The Role of Feed Additives in Reducing Carbon Emissions

12 April 202214 min reading

Generalizing conscious breeding for sustainable and ecological livestock, preferring the accurate amount and quality of feed and feed additives will be highly effective in preventing the possible effects of climate change in the future.

The rapid increase in the world population changes the consumption amount and habits. The increase in consumption accelerates agriculture and livestock practices and increases industry and energy requirements. This situation causes the negative effects of greenhouse gases to intensify as the amount of animal waste increases and the amount of methane released into the atmosphere is affected (Kılıç and Boğa, 2021). Greenhouse gases, which have an important place in climatic changes, cause warming of the atmosphere by holding on to the long-wave infrared rays reflected back to the atmosphere (Koyuncu and Akgün, 2018). While 40% of global methane emissions are of natural origin, 60% are anthropogenic, that is, enteric fermentation waste from agriculture and livestock (cattle breeding), human-made waste yards, sewage plants, rice fields and biomass incineration (Nosalewicz et al., 2011). It has been reported that the share of the livestock sector in global anthropogenic greenhouse gas emissions is 18%, while its share in methane emissions is 30-50%, and the effect of ruminant breeding reaches 80% within this share, while chicken and pig farming is 8-9% effective (Bayat and Shingfield, 2012; Gerber et al, 2013; Opio et al, 2013). In summary, improper and incorrect agricultural and livestock practices increase greenhouse gas emissions such as CO2 (carbon dioxide), CH4 (methane) and N2O (nitrogen oxide). In addition, they stated that methane, which is excreted from the body with feces, urine and burping, represents 5.5-6.5% of the gross energy intake for cattle, sheep and goats (Johnson and Ward, 1996). Therefore, besides its negative impact on the environment and climate, it also causes economic losses. For this reason, strategies to reduce greenhouse gas emissions are developed, especially in ruminant feeding, and it is recommended to use appropriate feed additives in rations on top of recommendations for the use of quality raw materials and the preparation of correct ration formulations. In order to estimate the methane release to the nature correctly, besides the feeding methods, animal species and number, live weight and yield information of animals are taken into consideration.

The main factors affecting methane emission in terms of animal feeding can be listed as feed quality and conversion rate of feeds, processing of feed, adding oil to the ration, using feed additives in ration such as probiotics, organic acids, herbal extracts, enzymes, clay minerals and algae, and using substances such as tannin and saponin.

When crude cellulose is broken down by bacteria in ruminants; pyruvic, succinic and lactic acids are formed as intermediate products, and volatile fatty acids (VFA), CO2 and methane are formed as last products. For this reason, choosing quality roughage and determining the roughage/concentrated feed ratios are effective in increasing the digestibility of feeds and preventing yield losses, while also reducing methane emissions. It is estimated that the production of CH4 and N₂O produced by high-yielding animals is lower than that of low-yielding animals because they consume less roughage. Interventions such as increasing the grain ratio in the ration, choosing corn silage, and increasing the oil level are effective in reducing methane emissions. The roughage/concentrated feed ratio is also effective in regulating CH4 production, as it is effective in changing acetate : propionate levels in the rumen. Because propionic acid reduces the rumen pH, preventing the reproduction of protozoa and thus preventing the protozoa from producing more H2 for methanogens (Kılıç and Taurus, 2021). It has been reported that legume forage crops with low fiber content and high dry matter content have less methane emissions because of their rapid digestion (Beauchemin et al, 2008). Moreover, it has been determined that methane production can be reduced significantly by grinding or pelleting the feeds (Moss et al, 2000). Apart from these, it is known that the addition of fat to the rations, especially in terms of meeting the energy needs of high-yielding dairy cows, is effective in reducing methane emissions (Kılıç and Boğa, 2021). Adding fat to the ration suppresses methanogens and cellulolytic bacteria and slows down the digestion of fibrous foods, using the H2 present in the rumen through hydrogenation of fatty acids. Thanks to this effect, it has been reported that adding oil to the ration can reduce methane production by 21%. Although fats contribute to the reduction of methanogens by affecting cellulose digestibility, it should be noted that when the fat ratio in the diet is above 5-6%, it may have negative effects on cellulolytic bacteria and protozoa.

