Long-term stochastic simulation of mountain beef cattle herds under diverse management strategies.

A stochastic simulation model was used to assess the effects of diverse management strategies on beef herds under mountain conditions in the Spanish Pyrenees. Animals grazed on different seasonal resources (valley meadows, forest pastures and mountain pastures) and were fed with forages and concentrates during winter. The simulated management strategies were winter calving (WC, weaning at 180Â days), autumn calving (AC, weaning at 160Â days), 8-month calving (8MC, weaning at 180Â days), and two calvings in 3 years, with weaning taking place at either 170Â days of age (2C3Y) or at 9Â months (2C3Y9Â M). Each strategy was tested for two types of production systems: (i) cow-calf farms that market calves just after weaning; and (ii) cow-calf/finishing farms that fatten the animals by means of an intensive feeding system until achieving a suitable weight for slaughter. A herd of 100 cows was simulated over 15Â years, but only data obtained after reaching the steady state (year 6) was used in the analysis. The strategies were evaluated by considering reproductive, productive and economic performance. The percentages of pregnant cows at the end of the mating season were highest for 8MC, 2C3Y and 2C3Y9M (between 92% and 94%). The percentage was intermediate for AC (88%) and lowest for WC (78%), which also showed greater variability between years. The two strategies that extensified management (2C3Y, 2C3Y9M) produced, as expected, a lower number of calves weaned per year (59 and 60), whereas this figure was the highest for 8MC (90). Although AC and 8MC resulted in higher productive performances, the increased labour requirements and winter feeding costs resulted in low economic margins for these strategies, which also meant poorer utilization of natural resources. In economic terms, WC was the best strategy for cow-calf/finishing farms, whereas 2C3Y was the worst of the two types of production systems, although it resulted in the most intense utilization of grazing resources. The long lactating period of 2C3Y9M did not affect the reproductive performance of cows, so this strategy yielded the highest economic margin at weaning. The extensification strategies (2C3Y and 2C3Y9M) were less sensitive to changes in the price of feedstuffs. The information obtained from the simulation of the different strategies is useful for evaluating the possible trade-offs between production, economics, use of natural resources and labour requirements.