Phosphorus Utilization in Lactating Dairy Cows Fed Increasing Amounts of Dried Distillers Grains with Solubles

Phosphorus (P) is an essential element for its role in different physiological and structural functions in livestock animals; however, excess feeding of P to dairy cows leads to increased P excretion in feces. Accurate formulation of dairy diets is necessary for two main reasons: 1) phosphorus is the most expensive macro element supplemented in the dairy diet, and 2) it represents the greatest pollution risk if excess is released into the environment. Two studies were conducted to: 1) investigate P availabilities from select concentrates in the rumen of lactating dairy cows and 2) to examine P utilization in diets containing either soybean (SB) products plus inorganic P (P1) or increasing amounts of dried distillers grains with solubles (DOG). The first study consisted of two in situ experiments where ruminal P disappearance kinetics were estimated in different concentrate sources including different DOG sources, one wet DG (WDG), corn, corn germ (CG), solvent extracted soybean meal ( 44% CP; SBM), expeller soybean meal (SoyPlus; SP), extruded soybeans (ES), and soyhulls (SH). Overall, P release varied significantly among the feedstuffs. The readily soluble fraction of P was significantly higher in DOG than in all other feedstuffs. Similarly the effective disappearance of P was greater from DDG sources and CG, intermediate in corn and soybean products with the exception of SH. Slight differences occurred among the DG sources. The readily soluble fraction of P seemed to be affected by the source of DG and the effective disappearance of P in WDG was lower than DDG sources. Corn and soybean byproducts tested, with the exception of SH, have high ruminal P availability as measured with the nylon bag technique. In the second experiment, the objective was to investigate the effect of P. concentration and source on its utilization in lactating dairy cows. Five multiparous cannulated Holstein cows were used in a replicated 5x5 Latin square design. Five experimental diets were formulated to contain different concentrations (0.28, 0.34 and 0.40 %) and sources of P (SB plus P1 and DDG). Phosphorus intake, fecal P output, net absorption and net retention of P increased with increasing dietary P concentration; however, none of these parameters was affected by altering the source of P. Phosphorus excreted in milk was greater in DG diets compared with SB diets, 28.9 and 25.8 g/d. Apparent P digestibility was similar to all diets, averaging 52.9%. Dietary P concentration and P source did not affect the water soluble P in feces. Data from this experiment suggest that DDG can be an effective source of P to sufficiently meet high producing dairy cow\u27s requirements without a supplementary mineral source