Introductory Chapter: Animal Feed Science and Nutrition - Production, Health and Environment

1. Introduction

Different earth health indicators for “safe operating space,” including degradation of land, climatic change, loss of biodiversity, deforestation, acidification of the ocean, and water scarcity, have deteriorated in recent decades, which is a great threat for the natural habitats along with human civilization [1]. Food animal production, which contributes significantly to gross domestic products in most of the countries of the world and provides nutritional and economic security of the farmers in low-income countries, has been recognized as significant divers of many ecological alterations in the Anthropocene period due to substantial share of greenhouse gas (GHG) emissions (methane and nitrous oxide) to the atmosphere [2]. Rapid increases in greenhouse gas (GHG) concentrations along with methane in the environment have become major drivers of climatic changes in the Anthropocene era [1]. Furthermore, food animal production faces many challenges, including shortage of high-quality feed ingredients, the contribution of pollutants to the environment, development of antimicrobial resistance due to inappropriate use of antibiotics and other antimicrobial chemical compounds, food safety, health, and welfare of animals. The demands of animal food products have risen sharply and will also increase considerably in the future owing to the growing human population, national economies, and urbanization. These changes will further intensify the challenges. The importance of animal feeding and nutrition is enormous in solving these challenges linked with food-fuel-feed competition, productivity, health and welfare, environment, product safety and quality [3]. In-depth analysis and better knowledge of the impacts of feeds and feeding on various domains of the livestock production systems focusing on the contribution of livestock in greenhouse gas emission, and providing solutions to challenges through improved technologies, policy, and institutional development measures are required [3]. In this chapter, some nutritional solutions to these challenges are described.

2. Identification of newer feed resources

Optimum potential performances of animals are not always expressed due to the improper supply of nutrients required for the physiological stages. This situation happens owing to the shortage of quality feeds for animals. Moreover, there is fuel-feed-food competition as feeds of livestock also include both human edible components and feedstock of biofuel production. With the increasing human population, human-edible feeds, such as cereal grains and soybeans, which constitute major ingredients for monogastric animals, may become less available for livestock. Maximum utilization of human-inedible feed ingredients will be required for sustainable livestock production. Many unconventional feeds have been identified to be used in the diets of different species of animals within specified limits. Some novel feed resources have been explored recently.

Several insect meals of different species are of interest recently as a protein source for monogastric animals due to their high protein composition and they are part of the natural diet of poultry. Insect meals could be sustainable protein feeds as they can be reared on low-grade biowastes, converting biowastes into high-quality protein sources. Amino acid composition and digestibility are promising, and studies have reported that insect meal can replace 50–100% soybean or fish meal depending upon animal species. The precise determination of amino acid digestibility and metabolizable energy content of different insect meals are required to properly balance the amino acids and energy in diets, particularly for monogastric species. It is technically possible to utilize insect meals as an alternative protein-rich feed ingredient [4].

Microalgae (green algae, blue-green algae, golden algae, and diatoms) are important marine resources and have the potential to become important sources of protein and bioactive compounds, vitamins, and minerals. Approximately, one-third of the world’s total microalgae production is utilized for animal applications [4]. Microalgae can also be produced with waste materials, for example, manure and solar energy. The protein content of microalgae varies among species with a range of 25–50% [4]. Microalgae are also rich in n-3 long-chain polyunsaturated fatty acids, which would improve the meat and milk quality when they are used in diets of animals [5]. The cost-effective production of microalgae is a challenge.

Seaweed or macroalgae, for example, Chlorophyta (green algae), Phaeophyceae (brown algae), and Rhodophyta (red algae) contain up to 60% polysaccharides but are also rich in high-value compounds, such as n-3 fatty acids, bioactive compounds, and colorants. The nutritional composition of seaweeds shows a broad range, depending on the seaweed species. Brown macroalgae contain 5–13% crude protein and are rich in minerals, whereas red algae contain 10–30% of crude protein, and green algae over 15% crude protein [4]. Production of seaweeds faces some similar problems as microalgae. The composition of essential amino acids in most seaweed species is not optimal, and all seaweeds have high mineral content, which restricts their use in the diets of animals unless balanced properly [4]. Besides the potential use of seaweeds as feed ingredients, they have antimethanogenic effects in the rumen, which may be further beneficial environmentally [6].

The distiller’s dried grains with soluble (DDGS) is a co-product from liquor and biofuel production. It contains high concentrations of protein and fats depending upon the grain stock used for ethanol production and can represent a valuable feed for livestock production. However, unlike cereal grains from which DDGS is derived, it mainly contains high amounts of low digestible fiber, such as cellulose, lignin, and arabinoxylans. Nonetheless, it may replace a certain amount of conventional costly feed ingredients and thus reduce the feed cost. Moreover, it contains fermented products with beneficial probiotic bacteria, prebiotics, enzymes, and bioactive metabolites to animals and thus could beneficially improve production performance [7].

