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

This study aimed to investigate ruminal and post-ruminal degradation of phytic acid (InsP 6 ) in diets containing either rapeseed meal (RSM) or soybean meal (SBM). In Experiment 1, the effective degradability of crude protein (CPED) and InsP 6 (InsP 6 ED) 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 (TiO 2 ) 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 InsP 6 ED of RSM (InsP 6 ED 2 : 83%; InsP 6 ED 5 : 64%) decreased almost identically to that of CPED with increasing passage rate (CPED 2 : 78%; CPED 5 : 63%) and was significantly lower than that of SBM (InsP 6 ED 2 : 93%; InsP 6 ED 5 : 85%). In Experiment 2, ruminal InsP 6 disappearance was significantly higher in wethers fed Diet SBM (89%) than in those fed Diet RSM (76%). Total post-ruminal InsP 6 degradation was 6% for Diet RSM and 4% for Diet SBM ( p  = 0.186). The total tract InsP 6 disappearance was higher in Diet SBM (93%) than in Diet RSM (82%). Considering higher InsP 6 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 InsP 6 . InsP 5 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 InsP 6 disappearance in wethers and in situ calculated InsP 6 ED 2 , along with the very low extent of post-ruminal InsP 6 degradation, suggests that at a low rumen passage rate, InsP 6 -P from the feed becoming available to ruminants is almost entirely from InsP 6 degradation in the rumen.