ANSC 301 - Feedstuff Analysis

• Laboratory assessment of feedstuffs includes chemical/proximate analysis, NIR, and in vitro digestion.
• In vivo animal assessments of feedstuffs are considered the gold standard for assessing nutritive value of feeds.
• The proximate analysis system, AKA the Weende System, is always on a DM basis and will determine protein, fat, fiber, organic mater, and nitrogen free extract.
• Moisture/DM is measured by weighing and drying a feed sample in the proximate analysis system.
• Drying a feed sample for DM analysis can cause irreversible chemical reactions that alter the nutritive profile, so the feed is first dried mostly at 55C and measured, and then dried the rest of the way at 105C.
• Nutrients are contained in the dry portion of the feed so balancing is typically done on a DM basis and converted to as-fed for feeding/sales.
• To calculate DM: %DM = (weight after drying/weight before drying) x 100
• In proximate analysis, crude protein is measured by determining nitrogen content based on a colorimetric change or combustion and calculated with the equation: CP = N x 6.25%
• Protein requirements are affected by age, body size, stage of production, and growth.
• In proximate analysis, crude fat is determined by ether extract, which may include waxes, pigments, etc in addition to dietary fat.
• Crude fiber, in proximate analysis, is determined through acid and alkali treatments to determine the amount of cell wall components (cellulose). Can sometimes unfavorably include more soluble fibers.
• In proximate analysis, crude ash is the inorganic/mineral content of the feed and is determined by burning off all of the organic material.
• In proximate analysis, nitrogen-free extract (NFE) includes starch, soluble fiber, and sugars. Determined with calculation: NFE = DM - %CP - %CF - %EE - %Ash
• The VanSoest/Detergent system separates cell wall components into more digestible and less digestible. Acid detergent fiber (ADF) and neutral detergent fiber (NDF).
• NDF includes cellulose, pectin, lignin, and hemicellulose and ADF includes everything except hemicellulose.
• The higher the difference between the NDF minus the ADF means a greater amount of digestible fiber.
• In chemical analyses, DM, Ash, CP, and EE are typically done with proximate analysis and NDF and ADF are done with VanSoest.
• Non-fiber carbohydrates (NFC) is similar to NFE but contains no hemicellulose, whereas there is a chance that the NFE number contained some that was not properly included in the CF determination.
• %NFC = 100 - (%CP + %NDF + %EE + %Ash)
• Non-structural carbohydrates (NSC) are purely sugars, starches, and fructans.
• Ash is the total mineral content, but individual minerals can be analyzed using ICP, AA, or calorimetry.
• Vitamins are typically lumped in with organic matter NFC or NFE, but can be individually analyzed with a complicated procedure.
• Near-infrared reflectance (NIR) analysis is done by shining an infrared light on sample and measuring the reflected light.
• NIR analysis is based on a calibration set that was generated from many previous wet chemistry analyses and put into a computer program for estimation.
• The NIR calibration set has to be the same feed as the sample and has to be pure. It is cheaper and faster than chemical analysis and is beneficial for NDF, ADF, and CF. Poor accuracy for vitamins and minerals due to high variability.
• Digestibility of forages can be estimated from ADF or lignin concentration.
• In-vitro analysis simulated both rumen digestion through incubation in rumen fluid at body temp and gastric digestion through incubation in pepsin solution at low pH.
• The four major approaches for animal assessment of feedstuff value are digestion trial, balance trial, metabolism trial, and production trial.