Sustainable anaerobic rumen methane and carbon dioxide productions from prickly pear cactus flour by organic acid salts addition
Introduction
Worldwide, agricultural byproducts produced during different agricultural practices are nutrients-rich feed ingredients with a large potential to be used for ruminants nutrition (Ahmed et al., 2015, Elghandour et al., 2016a); however, in many developing countries, agriculture byproducts always cause environmental problems resulting from their burning in the field. Such feeds can be used as a cleaner product of animal feed and environment (Elghandour et al., 2016b). Moreover, as the global population is increasing, the conventional feed for animal production, such as grains, legumes, etc. is in shortage and highly priced in many parts of the world. The soaring prices of cereals, such as barley, wheat and corn, which are the major energy sources in ruminant diets necessitate search for inexpensive alternatives that can partially substitute for the expensive grains. Feeding of unconventional feedstuffs, which are of no food value to humans, can be one of the solutions. However, apart from being cheap, such unconventional feed must be available all year round, particularly during the critical dry season, to guarantee sustainable continuous supply of feed; but they may affect methane (CH4) and carbon dioxide (CO2) productions from livestock as the CO2 and CH4 emissions from ruminants depend on diet degradability and chemical composition (Elghandour et al., 2016c). Methane and CO2 productions from ruminant livestock are one of the sources responsible for greenhouse gas emission (Intergovernmental Panel on Climate Change, 2008) due to ruminal fermentation of feed in the rumen resulting in a loss of digested energy (Johnson and Johnson, 1995). According to the Food and Agriculture Organization of the United Nations (FAO), CH4 emission from animal production sector is responsible for about 18% of all greenhouse gas emissions, while CO2 accounts for about 9% (FAO, 2006).
Cacti (Opuntia spp.) have been recognized as one of the most widely used low cost alternative feeds in semi-arid regions of the world due to their adaptation to different environmental conditions (Stintzing and Carle, 2005). They have become an important source of green fodder which ensures several livestock species survival in the semi-arid and arid regions of the world with frequent periods of prolonged droughts (Costa et al., 2009). The chemical composition (g/kg dry matter (DM)) of spineless cactus pear species as reported (Costa et al., 2009) is: 78.9 DM, 48.3 crude protein (CP), 10.6 ether extract (EE), 108.7 ash, 290.7 neutral detergent fiber (NDF) and 257.1 acid detergent fiber (ADF). Being rich in non-fibrous carbohydrates (617 g/kg DM), it is an excellent energy source with high DM digestibility coefficient (Wanderley et al., 2002). Replacement of energy feedstuff such as corn grain (CG) with prickly pear cactus (PC) may require some form of supplementation with organic salts and acids which are used as energy additives and rumen modifiers in ruminant diets. Rumen modifiers such as sodium or calcium propionate (Ferraro et al., 2009), disodium malate or calcium malate (Mungói et al., 2012), exogenous fibrolytic enzymes (Morsy et al., 2016) and Saccharomyces cerevisiae (Rodriguez et al., 2015) have been used as ingredients of rations for ruminants. However, little is known about the nutritive value of organic acid salts (OAS) in ruminant nutrition.
The in vitro gas production (GP) procedure, a useful tool to study potential rumen degradation of ruminant feeds (Getachew et al., 2002, Vallejo et al., 2016), allows estimation of short chain fatty acid (SCFA) from substrate and the energetic value of feed, and the determination of the amount of substrate truly fermented which is used to synthesis microbial protein (Blümmel et al., 2003, Elghandour et al., 2015a, Elghandour et al., 2015b). The current study aimed to investigate the impact of replacing CG of diet with PC in the presence of a fermentation modulator (i.e., OAS) at different levels on ruminal in vitro GP, CH4 and CO2 productions as well as fermentation kinetics.
Section snippets
Substrates and treatments
Three total mixed rations, used as incubation substrates, were prepared where CG was replaced with PC at three levels (/kg): 0 g (Control), 75 g (PC75) or 150 g (PC150). The chemical composition and ingredients is shown in Table 1. Organic acid salts (Rumalato®, Norel, Mexico), a product containing salts of organic acids including monopropylen glycol, calcium propionate, calcium malate and other active compounds (Table 2), was used at three supplemental levels: 0, 5 and 10 mg/g DM of substrates.
Results
Fig. 1 shows the in vitro rumen GP (mL/g incubated DM) of three different levels of PC as affected by different levels of OAS. Asymptotic GP was increased linearly (P < 0.001) and quadratically (P = 0.044) by the level of PC, but it was not influenced by inclusion of OAS (dose) and ration × OAS dose interaction, respectively. Fractional rate of GP was increased (P = 0.007) linearly with increasing level of PC, while effects of ration, and ration × dose interaction were not pronounced (P > 0.05)
Discussion
The extent of feed fermentation and digestibility is reflected by gas produced in in vitro fermentation. The linear and quadratic increases in asymptotic GP with increasing level of PC replacement for CG indicate an increasing fermentation of the insoluble but degradable fraction. The result suggests a steady increasing availability of carbohydrate fractions to the microbial population, in consonance with previous studies (Elghandour et al., 2015a, Elghandour et al., 2015b, Rodriguez et al.,
Conclusion
This study suggests that PC has a potential fermentation efficiency and fermentation profile superior to that of CG, and therefore could be included in concentrate ration to replace conventional energy sources (e.g., CG, barley and sorghum) in ruminant diets. Dietary inclusion of 150 g PC/kg DM (replacement of CG at 60%) may not require supplementation with rumen modifier such as OAS. Increasing gas production was paralleled by increasing CH4 production which cannot be an environmental friendly
Conflict of interest
All authors declare that there are no present or potential conflicts of interest among the authors and other people or organizations that could inappropriately bias their work.
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