Evaluation of Methane Emissions from Major Dairy Cattle Feed Resources and Identification of Low Methane-Emitting Feeds with Optimum Nutritional Quality in Central Ethiopia

Abstract This paper assesses the potential of major feed resources to mitigate methane (CH 4 ) emissions while improving animal productivity in Ethiopia. The objective was to evaluate methane emissions from major dairy cattle feed resources and identify low methane-emitting feeds with the required nutritional quality in central Ethiopia. In this study, twelve common dairy cattle feed resources were evaluated in terms of chemical composition, nutritive value, in vitro gas production, CH 4 production, and CH 4 concentration (%). The data were fitted to an exponential equation commonly used in comparable in vitro gas production studies. The effects of feed samples on nutritional composition and in vitro gas production were determined using a two-way ANOVA of R software version 4.2.3. The major feed resources differed significantly (p < 0.05) in chemical compositions, nutritive values, in vitro gas production, methane emission potential, and concentration. The current study found that all crop residues and natural pastures (roughages) had a crude protein (CP) concentration greater than 3.4± 0.11, whereas supplementary feed had more than 16.3±0.48 of DM. Natural pasture (7.1± 1.11) and bean straw (6.8± 0.11) had the highest CP level (p < 0.05), while wheat (3.4± 0.11), barley (3.8± 0.11), and teff straws (4.5 ± 0.11) had the lowest (p < 0.05). Similarly, noug seed cake (24.3± 0.48) and linseed cake (29.6± 0.48) had the highest CP level (p < 0.05), while compound feed (17.1± 0.48) and wheat bran (16.3± 0.48) had the lowest (p < 0.05) among supplementary feeds. The highest (p < 0.05) in vitro organic matter digestibility (IVOMD) and metabolizable energy (ME) were observed for natural pasture and wheat bran, while the lowest (p < 0.05) was for wheat straw and atela among roughages and supplementary feeds, respectively. Overall, the means of each chemical composition and the nutritive value of the selected major feeds were found within the ranges of previously reported values for Sub-Saharan African feeds. Hay produced the highest CH 4 (51.89 mL/0.2 g DM incubated) among roughages, while bean straw produced the lowest (40.25 mL/0.2 g DM). Among supplementary feeds, wheat bran produced the highest CH 4 (47.00 mL/0.2 g DM incubated), while atela produced the lowest (39 mL/0.2 g DM). Natural pasture had the lowest percentage of methane (19.33%), followed by barley straw (20.49%) and oat straw (26.23%). Similarly, wheat bran had the lowest methane concentration (4.64%), followed by compound feed (6.63%), compared to other types of supplementary feeds. Hay and wheat bran had the highest gas volume among roughages and supplementary feeds (p < 0.05) throughout the incubation periods. From the study, it was concluded that the identified supplementary feeds had high CP levels, suggesting that they can be used as high-protein and energy sources to supplement low-quality roughages. Therefore, wheat bran has the lowest methane concentration, the highest ME and IVOMD levels, and the fastest rate of fermentation (c), making it a reasonable supplement to low-quality roughages. Conversely, wheat straw exhibited the highest methane concentration, which can be effectively managed through chemical pre-treatment to improve nutritional qualities and reduce harmful methane emissions.