Submitted to: Journal of Dairy Science
Publication Type: Proceedings
Publication Acceptance Date: 7/28/2001
Publication Date: N/A
Citation: Interpretive Summary:
Technical Abstract: Surveys of nutritionists and extension specialists show that dairy producers are advised to feed .45-.50% phosphorus (P) (DM basis) in their lactating cow diets. This is 20% in excess of NRC (2001) requirements. Feeding to requirement would reduce P excretion by 25-30% and would reduce solubility and potential for runoff of the P that is applied to fields. Nitrogen (N) excretion by dairy cows can also be decreased, but by a lesse amount. Balancing RUP and RDP, and use of protected methionine along with strategic selection of protein supplements that are relatively rich in lysine, may permit a 10-15% reduction in total N excretion, with most of the reduction occurring in urinary N. Feedlot cattle routinely consume P in excess of NRC (1996) predicted requirements, and recent research suggests the NRC estimates of the P requirements are high. Decreasing dietary P from the industry average (.35% P) to the NRC predicted requirement (.22-.28%) decreased P input by 33 to 45% and excretion by 40-50% in nutrient balance studies. With grain-based feedlot diets, overfeeding P is inevitable. At minimum, supplemental P sources should be removed from diet formulations. More accurate formulation of feedlot diets for protein provides opportunity for reducing N excretion. Using the NRC model for metabolizable protein, and employing phase-feeding, N inputs may be decreased by 10-20% from the feedlot industry average of 13.5% dietary CP. This translates into a 12-21% reduction in N excretion, and 15-33% reduction in ammonia volitilization in open-dirt feedlot pens. Diet formulation can have an important impact on the amount of N and P excreted in both dairy and beef.