Ruminal Phosphorus Disappearance from Corn and Soybean Feedstuffs

Abstract

Byproducts of corn and soybeans have high phosphorus (P) content, but little is known about their P disappearance in the rumen of lactating dairy cows. In situ disappearance of P from corn and soybean feed-stuffs was determined in 2 experiments. In the first experiment, 3 ruminally cannulated lactating dairy cows were used to estimate in situ P disappearance of 9 feed ingredients that included 3 sources of dried distillers grains with solubles (DDG; DGa, DGb, DGc), corn, corn germ, solvent-extracted soybean meal, (44% CP; SBM), expeller soybean meal (SoyPlus; SP), extruded soybeans (ES), and soyhulls (SH). Nylon bags were incubated in the rumen of each cow for 2, 6, 12, 18, 24, 36, and 48h. The water-soluble fraction of P (AP) was greatest in DDG (mean 82.1%) followed by corn germ (77%), with SH having the least AP among all feedstuffs (45%). The remaining feedstuffs (SBM, SP, ES, and corn) were similar in AP (64.2%). The slowly available fraction of P (BP) was greatest in SH (45.6%), lowest in DDG (13.5%), and intermediate, averaging 31.4%, in SBM, ES, SP, and corn. The effective disappearance of P (EDP) was greatest for DDG (93.5%), whereas corn germ, ES, SBM, and SP followed with an EDP of 93.3, 88.0, 87.5, and 87.0%, respectively. The EDP was less for corn and SH than for the other feedstuffs at 83.3 and 69.1%, respectively. Rate of P disappearance was similar for all feedstuffs (16.2%/h). In the second experiment, 3 new sources of DDG (DG1, DG2, and DG3), and one wet distillers grains with solubles (WDG) source were incubated for 3, 6, 12, 24, and 36h on replicate days in the rumen of 2 cannulated lactating dairy cows. Fraction AP varied from 82.7 to 90.3%, with that in WDG being the least soluble. The WDG source had a greater BP fraction (15.8%) compared with the DDG sources (9.5%). The WDG had the lowest EDP (88.1%), whereas the DDG varied from 89.7 to 92.7%. Corn and soybean byproducts tested, with the exception of SH, have high ruminal P disappearance as measured with the Dacron bag technique.