The feed analysis includes all studies that are required to maintain the nutritional value and the pollutant content of the feed indicated.
The energy content of feed is of paramount importance for livestock husbandry today, while protein supply was often viewed as a limiting factor until the 1970s. The energy content is calculated using energy estimation formulas from the raw nutrients according to the Weender analysis or the fiber fractions according to van Soest or from in vitro analyzes.
The classic "Weender feed analysis" to determine the raw nutrient fractions was founded in the 19th century. Feeding science worldwide is based on the Weender feed analysis system . Newer processes or new feed analysis systems complement the Weender analysis today . Methods developed since the middle of the 20th century (e.g. fiber fractionation according to Peter J. van Soest ) are also of practical importance today.
The methods of feed analysis are in the method book Volume III. "The chemical analysis of animal feed" compiled by the VDLUFA .
Weender feed analysis
The Weender feed analysis (also called convention analysis) is the standard procedure for determining the ingredients of feed . A distinction is made between crude ash (CA or XA), crude fiber (CF or XF), crude protein (CP or XP), crude fat (CL or XL) and nitrogen-free extracts (NfE); the results are mostly related to the dry matter , less often to the fresh matter .
100 = water + crude ash + crude fiber + crude protein + crude fat + NfE (all data in% fresh mass)
This system was developed in 1860 by Wilhelm Henneberg and Friedrich Stohmann at the agricultural research station in Weende , a district of Göttingen . Henneberg and Stohmann optimized and standardized the crude fiber method in particular, and turned the individual methods into the Weender feed analysis system . The individual methods for determining the other parameters were already standardized at that time: crude protein determination according to Kjeldahl , crude fat determination according to Soxhlet .
At this point, no exact descriptions for the analysis of the individual ingredients are provided. This list is only intended to provide a general overview. All methods shown are convention methods; H. the result of the method is defined as the content of the parameter. A different approach can and in some cases will lead to different results, but would then no longer be the content of the parameter.
Part of the sample is dried to constant weight at a certain temperature. The duration and temperature (~ 103-105 ° C) depend on the feed. This process removes the raw water from the sample (but also volatile organic compounds : ammonia , alcohols , acetic acids ). The residue is defined as the dry matter content of the sample. This dry matter contains the essential usable food components such as proteins, fats, etc.
To determine the raw ash content, the sample is heated in a muffle furnace to constant weight at 550 ° C. As a result, all organic components are muffled (burned) and the residue is the crude ash content. That depends on the sample v. a. Minerals and sand . The value of the total mass of the feed minus the value of the raw ash is the organic mass (OM). The organic mass consists of crude protein, crude fiber, crude fat and NfE.
The raw fat content is the part of the feed that dissolves in fat solvents such as petroleum ether . The determination is carried out according to Soxhlet . The Weibull / Stoldt method is currently used and, since around 2012, extraction has been preferred with hexane instead of petroleum ether.
Is the sum of all compounds that contain nitrogen . To determine the proportion, the nitrogen content of the sample is usually determined first (e.g. by means of Kjeldahl's nitrogen determination ). The result is then multiplied by a factor that represents the reciprocal value of the typical N content of crude protein. An N content of 6.25 is generally assumed, unless it is specified differently by literature or legal requirements such as e.g. B. for milk and milk products with an N content of 6.38 is the case. The portion of the really usable crude protein is called digestible crude protein (vRP).
“Crude fiber” is to be understood as that portion of a feed that remains as an “indigestible” component after treatment with diluted acids and alkalis . Cellulose is the main component of this class of substances . Crude fiber must not be equated with dietary fiber , as only about a third of these consist of cellulose and contain many other indigestible components.
Nitrogen-free extracts (NfE)
The NfE content is determined by calculation: crude fat, crude protein and crude fiber are subtracted from the organic mass, the rest is NfE. These are e.g. B. soluble sugars , starch , pectins and organic acids . Lignin is also contained in the NfE, since lignin dissolves in the lye solution when determining the crude fiber.
Criticism and modern measurement methods
The Weender analysis is a simple standard method that is still used today, but has weaknesses:
- A big problem is the calculation of the NfE content. Possible analysis errors have a decisive influence on this value. The raw protein content should be mentioned here, as a mean factor for the N content is calculated. A flat rate of 16% N content is assumed, but this is not always applicable.
- It is not possible to subdivide the carbohydrates contained into starch and non-starch polysaccharides or structural and non-structural carbohydrates . This subdivision is only realized, albeit unclean, through an extended feed analysis.
