Carcass analysis technique

The equation for the NPU seems to ask, "Of the protein that is consumed, how much is retained " This contrasts with the BV which asks, "Of the protein that is absorbed, how much is retained " The NPU is of practical importance in agriculture. A poultry farmer may use NPU values to evaluate new feeds and to determine the cheapest way to produce the largest amount of poultry meat. The carcass analysis technique is often u.sed to determine the NPU. 

The problems associated with the factorial approach to mineral requirements are the same as those associated with factorial estimates of protein requirement. Whereas the mineral composition of liveweight gain may be readily (if laboriously) determined by carcass analysis, the assessment of endogenous losses, and therefore availabihty, is more difficult. Diets for ruminants that are completely free of an element are particularly difficult to prepare. Perhaps because of these difficulties with the technique, theoretical estimates of mineral requirements do not always agree with practical estimates. 

A classic technique employed in pharmacology and toxicology disposition studies for all routes of administration is the mass balance approach (Riviere, 1999). Mass balance analysis accounts for all of the topically applied dose of the compound, whether it is in the formulation, associated with the skin surface, penetrated into the stratum comeum, distributed into the carcass, or absorbed into and excreted from the blood into urine and feces. In this context, total recovery of 90% of the apphed dose is considered excellent recovery (Schaefer and Redelmeier, 1996). Mass balance studies are conducted by collecting all excreta after topical and parenteral administration. Data from a parenteral route such as intravenous dosing is required to correct for the fraction of absorbed compoimd appearing into the excreta collected if a precise estimate of bioavailability is to be determined and all routes of excretion are not collected (e.g., collection of urine and feces but not expired air) (Riviere, 1999). In such a study, absorption is calculated as follows ... 

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