optimal replacement strategy for dairy cows with diverse milk production capacity in fars province

the objective of this study was to determine the optimum replacement strategy using dynamic programming for dairy herds in fars province. a dairy cow is kept several lactations for milk production in the herd. after spending several lactations, milk production gradually begins to decline, while animal health problems rises simultaneously. so one of the most important management decisions of dairy herd is optimal replacement of dairy cow with a young heifer. dairy cows were described in terms of state variables that included parity, production capacity and reproductive status. the objective function was maximization of the net present value for cows over a 10 lactation planning horizon. data was related to 406 cows from dairy herds in fars province (2010). optimal replacement strategy was separately investigated for three group of production capacity. results of dynamic programming model showed that the optimal dairy cows keeping in the herd is two, four and six lactation, respectively for low, medium and high producers. marcov simulation under the optimal decision plan that is determined by dynamic programming showed an expected herd life (time from first calving until culling) of 4.32 yr. finally, after running the basic scenario, sensitivity analysis demonstrated changes in the price of heifers, milk price and salvage value of dairy cow effects on average herd life and net present value of dairy cows. optimal replacement strategy and culling dairy cow older than the optimum age is recommended to improve the profitability of dairy farm