State Key Laboratory of Animal Nutrition, Institute of Animal Science, Chinese Academy of Agricultural Sciences, Beijing, P R China.
J Dairy Sci. 2012 Jan;95(1):266-71. doi: 10.3168/jds.2011-4380.
Melamine might be degraded into cyanuric acid and some other analogs by the rumen microorganism. Thus, the metabolism of melamine in ruminants may be different from that in monogastric animals. The objective of this study was to investigate the pathway for the elimination of melamine in lactating dairy cows. Four late-lactation dairy cows (body weight=524±17 kg, days in milk=265±14 d) fitted with ruminal cannulas were dosed with melamine (purity ≥99.5%) at 800 mg/d per cow that divided into 2 equal daily doses. The trial lasted for 20 d (13-d preliminary period, followed by a 7-d sample-collecting period). The method of liquid chromatography and tandem mass spectrometry was used to determine melamine and cyanuric acid contents simultaneously. Before the trial started, no melamine or cyanuric acid was detected in samples of total mixed ration, milk, plasma, urine, and feces. The melamine concentration in rumen fluid (Y, mg/L) decreased exponentially after the morning feeding (X, h) (Y=3.85591e(-X/9.25674)+1.35924, R(2)=0.99), but no cyanuric acid was detected. Plasma melamine concentration (0.296±0.014 mg/L) was relatively stable in the 3 different sampling times. The percentages of melamine excreted through milk, urine, and feces were 0.48±0.06, 44.07±10.79 and 10.98±3.88%, respectively. It could be inferred that 44.47±7.98% of ingested melamine was degraded in the rumen, because cyanuric acid was detected in plasma, urine, and feces on the condition that no melamine was contained in the total mixed ration fed to the dairy cows. The results of the present study implied that the elimination pathway of melamine in lactating dairy cows was different from that in monogastric animals. A high percentage of melamine was degraded into cyanuric acid gradually by rumen microorganisms. Most ingested melamine was excreted in urine and feces, which are the main elimination pathways for melamine in lactating dairy cows.
三聚氰胺可能会被瘤胃微生物降解为氰尿酸和其他一些类似物。因此，反刍动物中三聚氰胺的代谢可能与单胃动物不同。本研究旨在探讨泌乳奶牛中三聚氰胺的消除途径。将 4 头泌乳后期奶牛（体重=524±17 kg，产奶天数=265±14 d）安装瘤胃套管，每头牛每天 800 mg 分为 2 等份剂量。试验持续 20 天（13 天预试期，随后 7 天采样期）。采用液相色谱-串联质谱法同时测定三聚氰胺和氰尿酸含量。试验开始前，全混合日粮、牛奶、血浆、尿液和粪便样品中均未检测到三聚氰胺或氰尿酸。瘤胃液（Y，mg/L）中的三聚氰胺浓度在上午饲喂后（X，h）呈指数下降（Y=3.85591e(-X/9.25674)+1.35924，R(2)=0.99），但未检测到氰尿酸。血浆三聚氰胺浓度（0.296±0.014 mg/L）在 3 个不同采样时间相对稳定。通过牛奶、尿液和粪便排泄的三聚氰胺百分比分别为 0.48±0.06、44.07±10.79 和 10.98±3.88%。可以推断，44.47±7.98%摄入的三聚氰胺在瘤胃中降解，因为在给奶牛饲喂的全混合日粮中不含三聚氰胺的情况下，在血浆、尿液和粪便中检测到了氰尿酸。本研究结果表明，泌乳奶牛中三聚氰胺的消除途径与单胃动物不同。大部分三聚氰胺被瘤胃微生物逐渐降解为氰尿酸。大部分摄入的三聚氰胺通过尿液和粪便排泄，这是泌乳奶牛中三聚氰胺的主要消除途径。
