TECHNICAL NOTE: Cost of reducing protein and phosphorus content of dairy rations

Reducing overfeeding of CP and phosphorus (P) is an effective method to reduce excess nutrient excretion by dairy cows. However market conditions frequently cause ingredients that are counterproductive to this goal to be the most economically attractive source of protein and energy. Less expensive feeds such as dried distillers grains and corn gluten feed are high in P or high in both CP and P. A linear program (Formulate2, Central Valley Nutritional Associates, Visalia, CA) was used to determine the effect of formulating rations for varying amounts of CP and P on ration cost for a 658-kg dairy cow at 90 DIM and producing 41 kg of milk. As dietary P decreased from 0.45 to 0.31% DM in increments of 0.02%, daily ration cost increased from $5.05 to $5.34. Ration cost increased because to achieve lower dietary P, relatively inexpensive by-product feeds were excluded from the ration. Likewise, as CP decreased from 18.0 to 16.0% in increments of 0.5%, daily feed cost increased from $4.99 to $5.59. The greatest increase in daily ration cost occurred between 16.5 and 16.0% CP because more expensive ingredients were needed to meet requirements for metabolizable protein. Little change in feed cost was observed between 16.5 and 18% CP. Under feed price conditions existing in February 2011, reducing dietary P increased ration cost.