Abstract: Barley grain (BG, Hordeum vulgare L.) is characterized by its fibrous coat, β-glucans and simplyarranged and less concentrated starch granules. With about 150 million metric tones world annual BG yield, European Union, Canada, US and Australia are among major BG producers and exporters. World production of BG is about 30% of that of Corn Grain (CG). The average BG is the third most readily degradable of cereals subsequent to oats and wheat. The average starch content in BG and CG are respectively 570 g kg^–1 and 720 g kg^–1 with crude protein of 115 g vs. 88 g kg^–1 of DM. Besides greater protein, BG is more concentrated in methionine, lysine, cysteine and tryptophan compared to CG. Due to its greater rumen starch fermentation relative to ground CG (e.g., 850 vs. 500 g kg^–1), BG provides more rapidly synchronous energy and nitrogen release than CG which may improve substrate incorporation efficiency into microbial mass. Hence, rumen fermentation may achieve its optimum potentials in Volatile Fatty Acids (VFA) and microbial mass yields more realistically with feeding BG vs. CG. Consequently, BG feeding can reduce needs for supplemental protected escape proteins. However, such exceptionalities in fueling microbial metabolism remain until rumen acidity is maintained within optimal ranges (e.g., >5.8-6.0) below which microbial maintenance requirements increase and as such mass yields decrease. In addition, microbial endotoxines release causes proinflammatory responses that weaken immune function and depress productive longevity. Thus, mismanagement in processing and feeding BG can easily make a debacle from the pearl of cereals. The paper delineates comparisons in physical and chemical structures between BG and other common cereals as well as differences in their response to processing techniques and feeding strategies. In so, doing, nutritional uniquenesses and conversely, disturbing consequences of improper BG feeding to ruminants are underscored. Steam-rolling may improve feed efficiency and post-rumen starch digestion; however, it may not improve production and feed intake. Due to limited BG responses to processing comparing corn, sorghum and wheat, setting more consistent and global standards for feeding and processing should be more feasible for BG than for other cereals. In high-starch diets, optimum feeding of BG reduces requirements for effective small intestinal starch assimilation, subsequently reducing hindgut starch use and fecal nutrient losses. Barley in many ruminant industries is usually less expensive and more available than corn and wheat which are highly demanded by non-ruminants and humans. With its nutritional exclusivities underlined, BG use will be a factual art that will either matchlessly profit or harm rumen microbes, cattle production, farm economics and the environmental.