1. Unit 2: Evaluating Feedstuffs for Farm Livestock

2. Unit 2: Evaluating Feedstuffs for Farm Livestock
Unit 2 Objectives:
Understanding of methods used to determine nutrient composition of feeds
Knowledge of sample collection methods
Identify and communicate how feed samples are reported
Comprehension of how feedstuff digestibility is determined
Understand various energy measurements and how they are used
Physical and economical evaluation of feeds

3. Unit 2: Evaluating Feedstuffs for Farm Livestock
Analytical Methods for Nutrient Composition
Three general types of methods can be used to determine effect of feedstuffs
Chemical procedures
Titration, colorimetry, etc.
Biological procedures
Feedstuff tested by a live animal (rat, chick)
More accurate
Much more tedious and expensive

4. Unit 2: Evaluating Feedstuffs for Farm Livestock
Microbiological procedures
Tested w/ isolated bacteria
Obtaining Samples for Analysis
Key to reliable feed nutrient evaluation is a representative sample
Identification
Thoroughly identify the feed tested
What might we include in our identification?
Sampling
Grains/Mixed Feeds
Sacked feeds – 2 samples/sack, 5-7 sacks, handful each

5. Unit 2: Evaluating Feedstuffs for Farm Livestock
Bulk Feeds – 12 to 15 samples, widely separate locations for sampling (while delivered or fed, if possible)
Mix samples in a clean pail, make sure feed doesn’t separate, send a 1 or 2lb. sample to the lab
Hay
Use a core sampler
Take a 12’ – 15” core sample that will include stem and leaves
12 – 15 samples are needed to be accurate (1/bale)
Try to get to middle of the stack if possible
“Grab” Samples can be used, but accuracy is variable

6. Unit 2: Evaluating Feedstuffs for Farm Livestock
Haylage or Silage
Upright silos – collect during feedout, several small samples, mix together for one composite
Pit/Bunker silos – 4-5 grab samples from a fresh face, do not collect spoiled material, do not collect within 12”-18” from edge
Freeze if you are collecting over multiple days
Refrigerate if you can’t mail immediately (what happens if you don’t do this?)
Harvest Sampling
Not recommended for any feed <30% DM
Same methods as discussed prior
12-15 samples, mix for one composite
Mark different fields as feed is stored (plastic marker, oats, etc.)

7. Unit 2: Evaluating Feedstuffs for Farm Livestock
General
Not beneficial unless you are going to use in designing a feeding program
Three benefits to using sampling for proper balance of feedstuffs – 1) minimize protein supplementation and reduce cost, 2) can properly balance if a nutrient is being underfed, 3) can confirm that a factor other than feed is limiting production
Proximate Analysis
Most generally used chemical analysis to describe nutrient composition of feeds

8. Unit 2: Evaluating Feedstuffs for Farm Livestock
Dry Matter (DM)
How do we determine DM content of a feedstuff?
Can we do this ourselves?
What is the benefit of knowing the DM content?
Ash (minerals)
Burned sample that removes all other nutrients
Only inorganic residue remains
May not be 100% accurate
Crude Protein (CP)
Digest to N through chemical process (Kjeldahl process)
How do we determine CP content from N concentration?
Does not distinguish between forms of N

9. Unit 2: Evaluating Feedstuffs for Farm Livestock
Ether Extract (Fat)
Use ether to extract fat contents for 4 hrs
Loss of wt = fat content
Includes some “fats” that are of no use to animals, so may not be 100% accurate
CHO
Crude Fiber (CF) – remove water & fat; then through chemical rxn. to remove protein, sugar, and starch; leaves cellulose, lignin, and minerals; (how are the minerals removed?)
Nitrogen-Free Extract (NFE) – sugars and starches (maybe some hemicellulose & lignin); not determined by an analysis; 100% - water, ash, protein, fiber, fat

10. Unit 2: Evaluating Feedstuffs for Farm Livestock
The Van Soest Method
Focuses on forage fiber
Divides fiber into digestible and indigestible fractions
Extraction w/ detergents
Predicts intake – NDF – index of gut fill
Predicts digestibility – ADF – indicates forage digestibility
Heat damaged forages – can help determine the amount of protein unavailable in feedstuff. What level of unavailable begins to cause problems?

11. Unit 2: Evaluating Feedstuffs for Farm Livestock
Near Infrared Reflectance Spectroscopy
Ability to sample quickly w/ little preparation (grinding); only uses one sample
Can be completed in <3 min.
Analyze multiple components in one operation
Measurements done by absorption/reflection of light
Not accurate for minerals
Expensive equipment, must be calibrated correctly
Wet-chemistry analysis is more accurate
Inexpensive

12. Unit 2: Evaluating Feedstuffs for Farm Livestock
Determination of Vitamins
No routine analysis available to determine vit content
Assays can be ordered to determine specific vitamins, if needed
Determination of Energy
Bomb Calorimeter
Sample is burned in an oxygen atmosphere
Liberated heat raises the temp of water surrounding the devise
This temp increase is the basis for determining the energy concentration
1 cal heat required to raise 1g water 1º C

13. Unit 2: Evaluating Feedstuffs for Farm Livestock
Nutrient Expression
DM basis
Most accurate/common way to express nutrient levels
Levels the playing field to compare feeds
As-Fed basis
Amount of nutrients contained in a feed as the animal would consume it
Air-Dry basis
Assumed to be ~90% DM