Tree foliages are very useful fodder resources for small ruminant animal production, especially in the arid and semi-arid regions of the world, which provide supplementary proteins and micronutrients in low-quality forage-based diets [8]. Tree leaves may also be exploited to decrease greenhouse gas production and improve ruminal fermentation [9]. Residues from human-edible crops, vegetables and fruits, and food wastes can be utilized in all types of livestock diets that are usually fed to animals in low-income countries to some extent. The proper valorization of food wastes and residues of fruit and other processing industries as animal feeds is crucial for the transformation of the linear economy to a circular and sustainable bioeconomy, which will also reduce environmental burdens. The use of agro-industrial by-products in animal nutrition is a promising strategy to reduce the food-feed competition, the diet cost at the farm level, and the environmental impact of animal-derived food production. Moreover, many fruit and industrial wastes contain several medicinal and phytochemicals, which could be used to improve livestock production and health. The recent focus has centered on the use of plant secondary metabolites to improve ruminal fermentation, ruminant production, and health while minimizing the environmental burdens [10, 11].

3. Livestock and environment

Worldwide food production systems (livestock and vegetable-origin foods) contribute 18 Gt greenhouse gas (GHG; CO₂, methane, nitrous oxide, and fluorinated gases) emissions in CO₂ equivalent (CO₂e) (non-CO₂ gases are expressed as CO₂e based on the warming potential of the gases) account one-third (34%) of total global GHG based on detailed life cycle assessment analysis [12]. Different livestock activities, such as livestock rearing, feed production, land use and land-use change, manure management, transport, slaughtering, processing, and storage, contribute significantly to the total anthropogenic GHG emissions and are considered an important driver of global climate change in the food-system emissions. In livestock production, direct methane emissions from enteric fermentation and manure, and nitrous oxide emission during the process of nitrification and denitrification of the manure nitrogen comprise about 9% of total GHG emissions, and livestock share about 70% of total emissions from the agriculture, forestry and other land use [13]. Total direct non-CO₂ GHG emissions of enteric and manure sources globally increased from 1.77 Gt CO₂e in 1961 to 2.77 Gt CO₂e in 2010 at an annual growth rate of 0.92% [14]. Reduction of enteric methane emissions is needed to lessen the accountability of livestock production for GHG emissions. Different chemical inhibitors (e.g., halogenated methane analogs), defaunating agents and approaches, and ionophores (e.g., monensin) lower methanogenesis directly or indirectly in the rumen, but they do not exert consistent effects for practical uses. A range of nutritional strategies, such as increasing the cereal grains, feeding of leguminous forages containing high content of tannins, supplementation of low-quality roughages with readily fermentable carbohydrates and protein, and addition of fats with high concentrations of medium-chain fatty acids or long-chain unsaturated fatty acids, show promise for ruminal methane mitigation. Several new potential technologies, such as the use of plant secondary metabolites (polyphenols, essential oils, saponins, and alkaloids), propionate enhancers, bacteriocins, bacteriophages, probiotics, stimulation of acetogens, immunization, methane oxidation by methylotrophs, and genetic selection of low methane-producing animals, and development of recombinant vaccines targeting archaeal-specific genes, and cell surface proteins, have emerged to lower methane production [15]. Many plant secondary compounds, predominantly polyphenols, essential oils, saponins, and alkaloids, have been explored to modulate ruminal microbial fermentation and decrease methane production because of their antimicrobial and antimethanogenic properties [15]. Mitigation strategies of ruminal methane emission are considered to be less expensive than the reduction of CO₂ emission. Mitigation of methane emission by some technologies usually does not exert many negative results on ruminal fermentation but sometimes is associated with improved efficiency of animal production, which is beneficial in both environmental and nutritional perspectives. Many new technologies for methane mitigation have been explored, but only a few of them are practical and cost-effective, which can be adopted to accomplish mitigation of methane emissions at farm levels. A recent methane inhibitor, 3-nitroxypropanol, can significantly (up to 36%) lower enteric methane with some positive effect on milk component yield and body weight gain in cattle [16]. Different methane mitigation strategies in combination should be adopted to substantially mitigate methane emission from ruminants. The methane mitigation options that show both nutritional and environmental advantages would likely be better adopted by the farmers. For example, dietary fat up to 6% level could lessen methane emission moderately as well as improve animal productivity [17]. Similarly, nitrate supplementation could reduce the expensive protein meals in diets while decreasing methanogenesis. If some mitigation technologies could be employed to improve the nutritional values of forages, they would have immense practical importance in tropical feeding situations. However, mitigation of methane production is not consistent due to the adaptation of ruminal microbiota to the agents, dose, dietary composition, species, and production stages [18, 19].

Livestock species excrete an enormous amount of nitrogen and phosphorus to the environment with 92 Tg/year of nitrogen and 17 Tg/year of phosphorus in 2000, and this excretion is greater than nitrogen and phosphorus fertilizer use in croplands and grasslands [20]. Manure nitrogen excretion imparts a substantial share to the global nitrogen cycle, which is accountable for air pollution, water quality deterioration, climate change, and imbalances in biodiversity. The livestock production system shares approximately 40% of the total anthropogenic nitrous oxide and ammonia emissions globally, which arise from livestock manure nitrogen [21]. Dietary amendments are required by improving their utilization efficiency to reduce nitrogen and phosphorus excretion to the environment.

