Methane production from commercial dairy rations estimated using an in vitro gas technique
Introduction
Ruminants depend on microorganisms to digest and ferment plant cell wall polysaccharides into energy sources, such as volatile fatty acids (VFA) and other organic acids. However, microbial fermentation in the rumen also produces waste products, such as carbon dioxide (CO2) and methane (CH4). Methane production in the rumen is an energetically wasteful process, since the portion of the animal's feed, which is converted to CH4, is eructated as gas. Approximately 6% of dietary gross intake energy is lost to the atmosphere as CH4 (Holter and Young, 1992, DeRamus et al., 2003). Recently, emission of CH4 and other volatile organic compounds from ruminants, and their effect on air quality, has attracted the attention of air regulatory agencies in many parts of the world, particularly in the San Joaquin Valley of California.
Methane contributes to climatic change and global warming (Johnson and Johnson, 1995) by trapping outgoing terrestrial infrared radiation 20 times more effectively than CO2, which leads to increased surface temperatures, and it indirectly affects atmospheric oxidation reactions that produce CO2. Thus, there is increased worldwide interest in addressing mitigation of CH4 in animal agriculture. There may be potential to reduce the extent of CH4 production by manipulating diet and management practices that influence ruminal microbial fermentation.
Total mixed rations (TMR) for dairy cattle are formulated to contain levels of energy, protein and minerals that are required for the desired levels of animal production. Use of a nutritionally balanced ration is extremely important to maximize efficiency of nutrient utilization, thereby reducing environmental pollution caused by excess nutrients leaving the animal as waste. Environmental pollution from dairy farms can be caused by overfeeding and/or poor synchronization of release of nutrients in the rumen. Increasing efficiency of utilization of nutrients and energy is one strategy to increase animal production per unit of feed consumed, thereby reducing environmental impact. An ideal ration is one that contains all required nutrients that digest in synchrony, thereby maximizing incorporation of degraded nutrients into rumen microbial biomass. Due to the substantial amount of energy lost in the form of CH4, and its deleterious impact on the environment, quantification of CH4 produced from dairy rations by dairy cows is critical to formulation of feasible mitigation strategies. However, direct quantification of CH4 produced by animals requires complex equipment, is labour intensive, time consuming and expensive. An in vitro gas production technique would offer an alternative, allowing several diets and diet combinations to be evaluated simultaneously, but only if it accurately estimated animal CH4 emissions.
The objective of this study was to measure CH4 production from TMR fed to lactating dairy cows on commercial dairies in California using an in vitro gas production technique and assess its accuracy relative to previously published CH4 emissions from dairy cattle based on in vivo, and other in vitro, techniques.
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Sample collection and preparation
Individual feed ingredients were sampled from six commercial dairy farms in the San Joaquin Valley of California (USA), and the UC Davis dairy, and TMR (Table 1) were created in the laboratory according to the ingredient proportion used at each farm. Samples of each TMR were dried at 50 °C in a forced air oven for 48 h, and ground to pass a 1 mm sieve using a Wiley mill (Arthur A. Thomas, Philadelphia, PA, USA).
Chemical composition, dry matter and fibre digestibility
Dry matter (DM) was determined by drying at 135 °C for 4 h followed by equilibration in a
Results
The wide variability in the feeds, and their levels, used to formulate the TMR among the dairies (Table 1) is common in California. Only alfalfa hay appeared in all TMR, which contained up to nine ingredients. In spite of the variability among TMR in their ingredient profiles, the chemical composition of the TMR were similar among dairies (Table 2), as was expected since all dairies utilized a qualified consulting nutritionist. The CP content ranged from 163 to 185 g/kg DM, with an average of
Discussion
Methane is the most abundant organic gas in the earth's atmosphere, and there is evidence that CH4 concentrations have recently been increasing globally at a rate between 0.7% and 1.0%/year (Crutzen, 1995). Domestic ruminants are responsible for about 12.5% of global CH4 emissions (Crutzen, 1995).
Methane emissions are influenced by the size of the animal, the quantity of feed consumed, and the efficiency by which the animal converts feed to products. Improving animal productivity decreases CH4
Conclusions
Methane was produced from incubation of TMR from commercial California dairy farms, and there were differences in CH4 production among TMR. The high cost and technical difficulties involved in animal experimentation to measure methane production makes in vitro techniques attractive for developing base data that can be used for planning detailed in vivo environmental studies. The general similarity between CH4 production determined with this in vitro gas technique, and values previously
Acknowledgments
The support of the American Feed Industry Association (AFIA) is appreciated. Research was conducted with support from the Kellogg Endowment and the California Agricultural Experiment Station at the University of California, Davis. The authors thank Jenni Pareas for her assistance with rumen fluid sampling and Dr. Frank Mitloehner for critical evaluation of the manuscript.
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