Browsing by Person "Chi, Yung-Ping"

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Investigations on phytate degradation of rapeseed meal and soybean meal in ruminants
(2023) Chi, Yung-Ping; Rodehutscord, Markus
Oilseed meals are widely used protein feeds in ruminant nutrition. However, aside from the high crude protein (CP) content, oilseed meals also contain high amounts of phosphorus (P), which is predominantly present in organic form as different salts of myo-inositol 1,2,3,4,5,6 hexakis dihydrogen phosphate (InsP6). To become available for intestinal absorption and further utilisation by animals, P must be cleaved from the InsP6 molecule by a specific group of phosphatases, which is known as phytase. Over the decades, ruminants were considered to be capable of utilising nearly all P bound in InsP6 because of the substantial phytase activity exhibited by rumen microbiota. Nevertheless, recent studies have reported variable extents of ruminal InsP6 degradation which seems to be influenced by different factors. In case of an incomplete ruminal InsP6 degradation, post-ruminal InsP6 degradation may be of higher relevance. However, post-ruminal InsP6 degradation has been rarely studied to date. The aim of this thesis was to systematically investigate InsP6 degradation of rapeseed meal (RSM) and soybean meal (SBM) in ruminants, including the possible influencing factors and their combinations. Different study methods (in vivo, in situ, and in vitro) were applied to evaluate the effects of RSM and SBM. The first study (Manuscript 1) was conducted to investigate ruminal and post-ruminal InsP6 degradation in wethers fed a diet containing RSM or SBM, and to link the ruminal disappearance determined in slaughtered wethers with in situ calculated rumen effective degradation of InsP6 (InsP6ED) from cows. Firstly, RSM and SBM was incubated according to a standard in situ procedure in three lactating Jersey cows for 2, 4, 6, 8, 16, 24, 48, and 72 h to obtain InsP6ED for the oilseed meals at rumen passage rates of 0.02 (InsP6ED2) and 0.05 h-1 (InsP6ED5). Secondly, eight wethers were randomly assigned to two treatment groups that were fed a diet containing equal amount of RSM (Diet RSM) or SBM (Diet SBM) for 8 weeks of adaptation. Then, digesta from the reticulo-rumen, omasum, abomasum, jejunum, colon, and rectum were sampled. In consistence with in situ calculated InsP6ED2 (83 and 93% for RSM and SBM, respectively), ruminal InsP6 disappearance was lower in wethers fed Diet RSM (76%) compared to those fed Diet SBM (89%). Post-ruminal InsP6 disappearance did not differ between dietary treatments (6% for Diet RSM vs. 4% for Diet SBM). A higher amount of ruminally degraded InsP6 was observed upon feeding RSM (4.5 g/d for Diet RSM and 3.4 g/d for Diet SBM). Due to the low rumen passage rate in this study, it was suggested that P from InsP6 being available to ruminants is almost entirely from InsP6 degradation in the rumen. As InsP6 is located in a protein-rich structure in seeds and InsP6 degradation has been recently reported to vary in a pattern similar to CP degradation for RSM, the second study (Manuscript 2) was carried out to investigate the variation of in situ ruminal InsP6 degradation of SBM and its relation to CP degradation. In this study, nine commercial solvent-extracted SBM from Europe and South America were incubated in three rumen-fistulated lactating Jersey cows with the same procedure performed in the first study. Rumen effective degradation of CP and InsP6 were calculated for a rumen passage rate of 0.06 h-1 (CPED6 and InsP6ED6). Chemical protein fractions of SBM variants were determined according to Cornell Net Carbohydrate and Protein System (CNCPS). The SBM variants exhibited a considerable variation in CP and InsP6 degradation. Significant correlations were found between InsP6ED6 and CPED6 and between InsP6ED6 and all CNCPS protein fractions, which confirmed the close relationship between CP and InsP6 degradation for SBM. The results suggested that using a general value of InsP6 degradation for diet formulation may not be precise enough, and InsP6ED may be predicted based on CPED or CNCPS protein fractions by using linear regression equations. The third study (Chapter 4.3) aimed to achieve a better understanding of how in vitro InsP6 degradation of RSM and SBM is influenced by different amounts of InsP6 in feed. The same batches of RSM and SBM as used in Manuscript 1 were incubated in a modified rumen simulation technique (RUSITEC) system with different amounts for 3, 6, 12, 24, and 48 h. Degradation of InsP6 from bag residues was calculated and expressed as amount and in percentage using the same equation as applied for in situ calculations. In vitro degradation of InsP6 in response to InsP6 amount differed between RSM and SBM, which may be attributed to the different internal structure and nutrient composition of the oilseed meals. Only when expressing in amounts, the calculated InsP6ED was observed to increase linearly with increasing InsP6 amount in feed. Accordingly, it was recommended to compare InsP6 degradation based on InsP6 amount in the feed and to express degradation as amount instead of using relative value which might not reflect the real degradation kinetics. In conclusion, the results of this thesis showed that the extent of ruminal InsP6 degradation differs when the diet contains either RSM or SBM, while post-ruminal InsP6 degradation is negligibly low given a long rumen retention time. By using linear regression equations, ruminal InsP6 degradation may be predicted from CP degradation due to the close relationship therebetween. Effects of InsP6 amount on InsP6 degradation is dependent on InsP6 source. Based on the high similarity among ruminal InsP6 degradation determined by different methods in this thesis, ruminal InsP6 degradation of oilseed meals measured by in situ or in vitro study may be applicable for in vivo conditions.