Climate change, Livestock, Breeding, Feeding, Fodder production, Manure, Management.

The global appetite for animal protein has steadily grown in recent decades, fueled by urbanization and population expansion (Froldi et al., 2022). Milk is a cornerstone of global agriculture, contributing significantly to both livestock and overall agricultural value. It accounts for 27% and 10% of the total added value of these sectors, respectively (IFAD, 2017). As one of the most produced and valuable agricultural commodities worldwide, milk plays a vital role in the global food system.

Climate change is transforming the planet's ecosystems, a warming planet endangering lives now and in the future. Slashing emissions is critical to avert catastrophic climate change and keep global warming below 2 C. While the livestock sector provides vital protein for billions, it also carries a hefty environmental cost, contributing roughly 14.5% of global green house gas emissions (Gerber et al., 2013). 

Methane emission is the largest contributor from livestock, accounting for 44% of human-caused (anthropogenic) emissions globally.  Nitrous oxide (N2O) contributes a substantial 53% of anthropogenic nitrous oxide emissions.  While the smallest contributor among the three, livestock still account for 5% of human-caused CO2 emissions (Gerber et al., 2013). The contributions of the GHG emission is depicted in Fig. 1.

Fig. 1.  Contribution of livestock to the total GHG anthropogenic emissions [Adapted from Rojas-Downing et al. (2017)].

Among the livestock population beef cattle is the largest contributor, responsible for roughly 41 % of the sector's emissions. Come in second is dairy cows at around 20% followed by swine (9 %), buffalo (8 %), poultry (8 %), and small ruminant (6 %)  (Gerber  et al., 2013). 

Enteric fermentation is the dominant source of greenhouse gas (GHG) emissions from ruminant livestock including cattle, buffalo and small ruminants (sheep and goats). It contributes a significant portion, ranging from 43 % to 63 % of the total GHG emissions from the livestock sector depicted in the Fig. 2.

Fig. 2. Total global livestock GHG emission by specie and product [Adapted from Gerber et al., (2013)].

Intensive livestock production is often associated with environmental concerns due to the generation of greenhouse gases, such as methane (CH4) and nitrous oxide (N2O), and the potential for pollution from enteric fermentation and inadequate waste management practices (Niloofar et al., 2021). Despite ambitious efforts to phase out fossil fuel emissions, achieving global climate targets will be challenging, if not impossible, without substantial reforms in animal agriculture (Ivanovich et al., 2023). Recent developments indicate increasing efforts to mitigate emissions from the food system. These include the FAO's roadmap for achieving zero hunger while limiting global warming to 1.5 and the Global Methane Pledge, which has garnered support from over 110 countries committed to reducing methane emissions by 30% by 2030 (Global Methane Pledge, 2023).

Unveiling a roadmap to a greener future for our food system, this review article explores groundbreaking solutions for reducing the livestock sector's climate footprint through advancements in breeding, feeding management, fodder production management and manure management.

Breeding for efficiency: Selecting climate -friendly animals. Traditionally, breeding focused on maximizing milk production and health traits. To address climate change, considering impact emissions in breeding goals is important. This will adjust the importance of existing traits or incorporating new ones related to reduce emissions.

A key strategy to reduce emissions in dairy cattle breeding is to factor in the cost of these emissions when choosing breeding animals. Wall et al. (2014) compared different selection indexes and found that prioritizing emission reduction (environmental index) led to significantly higher annual emission reductions compared to traditional economic indexes focused solely on production. This approach placed less emphasis on some health and fertility traits, but resulted in a more environmentally friendly outcome. Combining economic and environmental factors yielded reductions that depended on the assumed cost of emissions.

∙ Selective breeding for lower emissions: Genomic selection, employing genome-wide DNA markers, holds an advantage over conventional selection methods, particularly for selecting animals early in life and for traits that are challenging or expensive to measure, such as CH4 emissions and feed conversion efficiency in dairy cattle (Worka, 2024).  Selective breeding programs can then favor these traits, leading to herds with a reduced environmental footprint.