14. Unit 2: Evaluating Feedstuffs for Farm Livestock
Let’s practice some conversions
Thumb rules
Nutrient concentration should increase when converting to DM basis
Wt. will decrease on DM basis
Feeding Trials
Can give information as to acceptance and performance of a feed
Doesn’t tell why a feed performed the way it did

15. Unit 2: Evaluating Feedstuffs for Farm Livestock
Digestion or Metabolism Trial
Weakness of chemical analysis is that is doesn’t take into account digestibility very accurately
Steps of a digestion trial
Proximate feed analysis to know what you start w/
Feed a measured amount of feed, or feed at constant rate
Collect fecal matter
Proximate analysis on feces
Difference is the apparent digestibility of the feed

16. Unit 2: Evaluating Feedstuffs for Farm Livestock
Can use markers or indicators to identify feeds
Testing can be done in metabolism stalls where the animal is somewhat confined
Attached to collection instruments for feces and/or urine
Usually done in 2 phases
Preliminary phase
Frees digestive tract of any other types of feeds
Animal gets accustomed to the process and feed
3-5d in pigs, 8-10d in ruminants

17. Unit 2: Evaluating Feedstuffs for Farm Livestock
Collection phase
When feed and fecal collections are measured
What are some of the chances for error in this system?
Measures of Feedstuff Energy
Total Digestible Nutrients (TDN)
General, calculated amount
Does not account for important losses of digestion
Can be expressed as lbs., %, or kg

18. Unit 2: Evaluating Feedstuffs for Farm Livestock
Can be extremely variable/inaccurate (usually overestimate)
1lb. TDN from 1.2 lbs. corn = 1.2 Mcal NE
1lb. TDN from 2.1 lbs. hay = 1.0 Mcal NE
1lb. TDN from 2.4 lbs. poor hay = .8 Mcal NE
Nutrient Partitioning in Digestion & Metabolism
Energy Units
Calorie = amount of heat needed to raise 1g water 1ºC
Kilocalorie = 1000 calories
Megacalorie = 1000 kcal, or 1,000,000 calories (a.k.a. therm)

19. Unit 2: Evaluating Feedstuffs for Farm Livestock
Gross Energy (GE)
Total potential energy of a feedstuff consumed
Determined in a bomb calorimeter
Fecal Energy (FE)
Undigested residue that passes through the GI
Can be collected and tested same method as above
Digestible Energy (DE)
DE = GE – FE
Takes account of some losses during digestion
Gasseous Products of Digestion (GPD)
Combustible gasses that escape the body during digestion & absorption
Mostly methane; some H, CO, acetone, etc.

20. Unit 2: Evaluating Feedstuffs for Farm Livestock
Most common in ruminants
Hard to measure accurately
Urinary Energy (UE)
Includes materials that result directly from the digestion/absorption/enzymatic processes
Many endogenous sources as well
Metabolizable Energy (ME)
ME = DE – UE – GPD
More accurate measure of nutritive value than DE and TDN
Easy to determine in nonruminants because of the lack of GPD

21. Unit 2: Evaluating Feedstuffs for Farm Livestock
Heat Increment (HI)
Increase in heat production following feed consumption
Caused by the heats of fermentation, and heats of nutrient metabolism
Energy is wasted unless the environmental temperature is below the animal’s critical temperature zone
If it is used for temperature regulation, becomes part of NEm
Net Energy (NE)
NE = ME – HI
Amount of energy used for maintenance only, or for maintenance and production purposes
Function should be stated clearly when reporting/evaluating NE

22. Unit 2: Evaluating Feedstuffs for Farm Livestock
NEm (NE for Maintenance)
Part of total NE needed to keep animal in energy equilibrium
No gain/loss of energy in body tissue
Basal Metabolism – energy needed to maintain basic vital cellular activity
Energy of Voluntary Activity – energy needed for basic movement to obtain food, water, lying down, etc.
Heat to keep body warm – additional heat needed when environmental temp < animal’s critical temperature

23. Unit 2: Evaluating Feedstuffs for Farm Livestock
Heat to keep body cool – extra energy expended when environmental temp > animal’s thermo neutral zone
NEp (NE Production)
Additional energy required above NEm
What would be considered production?
NEl, NEg
Energy in Beef Cattle
This system can be used to accurately predict energy needs for wt. gain under normal conditions
Make adjustments for abnormal conditions
See tables 2-3, 2-4, and 2-5 for reference
We will discuss further later in the semester

24. Unit 2: Evaluating Feedstuffs for Farm Livestock
Energy in Dairy Cattle
NE values are much more accurate than any other system
Evaluate NEm, NEg, and NEl
NEl – includes energy requirements for pregnancy, reproduction, and milk production
NEl – most often used component in ration formulation and evaluation
Energy in Swine
Generally use ME or DE as their evaluating tools
Will eat to energy requirements if feed ad libitum
Will cover further later

25. Unit 2: Evaluating Feedstuffs for Farm Livestock
Physical Evaluation of Feedstuffs
Eye Appraisal
Used mostly w/ forages
Type
Color
% of leaves
Weed contamination
Spoilage
Palatability

26. Unit 2: Evaluating Feedstuffs for Farm Livestock
Factors Affecting Value
Soil fertility
Growing conditions
Harvesting
Stage of maturity
Losses
Processing & Storage
Evaluating Feeds Cost/Unit of Nutrient
Cost of feed/unit wt. divided by unit wt. * % nutrient concentration
Examples

27. Unit 2: Evaluating Feedstuffs for Farm Livestock
Unit 2 Assignment:
Review Problem Solving Questions
1-5
Take your time!!!!