In addition to capital and land, the other "stock" or "level" variable with important temporal dynamics is the livestock herd (LVHERD). The size of the herd size (LVHERD) in the first year is calculated simply as the base year value of meat production divided by the slaughter rate, slr . ^[1]

The growth of the herd size in future years is driven by changes in meat demand at both the national and global levels, changes in meat stocks at both the national and global levels, and changes in grazing land at the national level.

At the national level, herd sizes for the next year are first estimated as a function of changes in national meat demand, national meat stocks, national grazing land, and an adjustment factor related to national meat stocks:

The forecasts of meat demand (AGDEM_r,f=2) and grazing land (LD_r,l=2) are described in the Meat Demand section and the Changes in Grazing Land section, respectively. The national stock adjustment factors are calculated using the same ADJSTR function as used to adjust crop yields. In this case, the desired stock level is given as agdstltimes the sum of national meat demand (AGDEM_r,f=2) and  national meat production (AGP_r,f=2). As mentioned previously, agdstl is set to be 1.5 times dstl , which is a global parameter that can be adjusted by the user. Also, the two parameters that determine how much of an adjustment there is due to changes in stock levels from the previous years and the difference between the actual and desired stock levels are hard coded with values of -0.05 and -0.1, respectively.

At the global level, herd sizes for the next year are estimated as a function of changes in global meat demand, global meat stocks, and an adjustment factor related to global meat stocks:

The global stock adjustment factor is calculated in the same manner as the national stock adjustment factors, only using global values for actual and desired stocks.

Finally, the herd sizes for the next year are normalized so that the sum of the national values equals the global value: