Herd Structure Simulation (HSS) Model

V.E. Cabrera, UW-Madison Dairy Science and Pierre Meyer, Alltech Inc.

Tool Overview

Simulates on a monthly basis the dynamics of a dairy herd population, including the future make-up of the herd.

The model runs in 2 steps. The first step runs as long as needed to reach a “steady state” or equilibrium of the adult herd population and it is independent of the input running time value entered. Steady state is the condition of the nature on which the proportion of cows in each cow state remains constant over time. Assuming that a herd normally remains constant in size, all the animals leaving the herd are immediately replaced and over time this causes a baseline herd structure in steady state that represents the dairy herd being studied. Having for example the herd projected at 0 (zero) months in the model will give a herd structure expected when the herd is in steady state.

The second step runs assuming that all the heifers calving enter the adult cow population regardless of the balance of the cows leaving the herd and the need for replacements. This runs for as many months as requested by the user. For example using 120 months as the time of projection means that the model will calculate the number of animals in each state at the end of the month 120 (10 years) in the future. Depending on the input data, the herd size could either expand, contract or remain the same. (More Info)


≤ 2 months old
3 to 6 months old
≥ 7 months non pregnant
Cows 1st 2nd 3rd Later All
Pregnant Milking

Disclaimer: The authors and their respective institutions shall not be held responsible or liable for any decisions made or actions taken as a result of using the HSS Model.