4. Feed safety, health, and welfare

Livestock feed represents the initial point of food safety in the farm-to-table supply chains. Therefore, the use of safe feeds is fundamental to human food safety. Feeds can contain inherent toxicants or can be contaminated with biological, chemical, and physical hazards during harvesting of the raw ingredients, manufacturing, processing, storage, or transport. In particular, pesticides, fungal toxins, and heavy metals are widespread in feedstuff. Heavy metal (e.g., cadmium, arsenic, lead, mercury, copper, and chromium) contents in feeds and water are particularly widely prevalent in industrial, urban, and semi-urban regions. Ultimately, animal-derived foods may contain high concentrations of these heavy metals, which is of public health concern. Therefore, contamination of the heavy metals in these regions needs special attention and preventive measures to reduce the heavy metal contents in meat and milk by nutritional amendments [22].

In-feed antibiotics are commonly added in the animal industry, but they are concerned about the development of antimicrobial-resistant pathogens, posing a possible danger to human health. Though different opinions have been stated on antibiotic resistance gene transfer from animal pathogens to human pathogens, a possible connection between the use of antibiotics at subtherapeutic levels and the antimicrobial resistance development among the microbiota has been reported in many studies [23]. Several alternatives have been explored in recent decades, which include probiotics, probiotics, synbiotics, organic acids, phytogenics, enzymes, antimicrobial peptides, bacteriophages, clay, and metals. These feed additives have better effects with respect to immunomodulation, gut health, and antioxidant status compared with antibiotics. Although the positive results of many of the alternatives have been well reported, there is a lack of clear knowledge on their mode of action, efficacy, and advantages and disadvantages of their applications [23].

Animals face different kinds of stresses, namely, overproduction, overcrowding, transportation, and temperature, which are welfare issues for the livestock production systems. The stresses reduce animal performance, immunity, deteriorate product quality, gut health, and increase vulnerability to diseases. Different stresses can be alleviated by proper feeding practices, such as the use of medicinal plants, gut microbiota-acting agents, and antioxidant vitamins and minerals, which can improve antioxidant status, gut health, and immunity in animals along with animal production and product storage quality [24]. Overgrowth of broiler chickens and turkeys predisposes to many metabolic diseases related to mainly cardiovascular (e.g., ascites and pulmonary hypertension syndrome) and musculoskeletal (e.g., lameness, dyschondroplasia, and spondylolisthesis) disorders resulting from high nutrient intake or high metabolic rate, which causes more economic loss than the infectious diseases [25]. In high-producing cows, subacute ruminal acidosis commonly occurs due to the feeding of high proportions of grains to balance the energy requirements, which reduces milk production, ruminal health, and barrier function [26].

5. Food quality

Consumers are increasingly interested in healthy foods, giving rise to increasing demand for foods with beneficial health and well-being effects. The concentration of many health-promoting fatty acids in milk and meat can be effectively enhanced through strategic feeding. Several studies have been targeted to decrease the concentration of saturated fatty acids, and to enrich the n-3 fatty acid and rumenic acid (cis-9, trans-11 C18:2) content in milk and meat. A wide variety of plant secondary compounds, including polyphenols (simple phenolic compounds, tannins, and flavonoids), essential oils, and saponins, which have specific antimicrobial effects in the rumen responsible for fatty acid biohydrogenation, has been investigated with varying success [27]. The effectiveness of essential oils and tannins is still inconsistent with some studies showing no beneficial effects and others a positive result on inhibiting the first step or, less commonly, the final step of biohydrogenation of polyunsaturated fatty acids [28, 29]. Plant secondary compounds with higher antioxidative properties may reduce volatile compounds, such as skatole and indole (responsible for off-flavor in meat), enhance antioxidant status, and decrease lipid peroxidation and deterioration of meat and milk quality during storage. Further research would be needed to unravel the causes of contradictory effects, which may be attributed to the diverse active compounds, ruminant animal species, dose, diet composition, and physiological stages [29].

6. Conclusions

The livestock production system faces several challenges, including feed-fuel-food competition, shortage of high-quality feeds to support optimum potential performance, greenhouse gas emissions, environmental pollution, feed safety, consumers’ demands of better-quality animal-origin safe foods, antibiotic-resistant human pathogenic microorganisms, health and welfare of animals in recent decades. Some of these challenges may be further intensified in the future. Animal feeding and nutrition would play highly important roles in solving these challenges. Newer feed resources, including valorization of biowastes, vegetable, fruit processing by-products as animal feeds, are required to replace human-edible feeds and to improve dietary quality by supporting optimum production. Proper feeding management can reduce greenhouse gas emissions and environmental pollution and enrich health-promoting bioactive principles in animal-derived foods while improving the health and welfare of animals.

Conflict of interest

The author declares no conflict of interest.