Lecture 3- Feed Chemistry Flashcards
What does feed analysis consist of?
• Assessment of nutrient composition of feeds • Evaluate (potentially) availability of nutrient content of a feed (chemical integrity) • Ensure that dietary nutrient supply matches human or animal requirements for nutrients – a key issue in formulation chemistry -what are we looking at when doing a feed analysis? -just because a chemical is there does not mean it is available for the animal to use -crucial that the nutrients match the requirements of the species in that stage
What are the two main developments in laboratory analysis of feed?
• 1. Chemical evaluation: try to determine the chemical content of the feed • 2. In vitro methods: try to replicate what happens in the digestive system so to understand what will happen in the body
What is the feed analysis called?
-proximate or Weende analysis -standard method for feed composition
How does the feed analysis (proximate) divide nutrients in food?
• Partitions nutrients into five major fractions • Dry matter (DM) – basis of feed formulation (important to know since it tells us in what percentage of the feeds are there nutrients) • Crude Protein (CP) – sources of nitrogen • Ether extract (EE) – lipids and related compounds • Crude Fibre (CF) – structural and non structural CHO (carbohydrates) • Total ash (TA) – mineral matter • Nitrogen-free extract (NFE)
What is the Dry matter (DM) component in feed analysis?
• Heat sample in oven @ 105oC overnight % Dry matter =
What is the use of dry matter data?
• DM is the denominator for all nutrient contents of feeds. • DM is the basis of all formulation and rationing of animals. • DM does not provide information on the association of water to the feed particle – an important issue in water and mineral nutrition • Losses during drying do not always relate to loss of water per se and can reflect the concentration of volatile and fermentation compounds (e.g. silage)
What is the crude protein component of feed analysis?
-2. methods of estimating crude protein in feed, the Kjeldahl and the Dumas (LECO) method -1:• Kjeldahl method • Boil sample in concentrated (36 N) sulphuric acid [converts all nitrogen into (NH4)2SO4] • NH3 is liberated from the (NH4)2SO4 by adding 12N NaOH and steam distillation • NH3 is trapped into boric acid or sulphuric acid (0.02N), and the titrated using standard acid ———- • Method assumes that all nitrogen comes from protein containing (16% N) • Crude protein = N × 6.25 (100/16) -way of estimating protein content: -assumes all N exists as protein, which is not so -then multiply N by 6.25 (assuming that all protein contains 16% of N)
What is the second method of estimating crude protein in feed?
• Dumas (LECO) method • Vapourisation of sample to its constituent elemental components and determine the concentration of N • Recalculate CP content by multiplication of N x 6.25 • Suffers from similar problems to Kjeldahl methods -newer and quicker method
What are the problems associated with the two methods of estimating the crude protein content of feed?
• Problems associated with two methods • Not all N comes from protein other sources (free amino acids, amines and nucleic acids) • Ignores N from nitrates and nitrites • Amino acid composition of foods and feeds are variable and therefore %N in feed protein varies considerable. This leads to a variation in the coefficient 6.25 (eg. 6.38 for milk) • Over or under estimates protein content of feed • Analytical problems – incomplete capture of N (volatile N compounds)
What is an indirect assesment of crude protein content of feeds?
• Use of near infra-red spectrometry (NIRs) is a rapid method for determining the crude protein content of a feed. • Estimation of true protein is also feasible using NIRs and the feed does not require pre-treatment to precipitate the protein (e.g. classical methods use trichloroacetic acid to precipitate protein before Kjeldahl assessment. -new method: rapid method, you measure the infrared reflectance of the the feed and from that get protein -using this to determine the nutrient content and availability of the content -all you need to have is calibrated standards to which to compare
What do you use crude protein data for?
• Used as a basis for feed formulation • Provides no information on the availability of protein to digestion •Provides no information on essential amino acid -composition just by measuring the crude protein content we don’t know the amino acids in the feed, the animal doesn’t have a requirement for protein as such, it needs specific amino acids (the essential amino acids) in a particular ratio -it also doesn’t provide us with an estimate of the availability -lysine is the most limiting, as it is found at low levels of lysine in grains relative to other amino acids -we need to dig deeper
How do you measure EE the ether extract?
• Measure of fat content • Continuous extraction (4 -6 hours) with petroleum ether using reflux apparatus • Residue after solvent evaporation = ether extract • EE
Does ether extract analysis provide fat analysis?
• Ether extract does not provide information on the composition of fat • Generally, fat composition (chain length and degree of saturation) is determined using gas-liquid chromatography (GLC) • Ether extract methods do not provide information on essential fatty acids • Some fats are “volatile” e.g. short chain (C2, C3 and C4) and can be lost to analysis if care is not taken. -often it is particular fatty acids that we are interested in
What is the total ash component of feed analysis and how is it done?
• Residue after combustion of organic constituents • Procedure: • Ignite sample at 550oC in a muffle furnace until all organic matter is removed • Problems: • Fraction still contains sulphur and phosphorus •
What are the issues with total ash?
• Total ash method does not differentiate between mineral matter, soil and silica content. • Silica content is determined as acid insoluble ash – a useful parameter in passage rate studies • Soil content is generally determined at total titanium content
What is the nitrogen free extract (NFE) component of feed analysis?
- Approximates non-structural carbohydrate content (starch and sugars)
- Determined by the difference between total dry matter and the sum of the other four chemical components
- estimates starches and sugars: -it does it by difference - not measure just do the other ones and what is left
- • NFE is the only part of proximate analysis not determined directly
- NFE supposedly represents the soluble carbohydrate fraction of a feed as crude fibre is the “insoluble” carbohydrate fraction
- NFE contains accumulated errors from the estimation of DM, CP, CF, EE and total ash
-every issue with the other measurements accumulates here as we use those results
What is the summary of proximate analysis of feed?
-get wet feed (or normal condition), we determine the water content by the dry analysis and from the dry feed we determine the chemical constituents
What are the total digestible nutrients (TDN)?
- TDN= -multiply factor for EE as fat has high energy content
- from this we know more about the energy the animal is actually getting
- dCP = digestible CP
- dCF = digestible CF
- dNFE = digestible NFE
- EE = ether extract
- TDN is a link from chemical analysis to energy content of a feed
An example of calculating TDN:
- Calculation of TDN of field beans for ruminant feeding
- 86 grams per 100g of dry matter that the animal digests
What is a new method for performing fibre analysis?
• Conceptually subdivides total carbohydrate fraction • Cell wall