∙ Gene editing for sustainability: Gene editing technologies hold promise for creating animals with desirable traits, such as improved feed efficiency or reduced methane production. However, ethical considerations and public acceptance need careful consideration (Yunes et al., 2021).

Revolutionizing ruminant diets: Feeding for a greener future. Historically, conventional feeds like grains, legumes and forages have sustained ruminant population, their reliance raises concerns about long-term viability. This includes impacts on land and water sustainability, greenhouse gas emissions, and competition for arable land used for food, feed, and fuel production. Livestock feed production, particularly for ruminant animals, is a major contributor to emissions (Halmemies-Beauchet-Filleau et al., 2018).  Driven by the need for sustainable feed production and reduced greenhouse gas emissions, exploration of novel feed resources is essential. 

Innovative approaches through feed manipulations and feed additives to reduce the impact of climate change

Forage management. The impact of forage management on enteric methane (CH4) emissions can be evaluated at the farm level through regionally specific life cycle assessments (LCAs). These LCAs should account for variations in forage type, animal productivity, and other regional factors that influence greenhouse gas emissions (Króliczewska et al., 2023).

Alternate feeds. Promising alternatives include agro-industrial byproducts like molasses and plant oils, offering nutritional, economic, and environmental advantages. Additionally, forage legumes, insect-based feeds, and even horticulture food waste holds potential (De Evan et al., 2020; Vastolo et al., 2022; Ku-Vera et al., 2020). 

Tannin-rich forages. Studies by Gastelen et al. (2019) showed that sheep fed tannin-rich forages consumed 34% more dry matter, while methane production (both per unit of dry matter intake and as a percentage of gross energy intake) decreased by 23 % and 36 %, respectively. Replacing grass-based diets with tannin-rich forages offers a potential methane reduction strategy for sheep and dairy cattle. However, the effectiveness of tannin-rich feeds depends on the specific type, source, and molecular weight of the tannins, along with the rumen microbiome and forage concentration (around 20 g/kg of dry matter intake). Starch-rich concentrates like wheat, barley, and maize contribute less to methane (CH4) production compared to fibrous concentrates (Bes et al., 2022). Interestingly, studies suggest a threshold effect, when concentrate inclusion in the diet surpasses 50%, total CH4 emissions from goats might decrease, though the absolute amount may not (Lima et al., 2016). Alternative feed sources like orange leaves and rice straw, as shown with Murciano-Granadina goats, offer promising CH4 reduction without compromising energy balance (Romero et al., 2021). 

Tannins inhibit methanogenesis in a bactericidal and bacteriostatic manner by acting on fibrinolytic bacteria and are dependent on their chemical structure as well as the bacteria species (Liu et al., 2011; Vasta et al., 2019).

Essential oils and macroalgae. Emerging strategies to combat ruminant methane emissions include essential oils and macroalgae supplementation. While in vitro studies show essential oils can influence rumen fermentation and achieve impressive reductions in methane production, up to 90% in some cases, further research is needed (Caroprese et al., 2023). 

Macroalgae supplementation offers another promising avenue, with encouraging results for enteric methane reduction in ruminants (Wasson et al., 2022).

Saponins., Saponins might influence the activity or abundance of enzymes involved in methane production within methanogens. Saponins can favor certain bacteria over others, potentially reducing the abundance of methanogens in the rumen (Patra et al., 2009, Romero- Perez et al., 2011 ; Ramos-Morales et al., 2017.) 

Flavonoids. Flavonoid compounds, such as naringin and quercetin, have shown promise as rumen feed additives. These compounds may improve fermentation efficiency by promoting propionate production relative to acetate (Formato et al., 2022). Additionally, in vitro studies suggest that flavonoids can reduce methane (CH4) emissions, ciliate protozoa populations, and hydrogenotrophic methanogens (Oskoueian et al., 2013 ; Olagaray et al., 2019).

