Context:

One of the most important benefits of planting trees for livestock operators is the shade that they create for the animals. When animals experience heat stress, they eat less, using more energy to cool themselves and leading to less weight gain. Adding shade via trees enables greater weight gain compared to shadeless scenarios.

Although a built-in model does not exist to model cattle weight gain YET, users can adapt existing tools to generate shade-associated revenue in Overyield.

*Calculations and methodology are either from or based on the work done by Austin Unruh of Trees for Graziers

Calculation:

We recommend using the following base calculation to model revenue gains:

THI * .0104215lbs * AUper-acre * $lb-live-weight * %effective-shade

where THI = Temperature Humidity Index
- Currently using THI from this paper
- THI is a stand in to estimate how much heat stress an animal will experience in a given location.
- The losses from heat stress will be far less in VT than in TN, so the potential economic benefits of shade will vary as well - Select a THI from your state for the most accurate output.

.0104215 lbs / day
- The amount of extra pounds that a cow gains per day from having access to shade when there are heat stress conditions.
- This is a constant calculated by correlating weight gain with shade demonstrated in Paul et al.
AUper-acre = Animal Units per acre
- Animal Units are the primary units that graziers use to talk about their grazing operations.
- 1 Animal Unit = 1,000lbs of live animal (roughly the equivalent of one steer)
  - By using animal units instead of head (the actual number of animals) you can compare stocking density across species. i.e. 40 cows would be 40 AU, 80 sheep may also be 40AU.
  - If a grazer has 40 cows on 80 acres, they have 40AU/80acres, or a stocking density of 0.5AU/acre.
$lb-live-weight
- The price per lb of live animal (as opposed to price per lb of hanging weight, which is after the animal has been processed and offal removed).
% effective shade
- 100% effective shade means the animals are fully shaded (50% shade means 50% of the cows, or only half a cow, has access to shade).
- Importantly, this is different than the % shade maturity of the tree.
  - A cow needs 30-40 sqft of shade to be shaded. A tree might create 100sqft of shade at maturity. Once it creates 40sqft though, it has reached 100% effective shade, but is only producing 40% of its full shade. We care about effective shade.
  - Species selection and tree density will impact effective shade, meaning users should roughly estimate effective shade based on design data.

Adapting Crop Templates to Model Shade:

Crop templates can be used to calculate additional revenue gained from cattle weight gain on a per tree basis.

Step 1: Calculate "Target Yield per Tree"

This number reflects the amount of annual weight gained for all cattle for every individual tree planted.

1. First, input lbs weight gain per tree by calculating lbs weight gained per cow per year for your locality:

THI load per year * .0104215 lbs

THI loads can be estimated on a state-by-state basis via the following table.
- e.g. 12,000 THI * .0104215 lbs = 125 lbs per year

2. Next, multiply this by animal units per acre (e.g. 20)

((THI load * .0104215 lbs ) *(AUperAcre ))

e.g. 125 lbs/year * 20 AU/acre = 2500 lbs / acre

3. Finally, convert this per acre calculation to a per tree estimation

((THI load * .0104215 lbs ) *(AUperAcre ))*(SqftperTree/43560)

e.g. 2500 lbs * (100 sq ft /43560 sq ft)= 5.73 lbs per tree

Step 2. Input increases in effective shade within yield curve

Next input the amount of effective shade achieved per year within the "% target yield per year" field so as to reflect increases in shade as trees mature.

Using the recommendations of Austin Unruh from Trees for Graziers, % effective shade can be assumed to be 0% years 0-4, 50% effective years 5-9, and 100% effective years 10+ can help you begin to plug numbers into the model.