The data can be used as the basis for CNCPS under Austrian feeding conditions. In-situ technology is a very valuable and indeed essential method for characterizing feedstuffs; therefore, the rumen degradation parameters of nutrients should be available for the most important forage and concentrate feeds.

In the new feed evaluation systems (e.g., AFRC 1993, FOX et al. 2000 (CNCPS), NRC 2001), the classic Weende analysis is increasingly being replaced by more comprehensive analyses. The main reason for this is that the Weende analysis does not describe carbohydrates according to the specific conditions of digestion, and furthermore, the crude nutrients "crude fiber" and "nitrogen-free extract" do not correspond to any chemical groups (Van Soest 1994, NRC 2001).
A more accurate breakdown of carbohydrates is achieved through the so-called detergent analysis of cell wall components according to Van Soest (NDF, ADF, ADL), from which the structural carbohydrates cellulose, hemicellulose, and lignin can be calculated. Furthermore, non-structural carbohydrates (especially sugars and starches, pectin, and organic acids) can be indirectly determined by subtracting NDF, crude protein, crude fat, and crude ash from the total dry matter (Van Soest 1994, Fox et al. 2000, NRC 2001).
Structural and non-structural carbohydrates influence the pH value in the rumen differently via saliva production, thus creating optimal conditions for their respective fermentation by rumen microbes. Consequently, acetic acid is primarily formed from structural carbohydrates, and propionic acid is mainly formed from non-structural carbohydrates. These two main products of rumen metabolism perform entirely different functions in the host animal's metabolism: acetic acid as a precursor for fat synthesis and propionic acid as a precursor for gluconeogenesis, thus providing energy to the host animal. Furthermore, acetic and propionic acid bacteria differ significantly in their efficiency of microbial protein synthesis (Russel et al. 1992). It follows that the nutrient analysis used in the Cornell system (Fox et al. 2000) is very well-founded from a digestive physiology perspective. Therefore, the levels of the nutrient fractions of the Cornell system should also be determined for the most important basic and concentrated feedstuffs used in Austria.
The Cornell Net Carbohydrate and Protein System (CNCPS) distinguishes four carbohydrate and five protein fractions. The basis for assigning the fractions is the rate of nutrient degradation in the rumen (Sniffen et al. 1992, Fox et al. 2000):
4 carbohydrate fractions: A, B1, B2, C

Non-structural carbohydrates:
A: Sugars
B1: Starch

Structural carbohydrates:
B2: Available structural carbohydrates
C: Non-available structural carbohydrates

5 Protein fractions: A, B1, B2, B3, C
A: Non-protein nitrogen (NPN), immediately and completely available
B1: Rapidly degradable, soluble protein
B2: Protein with intermediate degradation rate
B3: Slowly degradable protein
C: Non-available, cell wall-bound nitrogen

Another important piece of information about feed value is therefore the extent and rate of nutrient degradation in the rumen. The so-called in-situ method has been used for years to determine these parameters (e.g., Nocek 1988, Orskov & Ryle 1990, Mertens 1993, Madsen & Hvelplund 1994, Huntington & Given 1995). In almost all modern protein evaluation systems, the proportion of feed protein that remains undegraded in the rumen is determined using the in-situ method (INRA 1989, AFRC 1993, Fox et al. 2000 (CNCPS), NRC 2001, etc., with the exception of GfE 2001). Furthermore, a close relationship has been demonstrated between nutrient degradation in the rumen (determined using the in-situ method) and feed intake (HOVELL et al. 1986, ORSKOV et al. 1988, CARRO et al. 1991, BLÜMMEL & ORSKOV 1993, KHAZAAL et al. 1995, CHERMITI et al. 1996, FERRET et al. 1997, DAWSON & STEEN 2000). In addition, the degradation rates of protein and carbohydrates also allow conclusions to be drawn about the temporal availability (synchrony) of these nutrients to the rumen microbes throughout the day (SINCLAIR et al. 1993 and 1995, BLANK et al. 1998, DLG 2001, FOX et al. 2001). The degradation kinetics are often described using the equation by ORSKOV & McDONALD (1979):
"deg" = a + b * (1 - exp(-c * t))

Therefore, in-situ technology is a very valuable and indeed necessary method for characterizing feedstuffs for several reasons, which is why relevant values ​​should be available for the most important basic and concentrated feedstuffs used in Austria.

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