Lipids. Lipids hold promise as a strategy to decrease methane (CH4) emissions in ruminant animals (Patra et al., 2017). Lipids can damage the cell membranes of methanogens and protozoa, leading to their death and reduced CH4 production (Machmüller et al., 2003). Essential oils appear to work by altering the microbial population in the rumen, the primary site of CH4 production in ruminants and reducing the abundance of methanogens, the microorganisms responsible for producing CH4 (Wallace, 2004).

Mitigation through manipulation of microbiome. Probiotics are microbiological feed additives affect rumen fermentation and improve animal health by modulating the gastrointestinal microflora (Tavendale et al., 2005)

Defaunation boosts bacterial population density, bacterial protein synthesis efficiency, and nitrogen flow to the duodenum, especially when the feed is low in protein relative to its energy content. Furthermore, defaunation reduces carbohydrate digestion of plant cell walls, significantly improves protein supply and livestock productivity, and lowers CH4 production. The removal of protozoa from ruminants' rumen is associated with decreased organic matter digestibility, particularly acid detergent fibre (ADF) and neutral detergent fibre (NDF), and decreased food intake (Newbold et al., 2015; Hristov et al., 2013). 

The development of vaccines for limiting methanogenesis is based on inducing the animal's immune system to produce antibodies in saliva, which upon entry into the rumen, should suppress the growth of methanogens (Subharat et al., 2016).

Mitigation through chemical additives

3- nitrooxy-propan-1-ol. 3- nitrooxy-propan-1-ol (3-NOP), a feed additive intended to reduce methane emissions in dairy cows, is extensively metabolized. At a dose of 60 mg/kg dry matter (DM), it breaks down primarily into 3-nitrooxypropionic acid (NOPA) and 3-hydroxypropionic acid (3-HPA) (Bampidis et al., 2021). Additionally, smaller amounts are converted to nitrate/nitrite (NO3- / NO2-) and carbon dioxide (CO2). Beyond nitrates, the remaining metabolites contribute to the production of essential milk components like lactose and glucose.

Nitrates. 3-NOP offers a promising approach to reducing methane emissions, nitrate (NO3-) is another established dietary supplement used for the same purpose. Typically provided as calcium, sodium, or potassium salt, nitrate can also decrease enteric CH4 production in cattle. However, there's a crucial difference: unlike 3-NOP, nitrate can have direct toxic effects on methanogens. This toxicity arises from the conversion of nitrate to nitrite (NO2-) during its breakdown in the rumen, a process that disrupts the methanogens' functioning (Van Zijderveld et al., 2011).

Ionophores. Ionophores offer another strategy to reduce methane production in the rumen. These additives selectively promote the growth of beneficial Gram-negative bacteria, like F. succinogenes. Ionophores indirectly suppress methane formation by limiting the availability of these key substrates for methanogenic archaea (Hristov et al., 2013).

Balancing Biodiversity through sustainable fodder practices. Polley et al. (2013); Thornton et al. (2009) suggest a temperature increase of 2 C will likely decrease both forage quantity and quality in these regions. This can lead to reduced pasture availability and lower livestock production. Benchaar et al. (2001) found, a decrease in forage quality leads to increased methane emissions per unit of energy consumed by animals.

Among livestock systems, grazing is likely to be most impacted by climate change because of its dependency to feed quality and availability. In order to reduce the impact of climate change on grazing livestock systems, adaptation measures should be implemented. Rojas-Downing et al. (2018) reported that the overall sensitivity assessment showed that the most resilient pasture composition under future climate scenarios was ryegrass with red clover and the least resilient was orchardgrass (Dactylis glomerata) with white clover (Trifolium repens).

Silvipastoral Systems (SPS)

∙ Increased cattle production: SPS can lead to a significant 4-fold increase in cattle production efficiency per hectare (Murgueitio et al., 2009). This is due to a combination of factors like improved forage quality and increased grazing area.

∙ Reduced feed dependence: Livestock in SPS often have access to higher quality forages from trees and improved pastures, reducing the need for external feed concentrates and grains (Ribeiro et al., 2016). This translates to lower feed costs and potentially a more sustainable operation.

