本试验采用动静脉血插管技术，以泌乳中期荷斯坦奶牛为研究对象，研究玉米秸秆饲粮条件下阴外动脉灌注氨基酸（AA）混合物对奶牛产奶性能、尾动脉血和乳静脉血中短链脂肪酸（SCFA）浓度及其比例以及乳腺内SCFA摄取规律的影响。采用2×2交叉试验设计，将体况良好、体重相近、日乳产量为（20.17±1.28） kg的8头经产（2~3胎）荷斯坦奶牛随机分为采食不同饲粮的2组[苜蓿组（MF组）和玉米秸秆组（CS组）]，每组4头。2组奶牛饲喂的饲粮精粗比均为45:55，精饲料组成相同，粗饲料组成不同，MF组粗饲料由苜蓿干草、玉米青贮和羊草组成，CS组以单一的玉米秸秆全部替代MF组饲粮中的粗饲料。试验分为2个阶段，每个阶段20 d，均分为饲粮适应期（预试期）14 d，载体灌注期3 d，正式灌注期3 d。在第1阶段，在载体灌注期，MF组奶牛接受载体灌注（阳性对照组1），CS组奶牛也接受载体灌注（对照组）；在正式灌注期，MF组奶牛继续接受载体灌注（阳性对照组2），CS组奶牛接受AA混合物灌注；在第2阶段，将2组动物互换后处理方法同第1阶段。每个正式灌注期的最后2 d采集乳样和血样。结果显示:CS组奶牛阴外动脉灌注AA混合物可显著提高乳蛋白率（P<0.05），对乳产量、4%乳脂校正乳（FCM）产量、乳脂率、乳脂产量、乳蛋白产量有一定促进效果，但部分指标仍然显著低于MF组（P<0.05）。CS组奶牛阴外动脉灌注AA混合物可趋于显著地提高乳静脉血中乙酸的浓度（P=0.09），显著降低乳腺内乙酸的动静脉差（P<0.05），缩小CS组与MF组奶牛在乳腺对乙酸的摄取量和摄取效率方面存在的差距。CS组奶牛阴外动脉灌注AA混合物对提高尾动脉血中乙酸/丙酸、（乙酸+丁酸）/丙酸有一定的促进效果（P>0.05）。由此得出，以玉米秸秆为粗饲料的奶牛阴外动脉灌注AA混合物可显著提高乳蛋白率，增加乳静脉血中的乙酸浓度，同时缩小与以苜蓿干草、玉米青贮和羊草为粗饲料的奶牛在乳腺对乙酸的摄取量和摄取效率方面存在的差距。

This experiment was conducted to study the effects of infusing amino acid (AA) mixture into external pubic artery on lactating performance, short chain fatty acid (SCFA) concentrations and their proportions in caudal artery and mammary vein blood, and the uptake rule of SCFA in mammary gland of mid-lactation Holstein cows under corn straw diet condition using arteriovenous blood intubation technique. The experiment used a 2×2 cross experiment design. Eight healthy multifarious (2 to 3 parities) Holstein cows with good body condition, similar body weight and the milk yield of (20.17±1.28) kg/d were randomly assigned in 2 groups[alfalfa group (MF group) and corn straw group (CS group)] which were fed different diets with 4 cows of each group. In MF group and CS group, the dietary forage-to-concentrate ratio both was 45:55 and the concentrate composition was the same, but the forage composition was different. The forage of MF group was composed of alfalfa hay, corn silage and Chinese wildrye, and in the CS group, the corn straw was used to replace the total forage of MF group diet. The experiment was divided into 2 stages, and each stage lasted for 20 days, including the diet adjustment period (pre feeding period) of 14 days, carrier infusion phase of 3 days and experimental infusion phase of 3 days. In the first stage, dairy cows of MF group (positive control group 1) and CS group (control group) were infused the carrier during carrier infusion phase. During experimental infusion phase, the dairy cows of MF group were infused carrier continuously (positive control group 2), and the dairy cows of CS group were infused AA mixture. In the second phase, the dairy cows of CS group and MF group were swapped, and the processing method was the same as the first stage. Blood and milk samples were taken from dairy cows on the last 2 days of infusion in each experimental infusion phase. The results showed as follows:infusing AA mixture into external pubic artery of dairy cows in CS group significantly improved milk protein rate (P<0.05), and milk yield, fat corrected milk (FCM) yield, milk fat rate, milk fat yield and milk protein yield were promoted, but some indices of them still significantly lower than MF group (P<0.05). Infusing AA mixture into external pubic artery of dairy cows in CS group had a tendency to increase the concentration of acetic acid in mammary vein blood (P=0.09), and significantly reduced the arteriovenous difference of acetic acid and the gaps of the uptake quantity and uptake efficiency of acetic acid in the mammary gland between CS group and MF group. Infusing AA mixture into external pubic artery of dairy cows in CS group had a certain promoting effect on increasing acetic acid/propionic acid and (acetic acid+butyric acid)/propionic acid in caudal artery blood (P>0.05). In conclusion, infusing AA mixture into external pubic artery of dairy cows using corn straw as forage can significantly improve milk protein rate, increase the concentration of acetic acid in internal mammary vein blood, and reduce the gaps of intake quantity and intake efficiency of acetic acid in mammary gland with the dairy cows using alfalfa hay, corn silage and Chinese wildrye as forage.