Integrating Feed Efficiency and Waste Management for Climate-resilient Farming: A Review

As the world’s population expands, the requirement for livestock-based goods such as milk, eggs and meat and their by-products are likely to increase dramatically. However, conventional livestock production practices frequently provide significant environmental issues, such as high emissions of GHG, a depletion of water and soil resources and degradation of biodiversity (Henchion et al., 2021). Integrating feed efficiency and waste management is crucial for building climate-resilient livestock production systems. By optimizing feed utilization, we minimize resource inputs like land and water, reducing the sector’s environmental footprint. Simultaneously, effective waste management strategies, such as anaerobic digestion or composting, transform animal waste into valuable resources like biogas or fertilizer, mitigating GHG emissions and enhancing soil fertility. This integrated approach not only promotes sustainable practices but also enhances the resilience of livestock systems to climate change impacts, ensuring food security and economic stability for both producers and consumers (Alary et al., 2022; Chen et al., 2022). The rapid increase of GHG emissions triggered global awareness over the last decade to climate change and how important it is for all human beings.. Specific to the list of GHG, CH₄ and nitrous oxide (N₂O) have been mostly produced by dairy industry and industries have had a significant impact releasing climate-warming gases by their many large-scale livestock operations, feeds production and trucking prior to stores. The dairy industry is under growing scrutiny around the world as it tries to become more environmentally friendly due to climate change (Muetzel et al., 2024). Moreover, the pursuit of higher efficiency in milk production has led to a remarkable global expansion of modern dairy farming practices. This growth has been driven by technological advancements and improved management techniques, aiming to increase milk yields while minimizing production costs. In response to these concerns, there has been a coordinated effort worldwide to develop and implement more sustainable dairy production systems that reduce the sector’s carbon footprints (Abdelbagi et al., 2023).
       
At the 26^th Conference of the Parties (COP26) to the United Nations Framework Convention on Climate Change (UNFCCC) held in Glasgow, a significant milestone was achieved. Over 120 countries pledged to reach net-zero emissions by mid-century, with target dates ranging from 2050 to 2070. This ambitious commitment represents a major step forward in the global effort to combat climate change and limit global warming to 1.5^oC (Soliman et al., 2023). Between 1980 and 2018, GHG emissions from the agriculture sector experienced a concerning 34% increase. This trend is projected to continue, with estimates indicating a further 33% rise in emissions by 2060. The growing demand for food, coupled with the expansion of intensive agricultural practices, are major drivers of this upward trajectory (UNEP, 2021). In 2020, China made a bold declaration of its intention to achieve carbon neutrality by 2060. This ambitious goal signifies a significant commitment from the world’s largest emitter of GHG to transition to a low-carbon economy. By setting this target, China aims to play a leading role in addressing the global climate crisis and promoting sustainable development (Chen et al., 2022). It has been discovered that epidemics exacerbate the effects of GHG emissions by reducing efficiency and productivity and by increasing the amount of resources required to treat the illness (Ezenwa et al., 2020). The raising of livestock is the foundation of the world’s food systems, giving billions of people access to essential micronutrients and protein.
       
Despite the advancements in modern dairy farming, the environmental impact of livestock production remains a significant concern. The industry’s reliance on natural resources, such as land, water and feed, can contribute to deforestation, water pollution and biodiversity loss. These negative effects highlight the need for sustainable practices that minimize the industry’s footprint and ensure the long-term health of our planet (Van-Heurck et al., 2020). Feed management, which includes acquiring, arranging and distributing feed to animals, is an essential component of livestock production. The sustainability of the environment can be impacted by the feed category, nutritional value and feed conversion efficiency. For instance, animal production’s ecological footprint can be lowered by using more sustainably obtained feed components, such as indigenous fodder or food processing wastes (Beldman et al., 2021). Globally, countries like Brazil, India and China are leading emitters due to large livestock populations and extensive agricultural practices. Developed nations, despite smaller livestock populations, contribute significantly due to high per capita meat consumption. On a global scale, cattle are the largest contributors to livestock-related GHG emissions, primarily driven by beef production. Pigs follow as the second-largest contributors, mainly from manure management. Poultry, while having relatively low per-animal emissions, contribute significantly due to their massive global populations (Shi et al., 2022). Beef production stands out as a major driver of livestock-related GHG emissions. The combination of factors such as the CH₄ produced by ruminant animals, the land and water resources required for feed cultivation and the energy-intensive processes involved in beef production contribute to its significant carbon footprint (Rotz, 2020). Addressing the environmental impact of livestock production requires a multi-pronged approach. This includes reducing global meat consumption, particularly beef, improving feed efficiency and reducing enteric fermentation in livestock, adopting sustainable manure management practices and implementing regulations and incentives to promote sustainable livestock production. By understanding the magnitude and sources of livestock-related GHG emissions, we can work towards more sustainable and environmentally friendly food systems (Wanapat et al., 2024). In response to this, some have suggested that replacing beef with chicken could be a more sustainable option. The industrial nature of chicken production often involves higher efficiency and lower emissions per unit of meat compared to beef. However, it’s important to note that the overall environmental impact of chicken production also depends on factors such as feed sources, transportation and waste management (Yan et al., 2024). This review aims to account significant variables such as feed management and waste disposal strategies to support the development of healthy and sustainable livestock. It seeks to give a thorough summary of recent studies and cutting-edge tactics that might lessen livestock farming’s negative environmental effects while enhancing animal welfare and output.
 