∙ Enhanced soil health: Trees in SPS contribute to improved soil properties in several ways. Their deep roots can access and cycle nutrients from deeper soil layers, while fallen leaves enrich the soil with organic matter. Additionally, nitrogen-fixing trees can increase overall soil nitrogen content (Cubillos et al., 2016). This translates to healthier soil with improved fertility and water retention.

∙ Greater carbon storage: SPS systems excel at carbon sequestration, storing more carbon in both aboveground trees and belowground biomass compared to treeless pastures (Montagnini et al., 2013). This makes them a valuable tool in mitigating climate change.

∙ Improved soil resilience: The presence of trees in SPS contributes to a more resilient soil structure, better able to withstand degradation, nutrient loss, and the effects of climate change (Murgueitio et al., 2011). This leads to a more sustainable land use system.

∙ Enhanced biodiversity: SPS systems create a more diverse habitat compared to open pastures. This attracts a wider variety of birds, insects, and other wildlife (Rivera et al., 2016). This biodiversity can benefit the overall health of the ecosystem.

∙ Improved animal welfare: Studies suggest that animals raised in SPS experience improved welfare compared to those in treeless pastures (Broom et al., 2013). This can be attributed to factors like shade from trees, access to diverse forage sources, and potentially a more natural environment.

Plate 1. Silvipasture system for livestock integration.

Overall, silvipastoral systems offer a compelling alternative to traditional grazing practices. Their potential benefits for both productivity and environmental sustainability make them a promising approach for the future of livestock production.

Manure management: From waste to resource. Manure management is a critical challenge for the livestock sector.  Livestock manure releases CH4 and N2O gas. The decomposition of the organic materials found in manure under anaerobic conditions releases methane. Steinfeld et al. (2006) reported that N2O emissions from stored manure are equivalent to 10 million tonnes N per year.

However, innovative approaches can transform this waste into a valuable resource:

∙ Anaerobic digestion: This process converts manure into biogas, a renewable energy source that can be used for heating, electricity generation, or powering farm equipment (Klassen et al., 2016). Digestate, the byproduct, can be used as a fertilizer.

∙ Composting: Composting manure creates a nutrient-rich soil amendment that can be used to replace synthetic fertilizers, reducing reliance on fossil fuel-based inputs.

∙ Nutrient recovery technologies: Emerging technologies are being developed to capture valuable nutrients like nitrogen and phosphorus from manure, allowing them to be recycled back into fertilizer production.

The rise of alternative proteins: Redefining meat consumption

While reducing meat consumption is crucial for climate change mitigation, alternative proteins offer promising options for consumers who crave meat-like textures and flavors:

∙ Plant based meat alternatives: Advancements in plant-based meat alternatives have led to products that closely mimic the taste and texture of real meat, often with a lower environmental footprint.

∙ Cellular agriculture: This technology uses animal cells to grow meat in a lab setting, offering the potential to produce meat without the environmental impact of traditional animal agriculture.

∙ Insect protein: Insects like crickets and mealworms can be a sustainable source of protein with a smaller land footprint and lower emissions compared to traditional livestock.

Moving forward: Collaborative efforts for a sustainable future. Realizing the full potential of these innovations requires a collaborative effort across various stakeholders:

∙ Farmers and ranchers: Early adoption of innovative practices by farmers and ranchers is crucial for driving change. Education, extension services, and financial incentives can play a significant role in promoting adoption.

∙ Policy makers: Policies like carbon pricing, support for research and development, and investment in infrastructure for sustainable practices can create an enabling environment for change.

∙ Consumers: Consumer demand for sustainable and ethically produced food products can incentivize the livestock sector to adopt more environmentally friendly practices.

To further advance sustainable livestock practices, research should focus on developing more precise genetic markers to identify traits linked to emissions reduction, investigating the long-term effects of alternative feed sources on animal health and productivity, scaling up innovative manure management technologies, and exploring the potential of hybrid food systems that combine traditional livestock production with alternative protein sources.

S. Gunasekaran and Karu Pasupathi  (2024). Mitigating Climate Impact: Novel Strategies for Reducing the Environmental Footprint of Livestock Production. Biological Forum – An International Journal, 16(8): 205-210.