Since the 1900s, proximate analysis has been the mainstream method of feed analysis. In addition to this method, the detergent method, which was developed in the 1960s, has become a popular methodology for feed composition and nutritive value evaluation. One fundamental characteristic of this method is that fractionated carbohydrates are classified as either the fiber of feed in terms of neutral detergent fiber (NDF) or non-fiber carbohydrates (NFC), which include sugar and starch. Meanwhile, in Japan another method, the enzymatic method, has been developed. The characteristic of this method is that fractionated carbohydrates are classified as either the fiber contained in feed in terms of organic cell wall (OCW) or nitrogen-cell wall free extracts (NCWFE, non-structural carbohydrates). One important fraction of feed nutrition is digestible carbohydrates, which are the sum of digestible non-structural carbohydrates and the digestible fiber. The content of digestible non-structural carbohydrates is obtained based on the nutritional uniformity of NFC and NCWFE in the detergent and enzymatic method, individually. The digestible fiber is obtained in the detergent method from the potential digestibility of NDF and lignifications, and obtained in the enzymatic method from the highly digestible organic a fraction and the poorly digestible organic b (Ob) fraction. The amount of digestible carbohydrates obtained by these two methods of analysis is sometimes significantly different. The Ob fraction obtained by the enzymatic method shows a significant negative correlation, and a 1% increase in the Ob content of hay dry matter suppresses the dry matter intake of dairy cattle by 0.17 kg.
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