Lecture 3 Flashcards
Evaluating Feeds - Efficient utilization of feeds by animals requires knowledge of:
Nutrient composition
Digestibility of nutrients
Ability of feed to provide energy
Presence of toxins/inhibitors
Need for processing
What is also important when evaluating feeds?
Knowledge of chemical composition of animal tissues
Goals of sampling of feeds for analysis:
To obtain a representative sample of the entire batch
How to receive representative samples for hay
Use pooled core samples (cross-sectional samples of entire bale), grind, mix, & sub-sample
Pooled core samples: Take samples from many bales (25-50 cores from one stack; represents nutrient content from a field many acres in size)
Assumption: Each core is similar to the total composition of the bale if sampled enough
How to receive representative samples for grains
Mix and take sub-samples
Mixing & sub-sampling methods:
-Ground hay core samples: Place on plastic sheet & mix
-Quartering method: Ensure the sample has the same proportion of particle types and sizes as the original feed
Sample is quartered into four pie slices, and two opposite slices are removed until the sample size is appropriate for analysis
-DO NOT shake hay samples in the bag before sampling (results in loss of small particles and enriched stem content)
Analytical methods for specific nutrients for an element or compounds. Chemical methods:
Provide quantitative measurements of nutrients
IMPORTANT: Quantitative measurements don’t indicate nutrient availability to the animal
Chemical methods may involve drastic degradation of feeds with reagents, giving accurate measurements but no information on the animal’s ability to utilize the nutrient.
Biological procedures for specific nutrients:
-More tedious & expensive
-Provides a more accurate estimate of the bioavailability of a specific nutrient
-Test subjects often include chickens or rats
Microbiological Methods for Specific Nutrients:
-More accurate but generally less expensive
-Bacteria isolated based on specific nutrient requirements
-Used to determine the availability of amino acids/vitamins
-Offers precision and cost-effectiveness
Proximate Analysis of Feeds:
-Combination of analytical procedures
-Similar faults as analytical methods (may not reflect biological availability)
-Still encouraged due to its utility
-Laws often require listing minimum/maximum amounts of components present
-Useful for an overall understanding of feed composition
Proximate Analysis vs Nutrient Determined
Analysis: vs Nutrient Determined
-Dry matter (DM) -> Water
-Crude Protein (CP) -> Protein (via nitrogen)
-Crude Fiber (CF) -> Poorly digestible carbs (fibers)
-Nitrogen-free extract (NFE) -> Easily digestible carbs
-Ether extract (EE) -> Lipids
-Ash -> Total mineral
-Individual vitamin/mineral analyses -> Individual vitamins/minerals
Proximate Analysis - Dry Matter (DM):
-Plant & animal tissues vary in water content
-Must specify “dry matter basis” or “as fed basis” when discussing feeds
-Comparison of nutrient concentrations is done on a DM basis due to water variability
How DM Content is Determined:
-Place sample in 100°C forced air convection oven for 2-3 days
-Weigh sample before and after drying to calculate % DM
-Drying methods: forced air convection oven or microwave
-Considerations for volatile compounds in drying, especially in silage and fermented feedstuffs
Proximate Analysis - Crude Protein (CP):
-Kjeldahl method (N x 6.25) is commonly used
-Nitrogen analyzer is a faster and safer alternative
-Non-ruminants have specific amino acid requirements, distinguishing from ruminants
-CP analysis does not differentiate forms of nitrogen
Proximate Analysis - Crude Fiber (CF):
-Ether-extracted sample boiled in weak acid, weak alkali, filtered, and dried
-Estimates indigestible portion (cellulose, hemicellulose, lignin)
-Less reliable and accurate, but still used in the pet food industry
