaughtered animals that are not directly consumed by humans are commonly used as feed ingredients, for example, meat meal, bone meal, feather meal, blood meal, skin, slaughterhouse waste such as rumen content [146]. There are two sources of dietary protein, namely animal-based proteins and plant-based proteins. Plant proteins are usually low in lysine and methionine and have less biological value [147]. In the diet of broiler chickens, feather meal, fish meal, poultry by-products, and meat and bone meal are mainly used [148]. One of these slaughterhouse wastes is the rumen content, and it is considered as a potential alternative protein source [146]. The rumen content is relatively rich in crude protein and other microflora such as fungi, protozoa, and bacteria, so they are dried and crushed and mixed into animal and poultry diets. Using it as animal feed also increases the economic efficiency of slaughterhouse by-products [149].

A good supply of animal fat, protein, calcium, and readily available phosphorus is meat and bone meal. However, the results of laboratory tests from different rendering plants show a wide variation in crude protein (67.7–38.5%), ash (13–56.5%), crude fat (4.3–15.3%), and gross energy showed 9.4 22.3 MJ/kg [150]. Due to the diversity in the composition of raw materials and rendering processes, meat and bone meal probably has the high diversity in nutrient quality [151]. Poultry waste is high in minerals, total digestible nutrients (TDN), and protein (approximately 25% protein equivalent). Feeding ruminants with poultry waste lowers feeding costs and lessens the impact of pollution on the environment in places where poultry farming occurs [152]. The use of chicken manure as a protein source in feeding ruminants not only reduces environmental problems, but can also replace part of the protein sources as a valuable food material and reduce the total price of the diet [153]. Dried poultry manure is utilized as ruminant feed and can greatly enhance dairy and meat production [154]. Poultry manure begins to breakdown quickly after disposal and emits ammonia, which in excessive amounts can harm the health and production of animals as well as farm employees’ health [155]. Feather meal is rich in amino acids such as serine, proline, glycine, arginine, phenylalanine and threonine [156] which is considered a suitable protein source in the case of proper processing and can be used as a substitute for part of the protein sources in the diet, especially in monogastric animals [157]. Adding fully hydrolyzed feather meal the diet of lactating cows was evaluated to investigate its effects on whole-body protein digestibility and energy utilization. This experiment showed that fully hydrolyzed feather meal in the diet of dairy cows can replace blood meal and even lead to more energy in the diet and the efficiency of energy use for milk production [158]. In the pre-starter (1 to 7 days old) and starter (8 to 21 days old) stages, broiler diets can contain up to 6% feather and blood meal (FBM) [159]. Feathers have a high crude protein content, mainly composed of keratins, simple proteins resistant to proteolytic enzymes in the animal’s stomach and intestines [160]. Table 1 provides chemical composition of some agricultural post-harvesting by-products.

	DM	CP	NDF	ADF	EE	Ash	Ca	P	Reference
Soybean meal	86.51	50.19	15.13	9.98	1.78	6.82	—	—	[161]
Cotton seed meal	94.2	29.0	50.0	36.5	6.1	4.0	—	—	[162]
Guar meal	95.5	49.6	15.1	6.62	4.7	5.1	—	—	[163]
Sunflower meal	88.3	36.5	56.6	35.9	4.1	7.2	—	—	[164]
Olive meal	91.37	7.61	61.37	52.34	9.11	4.06	0.20	0.16	[165]
Canola meal	94.9	44.0	27.5	20.8	2.4	6.2	—	—	[162]
Tomato pomace	91.54	12.37	55.25	48.18	0.25	4.35	0.34	0.20	[166]
Apple pomace	30.70	5.60	45.30	38.0	4.70	2.60	0.11	0.12	[167]
Grape pomace	—	13.8	24.3	19.3	3.17	18.9	—	—	[168]
Lemon pomace	32.26	17.52	31.01	25.96	8.11	10.42	—	—	[169]
Pomegranate pomace	33.02	9.2	35.35	30.61	6.33	3.2	—	—	[170]
Sugarcane bagasse	96.1	2.18	85.5	60.0	0.84	2.70	—	—	[171]
Barley straw	93.1	4.4	77.3	—	—	7.7	0.45	0.24	[172]
Oat straw	93.3	4.8	77.0	—	—	8.8	0.32	0.22	[172]
Wheat straw	93.6	4.6	77.0	—	—	7.7	0.23	0.14	[172]
Rice bran	92.0	15.0	24.0	—	—	10.7	1.72	—	[172]
Wheat bran	84.82	17.58	49.83	15.13	5.02	6.31	—	—	[161]

Table 1.

Chemical compositions (%DM) of some agricultural post-harvesting by-products used as animal feed.

Using 4% feather meal along with 4% poultry slaughterhouse waste powder in the diet of laying hens increased the feed conversion ratio compared to when the diet contained 5% feather meal and poultry slaughterhouse waste alone [173]. Fish meal is widely used to increase the content of DHA and n-3 unsaturated fatty acids in animal products such as chicken meat and eggs [174]. The traditional processing of fish meal, including cooking, pressing, drying, and grinding, is expensive and has a complex process, and the heat used to dry fish meal leads to a decrease in the digestibility of fish meal [175]. Supplementation with 100 grams of fish meal per cow per day resulted in the highest milk production compared to the control [176]. In another experiment, the use of fish meal at the level of 5% of the diet of cows with frequent estrus can improve the pregnancy condition and increase milk production [177]. Ruminal degradable protein supplement, especially fish powder, has a better effect than urea in increasing the flow of non-ammonia-N (NAN) from the rumen [178].

12. Conclusion

Animal feeding studies identified in the present chapter suggest that agricultural post-harvesting by-products are generally nutritious that can be converted into safe animal feed ingredients using advanced technologies. These by-products can be incorporated into animal diets without compromising animal health and performance. However, animal nutritionists, experts, and farm advisors have the opportunity to assist producers in lowering feed costs in certain regions of the country by incorporating agricultural post-harvest by-products into safe and effective rations. A basic understanding of the availability of the waste stream in certain regions and seasons, along with the knowledge of production and conversion, sanitary aspects in the storage of these by-products are necessary to ensure the absence of mold and bacterial contamination and pathogens.

Conflict of interest

The authors declare no conflict of interest.