N. R. St-Pierre 1
The Ohio State University Department of Animal Sciences
A simple model of animal flow from one year to the next was developed. In order to predict the average increase in herd size in a closed herd, the model was built on the principles that (1) all animals in year i must be accounted for in year i + 1, and (2) all animals in year i + 1 were either in the herd in year i, or were born during that year. The model calculates 11 transition coefficients that are factors of culling rate (CR; %/year), calving interval (CI; months), average age at first calving (AFC; months), dead on arrival (DOA; % of birth), and death and cull rate of replacement animals (DR; % of all heifers per year). The model can be cycled n times to forecast animal numbers and average annual herd growth rate (AAGR) over a period of n years. Sensitivity analysis showed that AAGR is most sensitive to changes in CR, followed by CI, AFC, DR, and DOA. The model is easily adapted to forecast animal numbers during periods of expansion in non-closed herds.
1For more information, contact at: The Ohio State University, 221A Animal Science Building, 2029 Fyffe Road, Columbus, OH 43210-1095; 614-292-6507; fax: 614-292-1515; e-mail: st-pierre.8@osu.edu.