1. Recommendations and Critical Factors in Determining Moisture in Animal Feeds
Midwest AOAC
June 6, 2018

2. Surveys were distributed Spring 2017
Aglabs
AAFCO LMSC list
NFTA
Individual contacts

3. 13 regulatory labs
7 research labs
16 private labs
36 total responses

4. please indicate how you determine moisture on the following matrices
Matrix Temp Drying Time Oven Type Method Reference
dry feeds forages, dry grains forages, wet oilseeds, unground liquid molasses feeds oilseeds, ground molasses block pet food, dry milk replacer pet food, canned suet, fats, oils pet food, semi-moist other distillers grains, dry distillers grains, wet

5. Red font – Official method or suggested method
Blue font – regulatory lab responses
Green font – research lab responses
Purple font – private lab responses
*labs who are following official or suggested method

6. DRY FEEDS
AOAC C 2 hr or AOAC C vac 5 hr
Should be AOAC (NFTA ) 104C 3 hr
*4 labs C MC 2 hr
*6 labs C MC 3 hr
*2 labs C vac 5 hr
*3 labs C MC 3-4 hr
*1 lab C vac time not stated
1 lab C 16 hr
*7 labs C MC 2 hr
*3 labs C MC 3 hr
1 lab C MC 6 hr
1 lab C MC 16 hr
1 lab C vac 20 hr
1 lab Infrared analyzer

7. OILSEEDS - GROUND
AOCS Ba 2a-3B C MC 2 hr
*1 lab C MC 2 hr
1 lab C MC 2 hr
4 labs C MC 3-4 hr
1 lab C vac 5 hr
2 labs 105C MC 3 hr
1 lab C MC 16 hr
1 lab C vac time not stated
*2 labs C MC 2 hr
4 labs C MC 2 hr
2 labs C MC 3 hr
1 lab C MC 6 hr

8. PET FOOD – CANNED
 none specified
1 lab C MC 4 hr lab C MC hr labs C MC 3-4 hr labs C MC 2 hr lab C MC hr lab C MC 16 hr lab C vac 5 hr lab Karl Fischer
1 lab C vac time not stated
2 labs C MC hr lab C MC 4 hr labs C MC 3 or 6 hr lab C MC 2 hr labs or 60C MC 5 or 16 hr lab C halogen moisture analyzer

9. DISTILLERS GRAINS - DRY
 AOAC C MC 3 hr
*6 labs C MC 3 hr lab C MC 4 hr lab C MC 2 hr lab C vac 5 hr lab Karl Fischer AOAC
*2 lab 105C GC 3 hr lab C MC 16 hr lab 2-step method 55C & 105C
*8 labs C MC 3 hr lab C MC 6 hr lab C MC 16 hr labs C MC 2 hr

10. LIQUID MOLASSES FEEDS
 AOAC C vac 18 hr or AOAC Karl Fischer
*1 lab 60C vac 18 hr lab 70C vac 5 hr lab C vac 16 hr lab 100C MC hr lab Karl Fischer AOAC
1 lab 105C FD >12 hr
*2 labs C vac hr lab C vac 16 hr labs C vac hr labs C FD 3 hr lab C MC 6 hr lab C FD >16 hr

11. MILK REPLACERS
 AOAC C vac 5 hr
*1 lab 100C vac 5 hr lab C vac 5 hr labs C MC 3 hr lab ±5C FD 4 hr±5 min lab C MC hr lab C MC 2 hr
*2 labs 100C vac 5 hr lab C vac 4 hr labs 105C MC 3 hr labs C FD hr

12. 16 labs use the same method for all or most of their matrices
6 labs C hr
1 lab C 4 hr
1 lab C 6 hr
1 lab C 16 hr
2 labs C 2 hr
2 labs C vac 5 hr
1 lab C vac time not specified
1 lab C >12 hr

13. Moisture Method by Matrix Table
Recommendations and Critical Factors for Determining Moisture in Animal Feed
Moisture Method by Matrix Table

14. Karl Fischer titration
DISCUSSION of METHODS
Direct Water Methods
Karl Fischer titration
Toluene Distillation

15. Loss on Drying AOAC 934.01 VACUUM OVEN
DISCUSSION of METHODS
Loss on Drying
AOAC VACUUM OVEN
Used by most labs in 1920s & 1930s
Became official in 1934 by establishing temperature to be between C and time to be 5 hours

