Department of Agricultural Research for Northern Sweden, Swedish University of Agricultural Sciences, Umeå, Sweden.
PLoS One. 2018 Sep 17;13(9):e0203385. doi: 10.1371/journal.pone.0203385. eCollection 2018.
An in vitro method based on 15N-labelled forage nitrogen (N) was developed to study ruminal N metabolism of soluble N (SN), insoluble N (ISN) and neutral detergent insoluble N (NDIN) fractions of timothy forage. Timothy grass was grown on replicated experimental plots with one plot receiving 15N-labelled and the other unlabelled N fertilizer. Harvested grass was preserved as dried grass or as formic acid treated or untreated silage. The intact forages and their corresponding N fractions were incubated in buffered rumen fluid in vitro to determine degradation parameters based on the 15N fluxes between labelled feed N and ammonia N pools. A high percentage (25-38%) of 15N-labelled ammonia disappeared from ammonia N pool during the first 15 min of incubation. Microbial uptake of dried grass SN fraction was higher than of silage SN fractions. Fractional degradation rates of SN from formic acid treated silage, untreated silage and dried grass during the first 6 hours of incubation were 0.145, 0.125 and 0.115 /h, respectively. By the end of the incubation period (28 h), 69, 66 and 43%, of the SN fraction of formic acid treated silage, untreated silage and dried grass, respectively were recovered as ammonia. The percentage of ISN fractions degraded to ammonia N were 9, 34 and 27%, respectively. Based on the changes in 15N-labelled ammonia N pool in blank incubation and appearance of 15N to ammonia N pool from 15N-labelled NDIN fractions, it was estimated that a significant portion of microbial lysis occurred when incubations were carried out for longer than 20 hours. With dried grass the contribution of ammonia N for microbial N synthesis was greater than with silages. Use of 15N-labelled forages together with this in vitro method is a promising technique for determining soluble N degradation parameters, but it requires further development to be used for determining degradation parameters of insoluble N fractions and work with whole feeds.
建立了一种基于 15N 标记饲料氮的体外方法，用于研究提莫西草饲料可溶性氮（SN）、不溶性氮（ISN）和中性洗涤剂不溶性氮（NDIN） fractions 的瘤胃氮代谢。提莫西草在具有一个接受 15N 标记和另一个未标记氮肥料的实验小区上进行重复种植。收获的草作为干草或甲酸处理或未处理的青贮饲料保存。将完整的饲料及其相应的氮 fractions 用缓冲的瘤胃液在体外孵育，以根据标记饲料氮和氨氮库之间的 15N 通量来确定降解参数。在孵育的最初 15 分钟内，氨氮库中 15N 标记的氨有很高的比例（25-38%）消失。与青贮饲料 SN fractions 相比，干燥草的 SN fractions 微生物吸收更高。在孵育的前 6 小时内，甲酸处理青贮饲料、未处理青贮饲料和干燥草的 SN fractions 的部分降解率分别为 0.145、0.125 和 0.115 /h。到孵育结束（28 小时）时，甲酸处理青贮饲料、未处理青贮饲料和干燥草的 SN fractions 中分别有 69%、66%和 43%以氨氮的形式回收。ISN fractions 降解为氨氮的比例分别为 9%、34%和 27%。基于空白孵育中 15N 标记氨氮库的变化和 15N 标记 NDIN fractions 中氨氮库中 15N 的出现，可以估计当孵育时间超过 20 小时时，会发生大量的微生物裂解。与青贮饲料相比，干燥草用于微生物氮合成的氨氮贡献更大。使用 15N 标记的饲料和这种体外方法是确定可溶性氮降解参数的有前途的技术，但需要进一步开发，以用于确定不溶性氮 fractions 的降解参数和整个饲料的工作。
