Bacterial yield in the Cornell model (Search: Agriculture, 1990) is defined as a static function of feed inputs. Inputs required to predict bacterial yield include: (i) a complete fibre analysis (Van Soest); (ii) total nitrogen and NPN; (iii) acid-detergent-insoluble nitrogen; (iv) neutral-detergent-insoluble nitrogen; (v) protein solubility; (vi) solvent soluble fat; and (vii) ash. These inputs are used to predict the growth rates of three separate pools of microbes as defined by the following equations:
where SCBactj = the yield of structural carbohydrate (SC)-fermenting bacteria from the jth feedstuff (g day :) and NSCBact. = the yield of non-structural carbohydrate (NSC)-ferment-ing bacteria from the jth feedstuff (g day-1). The NSC bacterial pool is further divided into starch-fermenting and sugar-fermenting pools. The efficiency of bacterial yield is calculated according to the following equation:
where Kma = the maintenance requirement of the ath pool of bacteria (a = SC-fermenting, sugar-fermenting, or starch- and pectin-fermenting; g carbohydrate g-1 bacteria h Kdaj = the rate of fermentation or growth of the ath pool of bacteria on the jth feed (h and YGa is the theoretical maximal yield of the ath pool of bacteria (g bacteria g-1 carbohydrate). This type of equation captures the principle that slowly fermented feeds will have a greater proportion of fermentable substrate utilized to maintain bacterial populations than feeds that are fermentable at higher rates. Similar equations are used for sugar- and starch-fermenting bacteria. Nitrogen availability affects the bacterial yield of NSCBact according to the following equations:
Rumen ammonia is calculated using the following static, factorial, empirical equation:
+ NSCAMMNR + SCAMMNR)
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