16. DISCUSSION of METHODS Loss on Drying AOAC 930.15 135C / 2 hr
Adopted tentatively as an alternative method to be used when a vacuum oven was not available.
Matrices evaluated were:
Oilcake meal
Fish meal
Meat meal
Bran cereal products
(wheat) shorts

17. DISCUSSION of METHODS Loss on Drying AOAC 930.15 Limitations
1931 – cannot be used on feeds with sugar content due to caramelization
1935 – not to be used when a fat determination is to be made on the same test portion (fat oxidation will occur)
Not applicable to feeds containing urea (decomposes at 132C)
AAFCO PT data – this is the most widely used LOD method

18. DISCUSSION of METHODS Loss on Drying
Thiex and Van Erem, SDSU, 1999
10 each partially dried hays, haylages, corn silage
Karl Fischer
135C 2 hr -- over estimated moisture
104C 3 hr -- most closely matched KF
104C 6 hr

19. DISCUSSION of METHODS Loss on Drying
Thiex and Van Erem, SDSU, 1999
10 different feeds containing no urea
Karl Fischer
135C 2 hr -- over estimated moisture
104C 3 hr
104C 6 hr
110C 3hr -- most closely matched KF
Vacuum 95C 5 hr

20. DISCUSSION of METHODS Loss on Drying
Thiex and Van Erem, SDSU, 1999
6 different feeds containing urea
Karl Fischer
135C 2 hr -- over estimated moisture
104C 3 hr -- most closely matched KF
104C 6 hr
110C 3hr
Vacuum 95C 5 hr

21. DISCUSSION of METHODS Loss on Drying
Thiex and Richardson, J Animal Sci, 2003, evaluated various moisture studies and concluded:
Drying at 135C should be eliminated or restricted to very few materials for which it has been validated.
Drying at 104 or 105C for 3 hr most closely matched KF moisture values.

22. DISCUSSION of METHODS Loss on Drying
National Forage Testing Assn Task Force in 2000
Concluded that drying at 105C for 3 hr provided the most accurate value.
NFTA Official Method 2.1.4

23. DISCUSSION of METHODS Loss on Drying
Thiex SDSU 2009 study
Analyzed 30 DDGs using 4 LOD & KF methods
Drying at 105C for 3 hr most closely matched KF
Poorest performing method 135C 2 hr

24. DISCUSSION of METHODS Loss on Drying
PET FOOD
No official methods
Published data includes only two pet food samples.
Dry cat food - 110°C/3 hr LOD most closely matched the KF moisture value.
Dry dog food --135°C/2 hr LOD closely matched the KF value.
Obviously more data is needed on pet foods.

25. DISCUSSION of METHODS Loss on Drying
Most LOD methods are designed for low moisture (<15%) materials that can be easily comminuted to 1 mm.

26. DISCUSSION of METHODS Other Methods
NIR
Infrared moisture analyzer
Halogen moisture analyzer

27. RECOMMENDED METHODS
Bidwell and Sterling stated in the JAOAC in “The ideal moisture method, which will probably never be found, would be applicable to all substances, would be rapid, would require little skill, would separate and determine uncombined water and nothing else, and preferably, would determine water directly and not by difference.”

28. Karl Fischer: the gold standard
RECOMMENDED METHODS
Karl Fischer: the gold standard
Use to validate all other moisture methods
AOAC – dry animal feeds, pet foods, grains and partially dried forages
 AOAC soft-moist & semi-moist pet foods
AOAC liquid molasses
AOAC oils and fats

29. RECOMMENDED METHODS Loss on Drying
The working group is recommending the discontinuation of the commonly used AOAC (135°C / 2 hr) method for animal feeds, forages and grains due to gross overestimation of water in most feed materials.
It is impossible to recommend one universal LOD method due to the diverse nature of animal feeds. The working group is recommending four different methods for the following matrix types.

