Optimization of dairy heifer management decisions based on production conditions of Pennsylvania

We used a dynamic programming model to determine optimum rearing decisions of dairy replacements. Heifers were described in the model by age, season, body weight, pregnancy state, and prepubertal growth rate. Prices and param eters were chosen to represent the dairy population of Pennsylvania. We cal culated monthly costs and revenues from calf value, feed costs, veterinary costs, semen costs, carcass value, and full-grown heifer value. The model c onsidered a stochastic variation in the onset of puberty, conception, invol untary disposal, and a seasonal variation in the prices of calves, heifers, and feed. Based on a critical prepubertal average daily gain of 0.9 kg/d and a maximu m achievable postpubertal growth rate of 1.1 kg/d, the optimum practice res ulted in an average age at first calving of 20.5 mo at a body weight of 563 kg. Discounted net returns equaled $107 per heifer per year. The optimum r earing practice was not sensitive to seasonal variation in prices. Neverthe less, the economic results per season of birth varied considerably; the hig hest income per heifer was obtained from heifers born in December ($142/yr) , whereas those born in May yielded the lowest ($100/yr). Sensitivity analyses demonstrated a considerable influence of growth rate r estrictions and variation in reproductive performance on both the optimal r earing practices as the expected net returns.