Another measure that can be taken in the field of animal nutrition in terms of reducing methane emission is the use of feed additives in rations. In this context, it is often recommended to use probiotics in rations, especially in order to maintain the balance of the rumen microbiome. Among the lactic acid bacteria, Lactococcus plantarum, L. casei, L. acidophilus and probiotics such as Enterococcus faecium, Megasphaera elsdenii, Aspergillus oryzae fermentation extract and Saccharomyces cerevisiae yeast culture that are effective in acetate and propionate production are being widely used (McAllister et al, 2011). Probiotics are effective in reducing H₂ production and CH₄ emission due to the increased number of bacteria due to the breakdown of degraded carbohydrates between microbial cells and fermented products (Newbold and Rode, 2006). In an in vitro study, it has been determined that the total volatile fatty acid production did not change with the addition of Saccharomyces cerevisiae to the ration and there was a significant decrease in the acetic acid: propionic acid ratio (Öztürk et al., 2015). The increase in propionic acid synthesis and the acceleration of fermentation in the rumen are the reasons that reduce methane production. It has been demonstrated in different studies that adding yeast to the ration increases the synthesis of propionic acid, reduces the number of protozoa, or decreases methane production by increasing animal productivity (Chaucheyras et al, 1995; Newbold et al, 1998; Öztürk et al, 2015; Gür and Öztürk, 2021). It has been reported that adding yeast to the ration accelerates the synthesis of acetic acid by acetogenic bacteria and suppresses methane synthesis through the depletion of metabolic H2 in the medium. Adding yeast to the ration also contributes to the stability of the rumen pH. Thus, it increases the resistance against subacute ruminal acidosis (SARA) in feeding with a ration containing high concentrate feed (Lila et al, 2004; Gür and Öztürk, 2021). Probiotics also prevent nitrite toxication by taking a role in the detoxification of toxic nitrite that occurs through the addition of nitrate to the ration, which is a very effective method in reducing methane production (Latham et al., 2018).

There is a consensus that methane production decreases when propionic acid production is increased in the rumen. Starting from this point of view, it has been noted that some organic acids (malic acid, fumaric acid and pyruvic acid) or sodium salts of organic acids, which are propionic acid primers, can reduce methane production by shifting the rumen fermentation towards propionic acid (Newbold and Rode, 2006; Sahoo and Jena, 2014; Carro and Underfeld, 2015). It is also known that organic acids such as malic and fumaric acid reduce enteric methane production.

The fact that antibiotics cause resistance development and residue formation in animal tissues increases the interest in natural additives in the feed additive production industry. These natural plants, which contain substances such as essential oil, saponin, and tannin, have come to the fore in regulating the rumen microbial population and nitrogen metabolism, reducing methane production, reducing the incidence of feeding-related problems such as acidosis, and improving the health and productivity of animals. Essential oils of fennel, clove, garlic, onion and ginger are known to inhibit in vitro and in vivo methane production (Kaya et al, 2012). It has been stated that there is a significant decrease in the production of CH4 and CO2 gases with the use of thyme, mint and orange oils in the rations, the number of methanogen bacteria is damaged due to the antimicrobial features of essential oils, and in this way, the production of CH4 and CO2 gas decreases with the formation of volatile fatty acids (VFA) in the rumen fluid (Canbolat et al. , 2011). It has also been determined that the addition of 400μg/ml of thymol to the rumen fluid reduces the production of CH4 gas (Evans and Martin, 2000). Tannins rich in phenolic substances have important properties that reduce nitrogen excretion in the urine, intestinal parasites and CH4 formation in the rumen. However, it should not be forgotten that the digestibility of feeds containing high tannins may decrease, cause constipation and adversely affect the performance (Beauchemin et al, 2008). Saponins, which are bioactive phytochemicals with strong antimicrobial effects that protect plants from insects and microorganisms, can also be used for similar purposes (Gür and Öztürk, 2021). It has been stated that saponins limit the presence of H₂ by reducing the number of rumen protozoa or methanogenic archaea, thus reducing the production of CH₄ (Bodas et al, 2012).

Enzymes such as cellulase and hemicellulase added to the ration are concentrated fermentation products and accelerate fiber digestion. Low fiber ratio in the ration and ration's consisting of easily digestible fibers reduce methane production. Since the acceleration of fiber digestion shortens the residence time of the content in the rumen, it has a reducing effect on methane production (Beauchemin et al, 2008). Accelerating fiber digestion also reduces the acetate: propionate ratio (Eun and Beauchemin, 2007). However, it should be noted that the effect of enzyme supplementation on fiber digestibility depends on the composition of the diet. Therefore, recommending a single enzyme formula does not seem possible (Beauchemin, 2008).

It is known that clay minerals (aluminum silicate, montmorillonite, bentonite, zeolite), which are frequently used in diets with their mycotoxin or pellet binding properties, can adsorb ammonia formed in the rumen. It has been stated that addition of zeolite (clinoptilolite) (30 g/kg) to urea-containing (20 g/kg) beef cattle rations decreased the ammonia nitrogen level, plasma urea and nitrogen levels in the rumen, increase the digestibility of the fibrous components (ADF and NDF) in the feed, but doesn't have any effect on fattening performance. (Sadeghi and Shawrang, 2006; Kaya et al, 2012).

Studies have shown that algae are also effective in reducing methane emissions. It has been determined that the use of red macroalgae, Asparagopsis taxiformis, in rations is effective in reducing CH4 released during enteric fermentation, and that microalgae may act in a similar way and cause significant improvements in the milk fatty acid profile (Janice et al, 2020).

As a result, in order to alleviate the climate crisis and global warming we are facing, feeding-based solutions have been developed especially in cattle breeding and it has been observed that different feed additives are effective in reducing methane emissions. Generalizing conscious breeding for sustainable and ecological livestock, preferring the accurate amount and quality of feed and feed additives will be highly effective in preventing the possible effects of climate change in the future.

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