Determination of in situ ruminal degradation of phytate phosphorus from single and compound feeds in dairy cows using chemical analysis and near-infrared spectroscopy

The ruminal degradation of P bound in phytate (InsP (6)) can vary between feeds, but data on ruminal degradation of InsP(6) from different feedstuffs for cattle are rare. One objective of this study was to increase the data base on ruminal effective degradation of InsP(6) (InsP (6) ED) and to assess if InsP(6)ED of compound feeds (CF) can be calculated from comprising single feeds. As a second objective, use of near-infrared spectroscopy (NIRS) to predict InsP(6) concentrations was tested. Nine single feeds (maize, wheat, barley, faba beans, soybeans, soybean meal (SBM), rapeseed meal (RSM), sunflower meal (SFM), dried distillers’ grains with solubles (DDGS)) and two CF (CF1/CF2), consisting of different amounts of the examined single feeds, were incubated for 2, 4, 8, 16, 24, 48 and 72 h in the rumen of three ruminally fistulated Jersey cows. Samples of CF were examined before (CF1/CF2 Mash) and after pelleting (CF1/CF2 Pellet), and InsP(6)ED was calculated for all feeds at two passage rates (InsP (6) ED (5): k = 5%/h; InsP (6) ED (8): k = 8%/h). For CF1 and CF2, InsP(6)ED was also calculated from values of the respective single feeds. Near-infrared spectra were recorded in duplicate and used to establish calibrations to predict InsP(6) concentration. Besides a global calibration, also local calibrations were evaluated by separating samples into different data sets based on their origin. The InsP(6)ED(8) was highest for faba beans (91%), followed by maize (90%), DDGS (89%), soybeans (85%), wheat (76%) and barley (74%). Lower values were determined for oilseed meals (48% RSM, 65% SFM, 66% SBM). Calculating InsP(6)ED of CF from values of single feeds underestimated observed values up to 11 percentage points. The NIRS calibrations in general showed a good performance, but statistical key data suggest that local calibrations should be established. The wide variation of InsP(6)ED between feeds indicates that the ruminal availability of P bound in InsP(6) should be evaluated individually for feeds. This requires further in situ studies with high amounts of samples for InsP(6) analysis. Near-infrared spectroscopy has the potential to simplify the analytical step of InsP(6) in the future, but the calibrations need to be expanded.