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Procedures for determining digestible and metabolizable energy contents of feedstuffs
A pig derives energy for cellular processes by oxidation of carbohydrates, amino acids, and fatty acids contained in feeds, and thus the resulting energy is equal to the sum of the energy produced from oxidation of these feed nutrients. The utilization of energy in a feed for pigs may be determined by total collection method in which pigs are fed test diet over a period of time and then feces and urine are collected for subsequent chemical analysis. Depending on the collected energy-containing components (feces and urine), either apparent digestible (DE) or metabolizable energy (ME) can be determined. Total quantitative collection of feces and urine from pigs fed the diet or ingredient is achieved by placing pigs in metabolism cages with feed intake and feces and urine output commonly determined over a 5-d period that is preceded by an adaptation period of 5 to 10 d. Ensuring that the feces collected originate from the feed provided during the 5-d collection period requires a marker that is added to the feed at the beginning and end of the collection period to signal the start and end of feces collection, respectively. Urine collection during the period when feces are collected starts and ends at the time of marker addition to the feed at the beginning and end of the collection period. The difference between the gross energy (GE) in the feed and that in the feces is DE. Subtracting the GE in urine from the DE of the diet gives ME. For most pig feed, the ME is between 92 and 98% of the DE.
Keywords: digestible energy, feed, metabolizable energy, pig