Kalscheur K F, Teter B B, Piperova L S, Erdman R A
University of Maryland, College Park 20472, USA.
J Dairy Sci. 1997 Sep;80(9):2104-14. doi: 10.3168/jds.S0022-0302(97)76156-3.
Milk fat depression in cows fed high grain diets has been shown to be related to increased trans-C18:1 fatty acids in milk. Trans-C18:1 fatty acids are produced as a result of incomplete biohydrogenation of dietary polyunsaturated fatty acids in the rumen. The objective of this study was to determine the effects of varying amounts of dietary concentrate and buffer addition on duodenal flow, apparent absorption, and incorporation of trans-C18:1 fatty acids into milk fat. Four ruminally and duodenally cannulated multiparous Holstein cows in midlactation were fed diets consisting of 60% (high) or 25% (low) forage with or without buffer (1.5% NaHCO3 and 0.5% MgO). Treatments were arranged in a 2 x 2 factorial within a 4 x 4 Latin square design. The diet containing low forage and no buffer increased the flow of trans-C18:1 fatty acids to the duodenum compared with the effects of other diets (120 vs. 57 to 66 g/d). Ruminal pH was lower for cows fed the low forage diets. The addition of buffer increased ruminal pH by 0.19 and 0.02 units for cows fed the low forage and high forage diets, respectively. Cows fed the diet containing low forage and no buffer produced milk with a lower fat percentage. The addition of buffer to the low forage diet partially corrected milk fat depression. Milk trans-C18:1 fatty acids were higher for cows fed the low forage diet without buffer than for cows fed the other diets (5.8% vs. 3.0%). Altered ruminal function resulting from low ruminal pH for cows fed the low forage diet and no buffer may play a role in the increased production of trans-C18:1 fatty acids in the rumen.
研究表明，给奶牛饲喂高谷物日粮会导致乳脂率降低，这与牛奶中反式C18:1脂肪酸含量增加有关。反式C18:1脂肪酸是日粮多不饱和脂肪酸在瘤胃中不完全生物氢化的产物。本研究的目的是确定不同日粮精料量和添加缓冲剂对十二指肠流量、表观吸收率以及反式C18:1脂肪酸掺入乳脂的影响。选用4头处于泌乳中期、瘤胃和十二指肠插管的经产荷斯坦奶牛，分别饲喂含60%（高）或25%（低）粗饲料的日粮，添加或不添加缓冲剂（1.5% NaHCO3和0.5% MgO）。处理方式采用4×4拉丁方设计中的2×2析因设计。与其他日粮相比，低粗饲料且不添加缓冲剂的日粮使反式C18:1脂肪酸流入十二指肠的量增加（120克/天，而其他日粮为57至66克/天）。饲喂低粗饲料日粮的奶牛瘤胃pH值较低。添加缓冲剂后，饲喂低粗饲料日粮和高粗饲料日粮的奶牛瘤胃pH值分别提高了0.19和0.02个单位。饲喂低粗饲料且不添加缓冲剂日粮的奶牛所产牛奶的脂肪百分比更低。在低粗饲料日粮中添加缓冲剂可部分纠正乳脂率降低的问题。不添加缓冲剂的低粗饲料日粮组奶牛所产牛奶中的反式C18:1脂肪酸含量高于其他日粮组奶牛（5.8%对3.0%）。饲喂低粗饲料且不添加缓冲剂日粮的奶牛，由于瘤胃pH值较低导致瘤胃功能改变，这可能是瘤胃中反式C18:1脂肪酸产量增加的原因之一。
