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International Futures Help System

Feed Demand for Crops

Feed demand represents the amount of crops that need to be produced to complement what livestock receive from grazing.

In the pre-processor, feed demand (FeedDem) is initially estimated as a percentage of the apparent consumption of cereals, which grows with average income, implying that as countries develop, more of their grain production is used to feed livestock. The function is depicted below [1] :

feed demand graph 1

If the model estimates that the productivity of grazing land in terms of feed equivalent produced per unit area is below a minimum level, however, then FeedDem is adjusted downward. It determines this by first estimating the feed requirements per unit livestock (fedreq). This is estimated as an increasing function of average income as shown in the figure below.

feed demand graph 2

This function takes into account the fact that at low levels of income most meat consumption is typically poultry (with a conversion ratio of grain to meat of about 2-to-1), while at higher levels of income, pork (4-to-1) and then beef (7-to-1) become increasing portions of meat demand (Brown, 1995: 45-47).

With the value of fedreq, the productivity of grazing land can be estimated as the difference between the total feed requirement for the number of livestock minus the feed demand divided by the amount of grazing land.

ag equation 37


LiveHerd is the size of the livestock herd

LDGraz is the amount of grazing land

If the value of GLandCAP is less than a minimum (MinLDProd—currently hard coded as 0.01 tons of meat per hectare, based on values for the Saudi desert), then FeedDem is recalculated as the difference between the total feed requirement for the number of livestock minus the amount of feed equivalent produced by grazing using the minimum productivity.

ag equation 38

Note that this occurs when the feed from crops meets most, if not all, of the total feed requirements, implying little or no need for feed equivalents from grazing land.

In the first year of the model, grazing land productivity (now called GLDCAP) and an adjustment to feed requirements per unit livestock (fedreqm) are calculated for each country. GLDCAP is initially back-calculated based on the known values of the size of the livestock herd (now called LVHERD), the feed requirement per unit livestock (fedreq —calculated as a function of GDPPC as shown above), the feed demand (now called FEDDEM), and the amount of grazing land (now called LDl=2):

ag equation 39

This yields a productivity of grazing land that perfectly meets the difference between the total feed requirement and that provided by crops.

Again, if the calculated value of GLDCAP is less than the assumed minimum level (MinLDProd), however, then adjustments are made. First, an adjustment factor (fedreqm) is calculated by assuming that a minimum amount of feed equivalents from grazing land are produced even if this results in a total amount of feed that is larger than necessary to meet the total feed requirement:

ag equation 40

Note that this value is always greater than or equal to 1 given the condition for making the adjustment. When no adjustment is made, fedreqm is set to 1.

After the calculation of this adjustment factor, GLDCAP is recalculated as 

ag equation 41

which basically implies that GLDCAP will always at least as large as MinLDProd after the adjustment.

The values of GLDCAP and fedreqm calculated in the first year are held constant for all forecast years

In the forecast years, FEDDEM is calculated as a function of the size of the livestock herd (LVHERD), the feed requirements per unit livestock (fedreq), the amount of grazing land (LDl=2), and the productivity of grazing land (GLDCAP), but adjustments are also made reflecting the effect of global crop prices on grazing intensity (WAPf=1), changes in the efficiency with which feed is converted into. meat, and the adjustment factor fedreqm calculated in the first year. There is also a parameter with which the user can cause a brute force increase or decrease in FEDDEM ( agdemmf=1 ).

The model first calculates the amount of crop equivalent produced from grazing land using the following equation:

ag equation 42


elglinpr  is a global parameter for the elasticity of livestock grazing intensity to annual changes in world crop prices; the basic assumption is that increasing prices should lead to increased grazing intensity and therefore greater productivity of grazing land [2] .

This production of crop equivalents from grazing land is then subtracted from total feed requirement in the following equation:

ag equation 43


livhdpro is a global parameter related to the rate at which the productivity of crops in producing meat improves over time. This part of the equation implies that the amount of feed needed to produce a unit of meat declines over time to a minimum of half the original amount required

agdemm (category 1) is a country-specific multiplier that can be used to increase or decrease crop demand


[1] The specific equation is 13.427 +14.421*ln(GDPPCP), up to GDPPCP=35. The code sets minimum and maximum values of 1 and 80 percent, respectively.

[2] The code, as written, ignores price effects that would reduce GLFeedEq. Since  elglinpr  is generally positive, this implies that decreases in world crop prices are ignored.