Enhancing feed efficiency
 
The efficiency with which animals convert feed into meat, milk, or eggs can significantly influence the environmental impact of livestock production. Variations in feed efficiency can affect productivity levels, resource utilization and the rate at which GHG are released from animal products. For example, animals that are more efficient at converting feed into meat or milk will require less feed to produce the same amount of product, reducing the overall land and water resources needed. Additionally, more efficient animals may produce less methane, a potent GHG, per unit of output (Herrero et al., 2013). To minimize emissions and the overall consumption of resources, livestock producers often select animals with a higher feed conversion ratio (FCR). This means that these animals are more efficient at converting feed into meat, milk, or eggs. By choosing animals with superior feed conversion, producers can reduce the amount of feed required to produce a given quantity of product, thereby decreasing the demand for land, water and other resources. Additionally, higher FCR can lead to lower emissions of GHG, such as methane, which is produced by ruminant animals (Prakash et al., 2020). Rapid changes in food production, preservation and distribution, driven by scientific and technological advancements, are significantly impacting livestock production systems, particularly in developing regions. These changes, while potentially beneficial, must be carefully managed to ensure sustainability, environmental protection and the well-being of both humans and animals, while considering the unique socio-economic contexts of different regions (Boyazoglu, 1998). N₂O, CH₄, carbon dioxide (CO₂) and ammonia (NH₃) are the primary gases emitted by poultry farms. Even though N₂O and CH₄ are emitted relatively little, they are important gases to research. The impact of CH₄ and N₂O is 25 and 298 times greater than CO₂, respectively (Sugiharto et al., 2023). When compared to other animal production systems, poultry farming methods have the lowest emissions of NH₃ and other GHG and the amount of emissions will go down as feed efficiency increases (Ferreira et al., 2019). Animals with higher FCR tend to produce lower emissions of CH₄ and N₂O. This is primarily due to a reduction in enteric fermentation, the process by which microorganisms in the animals’ digestive systems break down plant material and produce these GHG. When animals are more efficient at converting feed into products, they require less feed, which in turn leads to less enteric fermentation and lower emissions (Wang and Huang, 2005). In addition to reducing GHG emissions from enteric fermentation, higher feed efficiency can also lead to a decrease in waste production. When animals are more efficient at converting feed into products, they produce less waste, such as manure and urine. This reduction in waste can lower emissions of GHG associated with waste decomposition and storage (Hill and Azain, 2009). In a study conducted by De Verdal et al., (2010), a broiler strain selected for improved FCR was found to produce significantly lower emissions compared to a control group. The study demonstrated that this strain emitted 67.5% fewer GHG than the control, highlighting the potential of genetic selection to reduce the environmental impact of poultry production.
       
In the context of dairy cows, residual feed intake (RFI) is also known as net feed efficiency. This parameter was first introduced by Koch et al., (1963) as a way to evaluate the efficiency with which an animal utilizes feed. RFI is calculated by subtracting an animal’s expected feed intake, based on its growth, weight gain and production, from its actual feed intake. A negative RFI indicates that the animal is consuming less feed than expected for its level of performance, suggesting that it is more efficient in utilizing its feed resources (Rius et al., 2012). Animals with a low RFI  are those that require less feed to maintain a similar body condition score and growth rate compared to animals with a higher RFI. This suggests that these animals have a lower maintenance energy requirement and are therefore more efficient in utilizing their feed. Studies have shown that cattle with a low RFI emit 15-25% less gastric methane than those with a higher RFI. This reduction in CH₄ emissions is directly linked to the lower dry matter intake of animals with a low RFI. Since CH₄ production is influenced by the amount of feed consumed, animals that eat less will naturally produce less CH₄ (Basarab et al., 2013). According to a study by Aboagye et al., (2022), three widely used feed additives i.e. tylosin, monensin and beta-adrenergic agonists (βAA) can enhance animal performance and reduce the environmental impact of beef production. However, restricting the use of these additives could lead to a larger environmental footprint for beef produced both domestically and for export markets. This is because these additives can improve feed efficiency, reduce CH₄ emissions and enhance animal growth, ultimately contributing to a more sustainable beef production system.

