Low cost pasture based forage systems are a viable management alternative for dairy producers. A whole-farm analysis was conducted to evaluate the potential long-term environmental impact and economic benefit of varying the level of concentrate supplementation on spring-calving, grazing dairy farms using a whole-farm model (DAFOSYM). A representative grazing farm in central Pennsylvania was simulated with four levels of concentrate supplementation. These farms were then compared to a confinement farmproducing corn and alfalfa on the same land base where total mixed rations were fed. Stocking rate was set on each farm so forage consumed equaled forage production on the farm. Profitability increased as supplementation level increased in the grazing systems, but at a decreasing rate with each successive level of supplementation. At the highest levels of supplementation, the grazing dairy farms showed greater profitability than the confinement farm. Nitrogen leaching remained relatively unchanged as supplementation increased, but soil P accumulation increased. Concentrate supplementation of grazing lactating dairy cows provided an increase in profitability and a mixed impact on nutrient balance of the farm.
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