Excretion models

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Excretion models

• aka
• Pre-excretion models

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Dairy
Milking
Heifers 50
Dry 7.5
Milking 42.5
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Cow-calf 55
Calf after weaning 27
Finishing 18
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Example calculations for beef cows

• For 100 beef cows, then there would be
• Cow-calve pairs
• 0.80 (205/365) 100 45 cow-calve pairs
• Cows on maintenance
• (160/365) 100 11.2 cows
• 0.20 (205/365) 100 43.8 cows
• So with 100 cows, you would have about 45
  cow-calve pairs and 55 cows on maintenance.
• Calve numbers would not be used from the database.

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Broilers, turkeys, swine
Prestarter
Starter
Grower
Finisher (withdraw)
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Layers
Mature
Egg producing over two years
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Swine

• Weanling (5-20 kg)
• Finishing (20-120 kg)
• Gestating
• Lactating

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Equations

• ASAE D384.1. Manure Production and
  Characteristics. December 5, 2003

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If only one phase or period, then DME DME-T
and NE NE-T Also, see page 14 in handout.
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The use of default values
Because default values are used in most cases,
all variation in ammonia emissions will be due to
weather conditions or housing type and variation
due to diet will not exist. The relative
emissions from a given county may be important
but cannot be used as a quantitative base line
for that countys actual emissions no matter how
good the equations are. The only way this can be
accomplished is if every producer submitted a
detailed nutrient balance report similar to what
Denmark has implemented thereby incorporating the
true variation of input at the farm level.
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Improvements

• Animal numbers for each class of production or
  phase at the county or farm level
• Diet composition and intake at the county or farm
  level
• Production data at the county or farm level
• Data to validate model regionally across US
• More mechanistic excretion models

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Advantage of sensitivity analyses

• Detect parameters or inputs that are important
  for output to allow research efforts to focus in
  those areas
• Determine the magnitude of regional differences
• Validate equation across a range of changes