Investigation of Biological and Economic Changes in Herd of Dairy Cows Using Optimization Models

The aim of this study was to identify the factors affecting the culling of dairy cows and their impact on reproductive performance and costs of the herd so that optimal decisions can be made in replacing dairy cows and thereby increase the annual income of dairy cattle. For this purpose, data collected from four active cattle breeding units in Ardabil province (including biological parameters and financial information of herds) during the years 2017 to 2018 were used. To simulate the herd status under different conditions, a bio-economic model developed in Dairy VIP software was used, and the MATLAB software compecon toolbox was optimized for production system. Dynamic programming was used to determine the optimal replacement strategy. This planning is a mathematical approach that is suitable for solving problems with several successive decision steps. Dairy cattle were described with state variables including lactation period, milk production capacity and different animal health states. The average annual milk yield and forced removal rate were 13480 kg and 16.1%, respectively. According to the observed results, the highest total annual culling rate occurred when the rate of pregnancy of productive animal decreased by 5%. The major effective changes in economic performance due to the reduction in the rate of forced culling was related to the reduction in the cost of purchasing alternative heifers. The average herd optimal life (interval between first calving to removal) was obtained for the baseline scenario of 4.99 years. The optimal annual replacement rate, which is equal to the sum of the optional and non-optional elimination rates, was 20% for the baseline scenario in this study. So that culling of dairy cows older than the optimum age leads to increased profitability of livestock units. The results of the dynamic programming model also showed that optimal maintenance for medium and high-yielding cows is equal to seven and eight lactation periods. The results of this study can help producers to identify important factors in annual herd profitability and to make sound management decisions to improve economic profit.