The impact of reducing dietary crude protein and increasing total dietary fiber on hindgut fermentation, the methanogen community and gas emission in growing pigs
Introduction
The environmental impact of the intensified pig production in Europe is significant. Pig manure is a source of greenhouse gases (GHG) like methane (CH4) and other harmful gases such as ammonia (NH3). Increased public concern on the livestock environmental footprint made EU legislation to regulate the potential quota of atmospheric pollution (IPPC Directive; Directive EU 2016/2284 on the reduction of national emissions of certain atmospheric pollutants) where animal nutrition is considered as a key strategy. Under intensive production, ≈ 20% dietary N is retained in the animal’s body (Canh et al., 1997). Irreversible NH3-losses (through the urine and feces) may approach 50% of N intake (Ryden et al., 1987; Hartung and Phillips, 1994) due to the excess or unbalanced dietary protein together with manure-handling strategies. Methane is identified as a main contributor to global warming (Johnson et al., 2002) and represents an irreversible energy loss. Methane production in pigs has been commonly linked to dietary gross energy intake (1.2% of DE intake; Christensen, 1987), and a positive correlation between fiber intake and methanogens diversity (Cao et al., 2012) or abundance (Liu et al., 2012) has been reported. Methanogens have been identified in hindgut digesta and pig feces, being the genus Methanobrevibacter (Steinberg and Regan, 2009; Luo et al., 2012) the most abundant. CH4 production is the main disposal sink for reducing equivalents (H2), and a competition between H2-consuming organisms (hydrogenotrophic) and sulphate reducing bacteria (SRB) has been reported in the human colon (Bernalier et al., 1996) and rabbit caecum (Belenguer et al., 2011) but factors that determine the end-routes of reducing equivalents (H2) are not well understood.
This study was designed to determine the impact of dietary factors on emissions of harmful gases in pigs under commercial-like conditions and to analyze the ecology of lower gut methanogens to prevent the negative impact of CH4 production on energy utilization and the environment.
Section snippets
Materials and methods
All procedures were carried out under Project License CEEA 03/01-10 and approved by the in-house Ethics Committee for Animal Experiments at the University of Lleida. The care and use of animals were in accordance with the Spanish Policy for Animal Protection RD 53/2013, which meets the European Union Directive 2010/63 on the protection of animals used for experimental purposes.
Results
The experiment was carried out using a three phase feeding system, in which the amino acid supply was adjusted for each production stage to match nutrient intake with requirements. Intake, digestibility, growth and carcass characteristics were fully addressed and discussed previously in Morazán et al. (2015a).
Experimental approach
In the present approach CH4 emission and NH3 volatilization were analyzed simultaneously in an open-circuit system while trying to maintain the “standard” commercial housing conditions and minimizing the impacts of the experimental handling over the animals.
Total emissions included gases originating from the digestive tract and also those originated from the slurry storage; in this sense, authors are aware of a wide variation existing in both housing conditions (i.e. aeration level,
Conclusions
In the present approach, in an open-circuit system designed to maintain commercial-like conditions NH3-volatilization increased with dietary CP supply and growth phase and proportionally reduced as a whole, a mean values of 8.6% per each percentage unit (%) of CP reduction. Enteric origin constituted the main source for CH4 emission, although a relevant fraction (averaging 9.7%) did come from the slurry pit. Pigs of HF diets trended to increase CH4 emission. Methanogen concentration increased
Declarations of interest
None.
Acknowledgments
This work is part of the Feed-a-Gene project and was supported by the European Union's H2020 program under National Institutes of Health [grant number 633531, 2016]. Authors would like to thank Dr. David Parker who generously gave his assistance and constructive comments to the manuscript, his effort is sincerely appreciated.
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