Department of Animal Sciences and Industry, Kansas State University, Manhattan, KS.
J Anim Sci. 2020 Sep 1;98(9). doi: 10.1093/jas/skaa282.
This study assessed the relative bioavailability of guanidinoacetic acid (GAA) in cattle. Seven ruminally cannulated Holstein steers (initial body weight of 280 kg) were used in an experiment with a 5 × 5 Latin square design; the two additional steers received a treatment sequence identical to two steers in the Latin square. Treatments were: control (no GAA, water infusion), ruminal infusion of 10 or 20 g/d GAA, and abomasal infusion of 10 or 20 g/d GAA, with all infusions delivered continuously. Periods were 7 d in length, and on day 7, blood and urine samples were collected to determine the concentrations of GAA and its associated metabolites. Plasma creatine concentrations increased linearly (P < 0.01) with GAA infusion to the abomasum and tended to increase linearly (P = 0.06) when GAA was infused ruminally. Urinary creatine concentrations increased linearly with increasing amounts of GAA infused in the abomasum (P < 0.01) and the rumen (P < 0.05). There were no significant effects of GAA infusion to either the abomasum or rumen on plasma or urinary concentrations of GAA. Plasma creatinine concentrations were not affected by GAA infusion to the abomasum or rumen. Urinary creatinine concentrations decreased when GAA was infused abomasally (P < 0.05). Because plasma and urinary creatine concentrations yielded the statistically strongest linear responses, they were selected as the primary response criteria for quantifying ruminal escape of GAA. Calculated by slope-ratio methodology, estimates for the ruminal escape of GAA based on plasma creatine and urinary creatine concentrations were 47% and 49%, respectively. Ruminally infused GAA was about half as effective as abomasally infused GAA in elevating plasma and urinary concentrations of creatine.
本研究评估了胍基乙酸（GAA）在牛体内的相对生物利用度。采用 5×5 拉丁方设计，选用 7 头具有瘤胃瘘管的荷斯坦公牛进行试验；另外 2 头公牛接受与拉丁方中 2 头公牛相同的处理顺序。处理方法为：对照组（无 GAA，水灌注）、瘤胃灌注 10 或 20 g/d GAA 和皱胃灌注 10 或 20 g/d GAA，所有灌注均连续进行。每个周期为 7 天，在第 7 天采集血液和尿液样本，以测定 GAA 及其相关代谢物的浓度。血浆肌酸浓度随皱胃灌注 GAA 呈线性增加（P＜0.01），随瘤胃灌注 GAA 呈线性增加趋势（P＝0.06）。随着皱胃和瘤胃中灌注 GAA 量的增加，尿液肌酸浓度呈线性增加（P＜0.01，P＜0.05）。皱胃或瘤胃灌注 GAA 对血浆或尿液中 GAA 浓度均无显著影响。皱胃或瘤胃灌注 GAA 对血浆肌酐浓度无影响。皱胃灌注 GAA 时尿液肌酐浓度降低（P＜0.05）。由于血浆和尿液肌酸浓度产生了统计学上最强的线性响应，因此它们被选为量化 GAA 瘤胃逃逸的主要响应标准。根据斜率比法计算，基于血浆肌酸和尿液肌酸浓度的 GAA 瘤胃逃逸估计值分别为 47%和 49%。瘤胃灌注 GAA 提高血浆和尿液肌酸浓度的效果约为皱胃灌注 GAA 的一半。
