Ruminal and post-ruminal phytate degradation of diets containing rapeseed meal or soybean meal

Abstract

ABSTRACT This study aimed to investigate ruminal and post-ruminal degradation of phytic acid (InsP6) in diets containing either rapeseed meal (RSM) or soybean meal (SBM). In Experiment 1, the effective degradability of crude protein (CPED) and InsP6 (InsP6ED) was evaluated by incubating RSM and SBM in situ in three rumen-fistulated lactating Jersey cows for 2, 4, 6, 8, 16, 24, 48 and 72 h, and calculating effective degradability at rumen passage rates of 2% and 5%/h. In Experiment 2, eight wethers were assigned for 8 weeks to two dietary treatments (Diet RSM and Diet SBM) containing 150 g of either meal and 100 g of maize silage per feeding time and had free access to hay and water. Titanium dioxide (TiO2) was added to the diets for the last 5 days of the study. The wethers were then stunned, exsanguinated and digesta from the reticulo-rumen, omasum, abomasum, jejunum, colon, and rectum were sampled. In Experiment 1, the InsP6ED of RSM (InsP6ED2: 83%; InsP6ED5: 64%) decreased almost identically to that of CPED with increasing passage rate (CPED2: 78%; CPED5: 63%) and was significantly lower than that of SBM (InsP6ED2: 93%; InsP6ED5: 85%). In Experiment 2, ruminal InsP6 disappearance was significantly higher in wethers fed Diet SBM (89%) than in those fed Diet RSM (76%). Total post-ruminal InsP6 degradation was 6% for Diet RSM and 4% for Diet SBM (p = 0.186). The total tract InsP6 disappearance was higher in Diet SBM (93%) than in Diet RSM (82%). Considering higher InsP6 contents in RSM, Diet RSM resulted in significantly higher amounts of ruminally (Diet RSM: 4.5 g/d; Diet SBM: 3.4 g/d) and total tract (Diet RSM: 4.9 g/d; Diet SBM: 3.5 g/d) degraded InsP6. InsP5 was quantified in most of the digesta samples after feeding Diet RSM but was not detectable in the majority of digesta samples for Diet SBM. Concentrations of myo-inositol (MI) tended to be higher (p = 0.060) in the blood plasma of wethers fed Diet RSM. The consistency between ruminal InsP6 disappearance in wethers and in situ calculated InsP6ED2, along with the very low extent of post-ruminal InsP6 degradation, suggests that at a low rumen passage rate, InsP6-P from the feed becoming available to ruminants is almost entirely from InsP6 degradation in the rumen.