Some of the strategies for enhancing feed efficiency and reduction in GHG are explained in Table 1.



Livestock waste management
 
Enhancing animal manure management practices is essential for addressing multiple environmental challenges. By improving the handling, storage and utilization of manure, we can significantly reduce air pollution, mitigate the effects of global warming and promote sustainable agriculture. This involves implementing strategies such as proper storage to minimize odor emissions, anaerobic digestion to produce biogas and reduce GHG and the use of manure as a nutrient-rich fertilizer to enhance soil health and reduce reliance on synthetic inputs (Grassauer et al., 2023).
       
By implementing a range of mitigation strategies at different stages of the manure management cycle, it’s possible to significantly reduce the harmful effects of GHG emissions and air pollutants associated with livestock production. These strategies can include proper storage and handling practices to minimize odor and emissions, anaerobic digestion to convert manure into biogas and biofertilizers and the use of manure as a nutrient-rich soil amendment to reduce reliance on synthetic fertilizers.
       
A study conducted in the Ampara district of Sri Lanka revealed that cattle farmers primarily utilize farm waste as fertilizer, highlighting the potential for sustainable manure management practices. However, the study also emphasized the critical need for government support to further enhance the efficiency and sustainability of these practices (Dissanayakaa et al., 2022).
       
By adopting a comprehensive approach to manure management, we can contribute to a more sustainable and environmentally friendly livestock industry (Ershadi et al., 2020). To achieve agricultural sustainability and protect the environment, it is imperative to reduce GHG emissions from the livestock sector. Effective manure management practices can play a crucial role in achieving this goal. By implementing strategies such as regular manure removal, manure covering and manure composting at various stages of the manure management process, GHG emissions can be significantly reduced (Yan et al., 2024).

Calcium cyanamide (CaCN₂) has good potential to reduce the pH of the manure and it reduces the release of  NH₃. A study by Holtkamp et al., (2023) found that applying 300 mg/kg of CaCN₂ to livestock manure significantly inhibited the microbial degradation of volatile fatty acids (VFAs). This reduction in VFAs degradation led to an accumulation of VFAs in the sludge, which in turn lowered the pH. The decrease in pH had the unintended effect of reducing the release of NH₃, a potent GHG.
       
The partially permeable membrane-covered composting method has gained widespread popularity worldwide as a sustainable and efficient approach for the aerobic processing of biological waste. This innovative technique offers several advantages, including its superior responsiveness to environmental conditions, ease of operation and low environmental impact. By utilizing partially permeable membranes, this method effectively controls the exchange of gases and moisture within the composting process, optimizing the breakdown of organic matter and reducing odor emissions (Soto-Herranz et al., 2021).
               
Acidification has emerged as a promising technology for reducing CH₄ emissions from sludge storage. By lowering the pH of the sludge to 5.5, acidification can significantly inhibit the activity of methanogenic microorganisms, which are responsible for producing CH₄. Studies have demonstrated that this approach can reduce CH₄ emissions in stored cattle slurry by an impressive 65-99%, making it a highly effective mitigation strategy. As a result, acidification to pH 5.5 has become a widely accepted standard for minimizing CH₄ emissions from sludge storage facilities. Some of the strategies for manure management and reduction in GHG are explained in Table 2.

Addressing the environmental challenges posed by livestock production is a critical imperative. By prioritizing feed efficiency and waste management, we can significantly reduce the industry’s negative impacts on the environment. Sustainable livestock production requires optimizing FCR through precision feeding, feed additives and breeding for efficiency, while effective waste management methods like anaerobic digestion and composting can mitigate climate change impacts and create a more sustainable agricultural system. Enhancing feed efficiency not only lowers GHG emissions but also conserves land and water resources, promoting a more sustainable production system. Simultaneously, effective waste management practices mitigate pollution and recover valuable nutrients, fostering a more circular and environmentally friendly agricultural model. By synergistically implementing these strategies, cattle farming can achieve a holistic reduction in its environmental footprint, aligning with global sustainability goals and ensuring the industry’s long-term viability. Continued research, innovation and widespread adoption of these approaches are essential for fostering a more resilient and sustainable food system. This will ultimately help strike a delicate balance between agricultural productivity and environmental stewardship.

The authors declare no conflict of interest with perspective to the research, authorship and publication of this article.