The classic laboratory analysis, by modern spectroscopic methods such as NIR analytical system (Near Infrared, Near Infrared ) to be replaced. In feed analysis, it is already used in many places as a standard method in the laboratory. Continuous analysis (online analysis) is very well possible with NIR online spectrometers. However, the NIR is dependent on the underlying reference analysis and the preparation of the samples to be measured. The NIR measurement is evaluated using a mathematical estimate based on a calibration. In this calibration, a larger amount of representative samples should be available, the recorded spectra of which are assigned to the content determined by reference analysis.
Extended Weender Analysis
The extended Weender analysis (also detergent analysis of the cell wall components ) represents an extension of the Weender feed analysis for the examination of feed . This American analysis system of the fiber evaluation replaces in the Weender analysis the part of the imprecisely defined fractions crude fiber and NfE and not the entire analysis. Suggested by Peter J. van Soest u. a. this modified analysis has meanwhile found a "widespread use".
The crude fiber and NfE fractions mainly contain carbohydrates and some associated substances (including lignin ). The extended feed analysis allows a more extensive breakdown of the fractions.
Altogether there are two major groups:
- Cell constituents. This includes:
- Crude protein
- Raw ash
- Raw fat
- Proportions of the NfE fraction: the non-structural carbohydrates sugar and starch as well as a residual "organic residue"
Structural substances. This group mainly includes structural carbohydrates and associated substances; the group consists of the fraction crude fiber and part of the fraction NfE of the Weender feed analysis;
- The sum of the builders is the fraction of neutral detergent fiber (NDF, n eutral d etergent f iber).
- Acid detergent fiber ( ADF , a cid d etergent f iber) represents a proportion of the NDF is namely NDF without hemicelluloses .
- Finally, acid detergent lignin (ADL, a cid d etergent l ignin): Formed by definition, particularly the lignin, and a portion of the ADF: ADF without the cellulose.
Other provisions in the context of feed analysis
In vitro analyzes are very important for estimating the energy of ruminants. In-vitro analyzes simulate ruminant digestion in a test tube, often with the aid of rumen juice. These include B. the methods according to Tilly and Terry, the Hohenheim feed value test or the cellulase method.
In addition to raw nutrients and fiber fractionation, mineral analyzes (cations and anions) are very important for feeding today. In individual cases, an analysis of the pollutants can be of importance, which most often relates to mycotoxin analyzes (ZEA and DON), residue analysis for pesticides or the determination of prohibited ingredients (e.g. melamine, gossypol).
- ^ Committee for Requirement Standards of the Society of Nutrition Physiology (ed.): Proceedings of the Society of Nutrition Physiology: Reports of the Society for Nutrition Physiology; 62nd meeting from April 1-3, 2008 in Göttingen; Review, summaries of the original communications (abstracts), workshop contributions, communications from the Committee on Consumer Standards . DLG-Verlag, Frankfurt am Main 2008, ISBN 978-3-7690-4101-9 , chapter Prediction of Metabolisable Energy of compound feeds for pigs , p. 199-204 .
- ↑ M. Kirchgeßner among others: Animal nutrition. 12th, newly revised edition. DLG-Verlag, Frankfurt am Main 2008, ISBN 978-3-7690-0703-9 , p. 23.
- ↑ a b Leonhard Gruber: Analysis of basic and concentrated feed according to Cornell Net Carbohydrate and Protein System and in-situ method. HBLFA Raumberg-Gumpenstein, accessed on July 24, 2017.
- ↑ a b VDLUFA: The chemical analysis of animal feed. Method Book Volume III. VDLUFA-Verlag, Darmstadt 2007.
- ^ W. Henneberg, F. Stohmann: Contributions to the justification of a rational feeding of ruminants. Issue 1, Braunschweig 1860 ( digitized version ).
- ↑ M. Kirchgeßner among others: Animal nutrition. 12th, newly revised edition. DLG-Verlag, Frankfurt am Main 2008, ISBN 978-3-7690-0703-9 , p. 22.
- ↑ TU Dresden, Institute for Food Technology, Internship Technology 1 Determination of total nitrogen and protein content in milk ( Memento of the original from August 14, 2007 in the Internet Archive ) Info: The archive link was automatically inserted and not yet checked. Please check the original and archive link according to the instructions and then remove this notice.
- ↑ Spektrum.de protein calculation factors
- ^ PJ Van Soest, JB Robertson, BA Lewis: Methods for dietary fiber, neutral detergent fiber and non starch polysaccharides in relation to animal nutrition. In: Journal of Dairy Science. 74, 1991, pp. 3583-3597. PMID 1660498
- ↑ a b M. Kirchgeßner among others: animal nutrition. 12th, newly revised edition. DLG-Verlag, Frankfurt am Main 2008, ISBN 978-3-7690-0703-9 , p. 25.