lecture quiz 8: proximal analysis Flashcards
chemical evaluation
use of lab techniques to determine [specific nutrient] (& energy) in a feedstuffs/diet
- doesn’t tell you anything about bioavailabiilty, digestibility, palatability, etc.
biological evaluation
using animals to measure utilization of nutrients from a given feedstuffs/diet
- cannot assume effects on animals based on chemical composition alone
why is a biological evaluation necessary in addition to chemical evaluation?
- palatability → if animals won’t eat then nutrient composition is useless
- bioavailability
- digestion & absorption vs excretion
- performance
- effect on product quality (e.g. milk, meat color, marbeling, methane production)
first step of chemical evaluation
get a representative sample: small sample represents entire composition of feed (avg nutrients animal consumes)
common analytical methods used in chemical analysis of feeds/feedstuffs
- proximate analysis
- van soest detergent fiber analysis
- near-infrared spectroscopy (NIRS)
proximate analysis
- most widely used method for chemical analysis of feeds/feedstuffs
- aka Weende methods/procedures (developed in Weende experiment station in germany)
- proximate principles = compounds occurring naturally in animal & veg tissues & separatable by analytical methods
- partitions compounds w/in feed into 6 categories based on chem properties
- sum of 6 components = 100%
- moisture, ether extract (crude fat), crude fiber, crude protein, ash, nitrogen-free extract
categories of proximate analysis
- moisture (water)
- crude protein (CP) = true protein + NPN
- ether extract (EE = crude fat)
- crude fiber (CF) = cell wall fraction (fibrous carbs cellulose, hemicellulose, & lignin)
- ash = inorganic compounds/minerals (cannot burn)
- nitrogen-free extract (NFE) = ‘non-structural carbohydrates’ (sugars, starches) & vitamins → everything that is left over after other categories
DM made up of
organic matter + ash
organic matter can be partitioned into:
- crude protein
- crude fiber
- ether extract (crude fat)
- N-free extract
proximate analysis: moisture (water)
- all feed has moisture + DM
- to find water content: figure out DM & subtract from 100
- total matter = moisture + DM
- method:
- weight original sample
- heat sample at 105ºC for 24h to dry
- weigh dried sample immediately
- calculations:
- % moisture = (weight of water loss)/(weight of original sample) x 100
- % DM = 100 − % moisture
- OR % DM = (weight of heated sample)/(original weight) x 100
- official method = forced-air oven @ 105º & weigh samples before & after
- alternative methods: drying under vacuum or freeze-drying
sources of error during DM proximal analysis
heating can cause loss of volatile compounds that are DM during evaporation (e.g. silages or fermented products) ∴ overestimate moisture (underestimate DM)
- any time drying & smell = loss of volatile compounds (they are pungent)
- soln = freeze-drying → keep sensitive compounds (samples drying under vacuum & at low temps ∴ not lost in evaporation)
importance of knowing moisture & DM content
- proper moisture concentration for storage (too much moisture → mold)
- DM give basis to describe quantity of feed consumed to compare nutrients btwn feeds
- water is diluent of other feedstuffs → too much water in feed = less of other nutrients (“dilutes” food → e.g. equal weight of canned dog food & kibble: wet has less nutrients than kibble)
- moisture level affects economic value of feedstuffs (don’t want to pay for water, want to pay for DM where the nutrients/value are → e.g. don’t want to pay for bones when you’re buying meat)
as-fed basis
feed as it would be fed to the animal (including water)
DM basis
- assumes no water is present (100% DM)
- allows to accurately compare nutrient composition of various feedstuffs
- formulate diet on DM basis
air-dry basis
when feeds are allowed to air dry, most absorb water from envir & eventually equilibrate to ~90% DM (~10% moisture)
- how feed labels are priced
