*5.4.3 Use of synthetic amino acids to compensate for amino acid specification*

To increase the accuracy of feed formulations and fulfill the AA requirements, it is possible to effectively harness the differences in the AA digestibility of feeds. Nowadays, owing to the availability and utilization of feed-grade essential AA in synthetic forms, nutritionists may accomplish this. There has been a lot of interest in using decreased protein diets supplemented with synthetic AA to increase feed efficiency, decrease nitrogen and ammonia emissions, and ensure sustainable poultry production.

### *5.4.4 Commercial exogenous enzyme augmentation*

Over the past two decades, the commercial use of biotechnology and the acceptance of feed additives in poultry nutrition have created numerous opportunities to improve nutrient uptake, feed efficiency, and productivity. Exogenous feed enzymes are conceivably the most significant ingredient to enter the chicken feed industry. Since glycanases (xylanases and glucanases) have become more readily available in the 1990s, non-starch polysaccharides (NSP) have no longer been able to inhibit the use of viscous grains such as wheat and barley in poultry diets. Regarding the substitute ingredients, feed enzymes can (i) make it possible to utilize some ingredients (which might not be possible otherwise), (ii) get rid of nutritional restrictions and allow for larger inclusion levels, and (iii) broaden the variety of ingredients used in feed formulations.

## **6. Feed sustainability and efficiency**

### **6.1 Sustainability**

The value chain of the poultry industry is hampered by several issues. In addition to being economically feasible, production must also be socially and environmentally responsible. Nutritional advancements for poultry will help to meet these issues. It is clear how vital it is to use a holistic approach to successfully convert feed into highquality poultry protein in a sustainable manner. These high-yielding animals must be able to regularly consume, digest, absorb, and convert enough nutrients to reach their genetic potential, regardless of the time of year. The effective completion of this task will necessitate the increasing use of current technology, the development of new technology, and the expansion of our knowledge and information network to achieve high consistency production with acceptable risk [12].

According to Oladokun and Johnson [13], feed production accounts for 70% of the cost of producing eggs, over 50–85% of all life-cycle greenhouse gas emissions, 80% of energy use, and similarly significant proportions of other resource and environmental consequences. A focus on enhancing the sustainability of poultry feeds is unquestionably necessary given the growing awareness of the role that animal production plays in several sustainability concerns and the ongoing expansion of the egg industry [14].

### **6.2 The impact of feeding**

In the future decades, it is anticipated that global food demand, particularly for protein, would rise significantly as the world population approaches the estimated 10 billion mark in 2050 [15]. Among the primary meat varieties produced around the world over the past 50 years, poultry has seen the highest absolute and relative growth rates [16]. Poultry meat is expected to continue to be the key sector of overall meat production due to rising global demand (**Figure 1**).

This tendency has been primarily fueled by the convenience, purported health benefits, and reduced price of chicken meat compared to red meat, in addition to concerns of culture and religion [17]. The poultry sector will be critical in ensuring food security for a rising world population [18].

### **Figure 1.**

*Global production of the four main types of products (beef, pork, poultry, and sheep); evolution from 1970 to 2018 and projection from 2018 to 2028 [Data source: FAO, 2020].*

On the one hand, this gives a unique opportunity, but on the other, it also poses a significant challenge that must be overcome. Considering the growing public concerns about the pressure and competition for limited natural resources, loss of animal and vegetable biodiversity, the spread of antimicrobial resistance, as well as the environmental burden of livestock production, the concepts of "sustainable intensification" and "producing more with fewer resources" have been reinforced as refined strategies for feeding future generations [19].

### **6.3 Feed efficiency**

The most popular technique to define feed efficiency (FE) in poultry is the feed conversion ratio (FCR), which assesses the correlation between feed intake and body weight gain for a specific growth stage. FE can also be viewed from a different perspective as a homoeostatic process that determines the net result of "energy intake," which is determined by voluntary feed intake and the efficiency of digestive processes (i.e., nutrient digestion and absorption), and "energy expenditure," which is determined by maintenance requirements, particular nutrient redistribution mechanisms, and the rate of metabolic processes and intermediary metabolism in tissues and organs [20].

### **6.4 Broad benefits of feed efficiency**

Higher FE means that less feed is needed per unit of production output from a practical standpoint (i.e., 1 kg of chicken meat).

### *6.4.1 Human food security*

Any improvement in FE would promote food security for humans as feeding is a major production cost and would help the poultry industry remain economically viable.

### *6.4.2 Environmental impact*

Advances in FE can reduce greenhouse gas emissions, which are mostly brought on by the production of feed crops, the transportation and processing of feed ingredients, and the conversion of natural ecosystems into farmed land [21].

### *6.4.3 Reduction of eutrophication*

Furthermore, more productive hens have a higher ability to store dietary nitrogen and phosphorus, which reduce the excretion of nitrate and phosphate in manure and NH3 emissions into the environment. Higher FE can thereby lessen the likelihood of eutrophication and acidification of poultry production [22].

### *6.4.4 Energy consumption, biodiversity conservation, and feed-to-feed competition*

Improvements in FE can help with the conservation of animal and plant biodiversity, feed-to-food competitiveness, and energy utilization such as electricity and fossil fuels [23].

### *6.4.5 Impact on water utilization and climate change*

Concerns about climate change and the pervasive effects of drought have made the impact of FE on water footprint more significant. Mekonnen and Hoekstra [24] estimate that the manufacturing of feed ingredients has the greatest impact on the industry's astonishing water use (4.3 m3 H2O/ton of meat). Therefore, lowering the amount of feed needed per unit of output can lower the total amount of water used by the chicken meat supply chain, whether considering crop cultivation, the production of feed, or drinking water intake. How the increase in feed efficiency has led to improvements in other parameters is shown in **Figure 2**. Enhancing feed efficiency can help conserve both biological and non-biological environmental resources.

### **6.5 Additive-based feed improvement and sustainable expansion**

According to EU Regulation 1831/2003, the field of feed additives has grown rapidly in recent years, giving rise to a wide variety of products with different specialties. The following feeds have been added to the formulas, which have improved the feed:

### *6.5.1 Precise amino acid addition*

Dietary protein has always been a hot topic in chicken nutrition due to its value for bird performance and health, production costs, and environmental effects associated with nitrogen excretion [25]. One of the most challenging goals of the contemporary poultry industry is to reduce dietary crude protein concentrations in contrast to the current norms without impairing bird growth performance, FE, or health. Recent research has shown that such a reduction is possible but to a different extent provided the meal is kept at an appropriate level in terms of its amino acid profile to meet the demands of the bird [26].

**Figure 2.**

*Feed efficiency relationship with biotic and abiotic environmental domains.*

## *6.5.2 Protease*

By encouraging the activity of endogenous proteases, exogenous protease supplementation is a viable dietary method to increase dietary nitrogen absorption. Exogenous proteases have long been a component of enzyme combinations [27]. On the other hand, interest in this field of research has increased since the discovery of monocomponent proteases ten years ago. Protease can enhance both growth performance and environmental impact indicators because it increases dietary nitrogen retention [28].
