MP的AA谱影响奶牛的乳腺代谢和乳N效率。Further,膳食蛋白质补充的频率可能会影响N分配,导致N排泄减少。这项研究调查了瘤胃保护(RP)蛋白质补充的来源和频率对表观总道消化率的影响,牛奶生产,乳腺AA代谢,和奶牛的氮平衡。在随机完全区组设计中使用了28头荷斯坦-弗里斯奶牛(2.3±0.9泌乳;牛奶93±27d;平均值±SD),并饲喂了由41%玉米青贮饲料组成的基础总混合日粮(TMR),32%草青贮,和27%的浓缩物(DM基础),并配制以满足100%和95%的净能量和MP要求,分别。奶牛在免费的摊位谷仓中适应基础TMR7天,搬到单独的领带摊位,适应饮食治疗13天,然后进入气候呼吸室进行4天的测量。处理包括基础TMR(CON;159gCP/kgDM)或基础TMR,包括3种异MP补充剂中的1种:1)每日饲喂的RP豆粕和RP菜籽粕的315克混合物(ST-RPSR),2)384克RPHis混合物,RPLys,和RP每天喂食(ST-RPAA),和3)768-gRPHis混合物,RPLys,和RP每隔一天见面(OS-RPAA)。添加治疗补充剂的基础TMR设计为在48小时内提供100%的所需MP。他的混合物,Lys,并配制Met以相对于其在酪蛋白中的浓度的量递送可消化的AA。与ST-RPSR相比,ST-RPAA增加牛奶蛋白质和脂肪浓度,增加了总His的动脉浓度,Lys,和大都会(HLM),HLM的乳腺清除率下降,增加了Phe的清除,Leu和Tyr(倾向于Leu和Tyr)。瘤胃保护的蛋白质来源不影响N平衡,但ST-RPAA的边际利用效率(RP蛋白补充剂向乳蛋白的转移效率)(67%)高于ST-RPSR(17%)。与ST-RPAA相比,OS-RPAA降低了牛奶蛋白浓度。与OS-RPAA补充日相比,HLM的动脉浓度在未补充日增加,使用ST-RPAA的各组动脉HLM浓度没有差异。与OS-RPAA补充日相比,HLM的乳腺摄取在未补充日趋于增加。RPAA的补充频率不影响N平衡或整体牛奶N效率,但OS-RPAA的边际使用效率(49%)低于ST-RPAA。总的来说,乳腺对他的供应增加做出了反应,Lys,并在RPHis时通过减少其他EAA的外排来实现,RPLys,与RP植物蛋白相比,补充了RPMet。在OS-RPAA的非补充日,乳腺增加了EAA(主要是HLM)的隔离,但是根据24小时的振荡模式补充RPAA并没有比静态补充增加N效率。
The AA profile of MP affects mammary gland metabolism and milk N efficiency of dairy cattle. Further, the frequency of dietary protein supplementation may influence N partitioning leading to reduced N excretion. This study investigated the effect of source and frequency of rumen-protected (RP) protein supplementation on apparent total-tract digestibility, milk production, mammary gland AA metabolism, and N balance of dairy cattle. Twenty-eight Holstein-Friesian cows (2.3 ± 0.9 lactations; 93 ± 27 DIM; mean ± SD) were used in a randomized complete block design and fed a basal TMR consisting of 41% corn silage, 32% grass silage, and 27% concentrate (DM basis) and formulated to meet 100% and 95% of net energy and MP requirements, respectively. Cows were adapted to the basal TMR in a freestall barn for 7 d, moved to individual tiestalls for 13 d of adaptation to dietary treatments, and then moved into climate respiration chambers for a 4-d measurement period. Treatments consisted of the basal TMR (CON; 159 g CP/kg DM) or the basal TMR including 1 of 3 iso-MP supplements: (1) 315-g mixture of RP soybean meal and RP rapeseed meal fed daily (ST-RPSR), (2) 384-g mixture of RP His, RP Lys, and RP Met fed daily (ST-RPAA), and (3) 768-g mixture of RP His, RP Lys, and RP Met fed every other day (OS-RPAA). The basal TMR with the addition of treatment supplements was designed to deliver 100% of required MP over a 48-h period. The mixture of His, Lys, and Met was formulated to deliver digestible AA in amounts relative to their concentration in casein. Compared with ST-RPSR, ST-RPAA increased milk protein and fat concentration, increased the arterial concentration of total His, Lys, and Met (HLM), decreased mammary clearance of HLM, and increased clearance of Phe, Leu, and Tyr (tendency for Leu and Tyr). Rumen-protected protein source did not affect N balance, but the marginal use efficiency (efficiency of transfer of RP protein supplement into milk protein) of ST-RPAA (67%) was higher than that of ST-RPSR (17%). Milk protein concentration decreased with OS-RPAA compared with ST-RPAA. Arterial concentration of HLM increased on the nonsupplemented day compared with the supplemented day with OS-RPAA, and there was no difference in arterial HLM concentration across days with ST-RPAA. Mammary uptake of HLM tended to increase on the nonsupplemented day compared with the supplemented day with OS-RPAA. Supplementation frequency of RP AA did not affect N balance or overall milk N efficiency, but the marginal use efficiency of OS-RPAA (49%) was lower compared with ST-RPAA. Overall, mammary glands responded to an increased supply of His, Lys, and Met by reducing efflux of other EAA when RP His, RP Lys, and RP Met were supplemented compared with RP plant proteins. Mammary glands increased sequestration of EAA (primarily HLM) on the nonsupplemented day with OS-RPAA, but supplementing RP AA according to a 24-h oscillating pattern did not increase N efficiency over static supplementation.