30. RECOMMENDED METHODS Loss on Drying
Dry animal feeds, grains, partially dried forages
Drying in forced draft oven at 104°C for 3 hours (NFTA Method 2.1.4, AOAC Official Method & )

31. RECOMMENDED METHODS Loss on Drying
Forages, ensiled materials, wet feeds and grains
Two-step moisture method as follows:
Determine partial dry matter by drying the entire laboratory sample in a forced draft oven at 55°C overnight or until dry (NFTA )
Comminute the entire laboratory sample to 1 mm particle size
Determine laboratory dry matter by drying a test portion in forced draft oven at 104°C for 3 hours (NFTA Method 2.1.4)
Calculate total dry matter: % total dry matter = (% partial dry matter x % laboratory dry matter) / 100
Calculate total moisture: % total moisture = % total dry matter

32. RECOMMENDED METHODS
Loss on Drying
Liquid feeds
Drying in vacuum oven at 60°C for 18 hours (AOAC Official Method D)

33. RECOMMENDED METHODS Loss on Drying
Ingredients
Most ingredients used in feeds and pet foods can be analyzed for moisture using the 104C for 3 hours LOD method without introducing sources of error such as caramelization or loss of other volatiles.
In cases where a specific method has been validated or published for an ingredient by a body, and the customer requires, then the matrix specific method should be used and cited.
Oilseed meal – forced draft 130C for 2 hr (AOCS Ba2a-38)
Dried milk products – vacuum 100C 5 hr (AOAC )
Fish, seafood – forced draft 100C 1 hr (AOAC )
Meat & poultry – forced draft 125C 4 hr (AOAC B(b) 

34. RECOMMENDED METHODS Loss on Drying
Pet Food
The moisture working group is in the process of evaluating data on LOD methods for pet foods and will be making a recommendation in the near future.

35. RECOMMENDED METHODS
Reporting of Results
Moisture, loss on drying at 104°C / 3 hr
Moisture, loss on drying, vacuum 60°C / 18 hr
Moisture, Karl Fischer AOAC
Moisture, NIRS legume hay calibration

36. CRITICAL FACTORS Loss on Drying
Temperature
Must be consistent
Controlled to within ±1C
Check and record oven temp each time using a thermometer or thermocouple, not the digital display unless it has been certified annually
Temperature monitoring device needs to be calibrated against NIST thermometer at least annually.

37. CRITICAL FACTORS Loss on Drying
Time
Do not shorten specified time.
Can extend by minutes
Time starts when oven returns to designated temp

38. CRITICAL FACTORS Loss on Drying
Correct Method
Many laboratories inappropriately use the same drying temperature and time for all of their test materials. This is acceptable only if all materials tested are similar, such as in a manufacturing facility. The analyst needs to keep in mind when encountering a different matrix that it may require the use of a different method.

39. CRITICAL FACTORS Loss on Drying
Oven
Forced draft or mechanical convection
Control air velocity
Shelves and containers cannot inhibit air circulation
Short recovery time
Avoid overloading

40. CRITICAL FACTORS Loss on Drying
Drying Containers
Sufficiently large to provide a surface area that allows the test portion to be spread out to provide maximum exposure for drying
Should be shallow which will bring the heated oven air more closely over the surface of the test material
Aluminum is ideal since it has low specific heat resulting in rapid cooling
Covers not needed with electronic balances

41. CRITICAL FACTORS Loss on Drying
Desiccation
Desiccant needs to be changed or regenerated periodically
Use desiccant with color indicator
Desiccate for short time only – until cool and not overnight
Keep desiccator closed between weighings

42. CRITICAL FACTORS Loss on Drying
Balance
Verify calibration each day
Use weights that bracket the mass of the drying container & test portion
Use same balance
Calibrate annually

43. CRITICAL FACTORS Karl Fischer
Maintain dry conditions for titration vessel and reagents
Standardize against known quantity of H2O
Ensure all H2O is released from test material special solvents – formamide or octanol homogenizer for solids thermal extraction
Replicate test portions

44. CRITICAL FACTORS NIRS
Equations standardized against KF or KF validated LOD method
Update equations with recently analyzed test materials
Matrix match calibration equations to test material

45. CRITICAL FACTORS All Methods
Particle and Test Portion Sizes and Comminution
Comminute to small particle size to provide maximum surface area
Small particle size ensures more representative test portion of adequate mass
Avoid heat generation during comminution
Store in air-tight container

46. CRITICAL FACTORS All Methods
Quality Assurance
Validate moisture method
Proficiency testing program
QC material in each run
Control charting to monitor QC material

47. Questions?